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The biological pump supplies carbon to the oceans interior, driving long-term carbon sequestration and providing energy for deep-sea ecosystems1,2. Its efficiency is set by transformations of newly formed particles in the euphotic zone, followed by vertical flux attenuation via mesopelagic processes3. Depth attenuation of the particulate organic carbon (POC) flux is modulated by multiple processes involving zooplankton and/or microbes4,5. Nevertheless, it continues to be mainly parameterized using an empirically derived relationship, the Martin curve6. The derived power-law exponent is the standard metric used to compare flux attenuation patterns across oceanic provinces7,8. Here we present in situ experimental findings from C-RESPIRE9, a dual particle interceptor and incubator deployed at multiple mesopelagic depths, measuring microbially mediated POC flux attenuation. We find that across six contrasting oceanic regimes, representing a 30-fold range in POC flux, degradation by particle-attached microbes comprised 7-29 per cent of flux attenuation, implying a more influential role for zooplankton in flux attenuation. Microbial remineralization, normalized to POC flux, ranged by 20-fold across sites and depths, with the lowest rates at high POC fluxes. Vertical trends, of up to threefold changes, were linked to strong temperature gradients at low-latitude sites. In contrast, temperature played a lesser role at mid- and high-latitude sites, where vertical trends may be set jointly by particle biochemistry, fragmentation and microbial ecophysiology. This deconstruction of the Martin curve reveals the underpinning mechanisms that drive microbially mediated POC flux attenuation across oceanic provinces.

The impacts of microsporidia on host individuals are frequently subtle and can be context dependent. A key example of the latter comes from a recently discovered microsporidian symbiont of Daphnia, the net impact of which was found to shift from negative to positive based on environmental context. Given this, we hypothesized low baseline virulence of the microsporidian; here, we investigated the impact of infection on hosts in controlled conditions and the absence of other stressors. We also investigated its phylogenetic position, ecology, and host range. The genetic data indicate that the symbiont is Ordospora pajunii, a newly described microsporidian parasite of Daphnia. We show that O. pajunii infection damages the gut, causing infected epithelial cells to lose microvilli and then rupture. The prevalence of this microsporidian could be high (up to 100% in the lab and 77% of adults in the field). Its overall virulence was low in most cases, but some genotypes suffered reduced survival and/or reproduction. Susceptibility and virulence were strongly host-genotype dependent. We found that North American O. pajunii were able to infect multiple Daphnia species, including the European species Daphnia longispina, as well as Ceriodaphnia spp. Given the low, often undetectable virulence of this microsporidian and potentially far-reaching consequences of infections for the host when interacting with other pathogens or food, this Daphnia-O. pajunii symbiosis emerges as a valuable system for studying the mechanisms of context-dependent shifts between mutualism and parasitism, as well as for understanding how symbionts might alter host interactions with resources.ImportanceThe net outcome of symbiosis depends on the costs and benefits to each partner. Those can be context dependent, driving the potential for an interaction to change between parasitism and mutualism. Understanding the baseline fitness impact in an interaction can help us understand those shifts; for an organism that is generally parasitic, it should be easier for it to become a mutualist if its baseline virulence is relatively low. Recently, a microsporidian was found to become beneficial to its Daphnia hosts in certain ecological contexts, but little was known about the symbiont (including its species identity). Here, we identify it as the microsporidium Ordospora pajunii. Despite the parasitic nature of microsporidia, we found O. pajunii to be, at most, mildly virulent; this helps explain why it can shift toward mutualism in certain ecological contexts and helps establish O. pajunii is a valuable model for investigating shifts along the mutualism-parasitism continuum.

Environmental DNA (eDNA) is an increasingly useful method for detecting pelagic animals in the ocean but typically requires large water volumes to sample diverse assemblages. Ship-based pelagic sampling programs that could implement eDNA methods generally have restrictive water budgets. Studies that quantify how eDNA methods perform on low water volumes in the ocean are limited, especially in deep-sea habitats with low animal biomass and poorly described species assemblages. Using 12S rRNA and COI gene primers, we quantified assemblages comprised of micronekton, coastal forage fishes, and zooplankton from low volume eDNA seawater samples (n = 436, 380-1800 mL) collected at depths of 0-2200 m in the southern California Current. We compared diversity in eDNA samples to concurrently collected pelagic trawl samples (n = 27), detecting a higher diversity of vertebrate and invertebrate groups in the eDNA samples. Differences in assemblage composition could be explained by variability in size-selectivity among methods and DNA primer suitability across taxonomic groups. The number of reads and amplicon sequences variants (ASVs) did not vary substantially among shallow (600 m), but the proportion of invertebrate ASVs that could be assigned a species-level identification decreased with sampling depth. Using hierarchical clustering, we resolved horizontal and vertical variability in marine animal assemblages from samples characterized by a relatively low diversity of ecologically important species. Low volume eDNA samples will quantify greater taxonomic diversity as reference libraries, especially for deep-dwelling invertebrate species, continue to expand.

The San Francisco Estuary (estuary) and the Sacramento–San Joaquin Delta (the Delta) in California face significant challenges in managing water resources during extended droughts. Zooplankton are a vital trophic link between phytoplankton producers and higher-level consumers such as predatory zooplankton and fish. However, there is still much to be learned about what drives zooplankton abundance and how they respond to drastic changes in environmental conditions, such as droughts. We found that during drought years zooplankton abundance and distribution changes varied for examined taxa. Significant declines in the abundance of Daphnia spp. and the copepod Pseudodiaptomus forbesi occurred in the Suisun Marsh and Suisun Bay regions. In contrast, abundance of the non-native copepod Limnoithona tetraspina increased in Suisun Marsh and the South-Central Delta during those same drought conditions. Salinity is a strong determinant of the presence and abundance of the studied taxa, and we showed that changes in the distribution of salinity as a result of low outflow conditions were an important factor in the regional abundance of zooplankton. Because of the expected increase in the frequency and severity of regional droughts, understanding how these conditions affect zooplankton in the estuary will benefit scientists and resource managers who aim to improve conditions for native fishes.

Droughts have major effects on estuaries because freshwater entry is one of the defining features of an estuary, and freshwater flow is an important variable that determines the interannual change in the environment. In the upper San Francisco Estuary (the Sacramento–San Joaquin Delta, Suisun Bay, and Suisun Marsh), the Mediterranean climate includes frequent multi-year droughts. To assess ecosystem responses to droughts in the upper estuary, the Interagency Ecological Program Drought Synthesis Team assembled a set of flow, water quality, chlorophyll, zooplankton, and fish data from 1975 to 2021 to test for differences between multi-year droughts and multi-year wet periods and tested for linear relationships between each variable and the Sacramento Valley Hydrologic Index (see definitions and relationships as outlined in Appendix A). Our models showed droughts decreased Delta outflow, project exports, zooplankton in Suisun Bay, and some fish species. We also found that droughts increased water clarity, salinity, nutrients, chlorophyll in the South Delta, zooplankton in the South Delta, and water residence time. Although our analyses only tested correlations, we hypothesized that most of the food-web responses could be traced to increased residence time, decreased transport rates, or both. However, some responses may have been caused by secondary effects, including shifts in salinity gradients, regional changes in water quality, or differences in top-down effects of increased predation and grazing rates. With increased frequency of droughts in the future, this increasingly low-outflow, warming, clearing estuary—which is invaded by non-native species and has low pelagic fish production—is rapidly becoming the new “normal.”

ABSTRACT Aim Location Time Period Major Taxa Studied Methods Results Main Conclusions This systematic review aims to analyse the current status of research on marine bipolar and antitropical distribution patterns by exploring temporal trends, studied taxa, inconsistencies in definitions and the extent of molecular evidence in bipolar and antitropical species.Global marine environments, with a special focus on Polar Regions.1800s to 2024.Marine taxa across all phyla, ranging from algae and zooplankton groups to fish and cetaceans.A systematic literature search was conducted using Scopus, PubMed and Google Scholar databases. Studies were screened for relevant publications of marine taxa displaying bipolar or antitropical distributions, and data were extracted in order to perform a numerical summary of aspects including temporal trends, taxa representation and agreement with this article's standardised definitions. Additional data were gathered from The Arctic Register of Marine Species (ARMS) and The Register of Antarctic Marine Species (RAMS) databases. Distribution data were then extracted to verify the potential bipolarity of species present in both databases.From 221 articles, 665 marine taxa records were extracted, of which 517 records were categorised as antitropical and 148 as bipolar. Molecular evidence existed for 25% of non‐paleontological records. A considerable amount of records (44%) did not match the definitions used in this review. The data taken from ARMS and RAMS revealed 408 shared species, of which 41 species were listed as bipolar by the literature collected in this study.Marine bipolarity and antitropicality have been topics of interest since the 1800s, especially between 2008 and 2017. However, the discrepancy between the number of potentially bipolar species in publicly available species databases and literature‐based estimates underscores the need for further research of neglected taxa. Future research should prioritise including molecular evidence, transparent terminology and interdisciplinary approaches to address the complexities of marine disjunct distributions. [ABSTRACT FROM AUTHOR]

Accurately investigating the composition of zooplankton species is crucial for monitoring changes in marine ecosystems and assessing biodiversity. In this study, we utilized bulk DNA and environmental DNA metabarcoding in the Ulleung Basin, known for its high zooplankton species diversity among the seas surrounding the Korean Peninsula. Genomic DNA extracted from samples collected during three summer seasons in the survey area was analyzed using high-throughput sequencing of the cytochrome c oxidase I barcode region. We identified 350 species, which were three to six times more than those identified by traditional morphological methods. Furthermore, we observed significant differences in species composition and diversity between bulk DNA and eDNA samples. Notably, eDNA metabarcoding effectively detected species with high swimming ability and those that were difficult to capture using traditional sampling methods. This study underscores the significant impact of sampling methods on research outcomes in zooplankton species diversity studies and highlights the importance of integrating different sampling techniques. Specifically, it suggests the need for the active adoption of non-invasive methods, such as eDNA metabarcoding, for the comprehensive monitoring of diverse biological groups in marine ecosystems. [ABSTRACT FROM AUTHOR]

ABSTRACT Ecosystem‐based fisheries management (EBFM) remains an aspirational goal for management throughout the world. One of the primary limitations of EBFM is the incorporation of basic lower trophic level information, particularly for zooplankton, despite the importance of zooplankton to fish. The generation of zooplankton abundance estimates requires significant time and expertise to generate. The rapid zooplankton assessment (RZA) is introduced as a tool whereby nontaxonomic experts may produce rapid zooplankton counts shipboard that can be applied to management in near real time. Zooplankton are rapidly counted shipboard and placed into three broad groups of zooplankton relevant to higher trophic levels: large copepods (> 2 mm), small copepods (< 2 mm), and euphausiids. A Bayesian, hierarchical linear regression modeling approach was used to validate the relationship between RZA abundances and laboratory‐processed abundances to ensure the rapid method is a reliable indicator. Additional factors likely to impact the accuracy of the RZA abundance predictions were added to the initial regression model: RZA sorter, survey, season, and large marine ecosystem (Bering Sea, Chukchi/Beaufort Sea, and Gulf of Alaska). We tested models that included the random effect of sorter nested within survey, which improved fits for both large copepods (Bayes R2 = 0.80) and euphausiids (Bayes R2 = 0.84). These factors also improved the fit for small copepods when the fixed effect of season was also included (Bayes R2 = 0.65). Additional RZA data were used to predict laboratory‐processed abundances for each zooplankton category and the results were consistent with model training data: large copepods (Bayes R2 = 0.80), small copepods (Bayes R2 = 0.64), and euphausiids (Bayes R2 = 0.88). The Bayesian models were therefore able to predict laboratory‐processed abundances with an associated error when accounting for these fixed and random effects. To demonstrate the utility of zooplankton data in management, zooplankton time series from the Bering Sea shelf were shown to vary in relation to warm and cold conditions. This variability impacted commercially important fish, notably Walleye Pollock (Gadus chalcogrammus), and these time series were used by managers using a risk table approach. The RZA method provides a rapid zooplankton population estimation in near real time that can be applied to the management process quickly, thus helping to fill a gap in EBFM. [ABSTRACT FROM AUTHOR]

The aim of the present study was to analyze interannual and seasonal relationshisps between zooplankton communities and their trophic levels along with the physicochemical properties of Lake Eğirdir. Samplings were performed seasonally between January 2016 and October 2018 at five stations. Zooplankton communities comprised Rotifera (88%), Cladocera (3%) and Copepoda (9%). A total of 73 species were recorded. Four species Asplanchna priodonta, Polyarthra dolichoptera, Synchaeta pectinata and Bosmina longirostris were found dominant among the others. During the study, the number of zooplankton species decreased in 2018 compared to 2016 when the average zooplankton density increased in 2018. The variations of zooplankton community were estimated using Shannon–Wiener diversity, Evenness, and Simpson indices. The correlations between the species and environmental variables were analyzed with Canonical Correspondence Analysis (CCA). The variation in the species data was significantly (p < 0.05) related to a set of six environmental variables (electrical conductivity, chloride, ammonium, carbon, depth, temperature) which explains 84.6% of the total variation. CCA indicated that Keratella cochlearis, Lecane bulla, L. clostrocerca, Trichocerca similis and Copepoda spp. were positively correlated with temperature. According to the Brachionus: Trichocerca quotient (QB/T), Lake Eğirdir can be characterized within the mesotrophic-eutrophic trophic status. The lake showed mesotrophic status in terms of total phosphorus, Secchi disc and chl-a in 2016, 2017, 2018 according to the Carlson trophic status index. [ABSTRACT FROM AUTHOR]

Opportunities to enhance ecosystem functions exist in human‐dominated working landscapes, but understanding of key drivers is often lacking in these novel environments. In Suisun Marsh, California, USA, impounded managed wetlands designed to promote waterfowl incidentally support higher plankton densities—a key resource for imperilled pelagic fishes—than adjacent tidal habitats. Managed wetland operations could produce plankton at critical periods for fish and the aquatic food‐web more broadly, but drivers of plankton production in managed wetlands are poorly understood.We proposed that decaying vegetation resulting from controlled flooding in managed wetlands is important for stimulating plankton blooms, but that the effect varies by plant species and functional type. We conducted a mesocosm experiment to test the effects of different inundated plants on plankton production, including three forb species, three emergent graminoid species and a control treatment without added plant material.Forbs promoted larger phytoplankton blooms and higher zooplankton production—by an order of magnitude—than both emergent graminoids and the control treatment. Emergent graminoids supported larger phytoplankton blooms, but not higher zooplankton production, than the control treatment. Phytoplankton blooms exhibited pulse dynamics in all treatments, with densities increasing initially and crashing by the end of the experiment. Phytoplankton blooms in forb and emergent treatments lasted similar durations, counter to the expectation that emergent graminoids would support diminished production over a relatively prolonged period. Among zooplankton taxa, Daphnia magna and rotifers were strongly associated with all three forbs species while the nonnative cyclopoid copepod Limnothoina tetraspina were associated with cattails (Typha domingensis) and the control. Forbs temporarily depleted dissolved oxygen concentrations during the first week of the experiment, suggesting a tradeoff by which decaying forbs boost plankton production at risk of initial hypoxia.Our results suggest that seasonal drying and flooding operations in managed wetlands are likely to enhance plankton production because dry periods promote forb growth and subsequent flooding introduces labile forb material to the aquatic food web. Results also suggest that seasonal managed‐wetlands act as novel floodplain‐analogues, by which flood pulses drive productivity. Further research is needed to quantify production benefits and tradeoffs to the aquatic ecosystem at the landscape scale and to identify optimal management regimes that will help conserve imperilled species. [ABSTRACT FROM AUTHOR]

The Sontecomapan lagoon (Mexico) is a Ramsar site within the Los Tuxtlas Biosphere Reserve, facing the Gulf of Mexico. Although the site has a protected area status, it is vulnerable to microplastic contamination, whose long-term effects are uncertain. This study gives the first approach to the degree of contamination by microplastics in surface waters, zooplankton, and sediments in the lagoon. The samples in these three environmental compartments were collected in June 2018 and analyzed in the laboratory to extract and quantify the microplastics. The microplastics sampled were classified into fibers, fragments, and foams and identified as polyester, acrylic, and rayon, among others. In the surface waters, the mean concentration of microplastics was 7.5 ± 5.3 items/L, which is higher than the values registered in other protected coastal systems, perhaps because of differences in the methods used. Zooplankton, represented by copepods, luciferids, and chaetognaths, showed concentrations of 0.002 ± 0.005, 0.011 ± 0.011, and 0.019 ± 0.016 items/individual, respectively. These values were low compared to systems with high anthropic influence, and the differences between the three kinds of organisms were attributed to their feeding habits. In the sediments, the mean concentration was 8.5 ± 12.5 items/kg, lower than the values registered in sites of high human impact; the maximum value here found (43 items/kg) was recorded in the internal part of a lagoon arm of almost stagnant water. In general, the degree of contamination by microplastics in the lagoon was low; however, their presence indicates a potential risk to the biota. [ABSTRACT FROM AUTHOR]

Introduction: Bivalve aquaculture has direct and indirect effects on plankton communities, which are highly sensitive to short-term (seasonal, interannual) and long-term climate changes, although how these dynamics alter aquaculture ecosystem interactions is poorly understood. Methods: We investigate seasonal patterns in plankton abundance and community structure spanning several size fractions from 0.2 µm up to 5 mm, in a deep aquaculture embayment in northeast Newfoundland, Canada. Results: Using flow cytometry and FlowCam imaging, we observed a clear seasonal relationship between fraction sizes driven by water column stratification (freshwater input, nutrient availability, light availability, water temperature). Plankton abundance decreased proportionally with increasing size fraction, aligning with size spectra theory. Within the bay, greater mesozooplankton abundance, and a greater relative abundance of copepods, was observed closest to the aquaculture lease. No significant spatial effect was observed for phytoplankton composition. Discussion: While the months of August to October showed statistically similar plankton composition and size distribution slopes (i.e., food chain efficiency) and could be used for interannual variability comparisons of plankton composition, sampling for longer periods could capture long-term phenological shifts in plankton abundance and composition. Conclusions provide guidance on optimal sampling to monitor and assess aquaculture pathways of effects. [ABSTRACT FROM AUTHOR]

The problem with superintensive vannamei shrimp cultivation is the increase in N and P concentrations which can cause eutrophication and blooming algae. Therefore, this research aims to obtain data and information regarding plankton dynamics and water quality in super intensive vannamei shrimp cultivation at different densities. The research used 3 pond plots with a shrimp density of 750 individuals/m2 (A); 1,000 heads/m²; and 1,250 heads/m2. Plankton data was collected through observation by filtering pond water at five points using planktonnet no. 25, 20 liters at 5 sampling points or 100 liters of water per plot, and sampling was carried out every 7 days. The results of statistical analysis show spearman correlation analysis showed that shrimp density did not have a significant effect on plankton abundance, phytoplankton abundance, zooplankton abundance, TAN, NO2, NO3, PO4, and TSS because the sig value. 2-tailed P > 0.05. however, the abundance of phytoplankton had a significant influence on the abundance of zooplankton (P < 0.05). while zooplankton abundance was influenced by NO2 (P < 0.05). The close relationship between shrimp density and the abundance of plankton, phytoplankton, zooplankton, and water quality (TAN, NO2, NO3, PO4, and TSS) is very low (-0.85-2.79). positive and very close correlation between plankton density, phytoplankton density and zooplankton density (0.68-0.956), and negative correlation with water quality (TAN, NO2, NO3, PO4, and TSS). This causes the distribution of low levels of diversity (H) and evenness (E), so that the average dominance index is below 1, which indicates the absence of dominant individuals. Therefore, in the three treatments no dangerous plankton blooming was found. [ABSTRACT FROM AUTHOR]

An attempt to evaluate aluminum toxicity to living organisms was undertaken in the study. A laboratory experiment was conducted to determine aluminum bioaccumulation and toxicity in Chironomus and Chaoborus larvae and in Cyprinus carpio L. roe depending on aluminum concentration in water reflecting natural chemical composition. Water was examined for temperature, pH, electrical conductivity, dissolved oxygen, color, nitrate nitrogen, nitrite nitrogen, sulfates by spectrophotometric method; total hardness and chlorides by titration method; and calcium, magnesium, sodium by flame atomic absorption spectrometry, total aluminum by electrothermal atomic absorption spectrometry. Determination of aluminum levels in water, roe, and zooplankton was carried out after mineralization using electrothermal atomic absorption spectrometry. Aluminum bioaccumulation factor in roe was determined with respect to concentration in water. Moreover, acute toxicity (LC50) was calculated. In the roe experiment, aluminum concentration in water at the end of the experiment was 0.0635–0.1283 mgAl∙dm−3. The lowest values were noted for the control sample and the highest for water with 0.03 mgAl∙dm−3 aluminum content. The final aluminum level in roe was, like in water, the highest in roe treated with 0.03 mgAl∙dm−3 (18.95 mgAl∙kg−1), and the lowest in roe treated with 3.00 mgAl∙dm−3 (6.96 mgAl∙kg−1). Aluminum bioaccumulation in roe was the strongest in the control. Survival rate ranged from 2.00 to 97.00%, which shows higher sensitivity of roe to aluminum concentration. LC50 value for Chaoborus was 0.6464 mgAl⋅dm−3, and for Chironomus 0.2076 mgAl⋅dm−3 indicating that Chironomus is more sensitive to aluminum toxic effects. Concentration of 3.0 mgAl∙dm−3 caused the highest mortality. Aluminum in both species at each concentration reached the highest levels after one day (24 h), 254.58 mg⋅kg−1 for Chaoborus and 3107 mg⋅kg−1 for Chironomus. After another day, aluminum levels decreased. This demonstrated the differential accumulation of aluminum depending on the species, which predisposes Chironomus as a better indicator organism. This type of research is important from the point of view of aquaculture, which is a targeted activity with a high degree of economic importance, but is also important for aquatic organisms living in natural conditions. Fish reproduction takes place in both types of waters, so all these reservoirs regardless of their source of destination should be inspected. [ABSTRACT FROM AUTHOR]

Several experimental evidences and field data documented that zooplankton may alter its behavioral response in the presence of toxic phytoplankton, reducing its consumption to the point of starvation. This paper is devoted to the mathematical study of such interactions of toxic phytoplankton with grazer zooplankton. The non-toxic phytoplankton is assumed to adopt a density-dependent refuge strategy to avoid over-predation by zooplankton. Both groups of phytoplankton are assumed to suffer direct harm from anthropogenic toxicants, while zooplankton is affected indirectly by ingesting contaminated phytoplankton. We calibrate the proposed model with the field data from Talsari and Digha Mohana, India, and estimate some crucial model parameters consistent with the behavior of the observed data. Our results demonstrate that zooplankton grazing on toxic phytoplankton plays a key role in the emergence or mitigation of plankton blooms. We also highlight the system's potential to exhibit multiple stable configurations under the same ecological conditions. The plankton system experiences significant regime shifts, which are explored through various bifurcation scenarios, such as transcritical and saddle-node bifurcations. These shifts are influenced by changes in refuge capacity, species growth rates, and environmental carrying capacity. Furthermore, we incorporate environmental variations due to seasonal periodic or almost periodic changes, allowing the refuge parameter to be time-dependent. We observe that the forced system exhibits double periodic solutions. Moreover, stronger seasonal variations in the refuge pattern lead to irregular chaotic blooms. In conclusion, the results offer valuable insights into the sustainability of biodiversity, potentially shedding light on the origin of diverse plankton bloom phenomena. [ABSTRACT FROM AUTHOR]

Freshwater salinization is an increasing threat to lakes worldwide, but despite being a widespread issue, little is known about its impact on biological communities at the base of the food chain. Here we used a mesocosm set‐up coupled with modern high‐frequency sensor technology to identify short‐ and longer‐term responses of phytoplankton to salinization in an oligotrophic lake. We tested the effects of salinization over a gradient of increasing salt concentrations that can be found in natural lakes exposed to road salt contamination (added salt range: from 0 to 1500 mg Cl− L−1). The high‐frequency chlorophyll‐a (chl‐a) fluorescence measurements showed an increasing divergence of chl‐a concentrations along the salinization gradient over time, with substantially lower concentrations at higher salt levels. At the sub‐daily scale, we found a profound suppression of day–night signal cycles with increasing salinity, which could be related to physiological stress due to the impairment of photosynthesis via effects on the photosystem II or potential changes in the active migration of phytoplankton. Community analyses revealed a similar decline pattern for the total phytoplankton biomass and a collapse of the total zooplankton biomass. Interestingly, we found a loss of phytoplankton diversity coupled with a compositional re‐organization involving the loss of dominant green algae but increased biomass of salt‐tolerant cyanobacteria. Altogether, these results suggest that specific cyanobacterial taxa can benefit from freshwater salinization following the collapse of dominant phytoplankton competitors and zooplankton herbivores. The results also highlight the value of autonomous sensor technology to capture novel, small‐scale ecological responses to freshwater salinization, and thereby to track fast changes in primary producer communities. [ABSTRACT FROM AUTHOR]

The central Arabian Sea, a unique tropical basin, is profoundly impacted by monsoon wind reversal affecting its surface circulation and biogeochemistry. Phytoplankton blooms associated with high biological productivity and particle flux occur in the northern part of the central Arabian Sea due to summer-monsoon-induced open-ocean upwelling and winter convection. The core oxygen minimum zone (OMZ) at intermediate water depths is another important feature of the northern central Arabian Sea and fades southward. In this study, we attempt to interlink how these factors collectively impact phytodetrital export to the sediment. Short sediment core-top (1 cm) samples representing the recent particle flux signatures were analysed from five locations (21 to 11° N; 64° E) in the central Arabian Sea. Previously, we used core-top (0–0.5 cm) samples and observed a trend between diatom frustule abundance and diversity with bulk sedimentary parameters indicating a spatial variability in phytodetrital export to the sediment. To verify this observation further, lipid biomarkers of key phytoplankton groups and a sea surface temperature (SST) proxy have been analysed in addition to diatom frustules. The C37 alkenone-based SST proxy indicated cooler SST (27.6 ± 0.25 °C) in the north (21–15° N) mostly due to upwelling (summer) and convective mixing (winter). Warmer SSTs (+ 0.4 °C) are measured in the south, which usually remains nutrient-poor. This trend was consistent with satellite-derived average SST values (2017–2020). Lipid biomarker analysis suggests that dinoflagellates were likely to be the highest contributor, as indicated by dinosterol and its degradative product dinostanol, followed by brassicasterol and C37 alkenone, likely representing diatoms and coccolithophores, respectively. The north, which largely experiences periodic phytoplankton blooms and is influenced by the thick OMZ, revealed the highest contents of organic matter, diatom frustules (diversity and abundance), dominated by large, thickly silicified cells (e.g. Coscinodiscus and Rhizosolenia) and phytoplankton lipid biomarkers, as well as lower contents of zooplankton biomarkers (cholesterol and cholestanol). In contrast, relatively smaller chain-forming centric (e.g. Thalassiosira) and pennate (e.g. Pseudo-nitzschia, Nitzschia, Thalassionema) diatom frustules along with lower phytoplankton lipid biomarker contents were found in the south, where zooplankton biomarkers and silicious radiolarians were more abundant. The possible impacts of the OMZ on particle flux related to the phytoplankton community, including zooplankton grazing and other factors, have been discussed. [ABSTRACT FROM AUTHOR]

To better identify the responses of phytoplankton blooms to warming conditions as expected in a climate change context, an in situ mesocosm experiment was carried out in a coastal Mediterranean lagoon (Thau Lagoon, South of France) in April 2018. Our objective was to assess both the direct and indirect effects of warming on phytoplankton, particularly those mediated by top-down control. Four treatments were applied: 1) natural planktonic community with ambient water temperature (C); 2) natural planktonic community at +3°C elevated temperature (T); 3) exclusion of larger zooplankton (> 200 μm; mesozooplankton) leaving microzooplankton predominant with ambient water temperature (MicroZ); and 4) exclusion of larger zooplankton (> 200 μm; mesozooplankton) at +3°C elevated temperature (TMicroZ). Warming strongly depressed the amplitude of the phytoplankton bloom as the chlorophyll a concentration was twice lower in the T treatment. This decline under warmer conditions was most likely imputed to increase top-down control by zooplankton. However, removal of mesozooplankton resulted in an opposite trend, with a higher bloom amplitude observed under warmer conditions (MicroZ vs. TMicroZ) pointing at a strong interplay between micro- and mesozooplankton and the effect of warming for the spring phytoplankton blooms. Furthermore, both warming and mesozooplankton exclusion induced shifts in phytoplankton community composition during bloom and post-bloom periods, favoring dinoflagellates and small green algae at the expense of diatoms and prymnesiophytes. Moreover, warming altered phytoplankton succession by promoting an early bloom of small green flagellates, and a late bloom of diatoms. Our findings clearly highlighted the sensitivity of phytoplankton blooms amplitudes, community composition and succession patterns to temperature increases, as well as the key role of initial zooplankton community composition to elicit opposite response in bloom dynamics. It also points out that warmer conditions might favor dinoflagellates and small green algae, irrespective of zooplankton community composition, with potential implications for food web dynamics and energy transfer efficiency under future ocean condition. [ABSTRACT FROM AUTHOR]

Zooplankton monitoring is important for understanding their population dynamics and life history, ecosystem health, and environmental changes. Compared with traditional morphological identification, environmental DNA (eDNA) analysis allows for more sensitive and efficient monitoring of zooplankton diversity. Previous eDNA studies have primarily used metabarcoding approaches to reveal their richness and composition, whereas its performance in predicting zooplankton abundance remains understudied. We conducted water and bulk sampling in Lake Biwa, Japan, showing that the number of sequence reads by metabarcoding moderately correlated with eDNA concentrations estimated by quantitative real-time PCR (qPCR). In addition, the eDNA read number was significantly related to cladoceran and copepod abundance estimated by microscopy sorting, although there remained too much uncertainty in the read-abundance relationship. Moreover, there was a significant difference in species composition between eDNA metabarcoding and sorting. Although our results indicated the potential applicability of eDNA metabarcoding for quantifying multiple zooplankton abundance, several methodological validations in eDNA metabarcoding would also be required to optimize its performance in the future. [ABSTRACT FROM AUTHOR]

The present study aimed to evaluate the diversity of zooplankton including rotifers and cyclops in the various freshwater ecosystems in Assiut Governorate, Egypt. Rotifers can affect the prevalence of different protozoan organisms in water, such as Cryptosporidium species. Cyclops act as intermediate host of some helminthic parasites. Microscopic analysis of the collected samples identified 3 rotifer genera and one copepod in different freshwater supplies including poultry farms, animal farms, human tanks, and fish farms. In the present study, 59 out of 136 (43.3%) water samples were contaminated with plankton. Poultry freshwater showed the highest plankton diversity and prevalence with 29 samples (21.3%), whereas the least prevalence was in human drinking water, 3 (2.2%). In the fishpond, Cyclops were observed in 3 (2.2%) of total samples. The prevalence of rotifers and Cyclops is strongly related to the summer season. Our results enrich the diversity of zooplankton in different freshwater supplies as a bioindicator of water pollution. [ABSTRACT FROM AUTHOR]

The rapid growth of aquaculture over the last century has led to the widespread introduction of aquatic species to freshwater environments. Bighead carp (Cyprinidae: Hypophthalmichthys nobilis) and silver carp (Cyprinidae: Hypophthalmichthys molitrix), collectively referred to as bigheaded carp, are among the top finfishes produced in aquaculture. These filter feeders possess feeding structures that allow them to efficiently remove plankton and other particles from the water. Unfortunately, when introduced into the wild and outside their historical range, their feeding traits generally result in the exploitation and suppression of phytoplankton and zooplankton, reducing food resources for native invertebrates and vertebrates.We conducted a meta‐analysis of published experiments to examine how bigheaded carp directly and indirectly affect organisms in aquatic food webs to better understand their ecological role within ecosystems. Specifically, we addressed the following questions: (1) What is the overall magnitude and direction of bigheaded carp effects on different aquatic organisms? (2) Do bigheaded carp affect organisms in planktonic and benthic habitats? (3) Are effects similar between bighead carp and silver carp? (4) Are effects consistent among experimental arenas (i.e., mesocosm, ponds)?We detected direct and indirect effects of bigheaded carp across multiple trophic levels. Large zooplankton often exhibited the strongest negative effects, with taxa‐specific differences between carp species. The suppression of zooplankton cascaded down to primary producers, resulting in an increase in phytoplankton (i.e., indirect effect). However, we observed no compensatory increases in rotifers when large zooplankton were reduced. Growth rates of planktivorous native fishes were the slowest when stocked with bigheaded carp. Our results further indicated that egested waste from bigheaded carp appeared to subsidise (i.e., direct effect) some benthic invertebrates such as Chironomidae midges. Effects of carp on zooplankton were generally similar between mesocosms and ponds.Invasive bigheaded carp greatly restructure their surrounding food web, both positively and negatively, through a complex suite of direct and indirect effects. These changes manifested across multiple trophic levels and differing habitats. Our analysis provides a more complete understanding of how these invasive carps change their surroundings by exploiting food resources and transferring materials from planktonic to benthic habitats. Taken together, the suite of direct and indirect effects shows how an invasive species can create imbalances within aquatic ecosystems, often to the detriment of native taxa.Bigheaded carp are invasive in many countries across the globe because of their popularity in aquaculture. Our findings reaffirm the threat these planktivores pose to native freshwater organisms. [ABSTRACT FROM AUTHOR]

Small pelagic fish (SPF) are crucial in marine food webs, transferring energy from plankton to higher trophic levels. This study focuses on herring (Clupea harengus) and sprat (Sprattus sprattus), addressing knowledge gaps in their feeding ecology in a nursery area, the Dutch Wadden Sea. We conducted a year-long, monthly survey, and used DNA metabarcoding to analyse zooplankton samples and stomach contents of two size classes of herring and sprat. Intra-, interspecific, and seasonal variations in fish condition, stomach fullness, and diet composition, along with selective feeding, were studied. Our study showed that condition and diet composition of herring and sprat, along with zooplankton density, exhibited a clear seasonal pattern. Juvenile herring and sprat displayed opportunistic feeding behaviour, rather than showing distinct prey selection. Besides copepods, we regularly observed (larvae of) benthic invertebrates in their diet. This emphasizes the crucial role of SPF as energy transfer agents, not solely between trophic levels, but also from benthic to pelagic habitats. Furthermore, fish post-larvae were part of the diet of larger herring (10–15 cm). Because of its unprecedented temporal and taxonomical detail, this study advances the understanding of seasonal dynamics of dominant components at the base of the Wadden Sea food web. [ABSTRACT FROM AUTHOR]

Mesozooplankton is a key component of the ocean, regulating global processes such as the carbon pump, and ensuring energy transfer from lower to higher trophic levels. Yet, knowledge on mesozooplankton diversity, distribution and connectivity at global scale is still fragmented. To fill this gap, we applied DNA metabarcoding to mesozooplankton samples collected during the Malaspina‐2010 circumnavigation expedition across the Atlantic, Indian and Pacific oceans from the surface to bathypelagic depths. We highlight the still scarce knowledge on global mesozooplankton diversity and identify the Indian Ocean and the deep sea as the oceanic regions with the highest proportion of hidden diversity. We report no consistent alpha‐diversity patterns for mesozooplankton at a global scale, neither across vertical nor horizontal gradients. However, beta‐diversity analysis suggests horizontal and vertical structuring of mesozooplankton communities mostly attributed to turnover and reveals an increase in mesozooplankton beta‐diversity with depth, indicating reduced connectivity at deeper layers. Additionally, we identify a water mass type‐mediated structuring of mesozooplankton bathypelagic communities instead of an oceanic basin‐mediated as observed at upper layers. This suggests limited dispersal at deep ocean layers, most likely due to weaker currents and lower mixing of water mass types, thus reinforcing the importance of oceanic currents and barriers to dispersal in shaping global plankton communities. [ABSTRACT FROM AUTHOR]

Non-indigenous invasive topmouth gudgeon (Pseudorasbora parva) was introduced to Europe in 1960s and it has passed an ongoing invasion into many European countries. It forms numerous populations particularly in pond aquaculture systems and small stagnant water bodies. The study was carried out on a 0.3 ha pond inhabited solely by the population of topmouth gudgeon. Monthly samplings of environmental variables, zooplankton, macrozoobenthos and fish were performed in 2016–2017. Topmouth gudgeon recruitment correlated with decrease of oxygen concentration and transparency in summer months, apparently due to topmouth gudgeon predation on the cladocerans. The macrozoobenthos community was dominated by large chironomid larvae (Chironomus plumosus), whose density and biomass were not affected by the topmouth gudgeon population. The habitat preferences varied within the population. The 0 + age cohort were abundant in rocky rip-rap, muddy and macrophyte habitats with low abundance in free water zone. In contrast, the 1 + and older fish significantly preferred the rocky rip-rap habitat and free water zone over muddy and macrophyte substrates. In spring, the rocky rip-rap was occupied mainly by males, while later in June and July, females predominated in this habitat. The study also documented disapperance of topmouth gudgeon population due to sudden spate flash-flood. [ABSTRACT FROM AUTHOR]

Marine heatwaves (MHWs) are extreme weather events that have major impacts on the structure and functioning of marine ecosystems worldwide. Due to anthropogenic climate change, the occurrence of MHWs is predicted to increase in future. There is already evidence linking MHWs with reductions in biodiversity and incidence of mass mortality events in coastal ecosystems. However, because MHWs are unpredictable, the quantification of their effects on communities is challenging.Here, we use the Helgoland Roads long‐term time series (German Bight, North Sea), one of the richest marine time series in the world, and implement a modified before‐after control‐impact (BACI) design to evaluate MHW effect on mesozooplankton communities. Mesozooplankton play an essential role in connecting primary producers to higher trophic levels, and any changes in their community structure could have far‐reaching impacts on the entire ecosystem.The responses of mesozooplankton community to MHWs in terms of community structure and densities occurred mainly in spring and autumn. Abundances of seven taxa, including some of the most abundant groups (e.g. copepods), were affected either positively or negatively in response to MHWs. In contrast, we observed no clear evidence of an impact of summer and winter MHWs; instead, the density of the most common taxa remained unchanged.Our results highlight the seasonally dependent impacts of MHWs on mesozooplankton communities and the challenges in evaluating those impacts. Long‐term monitoring is an important contributor to the quantification of effects of MHWs on natural populations. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the effect of using different vegetable brans as organic carbon source in synbiotic system fertilization on the nitrification process, plankton composition, and growth of Penaeus vannamei in the nursery phase, also comparing it with the biofloc system. An extended nursery rearing was carried out for 53 days, at a density of 2000 shrimp m−3 (initial weight: 0.03 ± 0.01 g). The following treatments were established, with five repetitions: CW, clear water (control); BFT, biofloc system; RB, synbiotic system fertilized with rice bran; SB, synbiotic system fertilized with soybean bran; and WB, synbiotic system fertilized with wheat bran. The synbiotic fertilization protocol used a commercial blend of Bacillus subtilis and Bacillus licheniformis, molasses, sodium bicarbonate as buffer, and water. The fertilizers were processed by an anaerobic (24 h) and an aerobic (24 h) phase. BFT treatment used molasses as organic carbon source. At the end of the trial, final weight was higher in CW, BFT, and RB treatments than in WB. In RB, SB, and WB treatments, TAN was controlled between days 10 and 14 and NO2−-N was controlled from day 40 of the trial, resembling a newly started system. At the end of the trial, a higher abundance of coccoid and bacillus was observed in the RB treatment, while a higher abundance of vibrio bacteria was observed in WB. Rice bran proved to be the best alternative for the synbiotic fertilization, as it presented a final weight (3.27 g) similar to BFT and CW treatments, and higher than WB (2.61 g). Also, the use of rice bran produced a high load of microorganisms, which can improve shrimp growth. [ABSTRACT FROM AUTHOR]

Ecological stoichiometry of nitrogen (N) and phosphorus (P) has been well studied as a driver of zooplankton dynamics in lakes; yet, we still lack a thorough investigation of the impact of varying N loads, and the resulting variation in resource N:P stoichiometry. We used a mesocosm experiment in which we altered inputs of N and P to observe the impact of stoichiometric variation in nutrient concentrations on zooplankton density and community composition for a period of 10 weeks. Our experiment achieved a wide gradient of environmental N:P availability primarily by altering N loading, while keeping P inputs consistent across treatments. Across all treatments, we observed declines in zooplankton density through time and a reduction in cladocerans relative to copepods. These temporal patterns correlated to a loss of P in the water column and higher food resource N:P, as well as warming temperatures throughout the experiment. Our experiment highlights the potential importance of resource quality over quantity for supporting higher zooplankton densities, as well as the impacts of high temperatures. These results suggest disproportionately high N loads relative to P as is common in agricultural landscapes could reduce zooplankton populations, despite stimulating greater primary production. [ABSTRACT FROM AUTHOR]

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Integrated rice–fish farming, an agricultural practice that combines cultivating rice and breeding fish in the same field, has attracted widespread attention. However, there is limited research on how the rice–carp coculture impacts the community structure of phytoplankton and microzooplankton in paddy water. This study employed eDNA metabarcoding sequencing to analyze the composition of phytoplankton and microzooplankton in a rice monoculture system (RM) and a rice–carp coculture system (RF). Following annotation, we identified 9 phyla, 89 families, 275 genera, and 249 species of phytoplankton, along with 20 phyla (or subphyla and classes), 85 families, 222 genera, and 179 species of microzooplankton. The alpha diversity indices revealed significantly higher richness, diversity, and evenness in the RF group compared to the RM group during grain-filling stage. Principal coordinates analysis (PCoA) demonstrated notable differences in the phytoplankton and microzooplankton compositions between the two groups across various rice growth stages. Composition analysis showed that rice–carp coculture increased the relative abundance of dominant phytoplankton phyla such as Bacillariophyta, Chrysophyta, and Euglenophyta while decreasing that of Cryptophyta. In microzooplankton, the coculture resulted in an increased abundance of Intramacronucleata (subphylum) and a decrease in Conoidasida (class). In conclusion, the rice–carp coculture enhances the diversity of plankton, particularly during the grain-filling stage, and simultaneously alters the composition and abundance of dominant plankton species in the paddy water. These findings enhance understanding of the broader impacts of integrated rice–carp farming on agricultural ecosystems, emphasizing alterations in the diversity and composition of aquatic microorganisms [ABSTRACT FROM AUTHOR]

The characteristics of zooplankton communities and the relationships with the aquatic environment in the shallow waters of northern Liaodong Bay were investigated. Spot sampling surveys were carried out in April, June, September, and November 2018 to assess zooplankton species composition and diversity, abundance, biomass, and dominant species, and the associated relationships with environmental factors. A total of 45 species of zooplankton were recorded in the survey, comprising 18 Copepoda, 2 Amphipoda, 1 Mysidacea, 1 Decapoda, 1 Chaetognatha, 7 Hydrozoa, 1 Tunicate, and 14 planktonic larvae. Overall, the most dominant species was Aidanosagitta crassa (Tokioka, 1938), with copepods and planktonic larvae also dominating the zooplankton community. However, there was a seasonal alternation of species dominance. A cluster analysis showed that the zooplankton community in spring differed from other seasons and was mostly influenced by suspended particulate matter. Bioenv analysis indicated the main environmental factor affecting the zooplankton community in spring was suspended particulate matter. In summer, the determining variables were temperature, dissolved inorganic nitrogen (DIN), nitrate, and sediment pH. In autumn, temperature, DIN, and nitrate were determining variables, and dissolved oxygen (DO) and DIN in winter. Zooplankton abundance and biomass were influenced by salinity, suspended particulate matter, chemical oxygen demand (COD), chlorophyll, and water and sediment pH. In general, the shallow sea area north of Liaodong Bay is rich in zooplankton species and exhibits significant seasonal variations. Human activities have disturbed the biological community to a certain extent, and the environmental factors in this area are closely related to the diversity of zooplankton species. [ABSTRACT FROM AUTHOR]

Due to its fundamental position in the aquatic food chain linking primary producers (phytoplankton) to higher trophic levels (fish), zooplankton has a crucial influence on the structure and function of lakes. The scientific literature shows that zooplankton is an effective indicator of eutrophication. However, according to the requirements of the Water Framework Directive, zooplankton is still not included as one of the biological components for assessing the ecological status of lakes. In Poland, the zooplankton-based method (ZIPLAs) has been developed to assess the ecological status of deep stratified lakes. Shallow lakes function differently from deep lakes, and literature data show that the response of zooplankton indices to eutrophication parameters is much weaker than in deep lakes. This paper presents the Zooplankton Index for Shallow Lakes' Assessment (ZISLA), a new method for assessing ecological status based on zooplankton community structure. The ZISLA includes the body size index of Daphnia cucullata (BSI), the percentage share of high trophy-indicating rotifer species (IHTROT), the number of rotifer species (NROT), and the Margalef index (D). The ZISLA shows a strong, significant correlation with total phosphorus and total nitrogen (Spearman's coefficient (R = −0.77, R = −0.74; p < 0.0001) and slightly weaker with Secchi disk visibility (R = 0.72; p < 0.0001). The ZISLA index shows a statistically significant good/moderate distinction for all water quality parameters. [ABSTRACT FROM AUTHOR]

Over the entire period of studies in the water bodies in the Ural River basin, comprehensive hydrobiological studies have not been carried out in many areas both on the main watercourses of the Ural and Sakmara rivers and on a large number of tributaries of different levels. The results of such studies carried out by the Water Problems Institute, Russian Academy of Sciences, during expeditions in the summer and autumn 2022 are discussed. A large body of data on phytoplankton, zooplankton, zoobenthos, and juvenile fish was collected and processed. [ABSTRACT FROM AUTHOR]

A two-years study (March 2021 to February 2023) was carried out at the Kanewal Community Reservoir, an important water storage reservoir in central Gujarat, to assess the diversity and seasonal variation of the planktonic community. During the study period, a total of 60 phytoplankton species were recorded, belonging to 9 classes, 25 orders and 39 families. Class-wise percentage composition of phytoplankton showed a diverse array during the study period. The species gradient of phytoplankton was as follows: Bacillariophyceae (20) > Zygnematophyceae (14) > Cyanophyceae (10) > Chlorophyceae (9) > Euglenophyceae (2) > Trebouxiophyceae (2) > Dinophyceae (1) > Klebsormidiophyceae (1) > Ulvophyceae (1). Thirty (30) different zooplankton species were recorded during this study, belonging to 11 classes, 14 orders and 19 families. The number of abundant species remained constant throughout the study period. The recorded number of common zooplanktonic species also remained steady (14). However, the number of rare species slightly increased to two (2), which indicates a slight increase in the occurrence of less prevalent species. The highest density of zooplankton was observed during the summer, and the lowest in the monsoon season. Overall, it was found that KCR (Kanewal Community Reservoir) contains a higher number of phytoplankton species (60) compared to zooplankton (30), which could be a consequence of the voluminous hydrological regime with abundant occurrence of macrophyte elements. [ABSTRACT FROM AUTHOR]

Zooplankton are important food organisms in the marine ecosystem, and their community structure and distribution reflect the productivity of the waters. To investigate the zooplankton structure and the environmental factors affecting ecological niche differentiation in the waters of Tahe Bay, Lushun, a survey was conducted in September 2021 and March, April, and November 2022 in the waters of Tahe Bay. The results showed that there are 31 species representing four phyla, with an annual mean abundance of 12.42 × 103 ind/m3, dominated by Copepoda (13 species, 41.94%), with zooplankton richness indices ranging from 0.83 to 2.44, diversity indices ranging from 0.84 to 2.42, and evenness indices ranging from 0.14 to 0.84. Pearson's correlation of zooplankton abundance and community diversity with environmental factors, such as water temperature, salinity, dissolved oxygen, NH3-N, and NO3-N, was significant in the waters of Tahe Bay. There were 13 dominant species, mainly consisting of broad-niche species, among which Oithona similis was the dominant species in all four seasons; the degree of niche overlap of the dominant species was related to the seasons, with a serious niche overlap accounting for 81.0% in September 2021, and there was no niche overlap in March 2022; 33.3% of the species had a severe ecological niche overlap in April 2022, with a serious niche overlap accounting for 86.7% in November 2022. The results of redundancy analysis (RDA) indicated that water temperature, salinity, DO, and DIP are the main environmental factors affecting the ecological niche differentiation of the dominant species of zooplankton. [ABSTRACT FROM AUTHOR]

More heterogeneous environments allow for greater availability of ecological niches, thus favoring greater species diversity. However, it is not yet established how heterogeneity influences taxonomic and functional beta diversity. Therefore, we aimed to determine how environmental heterogeneity affects the patterns of taxonomic and functional beta diversity of planktonic microcrustaceans in reservoirs in different regions (semiarid and humid) in Northeast Brazil, in addition to verifying the influence of dry and rainy periods on these measures. Sampling from the semiarid region was carried out between 2013 and 2016, while samples from the humid region were collected between 2019 and 2021. Environmental heterogeneity and taxonomic and functional beta diversity were greater in the semiarid region, regardless of the hydrological period. However, regardless of the region, taxonomic beta diversity was greater during the dry period, while functional beta diversity did not differ between periods. Both types of diversity were driven mainly by local factors in the semiarid region, considered a region of high environmental heterogeneity due to the geomorphological and climatic characteristics that differentiate it from other regions. This type of study reinforces the need to conserve these reservoirs, especially those located in the semiarid region, as they support greater variability in species composition and functional traits. [ABSTRACT FROM AUTHOR]

This study aimed to achieve a better understanding of the features of zooplankton assemblages in small water bodies and their biodiversity and composition in relation to the presence of fish and accompanying environmental characteristics. This study was conducted in 16 mid-field ponds. Compositional and biodiversity indexes and ordination methods were used to analyze the relationship between zooplankton assemblages in unstable fishless and stable fish ponds. A total of 121 zooplankton taxa were identified. Compositional indicators revealed significant differences in zooplankton assemblages between fish ponds (FPs) and fishless ponds (FLPs). Canonical correspondence analysis indicated that variation in zooplankton assemblages depended on the ponds' features. Most of the high trophic state indicator species were present only in FPs or occurred sporadically in FLPs. Rarefaction and extrapolation indicated a higher number of zooplankton taxa in FPs than in FLPs. The stability of the ecosystem was essential for maintaining the high species richness of zooplankton. Diversity indices were not influenced by variations in species composition or environmental differences among ponds. Diversified pond types are necessary to maintain the heterogeneity of mid-field ponds, which support the high regional biodiversity of zooplankton assemblages. [ABSTRACT FROM AUTHOR]

The objects of this study were lakes Mielenko (LM) (7.8 ha, 1.9 m), Klasztorne Małe (LKM) (13.7 ha, 20.0 m), and Klasztorne Duże (LKD) (57.5 ha, 8.5 m), located in north Poland (Kashubian Lake District). These lakes received raw sanitary and storm wastewater, leading to extreme degradation of these water bodies. This study aimed to present changes in buffer indicators such as reaction, alkalinity, total hardness, and Ca and Mg content that occurred as an effect of their restoration using the sequential application of coagulants as an innovative approach to the phosphorus inactivation method. Sustainable phosphorus inactivation in the study lakes made it possible to achieve nutrient concentrations in the range of values typical for low-trophic lakes. A radical decrease in P concentration in the water resulted in a limitation of production processes. Moreover, after a, it was noticed that the water parameters determining its buffering properties did not show a clear vertical stratification with increasing values toward the bottom. For example, before restoration, the mean e value of alkalinity in LM fluctuated around 2.10 mval/L, and after restoration activities, the average value was 1.97 mval/L. In LKM, the mean alkalinity value in surface water layers was 2.53 mval/L, and in bottom water layers, it was 4.92 mval/L; after restoration treatments, the average alkalinity of surface water was 2.18 mval/L, and in bottom water, it was 2.99 mval/L. In the last LKD, under the influence of the applied restoration, the average alkalinity of surface waters changed from 2.21 to 2.07 mval/L, and in bottom water, it changed from 2.86 to 2.12 mval/L. The values of parameters determining the buffering properties of lake water after restoration activities allow their water to be classified as slightly or medium hard. The changes obtained can be considered beneficial because water that is too hard does not support the development of aquatic organisms, and the values obtained in the study lakes after sustainable restoration are optimal for the construction of plant walls, shells, and fish bones. [ABSTRACT FROM AUTHOR]

Context: Floodplain inundation creates a diversity of aquatic habitats that diverge in their physical, chemical and biological characteristics through space and time, influencing site-scale ecological processes, with implications for local and landscape-scale ecosystem functioning. Aims: In this study, we characterise conditions of pools on the floodplain and pools in the main channel of the Fitzroy River, north-western Australia. Methods: We used linear models to investigate the spatial and temporal dynamics of top–down and bottom–up forces acting on phytoplankton and zooplankton. Key results: Floodplain pools showed considerable heterogeneity compared with the main channel and were shallow and turbid with high nutrient loads, whereas main-channel pools were deep, clear and nutrient-limited. Phytoplankton and zooplankton biomass (mass per unit volume) were considerably greater and more variable in floodplain pools than in the main channel, where both were largely absent. On the floodplain, bottom–up processes drove water-column productivity (e.g. nutrients to phytoplankton to zooplankton) to a degree not observed in the main channel, providing a valuable resource pathway supporting consumer populations locally and catchment wide. We detected no top–down effects in floodplain pools and no top–down or bottom–up effects in the main channel. Conclusion: Maintaining flows that inundate the floodplain and promote habitat heterogeneity in the Fitzroy River is crucial for preserving local and landscape-scale ecosystem functioning. Implications: Water managers should take into account the important contribution of floodplain pools to the wider riverine ecosystem and ensure these habitats are not unduely affected by water resource development. Seasonal flooding promotes habitat diversity that influences biodiversity and ecological processes in river–floodplain ecosystems. We demonstrated that environmental conditions in floodplain pools on the Fitzroy River (WA) vary substantially compared with the main channel, providing an important habitat for organisms that contribute to landscape-scale ecosystem function. Floodplain pools fill a unique role in the wider river–floodplain ecosystem and should be protected from negative effects of water development. [ABSTRACT FROM AUTHOR]

Background: DNA metabarcoding applies high-throughput sequencing approaches to generate numerous DNA barcodes from mixed sample pools for mass species identification and community characterisation. To date, however, most metabarcoding studies employ second-generation sequencing platforms like Illumina, which are limited by short read lengths and longer turnaround times. While third-generation platforms such as the MinION (Oxford Nanopore Technologies) can sequence longer reads and even in real-time, application of these platforms for metabarcoding has remained limited possibly due to the relatively high read error rates as well as the paucity of specialised software for processing such reads. Results: We show that this is no longer the case by performing nanopore-based, cytochrome c oxidase subunit I (COI) metabarcoding on 34 zooplankton bulk samples, and benchmarking the results against conventional Illumina MiSeq sequencing. Nanopore R10.3 sequencing chemistry and super accurate (SUP) basecalling model reduced raw read error rates to ~ 4%, and consensus calling with amplicon_sorter (without further error correction) generated metabarcodes that were ≤ 1% erroneous. Although Illumina recovered a higher number of molecular operational taxonomic units (MOTUs) than nanopore sequencing (589 vs. 471), we found no significant differences in the zooplankton communities inferred between the sequencing platforms. Importantly, 406 of 444 (91.4%) shared MOTUs between Illumina and nanopore were also found to be free of indel errors, and 85% of the zooplankton richness could be recovered after just 12–15 h of sequencing. Conclusion: Our results demonstrate that nanopore sequencing can generate metabarcodes with Illumina-like accuracy, and we are the first study to show that nanopore metabarcodes are almost always indel-free. We also show that nanopore metabarcoding is viable for characterising species-rich communities rapidly, and that the same ecological conclusions can be obtained regardless of the sequencing platform used. Collectively, our study inspires confidence in nanopore sequencing and paves the way for greater utilisation of nanopore technology in various metabarcoding applications. [ABSTRACT FROM AUTHOR]

Most host-parasite associations are explained by phylogenetically conservative capabilities for host utilization, and therefore parasite switches between distantly related hosts are rare. Here we report the first evidence of a parasitic spillover of the burrowing sea anemone Edwardsiella carnea from the invasive ctenophore Mnemiopsis leidyi to two scyphozoan hosts: the native Mediterranean barrel jellyfish Rhizostoma pulmo and the invasive Indo-Pacific nomad jellyfish Rhopilema nomadica, collected from the Eastern Mediterranean Sea. Edwardsiella carnea planulae found in these jellyfish were identified using molecular analyses of the mitochondrial 16S and nuclear 18S rRNA genes. Overall, 93 planulae were found on tentacles, oral arms, and inside of the gastrovascular canals of the scyphomedusae, whereas no infection was observed in co-occurring ctenophores. DNA metabarcoding approach indicated seasonal presence of Edwardsiella sp. in the Eastern Mediterranean mesozooplankton, coinciding with jellyfish blooms in the region. Our findings suggest a non-specific parasitic relationship between Edwardsiella carnea and various gelatinous hosts based on shared functionality rather than evolutionary history, potentially driven by shifts in host availability due to jellyfish blooms. This spillover raises questions about the ecological impacts of parasitism on native and invasive scyphozoan hosts and the potential role of Edwardsiella in controlling their populations. [ABSTRACT FROM AUTHOR]

Polar cod (Boreogadus saida) is an endemic key species of the Arctic Ocean ecosystem. The ecology of this forage fish is well studied in Arctic shelf habitats where a large part of its population lives. However, knowledge about its ecology in the central Arctic Ocean (CAO), including its use of the sea‐ice habitat, is hitherto very limited. To increase this knowledge, samples were collected at the under‐ice surface during several expeditions to the CAO between 2012 and 2020, including the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. The diet of immature B. saida and the taxonomic composition of their potential prey were analysed, showing that both sympagic and pelagic species were important prey items. Stomach contents included expected prey such as copepods and amphipods. Surprisingly, more rarely observed prey such as appendicularians, chaetognaths, and euphausiids were also found to be important. Comparisons of the fish stomach contents with prey distribution data suggests opportunistic feeding. However, relative prey density and catchability are important factors that determine which type of prey is ingested. Prey that ensures limited energy expenditure on hunting and feeding is often found in the stomach contents even though it is not the dominant species present in the environment. To investigate the importance of prey quality and quantity for the growth of B. saida in this area, we measured energy content of dominant prey species and used a bioenergetic model to quantify the effect of variations in diet on growth rate potential. The modeling results suggest that diet variability was largely explained by stomach fullness and, to a lesser degree, the energetic content of the prey. Our results suggest that under climate change, immature B. saida may be at least equally sensitive to a loss in the number of efficiently hunted prey than to a reduction in the prey's energy content. Consequences for the growth and survival of B. saida will not depend on prey presence alone, but also on prey catchability, digestibility, and energy content. [ABSTRACT FROM AUTHOR]

The present study was conducted in one of the most significant water sources in Iraq, the Tigris River in Misan Province. The aim was to examine the zooplankton community, specifically Cladocera, Copepoda, and Rotifera. Samples were collected 30cm below the water surface using a plankton haul net with a mesh size of 64μm from September 2023 to February 2024. Sampling took place at three stations: the first in Kumait, located in the north of Misan Province; the second in Amarah City, the capital of Misan Province, and the third about 20km south of Amarah City. The results revealed seventeen species of zooplankton, belonging to two phyla, three classes, four orders, and eight families. A comparison between the historical and current status in the study area indicated a noticeable shift in zooplankton composition toward species more tolerant of pollution. For instance, the appearance of the family Brachionidae and its common species Brachionus sp. in the study area, alongside the absence of Daphnia species, suggests ecological degradation in the inland waters of Iraq, particularly in Misan Province. This study recommends incorporating zooplankton into water quality monitoring programs (WQMPS) in Iraq. [ABSTRACT FROM AUTHOR]

Plankton size spectra are important indicators of the ecosystem state, yet such measurements are typically biased by the available sampling methods. Here, we combined individual size measurement from two zooplankton imaging approaches— in situ observation by the Underwater Vision Profiler5 and Multinet-collection supplemented by ex situ imaging via Zooscan—obtained in the global ocean, to calculate zooplankton normalized biovolume size spectra (NBSS) for all organisms larger than 1 mm. The reconstructed NBSS combining both datasets resulted in increased biomass estimates by adding organisms poorly sampled by either of the methods. The optimal values measured by both methods are used to reconstruct the zooplankton biovolume and biomass distributions. The reconstructed slopes appeared steeper and closer to those measured only by the UVP5 (+7.6%) and flatter than those obtained only from the Multinet (−20%), particularly in tropical and temperate latitudes. The main difference in tropical and temperate NBSS from the two devices is due to the fragile rhizarians that were not accounted for when using net data. When possible, we suggest using in situ and ex situ technologies together, and we provide potential indications on how to correct for missing components of the community when only one method is available. [ABSTRACT FROM AUTHOR]

Classification of zooplankton to species with broadband echosounder data could increase the taxonomic resolution of acoustic surveys and reduce the dependence on net and trawl samples for 'ground truthing'. Supervised classification with broadband echosounder data is limited by the acquisition of validated data required to train machine learning algorithms ('classifiers'). We tested the hypothesis that acoustic scattering models could be used to train classifiers for remote classification of zooplankton. Three classifiers were trained with data from scattering models of four Arctic zooplankton groups (copepods, euphausiids, chaetognaths, and hydrozoans). We evaluated classifier predictions against observations of a mixed zooplankton community in a submerged purpose-built mesocosm (12 m3) insonified with broadband transmissions (185–255 kHz). The mesocosm was deployed from a wharf in Ny-Ålesund, Svalbard, during the Arctic polar night in January 2022. We detected 7722 tracked single targets, which were used to evaluate the classifier predictions of measured zooplankton targets. The classifiers could differentiate copepods from the other groups reasonably well, but they could not differentiate euphausiids, chaetognaths, and hydrozoans reliably due to the similarities in their modelled target spectra. We recommend that model-informed classification of zooplankton from broadband acoustic signals be used with caution until a better understanding of in situ target spectra variability is gained. [ABSTRACT FROM AUTHOR]

Diel vertical migration (DVM) is a behaviour observed across zooplankton taxa in marine and limnetic systems worldwide. DVM influences biogeochemical cycling and carbon drawdown in oceanic systems and alters prey availability for zooplanktivorous species. DVM has been well studied among zooplankton, and many exogenous and endogenous triggers as well as adaptive significances have been hypothesized. However, second-order variability in DVM timing, the deviation of DVM times to respective dawn and dusk times throughout the year, is a less-studied phenomenon that can help identify the factors influencing migration timing as well as demonstrate the changes of DVM behaviours within and across systems. Here, we quantified seasonal trends in second-order variability of DVM timing of euphausiids at Brooks Peninsula, Clayoquot Canyon, and Saanich Inlet near Vancouver Island, British Columbia, Canada, over multiple years using upward-facing moored echosounders. We used generalized additive mixed models to characterize this seasonality. DVM timing relative to civil twilight times showed strong seasonality at all locations, with euphausiids remaining near the surface longer than expected in spring and summer, and shorter than expected in winter. Euphausiids spent less time near the surface at Brooks Peninsula and Clayoquot Canyon than at Saanich Inlet throughout the year. Increased primary productivity in Saanich Inlet, which reduced light penetration and hid euphausiids from visual predators, likely drove this difference. Our findings confirm that proper understanding of DVM behaviours must account for seasonal variability due to context-specific oceanographic and ecological parameters. This is particularly pertinent when attempting to model the biogeochemical or predator–prey interactions influenced by DVM behaviours. [ABSTRACT FROM AUTHOR]

Biodiversity records are of great importance, especially in light of the biodiversity crisis. Here, we present a study on the diversity of rotifers in Bolivia based on an extensive investigation of the literature published so far. Through this approach and an analysis of samples from 207 water bodies of the country, we updated the checklist of reported species. This study revealed a total of 195 species of rotifers previously reported; we identified 153 species in our samples, with 84 of them being reported for the first time in Bolivia. Thus, a total of 279 species are known at present in this country. Our findings suggest that Bolivia has a rich and diverse rotifer community, with many species likely to be unique to the region. [ABSTRACT FROM AUTHOR]

Lipid‐rich copepods form an essential link between primary producers and higher trophic levels in high‐latitude oceans. These zooplankton can take advantage of ephemeral phytoplankton blooms to fuel development and reproduction. However, we have limited understanding of how the physiological condition of these animals varies in relation to environmental factors such as food availability. Due to high advection, it is likely that physiological plasticity, rather than local adaptation, is primarily responsible for physiological differences within a region. We use transcriptomics and other physiological metrics to understand how two species of copepods (Calanoides acutus and Calanus propinquus) vary across environmental gradients along the West Antarctic Peninsula. For the primarily herbivorous C. acutus, physiological separation between sampling locations appears to be driven by feeding status, and gene expression differences indicate differential expression of genes regulating lipid metabolism, reproduction, aerobic metabolism, and protein translation. For the more omnivorous C. propinquus, physiology and gene expression did not segregate as clearly by location, showed minimal signs of food deprivation at any location, and had a weaker relationship with chlorophyll compared to C. acutus. By comparing these results with concurrent starvation experiments, we find that spatial variation in gene expression reflects short‐term differences in food availability (particularly for C. acutus), and we identify genes whose expression indicates recent feeding status. Further examination of the relationships between food availability, copepod physiology, and population dynamics will ultimately improve our capacity to predict how copepod populations will respond to rapidly changing environmental conditions in the West Antarctic Peninsula ecosystem. [ABSTRACT FROM AUTHOR]

Zooplankton are important food organism in the marine ecosystem, and its community structure and population distribution reflect the productivity of the waters. In order to understand the interspecific relationship of the zooplankton community and the impact of changes in environmental factors on the niche differentiation of dominant species in the Bailanzi waters, basing on the zooplankton survey data in March and December of 2022 and June of 2023, we obtained the dominance index of zooplankton in this sea area through calculating the Levins niche width value and Pianka niche overlap value of the dominant species, and divided the niche types of the dominant species into broad niche species, medium niche species and narrow niche species. The redundancy analysis method was used to explore the main environmental factors affecting the niche differentiation of dominant species of zooplankton in Bailanzi waters. The results showed that there were 9 dominant species and all of them were wide ecological niche species in March 2022, 5 dominant species and all of them were wide ecological niche species in December 2022, and 6 dominant species, including 3 wide ecological niche species and 3 narrow ecological niche species, in June 2023. The niche overlap indexes of the dominant zooplankton species in March 2022 ranged from 0. 54 to 1. 00, and those in December 2022 ranged from 0. 60-0. 98 in March 2022, 0. 62-0. 99 in December 2022, and 0. 62-0. 99 in June 2023. Redundancy analysis showed that the main environmental factors affecting zooplankton distribution are temperature and salinity, followed by pH, dissolved oxygen （DO), ammonia nitrogen （NH3-N), dissolved inorganic phosphorus （DIP), dissolved inorganic nitrogen （DIN), chemical oxygen demand （COD). The research results are expected to provide basic information for an in-depth understanding of the interspecific relationships of zooplankton communities in Bailanzi waters and the adaptation mechanism of zooplankton to environmental changes, and provide a theoretical reference for high-quality marine ranch construction in this waters. [ABSTRACT FROM AUTHOR]

Southern Ocean zooplankton provide globally significant ecosystem services through their role in carbon sequestration, nutrient cycling and food webs. However, the remote and extreme nature of the Southern Ocean creates significant logistical difficulties for studying zooplankton all year round. Here, for the first time in the Southern Ocean, we present the seasonal occurrence of the zooplankton assemblage in the Northeast Scotia Sea using a sediment trap deployed throughout 2018 (P3 observation site, 52.80˚ S, 40.14˚ W). Results show that copepods and pteropods dominated trap abundance, representing 25.0–68.3% and 13.4–72.5% respectively, followed by amphipods (1.0–7.2%) and hydrozoa (0.2–15.6%). The dominant signal in copepods was consistent with previous observations using traditional (net) sampling methods while the relative contribution of pteropods, amphipods and hydrozoa was increased in our trap. Further, zooplankton showed taxon-specific seasonal signals, with a relatively high number of individuals throughout winter, including an increase in hydrozoa occurrences. This observation highlights the importance of zooplankton as source of nutrition for the benthic community in the winter. Our data reiterate the utility of sediment traps for observing zooplankton in remote locations and sampling specific taxa that might be otherwise understudied. [ABSTRACT FROM AUTHOR]

This study emphasises the importance of environmental filters in the dynamics of the zooplankton community and the ecological relationships with phytoplankton in three zones of a tropical mesotidal estuary.Thus, sampling was carried out in six different locations strategically positioned along the Preguiças River estuary, with the following objectives: to characterise the abundance of zooplankton and, through this, determine changes in the community's α‐ and β‐diversity indices depending on variables environmental; to define environmental filters that affect the indicator species of ecosystem zones; and to identify the interaction between phytoplankton and zooplankton along the estuarine gradient.The zooplankton community contained 80 species, including 14 phyla, with Arthropoda being the most diverse, followed by Ciliophora and Mollusca. The class Copepoda stood out, with Paracalanus crassirostris, Pseudodiaptomus gracilis, and Oithona nana dominating the community. In total, 21 species were selected as indicators, including Temora turbinata in the coastal zone, Rhizodomus tagatzi in the mixing zone, and Moina micrura in the tidal river zone. The environmental heterogeneity showed significant spatial differences, with variations governed mainly by salinity, temperature, and suspended organic matter, which acted as the principal environmental filters. The coastal zone and mixing zone species demonstrated direct ecological relationships with the blooms of the diatoms Skeletonema costatum and Asterionellopsis glacialis, in which the abundance of zooplankton was favoured by their occurrence, denoting top‐down control of the trophic network. For the partitioning of β diversity, the turnover component was responsible for the diversity value due to environmental heterogeneity, which distinguished communities across zones.Our findings represent the first comprehensive investigation into the relationship between environmental heterogeneity and zooplankton within this tropical ecosystem, subject to mesotides. These discoveries are pivotal in identifying environments highly susceptible to degradation (low β diversity) and those acting as dispersal centres (high β diversity), thereby facilitating targeted conservation efforts and more efficient management of estuarine systems. Therefore, our results provide a crucial basis for the sustainable management of similar coastal ecosystems in different parts of the world. [ABSTRACT FROM AUTHOR]