Changes In Plankton Communities Research Articles

Plankton Community Stability and Drive Factor Identification Guizhou Plateau Reservoir

In order to understand the stability of the zooplankton and phytoplankton communities in the Guizhou plateau reservoir environment, the process of reservoir water quality change affecting the stability of plankton was studied. The changes in the plankton community and water quality in three different nutrient reservoirs （Huaxi Reservoir, Goupitan Reservoir, and Hailong Reservoir） were studied from October 2020 to August 2021. The stability of the zooplankton and phytoplankton communities was studied using time-lag analysis （TLA）. Variance decomposition analysis （VPA） was used to explore the response of the two communities to environmental changes. The driving factors of plankton community changes in reservoirs were also revealed. The results showed that Huaxi Reservoir and Goupitan Reservoir were mesotrophic reservoirs, and Hailong Reservoir was a eutrophic reservoir. The average comprehensive nutrition indices of the three reservoirs were 44.07, 44.68, and 50.25. A total of 51 species of zooplankton rotifers, 39 species of rotifers, three species of copepods, and nine species of cladocera were identified. Among them, the abundance of rotifers was the highest, accounting for 85.96%. A total of seven phyla and 73 species of phytoplankton were identified, including 16 species in the phylum Cyanophyta, 32 species in the phylum Chlorophyta, 16 species in the phylum Diatoma, three species in the phylum Chlorophyta, four species in the phylum Euglenophyta, and one species each in the phyla Cryptophyta and Chrysophyta. Among them, the abundance of cyanobacteria and diatoms was the highest, accounting for 66.2% and 27.35%, respectively. The median absolute deviation （MAD） of the Bray-Curtis distance of zooplankton and phytoplankton community in the three reservoirs were 0.67 and 0.65 in Huaxi Reservoir, 0.80 and 0.69 in Goupitan Reservoir, and 0.85 and 0.47 in Hailong Reservoir, respectively. The larger the value, the greater the variation in the community. The absolute value of the slope of zooplankton was greater than that of phytoplankton in the TLA results, and the absolute values of the slopes were 0.018 and 0.004, respectively. The larger the absolute value of the slope, the faster the community variability. The zooplankton community in the three reservoirs was less stable than the phytoplankton community and more sensitive to environmental changes, and the degree of variation was greater. The higher the degree of eutrophication of the reservoir, the more obvious this phenomenon. VPA showed that the changes in plankton communities in Huaxi Reservoir and Hailong Reservoir were mainly influenced by water temperature and eutrophication factors. The changes in planktonic community in Goupitan Reservoir were mainly influenced by water temperature and chemical factors. The driving factors of Huaxi Reservoir were water temperature, TP, permanganate index, and SD. The driving factors of Goupitan Reservoir were water temperature, NO3-- N, and pH. The driving factors of Hailong Reservoir were water temperature and TP. Nutrients and water temperature were the main factors affecting the stability of plankton communities in reservoirs.

Plankton Community Changes and Nutrient Dynamics Associated with Blooms of the Pelagic Cyanobacterium Trichodesmium in the Gulf of Mexico and the Great Barrier Reef

Blooms of the harmful dinoflagellate Karenia brevis on the West Florida Shelf (WFS), Gulf of Mexico, are hypothesized to initiate in association with the colonial cyanobacterium Trichodesmium spp. and benefit from dissolved organic nitrogen (DON) release derived from N2-fixation by the cyanobacteria. Previous studies have detected DON release using direct experimental measurements, but there have been few studies that have followed nutrient release by in situ blooms of Trichodesmium and the associated plankton community. It was determined that long-term Trichodesmium spp. and Karenia brevis abundances on the WFS were related, following a 2-month lag. A separate Eulerian study of a Trichodesmium erythraeum bloom event was conducted over 9 days on the Great Barrier Reef. Concentrations of T. erythraeum increased over the course of the study, with coincident increases in dinoflagellate abundance and decreases in diatom abundance. Inside the bloom, concentrations of NH4+, PO43−, and DON increased significantly. The copepod grazer Macrosetella gracilis also increased in abundance as T. erythraeum numbers increased, contributing to nutrient release. Copepod grazing rates were measured, and N release rates estimated. Together, these studies show that Trichodesmium blooms have consequences for dinoflagellate abundance at both seasonal and ephemeral scales via direct and indirect N release.

Plankton community changes during the last 124 000years in the subarctic Bering Sea derived from sedimentary ancient DNA.

Current global warming results in rising sea-water temperatures, and the loss of sea ice in Arctic and subarctic oceans impacts the community composition of primary producers with cascading effects on the food web and potentially on carbon export rates. This study analyzes metagenomic shotgun and diatom rbcL amplicon sequencing data from sedimentary ancient DNA of the subarctic western Bering Sea that records phyto- and zooplankton community changes over the last glacial-interglacial cycles, including the last interglacial period (Eemian). Our data show that interglacial and glacial plankton communities differ, with distinct Eemian and Holocene plankton communities. The generally warm Holocene period is dominated by picosized cyanobacteria and bacteria-feeding heterotrophic protists, while the Eemian period is dominated by eukaryotic picosized chlorophytes and Triparmaceae. By contrast, the glacial period is characterized by microsized phototrophic protists, including sea ice-associated diatoms in the family Bacillariaceae and co-occurring diatom-feeding crustaceous zooplankton. Our deep-time record of plankton community changes reveals a long-term decrease in phytoplankton cell size coeval with increasing temperatures, resembling community changes in the currently warming Bering Sea. The phytoplankton community in the warmer-than-present Eemian period is distinct from modern communities and limits the use of the Eemian as an analog for future climate scenarios. However, under enhanced future warming, the expected shift toward the dominance of small-sized phytoplankton and heterotrophic protists might result in an increased productivity, whereas the community's potential of carbon export will be decreased, thereby weakening the subarctic Bering Sea's function as an effective carbon sink.

At what scale should we assess the health of pelagic habitats? Trade-offs between small-scale manageable pressures and the need for regional upscaling

Major planktonic lifeforms such as diatoms, dinoflagellates, meroplankton and holoplankton have recently shown significant and alarming changes in abundance - mainly downwards trends - around the northwest European shelf. This has major implications for food web connections and for ecosystem services including seafood provision and carbon storage. We have quantified these changes in abundance for 2006–2019/20 using a Plankton Index (PI) and show that the scale of spatial aggregation is critical to the ability of the PI to detect change, understand causal mechanisms, and provide advice to policymakers.We derived PI statistics in the Celtic and North Seas from data from the Continuous Plankton Recorder survey offshore and England’s Environment Agency inshore using three sets of spatial units: (i) Ecohydrodynamic (EHD) units based on hydro-biogeochemical modelling, (ii) ‘COMP4′ areas based on cluster analysis of satellite data for chlorophyll a and primary productivity, and (iii) English coastal and estuarine Water Framework Directive (WFD) waterbodies. For the largest scale areas, the EHD units (median size 87,000 km2), we find greater change in plankton communities than previously reported, suggesting that these shifts have continued and possibly intensified in recent years. The smaller-scale COMP4 areas (median size 6,700 km2) appear to encompass more spatially coherent changes in plankton community structure than EHD units; at this scale PI values indicate community shifts of greater magnitude. These COMP4 areas provide a reasonable compromise scale for linking offshore plankton communities to large-scale drivers of change such as climate warming. For inshore plankton communities, larger changes are detected at the smaller WFD waterbody scale (median size 11 km2). This scale allows direct links to coastal management measures and is more suitable for linking to land-sourced pressures.Recent integration of the UK’s OSPAR and WFD plankton monitoring data management enables the exploration of changes across spatial scales to develop a holistic understanding of ecosystem health. Regional-sea scale derivation of the PI for coastal waters provides a clear indication that changes are occurring, at least in phytoplankton communities, while localised PI statistics offer an additional layer of information which can be an important tool for linking to localised drivers of change including coastal anthropogenic pressures. Broadscale inshore zooplankton monitoring is needed to evaluate the coastal plankton community holistically; zooplankton communities offshore are also changing but these changes cannot currently be linked to coastal processes. Layering information across spatial scales provides a breadth of system-level understanding beyond what any one typology can provide.

A size‐based perspective on the decoupling between compositional and functional changes in planktonic communities

AbstractRecent studies have shown a decoupling in the way community composition and functions respond to environmental changes. A common pattern observed is that aggregated functions at the community level are more stable than community composition, which is likely the result of functional compensatory dynamics driven by interspecific differences in response to environmental change. However, the mechanisms by which these patterns emerge remain largely unexplored. Here we investigated in a mesocosm experiment for four weeks the compositional and functional responses of edible phytoplankton (<64 μm) and cladoceran zooplankton communities to climate warming (a constant increase of +3.5°C plus heat wave) and eutrophication (nutrient additions) from a size‐based perspective. Our results show that warming increases small‐sized taxa and decreases large‐sized taxa within both phytoplankton and zooplankton community composition. We found that such opposite responses of different‐sized taxa contributed to the stability of planktonic community functions and thereby resulted in a decoupling between compositional and functional changes. We also found that nutrient additions increased the abundance of all‐sized algal taxa, while phytoplankton community function remained stable. Nutrient additions did not alter the zooplankton community, neither compositionally nor functionally. Under the combined stress of warming and nutrient additions, the compositional and functional responses of planktonic communities were mainly driven by warming. In a broader perspective, our findings reveal a size‐dependent compensation mechanism and suggest that functional stability relies on compensatory effects among different‐sized taxa, and it is therefore important that communities host a large range of taxa differing in size to withstand an increasingly more variable environment in the future.

Effects of Environmental Concentrations of Total Phosphorus on the Plankton Community Structure and Function in a Microcosm Study.

The excessive nutrients in freshwater have been proven to promote eutrophication and harmful algae blooms, which have become great threats to water quality and human health. To elucidate the responses of the plankton community structure and function to total phosphorus (TP) at environmental concentrations in the freshwater ecosystem, a microcosm study was implemented. The results showed that plankton communities were significantly affected by the TP concentration ≥ 0.1 mg/L treatments. In terms of community structure, TP promoted the growth of Cyanophyta. This effect was transmitted to the zooplankton community, resulting in the promotion of Cladocera growth from day 42. The community diversities of phytoplankton and zooplankton had been continuously inhibited by TP. The principal response curve (PRC) analysis results demonstrated that the species composition of phytoplankton and zooplankton community in TP enrichment treatments significantly (p ≤ 0.05) deviated from the control. For community function, TP resulted in the decline in phytoplankton photosynthesis. The chlorophyll fluorescence parameters were significantly inhibited when TP concentration reached 0.4 mg/L. In TP ≥ 0.1 mg/L treatments, the reductions in total phytoplankton abundances led to a continuous decrease in pH. This study can directly prove that the plankton community changes significantly when TP concentrations are greater than 0.1 mg/L and can help managers to establish specific nutrient management strategies for surface water.

A low-cost, durable, submersible light trap and customisable LED design for pelagic deployment and capture of fish parasite Salmincola sp. copepodids

Documenting species invasions and assessments of ecological changes depend on detection. Here, we present a simple design of a plankton light trap with specific wavelength LEDs and modifications. We used PVC pipe to create standardised small, rigid, low-cost traps that can be deployed in lentic habitats. With a cost of under $30 US each, including lights and rechargeable batteries, our traps are affordable without the need for disposable chemical lights. These small traps rely on a vacuum to retain contents upon retrieval, eliminating complicated closing mechanisms and allowing bottom entry. Our design includes submersible LED lights that can withstand pressures of at least 5 atm. We expect that the included instructions for underwater light construction and rubber weights using sand may be broadly applicable. However, we designed and field-tested our traps focusing on the detection and capture of the infective copepodid lifestage of a freshwater parasitic copepod, Salmincola californiensis. This lifestage had previously only been observed by rearing in a laboratory setting and is of concern due to continued spread outside of its native range and detrimental impacts on salmonids, especially in freshwater reservoirs. We used a 445–450 nm wavelength LED light for capturing Salmincola copepodids, but the light design can be modified to any readily available LED and heat sink to attract other target organisms. In our case, the overall affordability of the trap and components allowed for the extensive trapping needed to capture and map the occurrence of rarely-observed species and lifestages, such as the copepodids of S. californiensis. In general, increasing the number of traps that can be deployed within or across sites can aid in the spatial comparisons of plankton distributions needed in studies of ecology and species life histories. Light traps may aid in the detection of introduced zooplankton, such as S. californiensis, outside of their native range and associated plankton community changes.

Regulation of cyanobacteria population density by cyanophage and its effect on material circulation in water

噬藻体是环境中一类以蓝藻为主要宿主的浮游病毒.由于其能特异性裂解蓝藻细胞，因而成为蓝藻种群密度的重要生物调控因子，并被探讨用作蓝藻水华的潜在生物治理方案.噬藻体与蓝藻的相互作用机制可以降低宿主细胞丰度、改变浮游生物群落构成，促进碳、氮、磷等关键生命元素在水体中的生物地球化学循环过程.本文总结了近60年来分离的噬藻体及其对宿主藻的侵染机制，重点介绍了噬藻体对蓝藻种群密度的调节作用，并分析了噬藻体裂解蓝藻对水生态系统中营养物质循环、浮游生物群落变化的影响，并评价了噬藻体对蓝藻水华调控的潜在生态效应.噬藻体实际环境治理应用仍存在较大的挑战，例如噬藻体在水体中易与蓝藻形成共存；噬藻体感染、裂解水华蓝藻后水体中藻毒素消长，在很大程度上决定其安全性，相关科学问题仍需要进一步探索.本文将有助于更加全面地了解噬藻体在水生态系统中的作用，并评估噬藻体对蓝藻群落结构的调控和水体中物质循环过程的影响.;Cyanophage is a kind of planktonic viruses with cyanobacteria as host in the environment. Because it can specifically lytic cyanobacteria cells, it has become an effective biological regulator of cyanobacteria population density and has been discussed as a potential biological treatment scheme for cyanobacteria bloom. The interaction mechanism between cyanophage and cyanobacteria can reduce the abundance of host cells, change the composition of plankton community, and promote the biogeochemical cycle of key life elements such as carbon, nitrogen and phosphorus in water. This paper reviews cyanophage isolated in different water bodies in recent 60 years, summarizes the infection mechanisms of cyanophage, and focuses on the adjustment of cyanophage in cyanobacteria population. The effects of cyanobacteria lysis by cyanophage on nutrient cycling and plankton community changes in aquatic ecosystem are analyzed, and the ecological effects of cyanophage on the regulation of cyanobacteria bloom are evaluated. However, it should be pointed out that there are still great challenges in the practical environmental treatment application of cyanophage. For example, cyanophage is easy to coexist with cyanobacteria in water, and the change trend of cyanotoxins in water after cyanophage infecting still needs to be further explored. This review will contribute to a more comprehensive understanding of cyanophage and evaluate the regulatory effect of cyanophage on cyanobacteria community structure and the process of material circulation in water.

Commercial fishery disturbance of the global ocean biological carbon sink

Plankton drive a major sink of carbon across the global oceans. Dead plankton, their faeces and the faeces of plankton feeders, form a huge rain of carbon sinking to the seabed and deep ocean, reducing atmospheric CO2 levels and thus helping to regulate the climate. Any change in plankton communities, ecosystems or habitats will perturb this carbon sink, potentially increasing atmospheric CO2. Fishing is a major cause of ocean ecosystem disturbance affecting all trophic levels including plankton, but its potential impact on the carbon sink is unknown. As both fisheries and the carbon sink depend on plankton, there is spatial overlap of these fundamental ecosystem services. Here, we provide the first global maps of this spatial overlap. Using an upper quartile analysis, we show that 21% of the total upper ocean carbon sink (export) and 39% of fishing effort globally are concentrated in zones of intensive overlap, representing 9% of the ocean surface area. This overlap is particularly evident in the Northeast Atlantic suggesting this region should be prioritized in terms of research and conservation measures to preserve the high levels of sinking carbon. Small pelagic fish dominate catches here and globally, and their exploitation could reduce important faecal pellet carbon sinks and cause trophic cascades affecting plankton communities. There is an urgent need to recognize that, alongside climate change, fishing might be a critical influence on the ability of the ocean to sequester atmospheric CO2. Improved understanding of this influence, and how it will change with the climate, will be important for realizing a sustainable balance of the twin needs for productive fisheries and strong carbon sinks.

A new method to estimate planktonic oxygen metabolism using high‐frequency sensor measurements in mesocosm experiments and considering daytime and nighttime respirations

AbstractUnderstanding how aquatic ecosystems respond to perturbations has emerged as a crucial way to predict the future of these ecosystems and to assess their capacity to produce oxygen and store atmospheric carbon. In this context, in situ mesocosm experiments are a useful approach for simulating disturbances and observing changes in planktonic communities over time and under controlled conditions. Within mesocosm experiments, the estimation of fundamental parameters such as gross primary production (GPP), net community production (NCP), and respiration (R) allows the evaluation of planktonic metabolic responses to a perturbation. The continuous estimation of these metabolic parameters in real time and at high frequency is made possible by employing noninvasive automated sensors in the water column. However, some uncertainties and methodological questions about the estimation of daytime respiration remain to be addressed for this method, and notably to address the fact that respiration could be significantly higher during the day than during the night. In this study, data from two in situ mesocosm experiments performed in fall and spring in a coastal Mediterranean area were used to develop a new method of estimating daytime respiration, and in turn daily GPP, R, and NCP, by considering the maximum instantaneous R, and that takes into account the variability of the coupling between day–night and dissolved oxygen cycles. This new method was compared with the Winkler incubation technique and with another existing method. Results showed that using this existing method, daytime R was significantly underestimated relative to estimates obtained with the newly proposed method.

Episodic nutrient enrichments stabilise protist coexistence in planktonic oligotrophic conditions

Abstract Seasonal compositional changes in plankton communities are usually considered as species replacements. Given the enormous number of individuals integrating the communities and our limited capacity to count and determine most of them, we likely observe only alternative population peaks of some of the coexisting species. The contemporary coexistence theory addresses coexistence in communities of competing species, considering relative fitness inequalities and stabilising niche differences as components of average long‐term growth rates. Here, we experimentally show that the response patterns predicted by the theory occur when varying nutrient pulses fertilise the planktonic community. We used gently self‐filling 100‐L enclosures to minimise the disturbance of the initial community and different pulse P and N additions to manipulate the apparently species‐poor epilimnetic community of an ultraoligotrophic P‐limited lake. We measured and compared the protist species growth response to gradients of P enrichment and N stoichiometric imbalance. The P and N levels used in most treatments were within the oligotrophic seasonal and inter‐annual variations of the lake and were higher in a few extreme treatments that provided mesotrophic conditions of the remote regions affected by N atmospheric contamination. We alternatively replicated all treatments using ammonium or nitrate as the N source. Most protist species, recorded in this lake across seasons in previous studies, were recovered, indicating a persistent assemblage of species that is seasonally hidden from observation. Recovery included some rare species observed only in the slush layers of the seasonal snow and ice cover. The coexistence‐stabilising mechanisms were indicated by treatment response features, such as frequency‐dependent growth, inverse relationship between fitness inequality and niche differentiation proxies, high‐rank taxonomic levels clustering across the limiting‐nutrient gradient but segregation at the species level according to the type of N supply and resting stage development depending on nutrient conditions. The response similarities between autotrophic and heterotrophic organisms indicate a network of interactions that may reinforce coexistence. Synthesis. The results indicate that many planktonic protist species in oligotrophic waters can show stable long‐term non‐equilibrium coexistence by alternately recovering from very low densities when episodic nutrient enrichments, of varying P and N amounts and composition, occur.

Reframing Lake Geneva ecological trajectory in a context of multiple but asynchronous pressures

Regime shifts are major reorganization of ecological processes, creating new sets of mechanisms that drive the new ecological regime. Such rearrangements can affect how and how much the system responds to pressures other than those that created the shift (interactive carryover). Lake Geneva still exhibits high levels of productivity despite reductions in phosphorus to its reference baseline; the continued high productivity is likely due to the synergistic effects of climate change. We tested whether the contemporary Lake Geneva plankton community response to air temperature, one symptom of climate change, differed from the responses to past changes in air temperature. We used paleoecology to quantify the changes in plankton communities, as a proxy of general ecological changes, over the past 1500 years. Our results show that from 563 AD (beginning of the record) to the twentieth century, the cladoceran assemblage remained stable, despite climate variability of 3 °C in air temperature. The plankton community of Lake Geneva appeared to shift for the first time in the 1500 year record in 1946, and dynamic linear models suggested that 1958–1961 was a critical transition period when the ecosystem changed state. Littoral species were lost, and the assemblage became dominated by pelagic species. The shift took place around the beginning of the current long-term monitoring program, when local perturbations (eutrophication) were escalating. Our results suggest that eutrophication acted as a switch towards a lake more vulnerable to climate change.

Exploring biogeochemical and ecological redundancy in phytoplankton communities in the global ocean.

Climate‐change‐induced alterations of oceanic conditions will lead to the ecological niches of some marine phytoplankton species disappearing, at least regionally. How will such losses affect the ecosystem and the coupled biogeochemical cycles? Here, we couch this question in terms of ecological redundancy (will other species be able to fill the ecological roles of the extinct species) and biogeochemical redundancy (can other species replace their biogeochemical roles). Prior laboratory and field studies point to a spectrum in the degree of redundancy. We use a global three‐dimensional computer model with diverse planktonic communities to explore these questions further. The model includes 35 phytoplankton types that differ in size, biogeochemical function and trophic strategy. We run two series of experiments in which single phytoplankton types are either partially or fully eliminated. The niches of the targeted types were not completely reoccupied, often with a reduction in the transfer of matter from autotrophs to heterotrophs. Primary production was often decreased, but sometimes increased due to reduction in grazing pressure. Complex trophic interactions (such as a decrease in the stocks of a predator's grazer) led to unexpected reshuffling of the community structure. Alterations in resource utilization may cause impacts beyond the regions where the type went extinct. Our results suggest a lack of redundancy, especially in the ‘knock on’ effects on higher trophic levels. Redundancy appeared lowest for types on the edges of trait space (e.g. smallest) or with unique competitive strategies. Though highly idealized, our modelling findings suggest that the results from laboratory or field studies often do not adequately capture the ramifications of functional redundancy. The modelled, often counterintuitive, responses—via complex food web interactions and bottom‐up versus top‐down controls—indicate that changes in planktonic community will be key determinants of future ocean global change ecology and biogeochemistry.

Plankton Community Changes From Warm to Cold Winters in the Oligotrophic Subtropical Ocean

Subtropical gyres are large areas of the ocean characterized by high stratification, low nutrients, and low primary production. The Canary Current System (CanCS) shows a rather strong seasonal thermocline during most of the annual cycle, which erodes from January to March promoting the so-called Late Winter Bloom (LWB). Atmospheric deposition from the Sahara desert is also another key feature of the CanCS providing additional nutrients to the euphotic zone. As a consequence of global warming, these oligotrophic regimes systems are expanding and the temperature increase affects phytoplankton, and reverberate on the food web structure and biogeochemical cycles. In this sense, the effect of warming and dust deposition on the planktonic community remains poorly know in the CanCS. Here, we show the effects of a 0.5ºC increase in ocean temperature during two consecutive years. During 2011, winter temperature allowed the development of the LWB, promoting the increase of autotrophic cells and the coexistence of the microbial loop and the “classic” trophic web. The former predominated before and after the LWB, while the latter prevailed during the LWB. The high temperature during 2010 prevented the LWB development, causing highly oligotrophic conditions and Saharan dust being the only nutrient input into the environment. During this warm year, we found a dominance of small cells such as nanoflagellates and dinoflagellates, and surprisingly high biomass of mesozooplankton, hinting at the “tunneling effect” as an alternative trophic pathway. These changes show the impact of a slight increase in temperature in this oligotrophic system and how future scenarios in the context of global warming could promote considerable shifts in the trophic web structure.

Composición y abundancia de macro zooplancton en aguas costeras de El Mogote

Background. Bahia de la Paz, Mexico have seasonal blooms of planktonic prey that support a range of marine species including whale sharks (Rhincodon typus). Goals. This study includes the first sampling cycle that covers all climatic seasons, to know changes in the abundance and composition of zooplankton in the coastal waters off the El Mogote Sandbar, in Bahia de La Paz, BCS, Mexico. Methods. A total of 96 plankton samples were collected at predetermined field stations, spanning the entire length of the El Mogote from June 2016 to May 2017. Results. Total biomass was significantly different between seasons (Kruskal-Wallis chi-squared = 29.993, p = 0.000001385), with the lowest biomass recorded in spring (176.28 ml 100 m-3, 10.1%); and highest observed for winter (703.04 ml 100 m-3, 40.4%). Zooplankton composition was largely comprised of two main taxonomic groups: Copepoda (396,234 organisms100 m-3, 43.1%) and Chaetognatha (196,986 organisms100 m-3, 21.4%). The total number of individuals (sum of all taxonomic groups) per season showed significant differences (Kruskal-Wallis chi-squared = 29.78, p = 0.000001533) with the highest concentrations recorded in winter (292,429 organisms100 m-3, 31.8%) and lowest in spring (162,995 organisms100 m-3; 17.7%). Conclusions. This information provides the first work focused solely in the El Mogote area as a main foraging site for whale sharks, with clear changes in plankton communities with respect to shifting climatic seasons, and the importance of certain taxonomic groups to the diet of whale sharks.

Fluctuations in plankton community structure of endorheic soda lakes of southeastern Transbaikalia (Russia)

The aim of present research is to study the patterns of phyto- and zooplankton fluctuations in endorheic soda lakes (Uldz Gol-Torey Basin, southeastern Transbaikalia, Russia) under arid conditions because studied area is becoming increasingly arid. Plankton samples were collected in summer during time intervals with different lake water levels using standard hydrobiological methods. We detected four patterns of change in plankton communities with changing environmental conditions (increasing total dissolved solid, pH and temperature, and decreasing depth). The first pattern is characterized by a predominance of green algae, charophytes, diatoms and euglenophytes; the species composition and dominant zooplankton assemblage are the same in different years. The second pattern is characterized by a loss of cryptophyte and chrysophyte algae, a dominance of green and blue-green algae, a decrease in zooplankton species diversity, and an increased abundance of zooplankton, the dominant species are consistent over time. The third pattern exhibits marked decreases in phytoplankton diversity and density, a dominance of green algae and diatoms, a further decrease in the species richness of zooplankton, and increased abundance and biomass of some species. The fourth pattern is a marked by a reduction in plankton species diversity to a monospecific community.

Seasonal modulation of mesoscale processes alters nutrient availability and plankton communities in the Red Sea

Hydrographic and atmospheric forcing set fundamental constraints on the biogeochemistry of aquatic ecosystems and manifest in the patterns of nutrient availability and recycling, species composition of communities, trophic dynamics, and ecosystem metabolism. In the Red Sea, latitudinal gradients in environmental conditions and primary production have been ascribed to fluctuations in Gulf of Aden Water inflow, upwelling/mixing, and regenerated nutrient utilization i.e. rapidly recycled nitrogen in upper layers. However, our understanding of upper layer dynamics and related changes in plankton communities, metabolism and carbon and nitrogen export is limited. We surmised that stratification and mesoscale eddies modulate the nutrient availability and taxonomic identity of plankton communities in the Red Sea. Based on remote-sensing data of sea level anomalies and high resolution in situ measurements (ScanFish) we selected stations for hydrographic CTD profiles, water sampling (nutrients, seawater oxygen stable isotopes [δ18OSW]), phytoplankton and zooplankton collections. In fall 2014, strong stratification subjected the plankton community to an overall nitrogen and phosphorus shortage. The nutrient deficiency increased numbers of heterotrophic dinoflagellates, microzooplankton, and diazotrophs (Trichodesmium, diatom-diazotroph associations [DDAs]), albeit largely decreased phytoplankton and mesozooplankton abundances. In spring 2015, mesoscale eddies increased the nutrient availability, and the thermohaline characteristics and low δ18OSW point to the interaction of eddies with Gulf of Aden Surface Water (GASW). Cyclonic eddies and, most likely, the availability of nutrients associated with the GASW, increased the abundances of autotrophs (diatoms, Prasinophytes) and supported larger numbers of zooplankton and their larvae. We demonstrate that the interplay of stratification, advection of Gulf of Aden water and mesoscale eddies are key elements to better understand changes in plankton community composition, ecosystem metabolism, and macronutrient export in the Red Sea in space and time.

A century of change in North Sea plankton communities explored through integrating historical datasets

Abstract Plankton communities make useful ecosystem indicators, and taking a historical perspective on plankton community composition provides insights into large-scale environmental change. Much of our understanding of long temporal-scale change in plankton communities in the North Sea has been provided by the Continuous Plankton Recorder (CPR) survey, operating since 1931, with consistent time-series data available since 1958. This article further increases the temporal scale of our understanding of community change in the North Sea by combining the CPR dataset with a digitized collection of plankton surveys undertaken by ICES from 1902 to 1912. After steps taken to integrate the two disparate datasets, differences in overall community composition between time periods suggest that the multidecadal changes observed through the CPR survey time period may have occurred from a non-stable baseline that was already on a trajectory of change. Therefore, a stable historical time period in which plankton communities are assessed against for any impact of human pressures may be hard to define for the North Sea and instead underlying variation needs to be encompassed within any baseline chosen. Further evidence for the influence of large-scale changes in sea surface temperature driving change in plankton community composition was found using the extended dataset.

The Role of Planktonic Algae in the Ecological Assessment of Storage-Reservoirs of the ILI-Balkhash Basin

Abstract The largest wastewater treatment systems include Sorbulak and Kurty reservoirs, and the small storage ponds were studied in the summer of 2017 and characterized mainly by organic pollution. Phytoplankton communities were represented by species tolerant of organic and toxic pollution. Cyanobacteria dominated in the reservoirs, and dinophyte algae were only in the Kurty Reservoir. According to the results of CCA analysis, only Cr and certain nutrients had a significant effect on the abundance of algae. A statistically positive significant association between the Shannon index and the average algal cell mass was established. The results obtained are a particular example reflecting the non-linearity of changes in plankton communities in the gradient of nutrient loading and eutrophication of aquatic ecosystems.

Plankton as prevailing conditions: A surveillance role for plankton indicators within the Marine Strategy Framework Directive

The Marine Strategy Framework Directive (MSFD) uses an indicator-based approach for ecosystem assessment; indicators of the state of ecosystem components ('state indicators') are used to determine whether, or not, these ecosystem components are at ‘Good Environmental Status’ relative to prevailing oceanographic conditions. Here, it is illustrated that metrics of change in plankton communities frequently provide indications of changing prevailing oceanographic conditions. Plankton indicators can therefore provide useful diagnostic information when interpreting results and determining assessment outcomes for analyses of state indicators across the food web. They can also perform a strategic role in assessing these state indicators by influencing target setting and management measures. In addition to their primary role of assessing the state of pelagic habitats against direct anthropogenic pressures, plankton community indicators can therefore also fulfil an important 'surveillance' role for other state indicators used to formally assess biodiversity status under the MSFD.