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It has long been hypothesized that benthic motile pennate diatoms use phototaxis to optimize photosynthesis and minimize photoinhibitory damage by adjusting their position within vertical light gradients in coastal benthic sediments. However, experimental evidence to test this hypothesis remains inconclusive, mainly due to methodological difficulties in studying cell behavior and photosynthesis over realistic spatial microscale gradients of irradiance and cell position. In this study, a novel experimental approach was developed and used to test the hypothesis of photosynthesis optimization through motility, based on the combination of single-cell in vivo chlorophyll fluorometry and microfluidic chips. The approach allows the concurrent study of behavior and photosynthetic activity of individual cells of the epipelic diatom species Craspedostauros britannicus exposed to a light microgradient of realistic dimensions, simulating the irradiance and distance scales of light microgradients in benthic sediments. Following exposure to light, (i) cells explored their light environment before initiating light-directed motility; (ii) cells used motility to lower their light dose, when exposed to the highest light intensities; and (iii) motility was combined with reversible non-photochemical quenching, to allow cells to avoid photoinhibition. The results of this proof-of-concept study not only strongly support the photoprotective nature of photobehavior in the studied species but also revealed considerable variability in how individual cells reacted to a light microgradient. The experimental setup can be readily applied to study motility and photosynthetic light responses of other diatom species or natural assemblages, as well as other photoautotrophic motile microorganisms, broadening the toolset for experimental microbial ecology research. [ABSTRACT FROM AUTHOR]

The study provides significant insights into the community structure, species diversity and the environmental factors affecting the diversity of MPB in the tropical estuarine habitat of the Cochin estuary. A significant outcome of the present study was the taxonomic identification of 59 species of MPB belonging to 22 genera, which comprised 49 species of diatoms, one species of dinoflagellate, six species of cyanobacteria, two species of euglenophytes and one species of chlorophyte. Major MPB identified in the study were Navicula erifuga, Gyrosigma wansbeckii, Navicula flanatica, Nitzschia sigma, Nitzschia fluminensis, Amphora cymbifera, Nitzschia clausii, Nitzschia lorenziana, Navicula arenaria and Gyrosigma balticum. Principal component analysis indicated that the porewater salinity, sediment temperature, sediment pH, dissolved oxygen (DO), C:N ratio, porewater silicate and sediment chlorophyll a were positively correlated with the diversity of MPB. The intensity of rainfall, OC%, C:S ratio, and TN% were negatively correlated with the diversity of MPB. The study provides a detailed taxonomic inventory of MPB diversity and environmental influences, offering additional insights into tropical estuarine ecology. [ABSTRACT FROM AUTHOR]

Epipelic, biofilm-forming diatoms are key drivers of the primary production of mudflats. Such primary production is strongly affected by the vertical migration of diatoms, which is modulated by diurnal photoperiods, tidal cycles, and photoprotection mechanisms. However, the role of vertical migration in the radiative energy budget (REB) of microphytobenthic biofilms remains largely unknown. Here we used microsensor measurements of temperature and O2 in combination with reflectance spectroscopy and variable chlorophyll fluorimetry to construct the REB of intertidal, epipelic diatom-dominated biofilms for different emersion times (1, 3 and 5 h after the beginning of the in-situ emersion) and photon irradiance regimes, i.e., 400 and 800 µmol photon m−2 s−1. The effect of migration on REBs was studied by inhibiting diatom motility with Latrunculin A (Lat-A). Photosynthetic activity and light utilization efficiency decreased slightly, after adding Lat-A, while the amount of reflected light energy remained constant at ~ 23% of the incident irradiance and the majority (76–78%) of the incident light energy was dissipated as heat. Of the energy dissipated as heat, < 24% was dissipated upward in Lat-A treated samples, while an increasing downward heat dissipation was observed in Lat-A treated samples, as compared to control samples under an irradiance of 800 µmol photon m−2 s−1. However, we found no statistical significant differences in the REB and physiological parameters in the different treatments. Thus, we did not find any evidence that vertical migration of diatoms affected photosynthesis and light efficiency in the microphytobenthic biofilm over an emersion cycle, and a clear effect of non-photochemical quenching in REB and heat dissipation fluxes was not observed. [ABSTRACT FROM AUTHOR]

Abstract This study aimed to investigate the presence and diversity of fungal parasites in Arctic coastal microphytobenthic communities. These communities represent a key component in the functioning of Arctic trophic food webs. Fungal parasites, particularly Chytridiomycota (chytrids), play significant roles by controlling microalgal bloom events, impacting genetic diversity, modifying microbial interactions, and accelerating nutrient and energy transfer to higher trophic levels. In the context of rapid Arctic warming and increased glacier meltwater, which significantly affects these communities, we used high-throughput sequencing to explore fungal community composition. Our results show that chytrids dominate fungal communities in Arctic benthic habitats and that the overall fungal diversity is primarily influenced by the salinity gradient. Chytrid representation is positively correlated with the presence of potential benthic diatom (Surirella, Nitzschia, Navicula) and green algae (Ulvophyceae) hosts, while microscopic observations provide further evidence for the presence of active chytrid infections.

Introduction: Microalgae form an essentia! group of benthic organisms that respond swiftly to environmental changes. They are widely used as bioindicators of anthropogenic stressors in freshwater ecosystems. We aimed to assess the responses of microalgae communities to multiple environmental stressors in the Kinzig River catchment, home to a long-term ecological monitoring site, in Germany. Methods: We used a photosynthetic biomass proxy alongside community composition of diatoms assessed by digital light microscopy, and of microalgae by 18S-V9 amplicon sequencing, to characterise microalgae at 19 sampling sites scattered across the catchment. Results: Our results revealed significant effects of physical and chemical factors on microalgae biomass and community compositions. We found that conductivity, water temperature and pH were the most important factors affecting microalgae community composition, as observed in both microscopy and amplicon analysis. In addition to these three variables, the effect of total phosphate on all microalgae, together with water discharge on the diatom (Bacillariophyta) communities, as assessed by amplicon analysis, may reveal taxon-specific variations in the ecological responses of different microalgal groups. Discussion: Our results highlighted the complex relationship between various environmental variables and microalgae biomass and community composition. Further investigations, involving the collection of time series data, are required to fully understand the underlying biotic and abiotic parameters that influence these microalgae communities. [ABSTRACT FROM AUTHOR]

As a consequence of anthropogenic activities and climate change, accelerated terrestrial sediment runoff is causing the gradual mudification of soft sediment estuarine habitats worldwide. Increased sediment mud content (< 63 µm) has been recognised to alter seagrass morphology and cause declines in primary production in unvegetated habitats. However, the effect of increased mud content on primary production in seagrass meadows remains largely unknown. To address this, primary production in intertidal seagrass meadows (Zostera muelleri) and adjacent unvegetated habitats was measured in situ using benthic incubation chambers across an existing sedimentary gradient (nine sites spanning 5–33% mud content). An additional two unvegetated mudflat sites (39–49% mud content) were also sampled to expand the gradient. Seagrass net (NPP) and gross primary production (GPP) was greater than in the adjacent unvegetated habitat and did not vary with mud content, even after standardising GPP by photosynthesising biomass (i.e. photosynthetic efficiency). In contrast, in the adjacent unvegetated habitat, photosynthetic efficiency declined with increasing mud content. Inclusion of the additional mudflat sites negatively impacted NPP, GPP, and photosynthetic efficiency in the unvegetated habitat. Thus, while primary production in seagrass meadows may have some resilience to future increases in mud content (up to ~33%), further degradation and loss of seagrass habitats could result in the expansion of unvegetated habitats and ultimately lead to production losses, likely to be most acute in areas with high mud content (≥ 39%). [ABSTRACT FROM AUTHOR]

The biogeochemical role of the sediments in the Guadalquivir River estuary, a vital region in the SW Iberian Peninsula, has been considerably neglected. The benthic microalgae (microphytobenthos, MPB) inhabiting the sediment surface could contribute to the autochthonous primary production and influence nutrient recycling in this hyper-turbid and hypernutrified estuary. Sediment-water column fluxes of O2 and dissolved inorganic nitrogen species (DIN = NH4 + +NO3 -+NO2 -) were assessed in laboratory incubations of sediment cores from Bonanza (mouth) and Lebrija (middle) during a 1-year study. Vertical profiles down to the 10-cm depth of photosynthetic pigments, organic C, total nitrogen, DIN, Fe2+, SO42-, and dissolved inorganic carbon (DIC) were also measured. Chlorophyll a in the sediment surface was higher at the estuarine mouth, exhibiting a seasonal pattern at both sites with highest values in winter and lowest in summer. Net community production (NCP) was higher in Bonanza compared with Lebrija and showed positive values most of the year, indicating that MPB contributed to the overall autochthonous primary production of the estuary. Seasonal changes in chlorophyll a and NCP were not parallel, suggesting different ecological controls. The sediment was generally a net sink of NO3 - and NH4 + in both sites, with several fold higher rates for NO3 - uptake. MPB N demand could account for the entire sediment DIN uptake in Bonanza and 21% in Lebrija. The remaining high NO3 - uptake rates indicate that they sustain elevated sediment denitrification rates. In contrast, rates of anaerobic oxidation of organic matter by Fe reduction and SO4 2-reduction, estimated from Fe2+ and SO4 2-vertical concentration profiles, were several orders of magnitude lower than the estimated water column-dependent denitrification rates. Overall, this study shows the importance of MPB in the Guadalquivir Estuary and the potential dominant role of denitrification in the anaerobic mineralization of organic matter. [ABSTRACT FROM AUTHOR]

This study characterized the benthic algal communities at the mouth of a large eutrophic-hypertrophic river, specifically during the vegetation period of 2019 and the summer-autumn period of 2020. Emphasis was placed on the composition, taxonomic structure, and the seasonal and interannual variability of abundance and diversity indicators. Detailed analysis was conducted on communities from bottom sediments, rocky substrates, and higher aquatic and coastal-water plants. Results show significant variations in composition and taxonomic structure across different substrate types and time frames. The dominant species complexes exhibited both temporal and substrate heterogeneity. Key findings highlight the importance of considering various substrate types and time periods, and they underline the observed changes in taxonomic group abundance. Such insights are crucial for comprehensive assessments of benthic algae communities in large eutrophic-hypertrophic rivers. [ABSTRACT FROM AUTHOR]

The microphytobenthos (MPB) are known to play important ecological roles in estuarine ecosystems. While tidal flat MPB are widely studied, mangrove MPB are often overlooked due to the common belief that the light-limited environment under the mangrove canopy is not conducive to MPB growth. We assessed the biomass and community characteristics of the MPB in two contrasting mangrove forests (silty substrate and brackish influence versus sandy substrate and oceanic influence), their seasonal photosynthetic performance, as well as their role in mediating porewater carbon flux. Biomass measured as chlorophyll a concentration indicated that MPB abundance was equal, if not higher, in mangroves than on tidal flats. While mangrove sediments fostered an equally rich assemblage of MPB (estimated 23 to 45 genera) as the adjacent tidal flat, the MPB genus composition was different across all habitats, sites, and seasons, indicating the strong environmental influence on MPB assemblages. This study identified porewater salinity, temperature, and pH, as well as irradiance level and surface soil temperature to be accountable for 23.5% of this variation. MPB in all sampling locations were dominated by pennate diatoms, while cyanobacteria were common in the estuarine (as opposed to oceanic) site. Compared to tidal flat MPB, mangrove MPB exhibited photosynthetic performance characteristic of lower light acclimation. A mesocosm experiment using enriched stable isotopes of carbon and nitrogen indicated that a tight coupling exists between mangrove-derived carbon and MPB. Mangrove MPB are abundant and different from tidal flat MPB, and are functional photosynthetic entities with a regulatory role in nutrient cycling in mangrove ecosystems. [ABSTRACT FROM AUTHOR]

Temporal variation in the taxonomic structure of microphytobenthos (MPB) in a riverine mangrove ecosystem was studied along the southwest coast of India. About 122 species of microphytobenthos comprising diatoms (113 species), cyanobacteria (seven species), dinoflagellate (one species), and euglenophyte (one species) were observed, in which pennate diatoms dominated by 92%. Major subclasses of diatoms identified were Bacillariophycidae, Fragilariophycidae, Thalassiosirophycidae, Melosirophycidae, and Coscinodiscophycidae. Average levels of fluvial nutrients estimated in the porewater were NO3–N (28 ± 19.7 µmol L−1), PO4–P (3.77 ± 4.6 µmol L−1), and SiO4–Si (33.12 ± 27.2 µmol L−1). The colonization and persistence of dense cyanobacterial mats during monsoon resulted in less abundance and diversity of diatoms than in other seasons. The numerical abundance of MPB was at its maximum during July (monsoon season) due to the dense cyanobacterial mat formed by Oscillatoria princeps. MPB diversity was at its maximum during MON (H´- 3.2), followed by POM (H´- 3.08) and lowest during PRM (H´- 2.23). The statistically significant seasonal variations in the diversity of MPB were noticed during the study period (ANOVA F value 8.120; df 2; p value < 0.05). The present study identifies sediment temperature and porewater salinity (freshwater preference) along with rainfall, sediment pH and C:N ratio as the major governing factors in the benthic microalgal mat formation of the study area. [ABSTRACT FROM AUTHOR]

IntroductionMicroalgae form an essential group of benthic organisms that respond swiftly to environmental changes. They are widely used as bioindicators of anthropogenic stressors in freshwater ecosystems. We aimed to assess the responses of microalgae communities to multiple environmental stressors in the Kinzig River catchment, home to a long-term ecological monitoring site, in Germany.MethodsWe used a photosynthetic biomass proxy alongside community composition of diatoms assessed by digital light microscopy, and of microalgae by 18S-V9 amplicon sequencing, to characterise microalgae at 19 sampling sites scattered across the catchment.ResultsOur results revealed significant effects of physical and chemical factors on microalgae biomass and community compositions. We found that conductivity, water temperature and pH were the most important factors affecting microalgae community composition, as observed in both microscopy and amplicon analysis. In addition to these three variables, the effect of total phosphate on all microalgae, together with water discharge on the diatom (Bacillariophyta) communities, as assessed by amplicon analysis, may reveal taxon-specific variations in the ecological responses of different microalgal groups.DiscussionOur results highlighted the complex relationship between various environmental variables and microalgae biomass and community composition. Further investigations, involving the collection of time series data, are required to fully understand the underlying biotic and abiotic parameters that influence these microalgae communities.

Dense congregations of shorebirds forage on tidal flats during long-distance migration, and their abundance is presumed to mirror the underlying ecological conditions. We quantified the nutritional content of intertidal biofilm (a thin layer of microalgae, bacteria, and other microorganisms embedded in a mucilaginous matrix that sits on the surface of tidal flats) to assess whether biofilm biomass, macronutrient content (lipid, protein, and carbohydrate), or both, provide a measure of habitat quality for migrating shorebirds. We compared shorebird use, biofilm biomass, macronutrient content, and stable isotope signatures at two mudflats on the Fraser River estuary, British Columbia, Canada, during summer 2020 (southward migration) and spring 2021 (northward migration). The abundances of Western Sandpiper (Calidris mauri) and Dunlin (Calidris alpina) were consistently higher (6–100×) at Brunswick Point relative to the Iona Foreshore site during both migration periods. Biofilm biomass (chlorophyll a) was 2× higher at Brunswick Point than Iona Foreshore during southward migration, and was similar between sites during northward migration, suggesting biofilm biomass alone was not a main determinant of shorebird use of these sites. Macronutrient content (lipid, protein, and carbohydrate) in intertidal biofilm was 1.4× to 3.8× higher at Brunswick Point than Iona Foreshore during both migration periods, indicating an association between macronutrient content and shorebird use. Carbohydrate content was higher during southward migration at both tidal flats, whereas protein and lipid content at Iona Foreshore did not show significant differences between years or migration periods. Carbon and nitrogen stable isotope signatures during spring 2021 did not differ between the two sites, suggesting that nutrients had similar relative inputs from marine and freshwater sources. While our comparative study does not eliminate alternative explanations that might act concomitantly (e.g., invertebrate abundance, predation risk, and disturbance), our results are consistent with the hypothesis that small-bodied shorebirds are more abundant at sites where intertidal biofilm has high macronutrient content. The latter can vary in complex ways depending on the taxonomic composition and physiological state of the microphytobenthos. Thus, the nutritional "quality" of intertidal biofilm can serve as a useful measure for determining restoration goals for tidal flats or assessing coastal areas for development projects. [ABSTRACT FROM AUTHOR]

The biogeochemical role of the sediments in the Guadalquivir River estuary, a vital region in the SW Iberian Peninsula, has been considerably neglected. The benthic microalgae (microphytobenthos, MPB) inhabiting the sediment surface could contribute to the autochthonous primary production and influence nutrient recycling in this hyper-turbid and hypernutrified estuary. Sediment–water column fluxes of O2 and dissolved inorganic nitrogen species (DIN = NH4+ + NO3− + NO2−) were assessed in laboratory incubations of sediment cores from Bonanza (mouth) and Lebrija (middle) during a 1-year study. Vertical profiles down to the 10-cm depth of photosynthetic pigments, organic C, total nitrogen, DIN, Fe2+, SO42−, and dissolved inorganic carbon (DIC) were also measured. Chlorophyll a in the sediment surface was higher at the estuarine mouth, exhibiting a seasonal pattern at both sites with highest values in winter and lowest in summer. Net community production (NCP) was higher in Bonanza compared with Lebrija and showed positive values most of the year, indicating that MPB contributed to the overall autochthonous primary production of the estuary. Seasonal changes in chlorophyll a and NCP were not parallel, suggesting different ecological controls. The sediment was generally a net sink of NO3− and NH4+ in both sites, with several fold higher rates for NO3− uptake. MPB N demand could account for the entire sediment DIN uptake in Bonanza and 21% in Lebrija. The remaining high NO3− uptake rates indicate that they sustain elevated sediment denitrification rates. In contrast, rates of anaerobic oxidation of organic matter by Fe reduction and SO42− reduction, estimated from Fe2+ and SO42− vertical concentration profiles, were several orders of magnitude lower than the estimated water column-dependent denitrification rates. Overall, this study shows the importance of MPB in the Guadalquivir Estuary and the potential dominant role of denitrification in the anaerobic mineralization of organic matter.

The man-made sea dike has disrupted the natural link between riverine and marine ecosystems and caused eutrophication within the aquatic ecosystem. The eutrophic water discharge has also raised concerns. As a representative tidal flat with the longest dike in the world, Saemangeum has experienced the problem of eutrophication. To elucidate the discharge water effects on the benthic food web dynamics, a four-year round sampling was conducted in/outside of the Saemangeum sea dike. Stable isotope analysis was applied to benthos (a total of 54 species) and their potential diets. Water discharge tripled in period II (2021–2022) compared to the period I (2019–2020). However, there were no significant impact changes in food web structure between the two periods due to improved lake water quality in period II. A positive correlation of nutrient concentration between the inner and outer areas of the dike revealed a direct effect of the water discharge on the outer tidal flat. The water discharge altered the spatial environmental conditions and the food web structure of the outer tidal flat. High TN concentrations stimulated the biomass of microphytobenthos (MPB) near the water gates, which in turn increased MPB consumption by benthos, demonstrating the in/direct impacts of water discharge on the food web. Furthermore, filter feeders exhibited a more sensitive response to spatial organic matter distribution compared to deposit feeders in diet utilization. Overall, our novel findings on food web dynamics in a representative tidal flat with artificial structures emphasize the necessity of continuous monitoring to ensure the sustainability of coastal ecosystems.

Ecology aims to comprehend species distribution and its interaction with environmental factors, from global to local scales. While global environmental changes affect marine biodiversity, understanding the drivers at smaller scales remains crucial. Tidal flats can be found on most of the world's coastlines and are particularly vulnerable to anthropogenic disturbances. They are important transient ecosystems between terrestrial and marine ecosystems, and their biodiversity provides important ecosystem services. Owing to this unique, terrestrial–marine transition, strong environmental gradients of elevation, sediment composition and food availability prevail. Here, we investigated which regional and local environmental factors drive the spatio‐temporal dynamics of macrozoobenthos communities on back‐barrier tidal flats in the East Frisian Wadden Sea. On the regional level, we found that species composition changed significantly from west to east on the East Frisian islands and that total abundance and species richness decreased from west to east. On the local abiotic level, we found that macrozoobenthos biomass decreased with higher elevation towards the salt marsh and that the total abundance of organisms in the sediment significantly increased with increasing mud content, while biodiversity and biomass were not changing significantly. In contrast to expectations, increasing Chl a availability as a measure of primary productivity did not result in changes in abundance, biomass or biodiversity, but extremely high total organic carbon (TOC) content was associated with a decrease in biomass and biodiversity. In conclusion, we found regional and local relationships that are similar to those observed in previous studies on macrozoobenthos in the Wadden Sea. Macrozoobenthos biomass, abundance and biodiversity are interrelated in a complex way with the physical, abiotic and biotic processes in and above the sediment. [ABSTRACT FROM AUTHOR]

Microbial nitrate reduction in wetland soils and sediments plays an important role mitigating the excess of nitrogen released into the environment. The reduction of nitrate to its reduced gaseous form, i.e. denitrification, is tightly linked to the oxidation of organic carbon. In intertidal wetlands, the organic carbon derived from aquatic or terrestrial primary producers strongly differs in composition, which in turn might affect nitrate reduction rates. In the current study the impact of carbon quality on benthic nitrate reduction in a temperate intertidal wetland sediment was determined. To this end, nitrate reduction rates were determined over a three-week period using an anoxic controlled flow-through reactor approach using sediments amended with carbon from different vegetation types. Organic carbon from algal or plants was mixed with the sediment at the same absolute quantity of carbon. A significant initial increase in nitrate reduction rates was observed in the presence of algal (microphytobenthos) derived organic carbon, most likely due to its labile structure; however, rates decreased rapidly, most likely due to a depletion of the labile source. This indicates the dependence of denitrifiers to the microalgae turnover in non-vegetated sediment. Despite a delay, the addition of plant derived organic carbon, increased nitrate reduction rates with a higher amount of total nitrate reduced over the duration of experiment compared to the microphytobenthos addition. These results highlight that presence of both labile and recalcitrant carbon sources in sediment is essential to support an efficient nitrogen biogeochemical cycle. [ABSTRACT FROM AUTHOR]

Context: Artificial breaching of intermittently closed estuaries has become more frequent in the face of global-change pressures. Aims: This study aimed to determine whether the ecological health of the Great Brak Estuary has been affected by the prolonged loss of marine connectivity arising from below-average inflow and failed breaching attempts. Methods: We characterised primary eutrophic symptoms (inorganic nutrients, dissolved oxygen, microalgae) typical of the various mouth states, i.e. open, closed and semi-closed. Key results: Initially, low inflow and closed mouth conditions facilitated the widespread occurrence of macroalgal blooms (Cladophora glomerata). Phytoplankton bloom conditions (>20 μg Chl- a L−1) ensued only in response to favourable hydrodynamic conditions (e.g. increased water residency, halocline formation) and increased nutrient availability from fluvial sources and macroalgal dieback. These blooms occurred in brackish conditions and comprised numerous taxa, including Cyclotella atomus var. marina , Cryptomonas sp. and Prorocentrum cordatum. Widespread hypoxia (<2 mg L−1) occurred during the semi-closed mouth phase because of the reduced flushing potential associated with the preceding high flow conditions. Conclusions: Global-change pressures and ineffective breaching practices will promote eutrophic conditions in intermittently closed estuaries in the future. Implications: Allocating sufficient environmental flows is key to preventing ecosystem degradation. Estuaries that disconnect from the marine environment are vulnerable to human impacts and warrant special interventions to prevent ecosystem degradation. One such example is the mechanical opening of estuary mouths to prevent flooding of low-lying developments and facilitate periods of marine connectivity. This study has highlighted the importance of allocating sufficient freshwater to ensure that these practices successfully achieve management objectives. [ABSTRACT FROM AUTHOR]

Abstract: Aim This study focused on the spatiotemporal variation of the benthic diatom community structure in salt marshes from the Patos Lagoon estuary and their relationship with environmental variables. Methods Samplings were carried out in the winter of 2010 and summer of 2011 (during El Niño and La Niña) in sites with different sediment granulometry, salinity, and distances from the Atlantic Ocean. The surface sediment was collected using a core (10 cm in diameter and 2 cm in depth) and the benthic diatoms were removed following the Trapping method, allowing the observation of live diatoms. Results The richness values (18 and 48 taxa), evenness (0.41 and 0.68), and Shannon diversity indices (2.02 and 3.31 bits/ind.) variations were not significative between the sites and seasons, although temperature and salinity differed significatively between winter and summer. However, the diatom's composition and distribution were related to temperature, salinity, and sediment particle size. Mainly the species Hippodonta hungarica, Luticola simplex Navicula cf. cryptotenelloides, N. erifuga, N. jacobii, Nitzschia filiformis var. conferta, Planothidium frequentissimum and Tryblionella calida were associated with lower temperature and lower salinity in the winter. The species Navicula cf. cryptocephala, N. phylleptosomaformis, Nitzschia pusilla, N. frustulum, N. scalpelliformis and Pseudostaurosiropsis geocollegarum were associated with higher temperature and higher salinity in the summer. Birraphid diatom taxa, mainly species of the genus Navicula and Nitzschia, were frequent or abundant in sandy sediments, and monoraphids, such as Planothidium frequentissimum, were frequent in sites where silt and clay predominated. Conclusions The composition of the benthic diatoms revealed variation between the sites in the winter and summer seasons, during El Niño and La Niña episodes. In winter, high rainfall and freshwater runoff maintained oligohaline condition in the marshes, while in summer, flooding with meso-poly-euhaline waters changed the diatom composition. The granulometry was an important factor in explaining the distribution of the birraphid and monorhapid taxa.

Microphytobenthos (MPB) is one of the most important primary producers in coastal and estuarine ecosystems, where it plays a substantial role in many ecological functions. Although the influence of several environmental factors on MPB biomass and productivity is well documented, the effects of macrofaunal bioturbation remain poorly assessed. The purpose of this study was to experimentally quantify the influence of sediment bioturbation processes (that is, sediment reworking and bioirrigation) on biogeochemical fluxes across the sediment–water interface and MPB biomass and photosynthetic capacities. Two infaunal deposit feeders (the polychaete Hediste diversicolor and the bivalve Scrobicularia plana) exhibiting contrasting bioturbation modes and rates were studied as model organisms. They differently affected MPB biomass and photosynthetic performance. Hence, through an intense bioirrigation activity and the stimulation of nutrient fluxes (NH4+ , NOx, PO42− and dSi) at the sediment surface, H. diversicolor enhanced MPB growth, which seemed to compensate for its direct consumption. Conversely, high sediment reworking rates generated by S. plana, associated with an extensive grazing pressure, drastically limited the development of MPB at the sediment surface. The negative impact of bivalves on MPB biomass increased with increasing density, whereas there was no significant relationship with polychaete density, possibly due to trophic competition. This study demonstrates that macrofaunal bioturbation is a key factor regulating MPB dynamics, with complex interactions that can result in a net either positive or negative effect depending on dominant species functional traits and abundances. This may, in particular, explain the strong spatial and temporal variability of the microbenthic primary productivity in intertidal mudflats. [ABSTRACT FROM AUTHOR]

This study aimed to assess the influence of nutrient enrichment on the development of microalgal biofilm on concrete and PVC cubes. Three mesocosms were utilized to create a nutrient gradient over a period of 28 days. Various parameters including biomass, photosynthetic activity, microtopography, and extracellular polymeric substances (EPS) were measured. Imaging PAM techniques were employed to obtain surface-wide data. Results revealed that nutrient availability had no significant impact on Chl a biomass and the maximum quantum efficiency of PSII ( F v / F m ). The photosynthetic capacity and efficiency were minimally affected by nutrient availability. Interestingly, the relationship between microphytobenthic (MPB) biomass and photosynthesis and surface rugosity exhibited distinct patterns. Negative reliefs showed a strong correlation with F v / F m , while no clear pattern emerged for biomass on rough concrete structures. Overall, our findings demonstrate that under conditions of heightened eutrophication, biofilm photosynthesis thrives in the fissures and crevasses of colonized structures regardless of nutrient levels. This investigation provides valuable insights into the interplay between nutrient availability and surface rugosity. [ABSTRACT FROM AUTHOR]

Salt pannes are marsh features in the supratidal zone that are devoid of macrophytic vegetation. Although these habitats appear barren, benthic microalgae (BMA) inhabit the sediments and are potentially important primary producers. In addition, salt pannes are habitats for dense accumulations of sand fiddler crabs (Leptuca pugilator; Bosc 1802). The purpose of this study was to determine the temporal changes in BMA biomass, community composition, and net primary productivity (NPP) for a supratidal salt panne and quantify sand fiddler crab grazing on BMA. The impact of crab grazing on BMA abundance in surface sediments was determined by measuring chl a concentrations in ungrazed and grazed sediments. BMA biomass peaked to a high of 16 µg chl a g sediment−1 in June and July, suggesting growth in the spring followed by a small decline in the warmer summer months. The BMA community was primarily composed of benthic diatoms, with lesser amounts of cyanobacteria. NPP increased to a median of 0.51 mmol O2 m−2 h−1 (6.12 mg C m−2 h−1) in July. In comparison with other BMA habitats in this estuary, NPP and biomass for salt pannes was lower than the other 5 habitat types (tall and short Spartina, intertidal mud and sandflats, phytoplankton, and submerged sediments). Sand fiddler crabs do not appear to consume significant amounts of BMA during grazing in salt pannes. This first ever study of BMA NPP demonstrates that estuarine salt pannes are likely a small contributor to ecosystem NPP. [ABSTRACT FROM AUTHOR]

Microphytobenthos (MPB), typically comprised mainly of diatoms, is a key contributor to nearshore energy flow and nutrient cycles. Deposit‐feeding invertebrates are known to alter the structure and activity of MPB. The eastern mud snail Ilyanassa obsoleta can reach extremely high densities in estuaries of the northwestern Atlantic, and their deposit‐feeding and locomotion strongly influence other invertebrates and microbes. Our objective was to explore quantitative and qualitative effects of this keystone deposit‐feeder on diatoms of intertidal sediments. We gathered snails from mudflat and sandflat habitats and collected their fresh fecal pellets in the laboratory. DNA metabarcoding allowed us to characterize diatom assemblages of ingested sediments and feces. We noted selective feeding such that reduction in MPB biomass with gut passage was difficult to quantify. Diatom α‐diversity was reduced with gut passage in snails from both sedimentary regimes. Mudflat and sandflat diatom assemblages were distinct and differed markedly between feces and sediment in mud‐feeding snails, whereas the difference in sand‐feeding snails was minor. The sandy habitat was dominated by a mix of epipelic and epipsammic diatoms. In contrast, mudflat samples were dominated by epipelic and planktonic diatoms. Compositional differences between sediment and feces reflected preferential removal of planktonic taxa. Our results suggest the importance of phytodetritus to the mud snail diet, particularly in hydrodynamically quiescent environments. Due to the natural spatial patchiness of the snails and the capacity for rapid microbial recolonization, field experiments are recommended to determine whether MPB community changes attributed to gut passage are manifested at the landscape scale. [ABSTRACT FROM AUTHOR]

Although the importance of time after disturbance is well established in the ecological literature, studies examining how differences in growth rate affect species recovery and persistence in relation to the interval between recurrent perturbations are rare. We examined the response of two ephemeral primary producers inhabiting high‐shore rock pools, epilithic microphytobenthos (EMPB), and green filamentous algae, to disturbance regimes varying for the time interval between consecutive events. Informed from an empirically parametrized growth model's outcomes, we tested the hypothesis that EMPB would be able to recover from more frequent disturbance compared with filamentous algae in a field experiment involving three physical disturbance patterns differing for the clustering degree: high, moderate, and low (20, 40, and 80 days between disturbances). We predicted that: high clustering would prevent the recovery of both taxa; moderate clustering would prevent the recovery of the slower growing taxon only (filamentous algae); both taxa would recover under low clustering. Results showed that EMPB persisted independently of the clustering degree, whereas filamentous algae did not withstand any disturbance regime. Dramatically different effects of disturbance on organisms with subtle differences in their growth rate indicate that even stronger responses may be expected from taxa with more markedly contrasting life histories. [ABSTRACT FROM AUTHOR]

Highly diverse microphyto and meiobenthic communities are associated with large-sized marine macroalgae. Both morphological traits and allelochemical responses of macroalgae affect the composition of these communities, but the relative importance of these factors remains incompletely understood. In this study we investigated the microphytobenthic and meiobenthic communities associated with some native macroalgae and a non-indigenous species (Sargassum muticum) of the north-western Adriatic Sea. These seaweeds were sampled in two coastal sites subjected to different impacts. The possible effects of the structural complexity of the macroalgae and the potential role of allelochemicals (specifically polyunsaturated aldehydes, PUAs) on the associated communities were examined using univariate and multivariate analyses. The results indicate that distinct assemblages were associated with the macroalgae collected at the two different sites. Differences in microphytobenthic communities could be ascribed to differences in the macroalgal morphological traits and in their PUAs production. Conversely, variation of the meiobenthic community seemed to be related mainly to differences in the macroalgal communities at the two sites. This apparent inconsistency between the two analyzed communities suggests that microphytobenthos and meiofauna were differently shaped by the environmental habitat provided by macroalgae in the two sites, that are subjected to different environmental conditions and human activities. Overall, these results indicate that interactions between organisms belonging to different trophic groups (e.g., microphytobenthos and meiofauna) should be investigated in detail to better understand the global role of macroalgae as habitat formers on coastal ecosystems, especially in the case of large-sized introduced species. [ABSTRACT FROM AUTHOR]

Microphytobenthos (MPB) are central to benthic tidal flat ecological networks. Large-scale information on total MPB biomass is difficult to obtain from traditional in-situ measurements. Here, we assessed the effectiveness of using surface sediment properties as proxies for predicting the total (depth-integrated) MPB biomass with Sentinel satellite data. First, the best subset regression was applied to the in-situ data to determine the properties that best predict the biomass decay rate with depth (sampling every cm up to 10 cm depth). Then, data from a controlled laboratory experiment were used to analyse the spectral response to different sediment properties (i.e., variations in sediment grain size, organic matter and water content). Subsequently, an algorithm was developed to obtain the spatial distribution of the sediment properties and the depth-integrated total MPB biomass from remote sensing data. Finally, we presented a case study in which the seasonal dynamics of total (depth-integrated) MPB biomass were obtained from Sentinel-2 Multispectral Instrument (MSI) satellite data using the Google Earth Engine (GEE) platform. The results showed that (1) the vertical distribution of MPB biomass on a tidal flat could be predicted by the surface MPB biomass, median grain-size (D50) and water content (W0) of the sediment (top 1 cm); (2) the near infrared (NIR) band absorption depth was a key feature in estimating D50 and W0; and (3) the seasonal variation in the total (depth-integrated) MPB biomass was prominent in Chongming Dongtan, Changjiang Estuary. We concluded that the depth-integrated exponential decay algorithm was useful for estimating total MPB biomass and, combined with mappable sediment-surface data, could help map the total MPB biomass in estuarine tidal flats at a large scale.

Abstract Although the importance of time after disturbance is well established in the ecological literature, studies examining how differences in growth rate affect species recovery and persistence in relation to the interval between recurrent perturbations are rare. We examined the response of two ephemeral primary producers inhabiting high‐shore rock pools, epilithic microphytobenthos (EMPB), and green filamentous algae, to disturbance regimes varying for the time interval between consecutive events. Informed from an empirically parametrized growth model's outcomes, we tested the hypothesis that EMPB would be able to recover from more frequent disturbance compared with filamentous algae in a field experiment involving three physical disturbance patterns differing for the clustering degree: high, moderate, and low (20, 40, and 80 days between disturbances). We predicted that: high clustering would prevent the recovery of both taxa; moderate clustering would prevent the recovery of the slower growing taxon only (filamentous algae); both taxa would recover under low clustering. Results showed that EMPB persisted independently of the clustering degree, whereas filamentous algae did not withstand any disturbance regime. Dramatically different effects of disturbance on organisms with subtle differences in their growth rate indicate that even stronger responses may be expected from taxa with more markedly contrasting life histories.

Despite their high productivity and their key role in coastal processes, microphytobenthic biofilm studies remain relatively scarce because in situ, meteorological hazards make it difficult to acquire reproducible measurements, also due to difficulties in properly reproducing field conditions in the laboratory. Therefore, in order to better understand the processes of microphytobenthic primary production, we have developed an automated laboratory system and procedure with variable light intensity, with a large number of replicates. This article aims to provide a description of the creation of a P-I curve based on a total of 128 vertical profiles recorded on a sediment core taken in situ, placed in the automated system and studied under controlled conditions of temperature and air humidity while light intensity was varied automatically, thus allowing to work in standard and replicable conditions. With measured production levels of up to 14.68 ± 3.70 mmol O2.m-2.h-1 and a productivity of 0.06 ± 0.01 mmol O2.m-2.h-1 per gram of Chl a corresponding to what is generally found in temperate environments, we have shown that our system is suitable for high frequency measurements and, by combining surficial measurements of modulated fluorescence and oxygen microprofiling in sediments, complementary information from a large dataset on photosynthetic and microphytobenthic migratory activity may be obtained under standard conditions. The development of this tool has made it possible to highlight a stabilization time for oxygen fluxes. For our study conducted in a temperate environment, we observed a time lag of a few minutes that should be considered when acquiring PE curves in the laboratory to study microphytobenthic photosynthetic capacities. This tool also allowed to describe microphytobenthic migration in response to light exposure, with successive steps observed through fluorescence and oxygen profiles. First, microphytobenthos migrated towards the surface until the optimal intensity of production at 475 µmol photons.m-2.s-1, then from this intensity as well as towards 780 µmol photons.m-2.s-1, downwards migratory movements were detected. This system is a working basis which can open interesting perspectives for the study of the effect of other abiotic (or biotic) parameters.

The availability of underwater light, as primary energy source for all aquatic photoautotrophs, is (and will further be) altered by changing precipitation, water turbidity, mixing depth, and terrestrial input of chromophoric dissolved organic matter (CDOM). While experimental manipulations of CDOM input and turbidity are frequent, they often involve multiple interdependent changes (light, nutrients, C‐supply). To create a baseline for the expected effects of light reduction alone, we performed a weighted meta‐analysis on 240 published experiments (from 108 studies yielding 2500 effect sizes) that directly reduced light availability and measured marine autotroph responses. Across all organisms, habitats, and response variables, reduced light led to an average 23% reduction in biomass‐related performance, whereas the effect sizes on physiological performance did not significantly differ from zero. Especially, pigment content increased with reduced light, which indicated a strong physiological plasticity in response to diminished light. This acclimation potential was also indicated by light reduction effects minimized if the experiments lasted longer. Nevertheless, the performance (especially biomass accrual) was reduced the more the less light intensity remained available. Light reduction effects were also more negative at higher temperatures if ambient light conditions were poor. Macrophytes or benthic systems were more negatively affected by light reduction than microalgae or plankton systems, especially in physiological responses were microalgae and plankton showed slightly positive responses. Otherwise, the effect magnitudes remained surprisingly consistent across habitats and aspects of experimental design. Therefore, the strong observed log–linear relationship between remaining light and autotrophic performance can be used as a baseline to predict marine primary production in future light climate. [ABSTRACT FROM AUTHOR]

Mangrove ecosystems are known for their role as nursery grounds for some fish. There are mixed and conflicting results on whether fish use mangrove ecosystems primarily for shelter or feeding sites. The purpose of this research is to investigate the relative importance of Avicennia marina organic matter in the feeding of Ilisha melastoma fish in the Mangrove Biosphere Reserve; It was stable isotope approach. Three primary food sources including mangrove tree leaves, microphytobenthos and suspended organic particles were analyzed isotopically. Samples of primary food sources and fish are converted into pure and simple gases such as CO, CO2 and N2 after minimizing their size and turning into powder [1]. Then the identified isotope ratios are compared with a measured standard and the exact amount of isotope formed in the sample is obtained. In this research, sampling was done seasonally in August in the summer season and February in the winter season of 2019 in the mangrove ecosystems of Bandar Khmer, Hormozgan province. Three primary food sources including mangrove tree leaves, microphytobenthos and suspended organic particles were analyzed isotopically. In the summer season, the average stable carbon isotope of primary food sources fluctuated from -28.07 units per thousand for mangrove leaves to -13.58 units per thousand for microphytobenthos. This average in the winter season was obtained from -28.05 units per thousand for mangrove leaves to -13.54 units per thousand for microphytobenthos. The average stable nitrogen isotope of primary food sources in the summer season fluctuated from 1.44 units per thousand for microphytobenthos to 10.72 units per thousand for suspended organic particles. In winter, this amount was calculated from 2.25 units per thousand for microphytobenthos to 8.10 units per thousand for suspended organic particles. The results of this research showed that in the summer season, suspended organic particles with 63% and in the winter season, microphytobenthos with 45% play the most important role in providing the food needed by the small shemsk fish. Investigating the relative importance of mangrove primary products as well as other primary food sources (microphytobenthos and suspended organic particles) in the nutrition of small sea bream using stable isotopes in the mangrove ecosystems of Bandar Khmer showed that the small sea bream has a high nutritional dependence on suspended organic particles in each It has two seasons, summer and winter. Investigating the relative importance of mangrove primary products as well as other primary food sources (microphytobenthos and suspended organic particles) in the nutrition of small sea bream using stable isotopes in the mangrove ecosystems of Bandar Khmer showed that the small sea bream has a high nutritional dependence on suspended organic particles in each It has two seasons, summer and winter. [ABSTRACT FROM AUTHOR]

The study of diatoms in the surface sediments of Academy Bay (Sea of Okhotsk) revealed a rich diatom flora (187 species and intraspecific taxa), represented mostly by marine and brackish water species. The predominance of benthic-planktonic and benthic species indicates a significant role of microphytobenthos in Academy Bay. The diatom assemblages distinguished with the use of cluster analysis are homogeneous in their taxonomic composition, but differ in ecological structure, which is mainly determined by water salinity. The concentration of diatoms in the sediments in the open part of Academy Bay and in the apex of Ulban Bay depends on a high productivity of waters and the lithological composition of sediments. A relatively low content of diatoms in the sediments is associated with the severe climatic conditions of the region that is close to the Arctic. [ABSTRACT FROM AUTHOR]

MOSE is a system of mobile gates engineered to temporarily isolate the Venice Lagoon from the Adriatic Sea and to protect the city from flooding during extreme high tides. Within the framework of the Venezia2021 program, we conducted two enclosure experiments in July 2019 (over 48 h) and October 2020 (over 28 h) by means of 18 mesocosms, in order to simulate the structural alterations that microphytobenthos (MPB) assemblages might encounter when the MOSE system is operational. The reduced hydrodynamics inside the mesocosms favored the deposition of organic matter and the sinking of cells from the water column towards the sediment. Consequently, MPB abundances increased over the course of both experiments and significant changes in the taxonomic composition of the community were recorded. Species richness increased in summer while it slightly decreased in autumn, this latter due to the increase in relative abundances of taxa favored by high organic loads and fine grain size. By coupling classical taxonomy with 18S rRNA gene metabarcoding we were able to obtain a comprehensive view of the whole community potential, highlighting the complementarity of these two approaches in ecological studies. Changes in the structure of MPB could affect sediment biostabilization, water turbidity and lagoon primary production. [ABSTRACT FROM AUTHOR]

The in-situ photosynthetic activity in tropical intertidal benthic diatom in response to environmental variation was assessed in this study by measuring chlorophyll fluorescence. The investigation was carried out during the lowest tide in January (non-rainy day) and February 2013 (post-rainy day) at two sampling sites (A and B) from each selected location (Pantai Jerejak, Teluk Bahang and Tanjung Bungah, Pulau Pinang, Malaysia). Samples of surface sediment (top 0.5 cm) were collected, and chlorophyll a extracted as biomass estimation. Assessments of the photosynthetic activity of benthic diatoms were made using a pulse-amplitude modulated (PAM) fluorometer. Fifty-three species were identified, representing 27 genera from the three studied locations. Both locations showed similarities in species diversity and abundance. Two-way ANOVA showed no significant differences (p = 0.430) in species richness (Margalef Index) among sampling locations, with an average value of 6.33±0.247. Both intertidal flats were dominated by Cocconeis, Navicula, Actinoptychus, and Diploneis. The community has low maximum quantum yields, Fv/Fm (ranging from 0.170 to 0.340) and is often light-limited (Photoacclimation Index, Ek, ranging from 67.96 to 236.71 µmol photons m-2 s-1). The relative electron transport rate (rETRmax) was low, with values ranging from 3.45 to 35.51 across three sampling locations. Fluctuation in salinity has caused a decrease in photosynthetic activity. This study suggests that the low values indicated a poorly adapted benthic microalgal community that is constantly light-limited. However, time-series data is needed to determine the ability of these communities to adapt to the changing environment. [ABSTRACT FROM AUTHOR]

Microphytobenthos (MPB) and bacterial biofilms play crucial roles in primary and secondary production, nutrient cycling and invertebrate settlement in coastal ecosystems, yet little is known of the effects of ocean acidification (OA) on these communities in intertidal soft sediments. To fill in this gap, a 28-day CO2 enhancement experiment was conducted for the benthic biofilms in soft intertidal sediments (muds and sands) from Qingdao, China. This experiment included three CO2 treatments: 400 ppm CO2 (control), 700 ppm CO2 and 1000 ppm CO2 (IPCC predicted value in 2100), which were established in a three-level CO2 incubator that can adjust the CO2 concentration in the overlying air. The effects of OA on benthic biofilms were assessed in the following three aspects: MPB biomass, biofilm community structure and microbial biogeochemical cycling (e.g., C-cycle, N-cycle and S-cycle). This study found that the 700 ppm CO2 treatment did not significantly affect the benthic biofilms in intertidal soft sediments, but the 1000 ppm CO2 treatment significantly altered the biofilm community composition and potentially their role in microbial biogeochemical cyc\ling in sediments (especially in sandy sediments). For the bacterial community in biofilms, the 1000 ppm CO2 enhancement increased the relative abundance of Alteromonadales and Bacillales but decreased the relative abundance of Rhodobacterales and Flavobacteriales. For microbial biogeochemical cycling, the 1000 ppm CO2 treatment enhanced the potential of chemoheterotrophic activity, nitrate reduction and sulfur respiration in sediments, likely resulting in a more stressful environment (hypoxic and enriched H2S) for most benthic organisms. Even though incubations in this study were only 28 days long and thus couldn’t fully accommodate the range of longer-term adaptions, it still suggests that benthic biofilms in intertidal sandy sediments are likely to change significantly near the end of the century if anthropogenic CO2 emissions unmitigated, with profound implications on local ecosystems and biogeochemical cycling.

Remote sensing is a relevant method to map inaccessible areas, such as intertidal mudflats. However, image classification is challenging due to spectral similarity between microphytobenthos and oyster reefs. Because these elements are strongly related to local geomorphic features, including biogenic structures, a new mapping method has been developed to overcome the current obstacles. This method is based on unmanned aerial vehicles (UAV), RGB, and multispectral (four bands: green, red, red-edge, and near-infrared) surveys that combine high spatial resolution (e.g., 5 cm pixel), geomorphic mapping, and machine learning random forest (RF) classification. A mudflat on the Atlantic coast of France (Marennes-Oléron bay) was surveyed based on this method and by using the structure from motion (SfM) photogrammetric approach to produce orthophotographs and digital surface models (DSM). Eight classes of mudflat surface based on indexes, such as NDVI and spectral bands normalised to NIR, were identified either on the whole image (i.e., standard RF classification) or after segmentation into five geomorphic units mapped from DSM (i.e., geomorphic-based RF classification). The classification accuracy was higher with the geomorphic-based RF classification (93.12%) than with the standard RF classification (73.45%), showing the added value of combining topographic and radiometric data to map soft-bottom intertidal areas and the user-friendly potential of this method in applications to other ecosystems, such as wetlands or peatlands. [ABSTRACT FROM AUTHOR]

Stable isotope analysis was used to investigate the food sources of benthic macroinvertebrates in the arid mangrove of the Persian Gulf. Stable carbon (δ13C) and nitrogen (δ15N) isotope values were analyzed for the 23 species and their potential food sources to examine the seasonal variation in the contribution of different potential food sources to macroinvertebrates. Primary food sources, e.g., mangrove leaves, microphytobenthos, sediment organic matter, and particulate organic matter, showed a wide range of δ13C values ranging between −28.07 and −13.54‰ and δ15N from 1.44 to 10.72‰. The wide range of the isotopic composition of consumers indicated that different food sources are important in the mangrove ecosystem of the Persian Gulf. The grazers tended to be more 13C-depleted than other feeding groups at both sampling seasons. In contrast, predators had significantly high δ13C, reflecting their carnivorous feeding habit of consuming 13C-enriched foods. The higher δ13C values of suspension feeders reflected the significant role of re-suspended microphytobenthos in the benthic-pelagic coupling of the mangrove ecosystem. The Bayesian stable isotope mixing model outputs suggested that the benthic food webs are supported by multiple primary sources. Microphytobenthos contribution was greater (> 40%), indicating their significant ecological role in structuring the food web of the arid mangroves. While sediment and particulate organic matter sources are involved in sustaining deposit feeders and partially suspension feeders, respectively, the mangrove-derived carbon played a significant role in maintaining herbivorous crabs. [ABSTRACT FROM AUTHOR]

Context: South African mangrove forests consist predominantly of three tree species wherein fiddler crabs live beneath the vegetation and act as important bioengineers. Aims: To examine whether, and to what extent, tree morphology and forest structure affect fiddler crab communities. Methods: Various physicochemical parameters (sediment pH, organic matter and microphytobenthos) and tree characteristics (e.g. tree density, canopy cover and importance value) were related to the abundance or presence of these crabs within eight South African mangrove-dominated estuaries by using multivariate models. Key results: Overall, fiddler crab abundance was driven by sediment organic matter. The abundance of Austruca occidentalis was negatively correlated with sediment organic matter (C = −0.369, P = 0.013), whereas abundance of Paraleptuca chlorophthalmus was positively correlated (C = 0.115; P = 0.008). Tubuca urvillei abundance was not affected by anything. Fiddler crab presence was largely driven by sediment organic matter for all species and pneumatophore density in A. occidentalis. Conclusions: Results indicated that mangrove tree structure influences fiddler crabs indirectly at the population level, by modulating physicochemical and biological variables. Implications: Understanding mangrove tree and macrobenthic fauna co-existence patterns will be essential in developing climate-responsive management strategies for these species and the systems within which they occur. Examining whether tree morphology and forest structure affect fiddler crab communities, various parameters and characteristics were related to the abundance or presence of these crabs within mangrove-dominated estuaries. Results indicated that mangrove trees influence fiddler crabs indirectly at the population level, by modulating physicochemical and biological variables. Understanding mangrove tree and macrobenthic fauna co-existence patterns will be essential in developing climate-responsive management strategies for these species and the systems within which they occur. [ABSTRACT FROM AUTHOR]

Estuaries are hotspots of primary productivity and nutrient transformation that contribute to food webs and ecosystem functioning locally and in adjacent ecosystems. The depth-dependence of nutrient transformation and primary productivity rates in the water column and the seafloor were investigated, and the lateral transport of solutes and materials across the estuary mouth were quantified. Using an estuary dominated by shallow soft-sediment habitats as a case study, the effects of sea level rise (SLR) on productivity and nutrient transformation processes were projected. The estuary was a net importer of dissolved nutrients from the coast, and a net exporter of suspended sediments and chlorophyll a, supporting the notion that estuaries are important nutrient transformation reactors. A significant depth (and light) effect on productivity indicates that increasing stressors associated with climate change that reduce light at the seafloor (SLR and increased turbidity) will negatively impact estuarine productivity. Intertidal and shallow subtidal benthic habitats were responsible for most of the productivity of the estuary and this is likely to be consistent for other shallow estuaries globally. SLR and anthropogenic intervention that prevents landward migration (i.e. seawalls and armouring), will result in the loss of these habitats and their significant contributions to adjacent coastal ecosystems. [ABSTRACT FROM AUTHOR]

Ionic liquids (IL) are regarded as the solution to the modern world's need to create and use compounds that exhibit a range of desirable properties while having a low environmental impact. However, recent reports are shattering the image of ionic liquids as environmentally friendly substances, especially in relation to the aquatic environment, revealing their potentially toxic effects. To assess the potential environmental impact of ILs, we conducted an experiment involving 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), a substance considered to be the least hazardous among the imidazolium chloride ILs, on Baltic microphytobenthic communities. Microphytobenthos collected from the environment was tested under controlled laboratory conditions, and both the cell counts and the chloroplast condition were used as endpoints. It was shown that [BMIM]Cl at concentrations of 10−3 and 10−2, considered safe based on a cumulative impact assessment, has a negative effect on the condition of the microalgal cells and causes a reduction in population size. Although, under the influence of [BMIM]Cl, only a small proportion of the species was eliminated from the communities, only two species among those important to the communities showed resistance to this compound and eventually began to dominate the communities. [ABSTRACT FROM AUTHOR]

Mangrove habitats support taxonomically diverse benthic communities, yet their effects on microphytobenthos remain understudied. This study investigated the benthic diatom community structure of 17 microtidal mangrove estuaries situated along the east coast of South Africa. High sediment organic content (≤ 18.1 %) and clay fraction (≤ 17.5 %) measured in the Avicennia marina and Rhizophora mucronata habitats favoured diverse communities (H′ > 3) and the presence of unique benthic diatom species such as Gyrosigma balticum. The habitat complexity and stabilisation provided by the mangrove forests served as microrefugia for colonisation of benthic diatoms. Taxa displayed a broad range of nutrient tolerance, with some nutrient tolerant species (e.g., Halamphora acutiuscula, Navicula clausii , Navicula gregaria, and Navicula radiosa) dominating the communities in the Mbashe and Mnyameni estuaries. The presence of these nutrient tolerant taxa in relatively pristine systems serves as an early warning for possible anthropogenic nutrient enrichment. • Low-nutrient conditions supported a diverse benthic diatom community. • Benthic diatom diversity was higher (H′ >3) in the mangrove habitats. • The finer cohesive mangrove sediments favoured the proliferation of select taxa. • Lower diversity (H′ < 2) due to higher flow were unique to the control habitat. • Some nutrient tolerant taxa were recorded in select estuaries. [ABSTRACT FROM AUTHOR]

Intertidal flats are important shallow-water habitats and buffers against coastal erosion. Strong, short-lasting meteorological events, such as storms and rainfall, are the main mechanisms of transporting (in)organic materials and sediments. Two in-situ mooring systems were installed simultaneously in the tidal channel and mudflat of Jeungdo, Korea, to understand the dynamic behaviors of suspended sediment and chlorophyll- a (chl- a) under the episodic events. During fair-weather periods with a distinct tidal cycle, the sediment in the mudflat was resuspended during the flood and then advected to the tidal channel during the ebb. The maximum suspended sediment concentration (SSC) and chl- a under storm event were approximately 9 and 2 times higher than those under fair-weather periods, respectively. Under rainfall event, the maxima were approximately 7 and 1.2 times higher than fair-weather, suggesting that sediment and microphytobenthos were highest resuspended by the meteorological events. In addition, a time lag (∼ 1.5 h) between SSC and chl- a occurred in the tidal channel during ebb tide with a rainfall event. During the post-rainfall periods, the SSC and chl- a increased, showing a positive relationship with the bed shear stress, suggesting that the rainfall event could reduce sediment stabilization. • We examined sediment and microphytobenthos dynamics during storm and rainfall events. • Episodic meteorological events influenced the redistributing sediment and chl- a. • The (de)coupling and resuspension time-lag between sediment and chl- a are evidenced. • Rainfall could reduce the stabilization of sediment and microphytobenthos. [ABSTRACT FROM AUTHOR]

The nitrogen‐fixing, non‐heterocystous cyanobacterium Hydrocoleum sp. (Oscillatoriales) is a common epiphytic and benthic bloom‐former in tropical and subtropical shallow water systems but shares high phylogenetic similarity with the planktonic, globally important diazotroph Trichodesmium. Multiphasic observations in this study resulted in unexpected identification of Hydrocoleum sp. in mass accumulations in a coastal lagoon in the Western temperate North Atlantic Ocean. Hydrocoleum physiology was examined in situ through measurements of N2 and CO2 fixation rates and expression of genes involved with N2 fixation, CO2 fixation, and phosphorus (P) stress. Bulk N2 fixation rates and Hydrocoleum nifH expression peaked at night and were strongly suppressed by dissolved inorganic nitrogen (DIN). The expression of high affinity phosphate transporter (pstS) and alkaline phosphatase (phoA) genes of Hydrocoleum was elevated during the night and negatively responded to phosphate amendments, as evidence that these mechanisms contribute to P acquisition during diazotrophic growth of Hydrocoleum in situ. This discovery at the edge of the previously known Hydrocoleum habitat range in the warming oceans raises intriguing questions about diazotrophic cyanobacterial adaptations and transitions on the benthic‐pelagic continuum. [ABSTRACT FROM AUTHOR]

To assess the temporary effects of the increased copper ion inflow on estuarine microphytobenthic communities, ecotoxicological tests were conducted using natural microphytobenthic assemblages obtained from an artificial substratum exposed to the waters of the southern Baltic Sea (Gulf of Gdańsk). The applied copper ion concentrations reflected permitted copper values established for waters of a good ecological status (2·10–5 g Cu·dm−3), and the maximum copper concentrations which, according to the current environmental regulations, are allowed to be discharged into the environment (2·10–3 g Cu·dm−3). In the studied communities, diverse responses of single species to CuCl2 exposure were recorded, including both growth inhibition and stimulatory effects as well. Despite the shift in the community composition and structure, total cell number remained at a similar level. The results of our investigations suggest that microphytobenthic assemblages are resistant to CuCl2 which is facilitated by the shift in the community composition resulting from the increasing cell number of copper tolerant species. [ABSTRACT FROM AUTHOR]

Colonisation of artificial structures by primary producers is an important determinant for eco-engineering projects. In this context, interactions between the colonisation by microphytobenthic biofilm and macroalgae were explored on 48 samples of marine infrastructures (MI) immersed for one year in the English Channel. Marine infrastructures samples with smooth and rough surface were compared to evaluate the influence of surface micro-scale rugosity. Microphytobenthos biomass (MPB), macroalgal diversity and photosynthetic parameters of both were assessed during colonisation. No significant differences were found as a function of the surface rugosity of MI samples, which was unexpected, but can be explained by biogenic rugosity provided by barnacles. Marine infrastructures were largely colonised by a red encrusting alga, Phymatolithon purpureum, which showed poor photosynthetic capacity compared to the microphytobenthos present next to it. Colonisation by monospecific encrusting algae tended to reduce the primary productivity of hard substrate. [ABSTRACT FROM AUTHOR]