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Phytoplankton communities typically comprise a few dominant species and numerous rare ones, but their responses to seasonal precipitation changes remain poorly understood. To address this knowledge gap, investigations were conducted on the environmental conditions and phytoplankton communities in the Lalin River Basin during the dry and rainy seasons. Structural equation modeling and co-occurrence network analysis were then utilized to explore the assembly processes of dominant and rare phytoplankton communities following a seasonal heavy rainfall event. Our results showed seasonal heavy rainfall events significantly altered the phytoplankton community composition and rare phytoplankton diversity (p < 0.05). Furthermore, the stochastic process was particularly pronounced for rare species (i.e., 4.44%, p < 0.01). Co-occurrence network analysis revealed that increasing precipitation enhances the complexity and stability of phytoplankton ecological networks. Additionally, the relative importance of dominant species decreases, while that of rare species increases. This phenomenon can be described as the seasonal heavy precipitation weakening the so-called "Matthew effect" in the ecosystem. In summary, our results shed light on the phytoplankton ecology of agricultural rivers and reveal how changes in precipitation influence the formation of phytoplankton sub-communities and the structure of their networks. [ABSTRACT FROM AUTHOR]

The material was obtained during cruise 92 of the R/V Akademik Mstislav Keldysh in the area with a latitudinal extent of 72°32.0′ to 73°14.5′ N, including the Ob River estuary and adjacent shallow shelf on October 12–13 in the period preceding seasonal ice formation. The estuarine front was well pronounced in terms of salinity (gradients 0.6 PSU/km) and temperature fields and had a quasi-meridional direction. Sharp boundaries in nutrient distribution typical of earlier seasons were not observed. The abundance and biomass of phytoplankton varied from 22 × 103 to 75 × 103 cells/L and 7.3 to 19.0 mg/m3, respectively, which were two to three orders of magnitude lower than the values obtained in July and September. The abundance (30–78%) and biomass (28–80%) of phytoplankton over the entire area were formed by diatoms, among which Fragilariopsis cylindrus dominated. The abundance of freshwater diatoms Aulacoseira was low and the species was represented only by dead cells. A scheme is presented that shows the boundaries between phytoplankton communities of different composition and quantitative characteristics, as well as the specifics of conditions in the eastern area of the wide external part of Ob river estuary. [ABSTRACT FROM AUTHOR]

The phytoplankton population of Qionghai Lake was surveyed in December 2015, March 2016, June 2016, September 2016, and March 2017. A total of 196 species (including varieties) belonging to 77 genera of 7 phyla were identified. The phytoplankton communities were dominated by Chlorophyta and diatoms, and there were significant differences across the five sampling sites. The phytoplankton abundance, which ranged between 13.85 × 104 and 335.54 × 104 cells·L−1, was significantly higher in spring and summer than in autumn and winter. Chlorella sp. and Cyclotella sp. were the dominant populations, and their dominance degree reached as high as 0.54 and 0.33, respectively. The diversity of the phytoplankton populations was significantly higher in spring and summer than in autumn and winter, and the Shannon–Wiener index and Margalef index ranged from 2.49–3.65 and 2.47–3.10, respectively. The water quality of Qionghai Lake was generally good. The trophic level index was between 30 and 60, showing that the water body was overall in a mesotrophic to slightly eutrophic state. The Spearman correlation analyses revealed that ammonium nitrogen (NH4+-N), water temperature (WT), permanganate index (CODMn), and transparency (SD) were the most important environmental factors that influenced the phytoplankton communities. For example, NH4+-N was significantly correlated with Chroococcus sp. (r = 0.41, p < 0.05) and Cryptomonas ovata Ehrenberg (r = 0.45, p < 0.05), and WT was significantly correlated with Cryptomonas marssonii Skuja (r = 0.43, p < 0.05) and Cryptomonas ovata (r = 0.53, p < 0.01). [ABSTRACT FROM AUTHOR]

The Southern Ocean (SO) is known for its atypical bio‐optical regime. This complicates the interpretation of proxies measured from satellite and in situ platforms equipped with optical sensors, which occupy an important niche for monitoring the vast and remote SO. A ship‐based field study in concert with time series observations from BioGeoChemical‐Argo (BGC‐Argo) profiling floats were used to investigate spatial and temporal variations in bio‐optical relationships in the open ocean waters surrounding the Kerguelen Plateau in the Indian sector of the SO. Compared to other regions with similar chlorophyll concentrations, chlorophyll‐specific phytoplankton absorption in the blue waveband presented a consistent negative anomaly. The anomaly was uniform over deep mixed layers and correlated with phytoplankton size, photoacclimation and atypically high concentrations of fucoxanthin. The BGC‐Argo observation‐based proxies revealed that the blue absorption anomaly increased with chlorophyll concentration both spatially and temporally and, while particularly pronounced in the naturally iron‐fertilized waters, was also found in the High Nutrient Low Chlorophyll region. While phytoplankton size was an important driver of the anomaly, photoacclimation associated with self‐shading of phytoplankton cells was also involved during intense booms. The backscattering coefficient exhibited negative and positive anomalies in the low and high biomass regimes, respectively. The large positive anomaly in high biomass regimes was attributed to the variable non‐algal particles characteristics associated with a relatively high production of bloom by‐products. With clear understanding of the bio‐optical anomalies, BGC‐Argo floats stand as unique tools for monitoring the bio‐optical spatio‐temporal complexity of the SO. Plain Language Summary: The Southern Ocean (SO) plays a key role in Earth's climate. However, its remoteness and harsh climate necessitate remote sensing approaches such as optical sensors on profiling floats and satellites. These require optical measurements and shipboard samples to relate optical signals to biological properties, called optical proxies. The SO optical proxies have been found to be very different from those measured in other oceanic regions. Here the proxies in the Kerguelen region are investigated along a ship's track crossing from subtropical to subpolar latitudes. The Kerguelen Plateau impedes both wind and currents such that deep waters upwell to the surface providing nutrients to primary producers. This region in the Indian sector of the SO provides a tremendous range in ecosystem properties from nutrient‐starved to nutrient‐rich, making these results applicable to other SO areas. The authors find that the differences in optical proxies can be explained by the presence of different phytoplankton communities and their responses to being mixed to depths where light is limited. This explains why the proxies vary so significantly across this region and change over the seasons. This knowledge makes the observations obtained by floats and satellites invaluable for understanding the entire SO. Key Points: Contribution by large diatoms and photoacclimation are major drivers of a negative anomaly in the blue chlorophyll‐specific phytoplankton absorption coefficientBioGeoChemical‐Argo observations indicate a bio‐optical anomaly exists over the entire year with maximal values associated with seasonal bloomsThe Indian Southern Ocean shows a large seasonal and regional variability in bio‐optical regimes that lie outside the global means [ABSTRACT FROM AUTHOR]

IntroductionB vitamins play a crucial role in shaping phytoplankton and zooplankton communities in marine ecosystems, yet their impact on community dynamics remains poorly understood.MethodsWe carried out in situ incubation experiments of B vitamins supplementation to explore the response pattern of phytoplankton and zooplankton community compositions.ResultsThe results showed that vitamins B1, B2, B6 and B12 promoted the growth of phytoplankton, and the total Chl α in 87.5% of the supplemented B vitamin treatments showed a significant positive response (p < 0.05). Supplementation with these B vitamins significantly altered the community composition of phytoplankton, and 75% of the B vitamin-supplemented treatments showed an increase in the relative abundance of Minutocellus, Thalassiosirales, Odontella, Prymnesiales and Ditylum, considered mainly to be the result of B vitamin auxotrophy. In contrast, a significant decrease in Copepoda, including Calanoida and Cyclopoida, was observed in 87.5% of treatments. The observed shifts in community composition were attributed to the auxotrophy of certain diatoms and Prymnesiales for B vitamins. These shifts subsequently led to negative correlations (Spearman Rho < -0.8) between the abundance of these phytoplankton species and Copepoda populations.DiscussionThese findings advance our understanding of the complex interactions between micronutrient availability and plankton community dynamics.

The Seine estuary is a typical model of a system in which phosphorus (P) inputs have been considerably reduced to reduce past eutrophication, with a parallel decrease in phytoplankton biomass. However, reducing P alone while concentrations of nitrate (N) remains high led to a dystrophic nutrient balance in the estuary (high N/P and N/Si). To identify the drivers of primary production and phytoplankton communities in the highly anthropised Seine estuary, sampling was performed along a 110-km stretch over a period of 3 years. Photosynthetic parameters were measured with a single turnover active fluorimeter and the phytoplankton community was assessed using a fluoroprobe and flow cytometry. The results revealed an annual primary production of 33 g C.m−2.y−1 which was largely controlled by light availability (turbidity) but also by nutrients in late spring and summer period. Massive blooms, not seen since 2002, were observed in a specific area of the estuary. None of the nutrients measured explained the particular location of the blooms but phytoplankton production and productivity indicators were higher in this specific zone excluding a biomass accumulation phenomenon. The local effect of tide slowdown increasing water residence time in this exact part of the estuary could explain the bloom area. The question thus arises: does phosphate play a role as a limiting nutrient? The diatom bloom led to total depletion of Si, but no clear limitation of P was observed. Nevertheless, the decrease in Si appears to have played a key role by triggering a succession from diatoms (microphytoplankton) to chlorophytes (nanophytoplankton) and hence affecting phytoplankton composition. The N/P balance appeared to be more important than the absolute concentration of P to explain the phytoplankton dynamics and the biomass decrease observed the last decades.

In the Western Tropical South Pacific (WTSP) Ocean, a hotspot of dinitrogen fixation has been identified. The survival of diazotrophs depends, among others, on the availability of dissolved iron (DFe) largely originating, as recently revealed, from shallow hydrothermal sources located along the Tonga-Kermadec arc that fertilize the Lau Basin with this element. On the opposite, these fluids, released directly close to the photic layer, can introduce numerous trace metals at concentrations that can be toxic to surface communities. Here, we performed an innovative 9-day experiment in 300 L reactors onboard the TONGA expedition, to examine the effects of hydrothermal fluids on natural plankton communities in the WTSP Ocean. Different volumes of fluids were mixed with non-hydrothermally influenced surface waters (mixing ratio from 0 to 14.5%) and the response of the communities was studied by monitoring numerous stocks and fluxes (phytoplankton biomass, community composition, net community production, N2 fixation, thiol production, organic carbon and metal concentrations in exported material). Despite an initial toxic effect of hydrothermal fluids on phytoplankton communities, these inputs led to higher net community production and N2 fixation rates, as well as elevated export of organic matter relative to control. This fertilizing effect was achieved through detoxification of the environment, rich in potentially toxic elements (e.g., Cu, Cd, Hg), likely by resistant Synechococcus ecotypes able to produce strong binding ligands, especially thiols (thioacetamide-like and glutathione-like compounds). The striking increase of thiols quickly after fluid addition likely detoxified the environment, rendering it more favorable for phytoplankton growth. Indeed, phytoplankton groups stressed by the addition of fluids were then able to recover important growth rates, probably favored by the supply of numerous fertilizing trace metals (notably Fe) from hydrothermal fluids and new nitrogen provided by N2 fixation. These experimental results are in good agreement with in-situ observations, proving the causal link between the supply of hydrothermal fluids emitted at shallow depth into the surface layer and the intense biological productivity largely supported by diazotrophs in the WTSP Ocean. This study highlights the importance of considering shallow hydrothermal systems for a better understanding of the biological carbon pump.

The Clarion-Clipperton Zone (CCZ) hosts one of the largest known oceanic nodule fields worldwide and is regulated by the International Seabed Authority. A baseline assessment of diversity and distribution patterns is essential for reliable predictions of disturbed ecosystem response scenarios for sustained commercial activities in the future. In the present study, the spatial patterns and diversity of phytoplankton communities were analyzed along with upper ocean biogeochemistry, in the licensed China Ocean Mineral Resources R&D Association (COMRA) contract area and the surrounding western CCZ between August 21 and October 8, 2017. Results indicated this was a typical low-nutrient low-chlorophyll a (Chl a) environment, characterized by low levels of phytoplankton abundance and diversity. In total 112 species belonging to 4 phyla were recorded (>10 µm), with species counts including 82 diatoms, 27 dinoflagellates, 1 cyanobacteria and 2 chrysophyte. Dominant taxa in successive order of descending abundance and occurrence included Nizschia marina, Cyclotella stylorum, Dactyliosolen mediterraneus, Rhizosolenia setigera, Pseudo-nitzschia delicatissima, Thalassiothrix frauenfeldii, Synedra sp., Chaetoceros simplex and Pseudo-nitzschia circumpora. The depth-averaged abundance and Chl a concentrations were (265±233) cells/L and (0.27±0.30) µg/L, respectively. Diatoms accounted for 90.94% of the community with (241±223) cells/L, while dinoflagellates accounted for 5.67% and (15±13) cells/L. The distribution pattern exhibited the same trend as abundance, Chl a and species richness, showing subsurface maximum levels at around 100 m, with stations near 10°N having higher levels than in the north. Cluster analysis was performed in two assemblages, relating to geographic locations to the south and north of 12°N. The subsurface maximum of abundance, Chl a, species richness, dissolved oxygen and nitrite were generally corresponding to the presence of high salinity North Pacific Central Water at depths of 50–120 m. Higher availability of nitrate, phosphate and silicic acid in the subsurface may account for the shift in phytoplankton distribution, as shown by redundancy correspondence and spearman correlation analysis. Diel variation in an anchor station demonstrated prominent species succession without significant differences in oceanographic variables, among which diatoms succession resulted from the light limitation, while dinoflagellate diel variation mainly related to lateral transport of water masses. The observed patchiness in spatial phytoplankton distributional patterns was attributed to upper ocean environmental gradients in the CCZ. The baseline generated in this study could be analyzed using current conservation strategy programs associated with deep-sea mining. [ABSTRACT FROM AUTHOR]

The FjordPhyto Citizen Science project is designed to engage the International Association of Antarctic Tour Operators and their Guests in hands-on science as they journey along the fjords of the west Antarctic Peninsula. The Antarctic Peninsula is one of the fastest warming regions in the world. Melting glaciers bring an influx of freshwater and nutrients into the fjords potentially altering the biology at the phytoplankton level. Phytoplankton play a critical role in regulating the atmosphere, drawing carbon dioxide into the ocean and producing over half the Earth’s oxygen. These microscopic drifting plants make up the foundation of the food system supporting whales, seals, and penguins. FjordPhyto aims to understand how glacial meltwater impacts phytoplankton communities among various fjords throughout the austral summer. Visitors will collect phytoplankton samples and photograph images using simple-to-operate tools. Equipment and educational material will be provided by the FjordPhyto research team as outlined in this Capstone Project. Citizen Science is a powerful tool bringing travelers and scientists together to answer critical science questions. FjordPhyto provides a fun and easy way to involve visitors in the legacy of research in Antarctica, while providing scientists with data that greatly expands the current knowledge of Antarctic fjord ecosystems.

Graphical representation of spring, summer and autumn blooms in three different fjords, in Nuup Kangerlua (NK) in Greenland influenced by tidewater glaciers, in Ramfjorden (RAM) in northern Norway influenced by vegetative catchments as their source of nutrients for initiating a summer bloom and in Adventfjorden (IsA) in Svalbard influenced by the Advent River (only in 2017 and 2019). [Display omitted] • Light, nutrients and grazing shaped bloom timing and magnitude regardless of season. • Spring blooms occurred in all studied systems despite differences in fjord characteristics. • Summer blooms only were fueled by terrestrial runoff and subglacial nutrient recycling. • Autumn blooms only were fueled by wind mixing. Phytoplankton communities and production in Arctic fjords undergo strong seasonal variations. Phytoplankton blooms are periods with high primary production, leading to elevated algal biomass fueling higher trophic levels. Blooms are typically driven bottom-up by light and nutrient availability but may also be top-down controlled by grazing. While phytoplankton spring blooms are common across all Arctic systems, summer and autumn blooms and their drivers are less predictable. Here we compare the long-term (≥4 years) bloom phenology and protist community composition in three Arctic fjords: Nuup Kangerlua in western Greenland, Ramfjorden in northern Norway, and Adventfjorden in western Svalbard. While Nuup Kangerlua is impacted by tidewater glaciers, Ramfjorden and Adventfjorden are impacted by river-runoff. We discuss and contrast the presence and predictability of spring, summer, and autumn blooms in these fjords and the main physical, chemical, and biological drivers. Spring blooms occurred in all three fjords in April/May as soon as sufficient sunlight was available and typically terminated when nutrients were depleted. Chain-forming diatoms together with the haptophyte Phaeocystis pouchetii were key spring bloom taxa in all three fjords. Summer blooms were found in Nuup Kangerlua and Ramfjorden but were not common in Adventfjorden. In Nuup Kangerlua nutrient supply via subglacial upwelling was the key driver of a diatom-dominated summer bloom. This summer bloom extended far into autumn with strong winds resupplying nutrients to the surface later in the season. In Ramfjorden runoff from a vegetated catchment provided organic nutrients for a flagellate-dominated summer bloom in 2019. A late autumn bloom dominated by S keletonema spp. and other chain-forming diatoms was present after nutrients were resupplied by wind mixing. In Adventfjorden, we observed only minor summer blooms in 2 of the 8 years, while autumn blooms were never observed. With global warming, we suggest that summer blooms will be negatively impacted in fjords where tidewater glaciers retreat and become land terminating. In fjords with rich vegetated catchments, harmful algal blooms may occur more frequently as summers and autumns become warmer and wetter. However, for fjords in high-Arctic latitudes (>78 N), the day length will continue to restrict the potential for autumn blooms. [ABSTRACT FROM AUTHOR]

The Gulf of Ob is among the largest estuaries in the World Ocean in terms of area, watershed basin, and freshwater discharge. In this work, we describe the roles of river discharge and wind forcing on the water exchange between the Gulf of Ob and the Kara Sea during ice-free seasons. This work is based on the extensive in situ measurements performed during 10 oceanographic surveys in 2007–2019. Due to large river runoff (∼530 km3 annually) and low tidal forcing (

Ecological memory (EM) recognizes the importance of previous stress encounters in promoting community tolerance and thereby enhances ecosystem stability, provided that gained tolerances are preserved during non-stress periods. Drawing from this concept, we hypothesized that the recruitment of tolerant species can be facilitated by imposing an initial sorting process (conditioning) during the early stages of community assembly, which should result in higher production (biomass development and photosynthetic efficiency) and stable community composition. To test this, phytoplankton resting stages were germinated from lake sediments originating from two catchments that differed in contamination history: one impacted by long-term herbicides and pesticides exposures (historically contaminated lake) from an agricultural catchment compared to a low-impacted one (near-pristine lake) from a forested catchment. Conditioning was achieved by adding an herbicide (Isoproturon, which was commonly used in the catchment of the historically contaminated lake) during germination. Afterward, the communities obtained from germination were exposed to an increasing gradient of Isoproturon. As hypothesized, upon conditioning, the phytoplankton assemblages from the historically contaminated lake were able to rapidly restore photosynthetic efficiency (p > 0.01) and became structurally (community composition) more resistant to Isoproturon. The communities of the near-pristine lake did not yield these positive effects regardless of conditioning, supporting that EM was a unique attribute of the historically stressed ecosystem. Moreover, assemblages that displayed higher structural resistance concurrently yielded lower biomass, indicating that benefits of EM in increasing structural stability may trade-off with production. Our results clearly indicate that EM can foster ecosystem stability to a recurring stressor. [ABSTRACT FROM AUTHOR]

[Objective] The present paper aimed to know the seasonal and spatial variations of environmental factors and phytoplankton communities, and then analyze the correlations of them in Guandi reservoir. [Method] Form October 2018 to November 2019, the physicochemical property and nutrients of the reservoir were measured in different seasons. The species of algae in the water also were identified, and its numbers were counted in per unite water. With SPSS 22. 0 and Canoco 4. 5 software, the correlations of environmental factors and phyto-plankton communities were analyzed. [Result] Annual mean values of water temperature (WT), dissolved oxygen (DO), pH, Transparency (SD), Hardness of Groundwater (HG), Conductivity (CT) and chemical oxygen demand (COD) were 14. 9 "C, 10. 8 mg/L,8. 51,238 cm,4. 0 mmoVL,243. 4 μ,sf cm and 5. 1 mg.IL In winter and spring, the water had high total nitrogen (TN) content, but extremely low total phosphorus (TP) content. In summer and autumn, it had low TN content and high TP. Except sampling site B in winter and spring, Shannon-Wiener Index, Pielou' s Evenness Index and Simpson's diversity index was high. The identification showed that there was a total of 84 algae species which belonged to 6 phylum. There were 26 algae species which had high annual dominance. The numbers of species of Chlorophyta and Bacillariophyta were the largest and second. The numbers of phylum and species in autumn were significantly lower. The algae' s density increased gradually from upstream to downstream, and the annual mean value of Guandi reservoir was 139. 8 x 104 cell/L [Conclusion] The water temperature was low, but the DO was high, and the water was weakly alkaline. It had low nutrient contents, and belonged to oligotrophic water. According to ' Environmental quality standards for surface water' (GB 3838- 2002), the water quality was between grade I and Ill. The high diversity indexes indicated that the water quality was good. In winter and spring, the algae of Bacillariophyta, Chlorophyta and Cyanophyta had advantage. In summer and autumn, the algae of Bacillariophyta and Chlorophyta had advantage. So the algae of Bacillariophyta and Chlorophyta were the main on the whole in the Guandi reservoir. HG, WT, COD and TP, especially WT, were the main environmental factors which caused the variations of phytoplankton communities. By comparison, TP in winter and spring was one of the main limiting environmental factors of algae growth, and it was TN in summer and autumn. [ABSTRACT FROM AUTHOR]

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In a changing world, phytoplankton communities face a large variety of challenges including altered light regimes. These alterations are caused by more pronounced stratification due to rising temperatures, enhanced eutrophication, and browning of lakes. Community responses toward these effects can emerge as alterations in physiology, biomass, biochemical composition, or diversity. In this study, we addressed the combined effects of changes in light and nutrient conditions on community responses. In particular, we investigated how light intensity and variability under two nutrient conditions influence (1) fast responses such as adjustments in photosynthesis, (2) intermediate responses such as pigment adaptation and (3) slow responses such as changes in community biomass and species composition. Therefore, we exposed communities consisting of five phytoplankton species belonging to different taxonomic groups to two constant and two variable light intensity treatments combined with two levels of phosphorus supply. The tested phytoplankton communities exhibited increased fast reactions of photosynthetic processes to light variability and light intensity. The adjustment of their light harvesting mechanisms via community pigment composition was not affected by light intensity, variability, or nutrient supply. However, pigment specific effects of light intensity, light variability, and nutrient supply on the proportion of the respective pigments were detected. Biomass was positively affected by higher light intensity and nutrient concentrations while the direction of the effect of variability was modulated by light intensity. Light variability had a negative impact on biomass at low, but a positive impact at high light intensity. The effects on community composition were species specific. Generally, the proportion of green algae was higher under high light intensity, whereas the cyanobacterium performed better under low light conditions. In addition to that, the diatom and the cryptophyte performed better with high nutrient supply while the green algae as well as the cyanobacterium performed better at low nutrient conditions. This shows that light intensity, light variability, and nutrient supply interactively affect communities. Furthermore, the responses are highly species and pigment specific, thus to clarify the effects of climate change a deeper understanding of the effects of light variability and species interactions within communities is important.

The research is based on the materials collected during cruise 66 of R/V Akademik Mstislav Keldysh in the Yenisei estuary and over the adjacent Kara Sea shelf in the latitudinal range from 71°50.5′ to 75°55.0′ N. The studies were performed from July 25 to 27, 2016, three weeks after the end of the flood period. Two hundred fifty species of plankton algae were recorded. Well-pronounced latitudinal zoning in phytoplankton communities structure associated with changes in the hydrophysical and hydochemical conditions of the pelagic environmental was determined. The maximum species diversity was formed by diatoms, green and blue-green algae in the southern desalinated part of the estuary (<1 PSU) and by diatoms and dinoflagellates in the offshore areas. The highest algae abundance and biomass, 2.7–2.9 × 106 cell/L and 1.1–1.5 g/m3, respectively, were recorded in the inner desalinated part of the estuary, where freshwater diatoms of the genus Aulacoseira dominated. The distribution of freshwater algae northwards was bounded by the 12–15 PSU surface isohaline (74°20′ N). The most pronounced decline in phytoplankton abundance and biomass was found in the outer part of the estuary north of ~73° N. In the middle shelf to the north of the Yenisei estuary, the maximum abundance (up to 740 × 103 cell/L) and biomass (up to 240 mg/m3) of phytoplankton were recorded at the depths of 30–40 m with low illumination and high nutrient concentration, which was also typical of the Ob region in spring–summer. [ABSTRACT FROM AUTHOR]

The presence of a multitude of bioactive organic pollutants collectively classified as pharmaceuticals and personal care products (PPCPs) in freshwaters is of concern, considering that ecological assessments of their potential impacts on natural systems are still scarce. In this field experiment we tested whether a single pulse exposure to a mixture of 12 pharmaceuticals and personal care products, which are commonly found in European inland waters, can influence the size distributions of natural lake phytoplankton communities. Size is one of the most influential determinants of community structure and functioning, particularly in planktonic communities and food webs. Using an in-situ microcosm approach, phytoplankton communities in two lakes with different nutrient levels (mesotrophic and eutrophic) were exposed to a concentration gradient of the PPCPs mixture at five levels. We tested whether sub-lethal PPCPs doses affect the scaling of organisms' abundances with their size, and the slope of these size spectra, which describe changes in the abundances of small relative to large phytoplankton. Our results showed that a large proportion (approximately 80%) of the dataset followed a power-law distribution, thus suggesting evidence of scale invariance of abundances, as expected in steady state ecosystems. PPCPs were however found to induce significant changes in the size spectra and community structure of natural phytoplankton assemblages. The two highest treatment levels of PPCPs were associated with decreased abundance of the most dominant size class (nano-phytoplankton: 2–5 μm), leading to a flattening of the size spectra slope. These results suggest that a pulse exposure to PPCPs induce changes that potentially lead to unsteady ecosystem states and cascading effects in the aquatic food webs, by favoring larger non-edible algae at the expense of small edible species. We propose higher susceptibility due to higher surface to volume ratio in small species as the likely cause of these structural changes. Unlabelled Image • Ecological consequences of diffuse contaminants in natural systems are still scarce. • PPCPs affect the scaling of abundances relative to organisms' size in phytoplankton. • Vulnerability of smaller phytoplankton to contaminants resulted in structural changes. • Changes in the phytoplankton community composition were similarly observed. [ABSTRACT FROM AUTHOR]

Climate warming has a significant impact on the sea ice and ecosystem of the Arctic Ocean. Under the increasing numbers of melt ponds in Arctic sea ice, the phytoplankton communities associated with the ice system are changing. During the 7th Chinese National Arctic Research Expedition cruise in summer 2016, photosynthesis pigments and nutrients were analyzed, revealing differences in phytoplankton communities between melt ponds and open water in the central Arctic. Photo synthetic pigment analysis suggested that Fuco (5-91 μg m-3 and Diadino (4-21 μg m-3) were the main pigments in the open water. However, the melt ponds had high concentrations of Viola (7-30 μg m-3), Lut (4-59 μg m-3) and Chl b (11-38 μg m-3), suggesting that green algae dominated phytoplankton communities in the melt ponds. The significant differences in phytoplankton communities between melt ponds and open water might be due to the salinity difference. Moreover, green algae may play a more important role in Arctic sea ice ecosystems with the expected growing number of melt ponds in the central Arctic Ocean. [ABSTRACT FROM AUTHOR]

• The relative abundance and biomass of phytoplankton is exponential distribution. • Three new indices including a, k and N were established. • The a was the critical relative abundance of extinction. • The k and N were competition coefficient and the environmental taxa capacity. • Relationship among a, k and N and traditional diversity indices was analysed. Phytoplankton are primary producers in aquatic ecosystems and their diversity directly affects the community stability and primary productivity. However, the commonly used diversity indices (such as Shannon and Pielou indices) were originally derived from other fields rather than ecology and did not have a direct biological explanatory function. There is still a need to incorporate biological explanatory functions into diversity evaluation methods and theories to bridge the gap between phytoplankton biodiversity and biological characteristics. This study aimed to explicate the intrinsic distribution patterns of phytoplankton relative abundance and biomass. Our study demonstrated an exponential distribution pattern of phytoplankton relative abundance and biomass ranking through field investigations of 367 phytoplankton samples in China and microcosm experiments, respectively. Microcosm experiments illustrated that the linear distribution of the specific growth rate ranking resulted in an exponential distribution of the relative phytoplankton biomass ranking due to exponential growth patterns. Through mathematical deduction, it was found that the three indices a, k and N in the exponential distribution could be considered as the critical relative abundance of extinction, competition coefficient and the environmental taxa capacity, respectively. We found that a was positively correlated with Shannon index and Pielou index, k was negatively correlated with Shannon index, Pielou index and Chao1 index. In addition, N and Chao1 index were almost exactly the same. Our study obtained these indices based on the distribution pattern of phytoplankton, enabling a comprehensive analysis of the phytoplankton community and providing novel insights for further evaluating the health of aquatic ecosystems. [Display omitted] [ABSTRACT FROM AUTHOR]

Phytoplankton bloom phenology studies are fundamental for the understanding of marine ecosystems. Mismatches between fish spawning and plankton peak biomass will become more frequent with climate change, highlighting the need for thorough phenology studies in coastal areas. This study was the first to assess phytoplankton bloom phenology in the Western Iberian Coast (WIC), a complex coastal region in SW Europe, using a multisensor long-term ocean color remote sensing dataset with daily resolution. Using surface chlorophyll a (chl-a) and biogeophysical datasets, five phenoregions (i.e., areas with coherent phenology patterns) were defined. Oceanic phytoplankton communities were seen to form long, low-biomass spring blooms, mainly influenced by atmospheric phenomena and water column conditions. Blooms in northern waters are more akin to the classical spring bloom, while blooms in southern waters typically initiate in late autumn and terminate in late spring. Coastal phytoplankton are characterized by short, high-biomass, highly heterogeneous blooms, as nutrients, sea surface height, and horizontal water transport are essential in shaping phenology. Wind-driven upwelling and riverine input were major factors influencing bloom phenology in the coastal areas. This work is expected to contribute to the management of the WIC and other upwelling systems, particularly under the threat of climate change.

Riverine nutrients act in concert with local hydrographic conditions to create distinct ecological niches for phytoplankton communities across river-ocean continuums. Here we compare two of the world’s largest river-ocean systems, the Amazon River Plume (ARP) which outflows into the Western Tropical North Atlantic and the Changjiang Diluted Water (CDW) which empties into the East China Sea to show how distinctly different N: P supply ratios of their source waters, shape phytoplankton communities along the river-ocean continuum. Sampling in the relatively unpolluted surface waters of the ARP during peak river discharge revealed that phytoplankton communities along the river-ocean continuum were strongly limited by Dissolved Inorganic Nitrogen (DIN, nitrate plus nitrite) which was low or beyond detectable, while Dissolved Inorganic Phosphorous (DIP, phosphate) and Silica were not limiting. The resulting low N:P supply ratio allowed diazotrophs to co-exist with non-diazotrophs. Diatom-Diazotroph Associations (DDAs) such as Hemiaulus hauckii-Richelia proliferated, while in the oligotrophic oceanic waters, Trichodesmium spp. thrived. In contrast, in the CDW, anthropogenic nitrogen inputs from human pressures in the Changjiang River system has led to a system where the changing supply rate of the single nutrient (DIP) is responsible for the interannual variability seen in the phytoplankton community structure of the CDW. During years of low discharge, DIP limitation can be ameliorated by on-shelf upwelling of DIP rich Kuroshio Intermediate Waters leading to domination of diatoms and dinoflagellates. Conversely, during years of heavy discharge, the westward flowing CDW plume was severely DIP limited, probably because water column stratification dampened upwelling of subsurface waters. The consequent DIP limitation led to the proliferation of small phytoplankton such as Chlorophytes and Cyanobacteria. The absence of diazotrophs in the CDW, leads us to hypothesize that river-ocean continuums, whose source waters are heavily impacted by anthropogenic activities and with high nitrate concentrations often substantially in excess of Redfield ratios, may not support diatoms offshore on account of DIP limitation nor diazotrophy because of excess DIN.

The toxicity of polycyclic aromatic hydrocarbons (PAHs) mixtures was evaluated on natural phytoplankton communities sampled from lagoons of Bizerte (South-western Mediterranean Sea) and Thau (North-western Mediterranean Sea). PAHs induced short-term dose and ecosystem-dependant decreases in photosynthetic potential. Chlorophyll a was negatively affected by increasing PAHs concentrations, together with dramatic changes in phytoplankton community composition. Size classes were strongly affected in the Bizerte compare to the Thau lagoon, with a decrease in nano- and microphytoplankton densities compare to picophytoplankton. In both locations, the diatom Entomoneis paludosa appeared favoured under PAH exposure as evidenced by increase in cell density, whereas autotrophic flagellates and dinophytes were strongly reduced. Smaller cells were more tolerant to exposure to highest PAHs concentrations, with persistent picophytoplankton carbon biomass at the end of the incubations. Apparent recovery of photosynthetic potential, accompanied with a regrowth of chlorophyll a under the lowest PAH doses, coincided with a significantly altered community composition in both lagoons. Furthermore, sensitivity to PAHs was not related to the phytoplankton cell size, and toxicity-induced modification of top-down control by grazers during the experiment cannot be excluded. [ABSTRACT FROM AUTHOR]

In some regions, tidal energy can be a key factor in the generation of variability in physical and biogeochemical properties throughout the water column. We use a numerical model resolving tidal cycles and simulating diversity in phytoplankton to assess the impact of tidal mixing on vertical stability and phytoplankton community (total biomass and diversity) in a macrotidal sea (Iroise Sea, France). Two different time scales have been considered: semidiurnal and spring/neap tidal cycles. Our results show that the latter is the one primarily influencing the phytoplankton growth conditions by modifying the vertical stratification. During spring tide, the growth is rather light limited, whereas neap tide conditions lead to vertical stabilization and better light conditions in the shallow surface layer. The transition from high to low tidal mixing conditions is thus associated with a total phytoplankton biomass increase (caused by the rapid development of fast-growing diatoms) and reduced phytoplankton diversity. [ABSTRACT FROM AUTHOR]

The polar regions (Arctic and Antarctic) constitute up to 14% of the biosphere and offer some of the coldest and most arid Earth's environments. Nevertheless several oxygenic phototrophs including some higher plants, mosses, lichens, various algal groups and cyanobacteria, survive that harsh climate and create the base of the trophic relationships in fragile ecosystems of polar environments. Ecosystems in polar regions are characterized by low primary productivity and slow growth rates, therefore they are more vulnerable to disturbance, than those in temperate regions. From this reason, chemical contaminants influencing the growth of photoautotrophic producers might induce serious disorders in the integrity of polar ecosystems. However, for a long time these areas were believed to be free of chemical contamination, and relatively protected from widespread anthropogenic pressure, due their remoteness and extreme climate conditions. Nowadays, there is a growing amount of data that prove that xenobiotics are transported thousands of kilometers by the air and ocean currents and then they are deposed in colder regions and accumulate in many environments, including the habitats of marine and freshwater cyanobacteria. Cyanobacteria (blue green algae), as a natural part of phytoplankton assemblages, are globally distributed, but in high polar ecosystems they represent the dominant primary producers. These microorganisms are continuously exposed to various concentration levels of the compounds that are present in their habitats and act as nourishment or the factors influencing the growth and development of cyanobacteria in other way. The most common group of contaminants in Arctic and Antarctic are persistent organic pollutants (POPs), characterized by durability and resistance to degradation. It is important to determine their concentrations in all phytoplankton species cells and in their environment to get to know the possibility of contaminants to transfer to higher trophic levels, considering however that some strains of microalgae are capable of metabolizing xenobiotics, make them less toxic or even remove them from the environment. [ABSTRACT FROM AUTHOR]

Ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) as an important enzyme in photosynthetic process exists in various marine phytoplankton. To investigate the photosynthetic phytoplankton communities, conservative encoding gene of RubisCO large subunit ( rbcL) was chosen as a target gene in this study. We constructed 33 clone libraries from samples collected in the north of South China Sea (NSCS) and retained 3173 sequences for further analysis. Results of BLASTp showed Stramenopiles and Haptophyta were predominant taxonomic groups in this area, while only five harmful species of Dinophyta were observed. According to the estimators of biodiversity, the photosynthetic community of N709 had very low genetic diversity and richness, which could be explained by the influence of brackish estuarine environment. Beta diversity showed that all samples could be clustered into three groups and those samples with approximately the same distance to land clustered together. Temperature, depth, and latitude of stations as biogeographic factors were indicated to have a significantly positive or negative relation with biodiversity estimators of the phytoplankton community. We concluded that biogeographic factors could be linked with difference in diversity and population of natural phytoplankton assemblages in horizontal surface of NSCS in summer 2007. [ABSTRACT FROM AUTHOR]

Phytoplankton community' dynamics were studied in Salgados coastal lagoon in order to evaluate the effects of excessive organic loads and also physical stress caused by the irregular opening of the lagoon. Salgados is a hypereutrophic intermittently open coastal lagoon, which received freshwater inputs from small rivers and from a wastewater treatment plant. Cyanophyceae dominated the phytoplankton communities most of the time; Bacillariophyceae became the main taxonomic group in winter when the lagoon was closed; Chlorophyceae was the major class in early summer; pico-nano flagellate algae accounted for a high percentage of total phytoplankton during spring. Potentially harmful taxa were observed during most of the sampling periods, forming blooms and accounting for a considerable percentage of total phytoplankton abundance. A strong differentiation among dry and wet seasons could be noticed. The dry season was dominated by Microsystis aeruginosa , Rhodomonas sp., pico-nano flagellate algae, Cyclotella spp. and Planktothrix sp., while the wet season, although still with the presence of Microsystis aeruginosa , was dominated by Dolichospermum spiroides . The best environmental variables explaining stations patterns and based on phytoplankton taxa were days of isolation, pH, and salinity. Temperature, cumulative rain and total phosphorus were also related with species and stations patterns. The high nutrient load in Salgados lagoon promoted the development and persistence of harmful algae blooms. Proper management of coastal lagoons involves not only the control of direct discharges of nutrients, but also of other factors, including water level and communication with the sea. [ABSTRACT FROM AUTHOR]

The article presents a study on the phytoplankton dynamics and its environmental control throughout the Canadian High Arctic (CHA). The researchers calculated the daily incident downwelling irradiance at every station and tested all the biological and environmental variables for homoscedasticity and normality of distribution before the statistical analyses. They also performed a redundancy analysis (RDA) to assess interactions between biological and environmental variables and major taxonomic groups of protists.

Phytoplankton community structure was investigated in a 1-year study period from January to December 2006 in the Tunis North Lagoon (South Mediterranean). Twice a month, sampling was carried out from the whole water column. Phytoplankton species composition showed seasonal dynamics following the general environmental variable trends in the study area, with variation in species abundance levels within each season characterised by the presence of different phytoplankton communities. Analysis of environmental variables indicated that phytoplankton-dominant communities were associated with various water physicochemical characteristics, especially water temperature and salinity. Accordingly, significant correlation was recorded between water temperature and dinoflagellates ( r = 0.35; p < 0.05) in summer and diatoms ( r = 0.69; p < 0.05) in autumn, whereas euglenophytes, cyanophytes and chlorophytes were slightly correlated with temperature in autumn. Salinity was positively correlated with dichtyophytes ( r = 0.41; p < 0.05) in winter and with diatoms ( r = 0.65; p < 0.05) and euglenophytes ( r = 0.57; p < 0.05) in autumn. On the other hand, relationships between high nitrogen nutrient concentration and phytoplankton concentration were recorded for diatoms ( r = 0.43; p < 0.05 with NO; r = 0.49; p < 0.05 with NO) in winter. Silicate concentration supported proliferation of diatoms ( r = 0.58; p < 0.05) in autumn in our study period. In contrast, increase of dinoflagellate concentration was associated with the decrease of these parameters in spring and summer. [ABSTRACT FROM AUTHOR]

Abstract: Annual phytoplankton blooms are observed around most sub-Antarctic islands during austral spring and summer, but are absent in the surrounding high-nutrient low-chlorophyll (HNLC) ocean. The CROZEX study (2004/2005) tested the hypothesis that annual blooms occurring immediately north of the Crozet islands in the Polar Frontal Zone (PFZ) develop because of natural iron fertilisation, while to their south in HNLC waters, there is insufficient iron (Fe) to promote blooms. Size-fractionated nitrogen uptake (ρN) experiments using 15N-NO3 −, NH4 + and urea addressed three major goals. Firstly, measurements of NO3 − uptake (ρNO3 −) aimed to establish whether ρNO3 − responds to natural Fe fertilisation. Secondly, we compared regional ρNO3 − rates, hypothesising that in Fe-fertilised regions, ρNO3 − should exceed that in HNLC regions. Thirdly, by using satellite imagery, we extrapolated ρNO3 − measurements made during a declining bloom to reconstruct seasonal ρNO3 − by the spring bloom. Finally, we estimated the ‘new’ Fe demand required to support ρNO3 −, comparing this with estimated Fe fluxes. Diatoms and colonial Phaeocystis dominated phytoplankton communities north of the islands, while to the south, Phaeocystis was absent. Total ρN was elevated north of the islands (∼400μmolm−2 d−1) relative to south of the islands (∼250μmolm−2 d−1). Nitrate uptake showed a clear response to Fe fertilisation, exhibiting a strong north (∼198μmolm−2 d−1) to south (∼74μmolm−2 d−1) gradient, while neither ρNH4 + nor ρurea showed such significant latitudinal gradients. The N–S integrated f-ratio gradient was 0.47–0.28 while specific N uptake ( d−1) rates were significantly higher in the Fe-fertilised region relative to those in the southern HNLC region. The potential for NH4 + inhibition of ρNO3 − did not appear to be significant. High PON:chl-a ratios combined with relatively low 14C:15N uptake ratios suggested that most phytoplankton were relatively chlorotic and carbon stressed, with the exception of those growing actively within a cyclonic eddy where neither Fe nor light appeared to be limiting. Size-fractionated ρNO3 − and f-ratios exhibited a complex response to NH4 + and Fe availability, with f-ratios in the >20-μm fraction being low (∼0.3) in the HNLC region, but significantly higher (∼0.7) in a localised diatom-dominated bloom in the northern Fe-fertilised region. In contrast, f-ratios in the <2-μm size class were similar everywhere (∼0.44), indicative of Fe-limitation for large-celled diatoms in the southern HNLC region. As a result of Fe-regulated ρNO3 −, new production showed a N–S gradient of ∼24 to ∼15mmolCm−2 d−1, very similar to carbon export determined from NO3 − ‘draw-down’ and from 234Th measurements. The estimated DFe demand required to support seasonal ρNO3 − in the northern region, based on conservative cellular Fe:N quotas, required surface (to 100m) pre spring-bloom DFe concentrations of ∼0.75nmoll−1. Our results support the hypothesis that phytoplankton blooms north of the islands are stimulated by natural Fe fertilisation, with a direct impact on ρNO3 −, particularly for larger cells, resulting in higher new production rates relative to those from the Fe-limited HNLC region south of the Crozet islands. [Copyright &y& Elsevier]

Size-fractionated chlorophyll a (Chl a) biomass and phytoplankton community distributions were investigated along two transects located in the Indian Ocean frontal region between 43–46°S and 62–65°E during late summer 1999. Chl a distribution was linked to the merged Subantarctic Front (SAF) and the Subtropical Front (STF) which marked the border between the cold and less saline subantarctic waters and the warm and more saline subtropical waters. Chl a concentrations increased from <0.3 μg l-1 in the subantarctic waters to 0.80 μg l-1 in the subtropical waters. In the northeastern region, a patch of high Chl a concentrations was associated with the meandering of the fronts which were in very close proximity. Pico-sized phytoplankton fractions were always dominant over the survey area contributing 54–71% to the total Chl a standing stock. In the subtropical waters, cyanobacteria were the major components of the pico-size fractions. Synechococcus spp. showed a northward positive gradient from 2–5×103 cells ml-1 in the subantarctic waters to 6×104 cells ml-1 in the subtropical waters. Prochlorococcus spp. were only present in the warmer subsurface waters north of the SAF/STF. They reached a maximum of 15.6×104 cells l-1 north of the Agulhas Front (AF). Except for the AF where the coccolithophorid Emiliana huxleyi formed 70% of the total carbon stocks, dinoflagellates <20 μm were the major contributors (50–90%) to the total carbon biomass. They were mainly composed of Gymnodinium/Gyrodinium, Prorocentrum spp. and Oxytoxum laticeps with peaks in the STF and subtropical waters. Nanoflagellates and diatoms formed together 0.2–3.9% of the entire cell carbon biomass. Diatoms (mainly, Pseudonitzschia delicatissima and Pseudonitzschia turgidula) were poorly represented in the entire survey area. The low biomass associated with low nutrient concentrations suggested a postbloom situation with a shift towards nonsiliceous pico-size communities. The low biological activity observed during this cruise was confirmed by the low RNA:DNA ratios. [Copyright &y& Elsevier]

The relationship between environmental factors, community composition and the sensitivity of pelagic phytoplankton to the antifouling agents zinc pyrithione (ZPT) and copper pyrithione (CPT) was studied using phytoplankton communities collected from March until August 2001 in Roskilde fjord, Denmark. Sensitivity to ZPT and CPT was measured as EC50 values obtained from dose–response curves of photosynthesis to ZPT and CPT. EC50 for ZPT and CPT varied between 2 and 60 nM and 4 and 25 nM, respectively. Changes in sensitivity throughout the season were related to changes in phytoplankton community composition and density, and to nutrient levels. It was found that the variation in sensitivity of ZPT and CPT was related to the abundance of the groups Cryptophyceae, Bacillariophycaea and Dinophyceae when they were dominating the community. Furthermore, the sensitivity to ZPT was increased at low concentrations of phosphate per cell (<0.2 nmol/cell). For CPT there was a negative correlation between toxicity and phosphate concentration in the water. Consequently, in aquatic environments where phytoplankton is phosphate limited the effect of ZPT and CPT may be enhanced. [Copyright &y& Elsevier]

Two pristine forest lakes have been sampled for 12 years in order to follow the long term variation of phytoplankton biomass and species composition together with environmental parameters. The lakes Iso Hietajärvi and Pieni Hietajärvi are shallow headwater lakes situated in the Patvinsuo National Park, eastern Finland. Lake Iso Hietajärvi was weakly stratified during the open water season in 1988–2001, in contrast to Lake Pieni Hietajärvi, which was always strongly stratified mainly because of its wind-sheltered location and dark water. During the long study period, the main changes in water quality have been slight increases of alkalinity and pH-value and also some decrease of the nitrate content. The phytoplankton (wet) biomass in surface water varied from 0.07 to 0.51 mg l-1 in Lake Iso Hietajärvi and from 0.18 to 0.60 mg l-1 in Lake Pieni Hietajärvi in 1991, during the intensive weekly sampling. The biomass was mainly composed of Cryptophyceae, Chrysophyceae and Bacillariophyceae in Lake Iso Hietajärvi, and Cryptophyceae in Lake Pieni Hietajärvi. In Lake Iso Hietajärvi, the differences in the vertical distribution of phytoplankton biomass and species composition were small and the productive layer reached down to 4 m, whereas in the dark coloured Lake Pieni Hietajärvi the productive layer was shallow, ≤1 m. When the whole productive water column is considered, the unstratified clear water Lake Iso Hietajärvi is more productive than the stratified dark coloured Lake Pieni Hietajärvi. The seasonal succession of phytoplankton species composition is different in these adjacent lakes; more variation was found in the unstratified Lake Iso Hietajärvi compared to the smaller stratified lake. [ABSTRACT FROM AUTHOR]

Potentially toxic Cylindrospermopsis raciborskii blooms are of emerging concerns, as its scale is spreading from tropical regions to high latitudes, increasing the risk of aquatic biota being exposed to cylindrospermopsin (CYN). So far, CYN-producing C. raciborskii strains have only been reported in tropical waters which are commonly phosphorus (P)-deficient, where they can dominate phytoplankton communities. However, the influence of CYN on phytoplankton communities under different P status remains unclear. In this study, we first analyzed the summer observations of 120 tropical reservoirs in Guangdong Province. The proportion of potential CYN-producers was significantly higher in P-deficient and CYN-present reservoirs than that in P-sufficient or CYN-absent ones. This suggested that in P-deficient condition, the potential CYN producers might gain more advantages by the help of CYN. Then, in laboratory experiments we found that upon P deprivation, CYN did not inhibit the cell growth of other algal cells, but significantly stimulates them to secret more alkaline phosphatase (ALP) than in P-sufficient condition. Through transcriptomics, we further revealed that under such P-deficient condition, CYN remarkably induced intracellular nitrogen allocation and protein export system by activating the PIK3/Akt-cGMP/PKG signaling pathways in Scenedesmus bijugatus , thus enhancing its ALP secretion. Our study implies that CYN-induced ALP secretion is facilitated upon P deficiency, thus supporting the dominance of its producers C. raciborskii. [Display omitted] • Potential CYN-producer gain more advantage in P-deficient CYN-present reservoirs. • P deficiency enhanced the CYN-induced ALP secretion. • CYN did not inhibit the growth of three algal cells irrespective of P status. • CYN could trigger the growth of P-sufficient chlorophytes. • CYN activated N allocation and protein export to induce ALP secretion. [ABSTRACT FROM AUTHOR]

When assessing trends among a group of variables, there may be a joint underlying trend not evident from direct plots of the individual variables against time. To provide a simple summary of this underlying trend, linear projections of multiple time series are constructed to maximize the variance explained by a fitted smoother. A number of tests for assessing the significance of the fitted trend are given. The method is applied to densities of phytoplankton groups observed over a 13-month period and used to contrast the trends observed in two different areas within the southern North Sea. [ABSTRACT FROM PUBLISHER]

Phytoplankton bloom phenology studies are fundamental for the understanding of marine ecosystems. Mismatches between fish spawning and plankton peak biomass will become more frequent with climate change, highlighting the need for thorough phenology studies in coastal areas. This study was the first to assess phytoplankton bloom phenology in the Western Iberian Coast (WIC), a complex coastal region in SW Europe, using a multisensor long-term ocean color remote sensing dataset with daily resolution. Using surface chlorophyll a (chl-a) and biogeophysical datasets, five phenoregions (i.e., areas with coherent phenology patterns) were defined. Oceanic phytoplankton communities were seen to form long, low-biomass spring blooms, mainly influenced by atmospheric phenomena and water column conditions. Blooms in northern waters are more akin to the classical spring bloom, while blooms in southern waters typically initiate in late autumn and terminate in late spring. Coastal phytoplankton are characterized by short, high-biomass, highly heterogeneous blooms, as nutrients, sea surface height, and horizontal water transport are essential in shaping phenology. Wind-driven upwelling and riverine input were major factors influencing bloom phenology in the coastal areas. This work is expected to contribute to the management of the WIC and other upwelling systems, particularly under the threat of climate change. [ABSTRACT FROM AUTHOR]

The use of discontinuity analysis to assess resilience and alternative regimes of ecosystems has mostly been based on animal size. We so far lack systematic comparisons of size-based and abundance-based approaches necessary for assessing the performance and suitability of the discontinuity analysis across a broader range of organism groups. We used an outdoor mesocosm setup to mimic shallow lake ecosystems with different depths (1.2 m deep, "shallow"; 2.2 m deep, "deep") and trophic status (i.e. low and high nutrient status characteristic of mesotrophic and hypertrophic lakes, respectively). We compared resilience assessments, based on four indicators (cross-scale structure, within-scale structure, aggregation length and gap size) inferred from the size and abundance (biovolume) structure of phytoplankton communities. Our results indicate that resilience assessments based on size and biovolume were largely comparable, which is likely related to similar variability in the size and abundance of phytoplankton as a function of nutrient concentrations. Also, nutrient enrichment rather than water depth influenced resilience, manifested in decreased cross-scale structure and increased aggregation lengths and gap sizes in the high-nutrient treatment. These resilience patterns coupled with decreased phytoplankton diversity and dominance of cyanobacteria in the high nutrient treatment support the use of discontinuity analysis for testing alternative regimes theory. Concordance of size-based and abundance-based results highlights the approach as being potentially robust to infer resilience in organism groups that lack discrete size structures. Unlabelled Image • Resilience of phytoplankton to nutrients and water depth manipulations was assessed. • Resilience was inferred and compared from size- and abundance-based approaches. • Both approaches, size- and abundance-based resilience assessment, were comparable. • Nutrient enrichment rather than water depth influenced resilience. [ABSTRACT FROM AUTHOR]