Zooplankton Species Richness Research Articles

A belly full of jelly? DNA metabarcoding shows evidence for gelatinous zooplankton predation by several fish species in Greenland waters.

The waters of Greenland harbour a high species richness and biomass of gelatinous zooplankton (GZP); however, their role in the diet of the many fish species, including commercially exploited species, has not yet been verified. Traditionally, GZP was considered to be a trophic dead end, i.e. with a limited contribution as prey for higher trophic levels. We applied DNA metabarcoding of two gene fragments (COI, 18S V1-V2) to the stomach contents of seven pelagic and demersal fish species in Greenland waters, to identify their prey composition as well as the occurrence of GZP predation. We detected GZP DNA reads in the stomachs of all investigated fish species, with frequency of occurrences ranging from 12.5% (for Melanogrammus aeglefinus) to 50% (for Argentina silus). GZP predation had not yet been reported for several of these species. GZP were found to majorly contribute to the diet of A. silus and Anarhichas denticulatus, particularly, the siphonophore Nanomia cara and the scyphozoan Atolla were of a high importance as prey, respectively. The use of multiple genetic markers enabled us to detect a total of 59 GZP taxa in the fish stomachs with several GZP species being detected only by one of the markers.

How Do Zooplankton Communities Respond to Environmental Factors across the Subsidence Wetlands Created by Underground Coal Mining in the North China Plain?

The degradation and loss of natural wetlands has caused severe crises for wetland taxa. Meanwhile, constructed wetlands are expanding significantly and facing dramatic environmental changes. Exploring the responses of wetland organisms, particularly zooplankton, may have important implications for the management of wetlands. Environmental and zooplankton samples were collected from 34 subsidence wetlands created by underground coal mining across the North China Plain in August 2021. We used generalized linear models and redundancy analysis to test zooplankton responses to environmental variables, with the relative importance quantified by variation partitioning. We identified 91 species, divided into 7 functional groups, with the highest density of rotifer filter feeders (RF, 2243.4 ± 499.4 ind./L). Zooplankton species richness was negatively correlated with electrical conductivity (EC), chlorophyll-a, total phosphorus, and pH. The Shannon–Weiner and Pielou evenness indices were positively correlated with transparency and negatively correlated with the photovoltaic panel area (AS). Rotifer predators (RCs) and RF densities were positively correlated with cropland area and dissolved oxygen, but negatively correlated with AS. Small crustacean filter feeders positively correlated with AS, whereas medium crustacean feeders (MCFs) positively correlated with EC. AS was the most critical variable affecting the zooplankton community. Our study showed that the spatial pattern of zooplankton communities was shaped by environmental heterogeneity across the subsidence wetlands, providing implications for the management and conservation of these constructed wetlands.

Multiple signs of ecosystem change in the zooplankton community of a large temperate lake

Large lakes, such as Lake Simcoe, Ontario, Canada, are undergoing significant change due to local and global stressors. Uni- and multivariate analyses of Lake Simcoe's zooplankton community from 1986 to 2012 indicated multiple events of ecosystem change that were synchronous across three lake stations . In the mid-1990s, shifts in zooplankton species abundance and richness, and total cladoceran body size were strongly correlated with the invasion of the zooplanktivore, Bythotrephes cederstroemii. In the early 2000s, additional shifts in zooplankton abundance, as well as copepod body size, coincided with increased water clarity (linked to filter feeding by the invader Dreissena polymorpha) and hypolimnetic water temperature. Further community changes occurred in the 2000s when Bythotrephes declined and many vulnerable cladoceran species recovered. However, the Lake Simcoe community did not fully return to its pre-invasion state as the cold-water herbivores, Daphnia longiremis and Daphnia pulicaria, remained absent. The Lake Simcoe zooplankton community illustrates ongoing ecosystem change that propagated throughout the lake food web and may be reflected in other lakes experiencing global stressors of climate change and species invasions.

Divergence of zooplankton assemblages in unstable fishless and stable fish ponds

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

Geographical patterns of mesozooplankton functional diversity in the northwestern Pacific

To better understand how communities response to environmental change and how biodiversity affects ecosystem function, it is essential to quantify the functional diversity of communities. However, the current understanding of zooplankton functional traits and functional diversity in the northwestern Pacific (NWP) is inadequate. In this study, we analyzed the latitudinal changes in functional traits, diversities, and functional space of zooplankton in five biogeographic regions of the tropical and subtropical NWP. Zooplankton species richness varied unimodally over latitude, with the North Pacific Subtropical Gyre (NPSG) hosting the greatest number of species (367 taxa). The NWP was dominated by zooplankton of small and medium size (<2 mm; 72 %), current-feeding (47 %), omnivore–herbivore (71 %), and broadcast spawner (53 %). The functional trait composition of zooplankton varied significantly; for instance, omnivore–detritivores were prevalent in the Kuroshio Extension zone but few in the oligotrophic NPSG and North Equatorial Current regions. Protozoans with binary fission (primarily foraminifers) declined from the equator to high latitudes. The latitudinal variations of functional evenness, functional dispersion, and hypervolume of trait space of the zooplankton community were unimodal, with the maximum values occurring in the NPSG. This would suggest that the zooplankton community in the NPSG was more efficient in utilizing resources than in other regions, and the competition across functional groups was mild. Stochastic processes were crucial in zooplankton community assembly in tropical and subtropical NWP. This study enhanced our understanding of zooplankton community assembly and offered new insights into the functional traits of zooplankton communities in the NWP.

An accidental encounter with bloom of diatom Palmerina hardmaniana (Greville) Hasle in Sundarbans, India: Impact on zooplankton community structure in tidal creek environment

The present study reports on a transient diatom bloom of Palmerina hardmaniana (Greville) Hasle 1996 encountered accidentally in May 2018 in the world's largest mangrove forest of Sundarbans, India. This bloom was the sixth record of diatom blooms from Indian coastal waters and the fourth from Sundarbans waters. The diatom cell count ranged from 2.571 × 104 to 6.857 × 104 cells L−1 during the bloom. The zooplankton taxa count decreased from 39 during the pre-bloom to 30 during bloom and 31 during the post-bloom phase. However, no significant (p < 0.05) change in zooplankton species richness was observed between the three different phases. The consistent occurrence of copepod Bestiolina simlis across sampling points indicated a high tolerance to environmental parameters. The zooplankton population also did not respond vehemently to bloom-forming P. hardmaniana in this creek environment. These observations warrant further studies to examine the effect of blooms on the overall marine ecological food chain of creek ecosystems.

Revealing zooplankton diversity in the midnight zone

Zooplankton diversity in the deep “midnight zone” (&amp;gt;1000 m), where sunlight does not reach, remains largely unknown. Uncovering such diversity has been challenging because of the major difficulties in sampling deep pelagic fauna and identifying many (unknown) species that belong to these complex swimmer assemblages. In this study, we evaluated zooplankton diversity using two taxonomic marker genes: mitochondrial cytochrome oxidase subunit 1 (COI) and nuclear 18S ribosomal RNA (18S). We collected samples from plankton net tows, ranging from the surface to a depth of 5000 m above the Atacama Trench in the Southeast Pacific. Our study aimed to assess the zooplankton diversity among layers from the upper 1000 m to the ultra-deep abyssopelagic zone to test the hypothesis of decreasing diversity with depth resulting from limited carbon sources. The results showed unique, highly vertically structured communities within the five depth strata sampled, with maximal species richness observed in the upper bathypelagic layer (1000–2000 m). The high species richness of zooplankton (&amp;gt;750 OTUS) at these depths was higher than that found in the upper 1000 m. The vertical diversity trend exhibited a pattern similar to the well-known vertical pattern described for the benthic system. However, a large part of this diversity was either unknown (&amp;gt;50%) or could not be assigned to any known species in current genetic diversity databases. DNA analysis showed that the Calanoid copepods, mostly represented by Subeucalanus monachus, the Euphausiacea, Euphausia mucronata, and the halocypridade, Paraconchoecia dasyophthalma, dominated the community. Water column temperature, dissolved oxygen, particulate carbon, and nitrogen appeared to be related to the observed vertical diversity pattern. Our findings revealed rich and little-known zooplankton diversity in the deep sea, emphasizing the importance of further exploration of this ecosystem to conserve and protect its unique biota.

Viability of zooplankton resting eggs in rice field sediment after pesticide applications.

Many herbicide products are commonly used in agricultural areas to prevent and eliminate weeds. Contamination from these toxicants in water might affect aquatic organisms not only in the active stage, but also in the diapause stage. To test the effect of herbicide on the resting eggs of zooplankton, we prepared two rice fields: one field without the application of pesticides (RF-NPA) and one with the application of pesticides (RF-PA) in a sampling year. We conducted a hatching experiment for 30 days. Twenty-four taxa of zooplankton were found. Sixteen species of these were rotifers, seven species were cladocerans and one taxon was an unidentified nauplius copepod. The species richness of zooplankton between RF-NPA (17 taxa) and RF-PA (16 taxa) was close, but species compositions between RF-NPA and RF-PA were different, indicated by the similarity index of 0.545. Lecanidae was the most diverse family of rotifers in both rice fields with nine species, while Chydoridae was the most diverse family of cladocerans (four species). The total abundance of zooplankton of RF-NPA was higher than RF-PA with 1,897 and 1,286 individuals, respectively. The Shannon-Wiener diversity index (H´) and Pielou's evenness (J) in RF-NPA were higher than in RF-PA. The high species richness of zooplankton in both rice fields occurred on days 18 to 30. On the other hand, the highest abundance was recorded on day 18 for RF-NPA and on day 24 for RF-PA. The non-metric multidimensional scaling (NMDS) demonstrated significant differences in zooplankton community composition between RF-NPA and RF-PA (p < 0.05; ANOSIM test). According to the diversity indices, the RF-NPA has more diversity than the RF-PA, which might be a result of herbicide application in the sampling year. This study suggests that the toxicity of glyphosate should be a concern in terms of the biodiversity of rice field ecosystems.

Muddying the unexplored post-industrial waters: Biodiversity and conservation potential of freshwater habitats in fly ash sedimentation lagoons

Deposits of fly ash and other coal combustion wastes are common remnants of the energy industry. Despite their environmental risks from heavy metals and trace elements, they have been revealed as refuges for threatened terrestrial biodiversity. Surprisingly, freshwater biodiversity of fly ash sedimentation lagoons remains unknown despite such lack of knowledge strongly limits the efficient restoration of fly ash deposits. We bring the first comprehensive survey of freshwater biodiversity, including nekton, benthos, zooplankton, phytoplankton, and macrophytes, in fly ash lagoons across industrial regions of the Czech Republic. To assess their conservation potential, we compared their biodiversity with abandoned post-mining ponds, the known strongholds of endangered aquatic species in the region with a shortage of natural ponds. Of 28 recorded threatened species, 15 occurred in the studied fly ash lagoons, some of which were less abundant or even absent in the post-mining ponds. These are often species of nutrient-poor, fishless waters with rich vegetation, although some are specialised extremophiles. Species richness and conservation value of most groups in the fly ash lagoons did not significantly differ from the post-mining ponds, except for species richness of benthos, zooplankton, and macrophytes, which were slightly lower in the fly ash lagoons. Although the concentrations of some heavy metals (mainly Se, V, and As) were significantly higher in the fly ash lagoons, they did not significantly affect species richness or conservation value of the local communities. The differences in species composition therefore does not seem to be caused by water chemistry. Altogether, we have shown that fly ash lagoons are refuges for threatened aquatic species, and we thus suggest maintaining water bodies during site restoration after the cessation of fly ash deposition. Based on our analyses of environmental variables, we discuss suitable restoration practices that efficiently combine biodiversity protection and environmental risk reduction.

Zooplankton Diversity and Ecological Variations of Coastal Wetlands of Bakerganj, Bangladesh

Ecology and diversity of zooplankton species in relation to some physico-chemical parameters at three sites namely Thana Health Complex Pond, Tulatoli River and Harun Dakua’s Pond of the coastal ecosystems of Bakerganj were studied from January 2008 to December 2009. A total of 56 zooplankton species were recorded out of which 35 were rotifers, 6 protozoan, 8 copepods, 5 cladocerans and 2 ostracods species. During study, rotifera was the most abundant group (61.44 % in Thana Health Complex pond, 38.36 % in Tulatoli River, and 86.03 % in Harun Dakua’s pond), while the ostracoda were the least abundant group (0.2 % in Harun Dakua’s pond). The highest monthly average value of zooplankton was 707.75 ± 189.56 indv /L at Thana Health Complex pond and the lowest was 127.42 ± 19.95 indv /L at Tulatoli River of Bakerganj. Zooplankton species richness (R1 and R2) was comparatively higher (R1: 1.63 ± 0.10; R2: 0.64 ± 0.06) in Harun Dakua’s pond while both the species diversity (Shanon Weiner Index) (H' = 0.87 ± 0.08; eH' = 2.52 ± 0.17) and species evenness (E1 and E2) (E1 = 0.44 ± 0.04; E2 = 0.43 ± 0.05) were higher in the Tulatoli River. The zooplankton population showed positive correlation with physico-chemical parameters like water temperature, air temperature and water depth, whereas negatively correlated with pH, DO, TDS, conductivity and salinity with a few exception. Bangladesh J. Zool. 50(3): 321-335, 2022

Mechanistic Models of Trophic Interactions: Opportunities for Species Richness and Challenges for Modern Coexistence Theory.

AbstractMany potential mechanisms promote species coexistence, but we know little about their relative importance. To compare multiple mechanisms, we modeled a two-trophic planktonic food web based on mechanistic species interactions and empirically measured species traits. We simulated thousands of possible communities under realistic and altered interaction strengths to assess the relative importance of three potential drivers of phytoplankton and zooplankton species richness: resource-mediated coexistence mechanisms, predator-prey interactions, and trait trade-offs. Next, we computed niche and fitness differences of competing zooplankton to obtain a deeper understanding of how these mechanisms determine species richness. We found that predator-prey interactions were the most important driver of phytoplankton and zooplankton species richness and that large zooplankton fitness differences were associated with low species richness, but zooplankton niche differences were not associated with species richness. However, for many communities we could not apply modern coexistence theory to compute niche and fitness differences of zooplankton because of conceptual issues with the invasion growth rates arising from trophic interactions. We therefore need to expand modern coexistence theory to fully investigate multitrophic-level communities.

Species Diversity and Driving Factors of Benthic and Zooplanktonic Assemblages at Different Stages of Thermokarst Lake Development: A Case Study in the Lena River Delta (Middle Siberia)

Global climate change might result in permafrost thaw and the formation of thermokarst landscapes that release long-term carbon stocks as greenhouse into the atmosphere, thereby initiating a positive climate feedback. These processes are mediated by biological activity, including by microbes, vascular plants and animals, whereas the role of invertebrates in thermokarst ecosystems remains poorly understood. We investigated the diversity and assemblage structures of zooplankton (mainly Copepoda, Cladocera), microbenthos (testate amoebae) and meio- (Copepoda and Cladocera) and macrozoobenthos (mollusks, crustaceans, insects and annelids) from a range of water bodies representing different stages of thermokarst lake formation in the southern part of the Lena River Delta (Central Siberia). Altogether, 206 species of testate amoeba, mollusk, crustacean, insect and annelid taxa were identified. A total of 60 species of macrozoobenthos (mainly insects) and 62 species of testate amoebae were detected in the water bodies of the Lena River Delta for the first time. The species richness of zooplankton and meio- and macrozoobenthos was greater in the large thermokarst lakes than in the polygonal ponds due to the freezing of the latter in the winter. In contrast, the species richness of protists was higher in the polygonal ponds, which was related to the habitat preferences of testate amoebae. Fish grazing strongly affected the macrobenthos assemblages but not the smaller-sized organisms. Water acidity and temperature were the main environmental drivers of the assemblage structure of testate amoeba and microcrustacean. The species structure of the macroinvertebrate assemblages was significantly explained by water acidity, permafrost depth and size of the water area. It means that small size organisms with their short generation times are sensitive to more dynamic factors such as temperature and may serve as indicators of ecosystem changes due to global climate warming. In contrast, large size organisms are affected by driven factors that appear during thermokarst lakes formation and permafrost degradation.

A moderate differential effect of organic and conventional agriculture across taxonomic groups inhabiting farmland ponds

Abstract Organic agriculture is increasingly promoted as a more environmentally friendly alternative to conventional agriculture, as it restricts the use of fertilisers and synthetic pesticides. However, the impact of both farming systems on aquatic biodiversity is strongly debated. Ponds are abundant in agricultural landscapes and strongly contribute to biodiversity. They also respond strongly to land use on a very local scale. The present study assessed the effects of conventional and organic agriculture on the taxonomic diversity of multiple groups of aquatic organisms at local and regional spatial scales. We conducted a broad scale field survey to quantify the differential impact of conventional and organic agriculture on local environmental conditions in ponds, on community composition and on local, among site and regional diversity of macrophytes, cladoceran zooplankton and selected macroinvertebrates in Belgian farmland ponds (Flanders). We observed that organic agriculture was moderately positively associated with higher local species richness for shoreline vegetation, but not for other organism groups. Only minor differences were observed for among‐pond variation, and these were mostly related to rare species of cladocerans and heteropterans. At the regional scale, ponds in organic showed higher species richness than in conventional farmland for shoreline vegetation, emergent vegetation, and cladoceran zooplankton, but lower for coleopterans and gastropods. There was no significant effect of agricultural type on water quality. We conclude that organic farming is associated with moderate positive effects on pond biodiversity and regional species richness of plants and zooplankton. We observed no systematic differences between the two types of agriculture in local environmental conditions in ponds. The absence of large differences in biodiversity and water quality between ponds located in organic and conventional farmland might be related to the dominance of intensive conventional farming in our study region and the history of conventional farming around ponds that are now surrounded by organic farming. Future studies should include other factors such as the structure of the landscape and the role of natural elements such as buffer strips surrounding the ponds.

Effects of Water Stratification and Mixing on Plankton Community Structure in a Floating Solar Power Plant

Plankton community structure play pivotal roles in aquatic ecosystems, influencing their structure, function and services. However, little is known about the effects of water stratification and mixing on the dynamics of aquatic ecosystems. The influence of water stratification and mixing on plankton community structure was studied in the Floating Da Mi Solar Power Plant was done between March 2020 and September 2022, encompassing both dry and rainy seasons. Data from 4 sites were used as a representative example for the study area to conduct a qualitative study. To implement this assessment, the analyses were based on MRC methods and classifications, these improved by the scientific group. The results showed that 86 species of phytoplankton and 23 species of zooplankton were found in the study area. The density of phytoplankton at each site ranged from 279 to 32,282 individuals/sample, while the density of zooplankton at each site fluctuated from 5 to 33 individuals/sample. The calculated values for the diversity index (H’) of phytoplankton and zooplankton fluctuated from medium to quite high levels from 1.55 to 3.69; 1.562.95 respectively. The results also showed that several environmental variables, including temperature, dissolved oxygen, and chlorophyll-a were correlated with species richness, density and diversity index of phytoplankton and zooplankton. The obtained results will be useful for the monitoring of changes of aquatic ecosystem at the study area, in particular the sensitivity of aquatic flora and fauna to changes in environmental variables.

An analysis of interannual data on phytoplankton and zooplankton associations in fluctuating soda lakes

Aquatic ecosystems in arid regions are important and unique habitats for aquatic wildlife and support species biodiversity. Endorheic soda lakes in Central Asia are subject to great fluctuations in its size depending on climatic conditions. Here we present research results covering the last 20 years, including the period from the maximum filling of the Torey lakes (Transbaikalia, Russia) to their aridification and the initial phase of their refilling. Barun-Torey and Zun-Torey lakes are the largest soda lakes in the arid zone with a large water surface area. A unique feature of lakes is the unstable hydrological regime. The reason for the water level change is the periodic filling and drying of lakes due to cyclic climatic changes in humidity and temperature. We aim to determine the response of the plankton communities to environmental change in the Torey lakes over this period. We analysed the interannual variations in phytoplankton and zooplankton species richness, structure and density. We conducted our studies during various phases of the hydrological cycle, including three periods for Zun-Torey Lake (high (1999 and 2003), intermediate (2007, 2011) and low (2014 and 2016) lake levels) and two periods for Barun-Torey (high water level (1999 and 2003) and the initial filling phase (2014, 2016, 2018, 2020, 2021)). Barun-Torey Lake dried up completely in summer 2009 and since 2013 the initial refilling has been observed. Zun-Torey Lake dried up in fall 2017. Changes in water level and water chemistry determined plankton biodiversity transformation. Fluctuations of plankton communities were different for each lake and conformed the phases of the hydrological cycle. We identified four stage changes in plankton associations during the aridification of Zun-Torey Lake, and three stage changes in plankton associations as the water level fell and through the initial refilling phase for Barun-Torey Lake.

ЕКОЛОГО-ФАУНІСТИЧНІ ОСОБЛИВОСТІ УГРУПОВАНЬ ЗООПЛАНКТОНУ, ІХТІОФАУНИ У РІЧЦІ ІРПІНЬ

B a c k g r o u n d . Monitoring of ecosystems affected by military actions is an element of a comprehensive assessment of the state of the ecosystem in the post-war period. The results of this study are key for the post-war recovery of the war-affected region and assessment of the state and quality of water resources in the area for their further use, as well as for the assessment of the consequences of Russian armed aggression for local water ecosystems and the hydrological network of the region in general. In February-March 2022, the Kozarovytska dam was blown up, which caused flooding of the floodplain more than 20 km downstream. M e t h o d s . As a result of the flooding of agricultural lands, the waters of the Irpin River were polluted with products of human life (burial sites, cattle cemeteries, village toilets, places where livestock and birds are kept, fertilizers, decay products of plant remains) and flooded military equipment and ammunition. The purpose of this work is to study the zooplankton and ichthyofauna in the Irpin River and its tributaries the Moschunka and the Gorenka rivers. The study was conducted in the summer of 2023. A conical plankton net was used for zooplankton sampling. Quantitative parameters of zooplankton were determined according to Hensen's computational method in Bogorov's chamber using binoculars. R e s u l t s . Determination of the saprobiological state of the investigated water bodies was carried out according to the Pantle-Bucca method. Ichthyological samples were taken using a dip bag. During the experimental period, 10 species of zooplankton were found, which included rotifers, cladocera and copepods, and 3 species of fish. C o n c l u s I o n s . The obtained results indicate a significant decrease in the species richness of zooplankton in the studied reservoirs in comparison with last year's indicators, which can be explained by the consequences of anthropogenic load on the studied water ecosystems during the phase of active military operations within the Buchansky district.

Структура зоопланктона и гидрохимическая характеристика горных водоемов Северного Тянь-Шаня

The study of hydrochemical parameters and zooplankton structure of three mountain reservoirs of the Northern Tien Shan (Lower Kolsai Lake, Tekes and Bestyubinskoe reservoirs) was carried out in August 2022. Hydrochemical analysis showed that the water in all reservoirs is fresh, soft, carbonate class, calcium group of the second type. The average content of easily oxidizing organic substances reached 5.6–7.6 mg/dm3, nitrite nitrogen – 0.011–0.044 mg/dm3, nitrate nitrogen – 0.274–0.830, ammonium nitrogen –0.045–0.091, phosphates – 0.023–0.031, iron – 0.090–0.166, silicon – 3.0–5.4, manganese - 0.011–0.025 mg/dm3. Zooplankton was represented by 41 species. Zooplankton abundance varied between 11081-69061 ex/m3. Zooplankton biomass reached 11.7–700.2 mg/m3. Cluster analysis based on the calculation of the Bray-Curtis index showed changes in the species composition of planktonic invertebrates over the past fifty years. The growth of species richness in the Lower Kolsai against the background of an increase in the quantitative indicators of planktonic invertebrates is due to the increasing recreational load on the lake and the adjacent land area. The decrease in the species richness and abundance of zooplankton in the Tekes reservoir may be due to sharp fluctuations in the water level in the seasonal and interannual aspect and its periodic filling with river water not enriched with nutrients.

Spatial heterogeneity of chemistry of the Small Aral Sea and the Syr Darya River and its impact on plankton communities

The shrinking of the Aral Sea represents one of the greatest ecological disasters of modern time. The data on the surviving northern part (Small Aral) is scarce and requires an update. This study aimed to analyze the chemistry, phyto- and zooplankton composition, and their relation in the waters of the Small Aral and its tributary, Syr Darya River. The chemistry of both ecosystems was significantly different. Small Aral was characterized by higher ionic concentrations, salinity, and electric conductivity and more significant spatial variation of chemical properties. The area near the river mouth was more pristine, while the ions concentration and salinity in the distant bays were much higher (>10‰). The highest concentrations of nitrates and total phosphorus in the Syr Darya were observed near Kyzylorda, indicating urban pollution. Overall, 109 phytoplankton taxa were identified in both ecosystems, with diatoms, green algae, and cyanobacteria being most abundantly represented. Oligohalobes dominated, but no polyhalobes and euhalobes algal species were identified. In total, 27 taxa of zooplankton were identified in both studied ecosystems, with the domination of rotifers over microcrustaceans. An exceptionally high level of dominance (65–91%) of rotifer Keratella cochlearis in the Syr Darya was found. The phyto- and zooplankton species richness was higher in the Syr Darya. Plankton communities of the Small Aral reflected horizontal variability of chemical properties. The total phosphorus promoted the prevalence of diatoms, rotifers, and crustaceans. Increased nitrogen concentration promoted cyanobacteria, chlorophytes, cryptophytes and chrysophytes, and rotifers Keratella cochlearis and K. quadrata. The abundance of dinophytes, diatoms Navicula cryptotenella and Cocconeis placentula, green algae Mychonastes jurisii and rotifer Keratella tecta was driven by the higher alkalinity and conductivity/salinity levels. The results represent a reference point for future monitoring of the area and add to understanding the complexity of biological transformations in the Aral Sea and its tributary.

Metabarcoding analysis of marine zooplankton confirms the ecological role of a sheltered bight along an exposed continental shelf.

Zooplankton plays an essential role in marine ecosystems as the link between primary producers (phytoplankton) and higher trophic levels in food webs, and as a dynamic pool of recruits for invertebrates and fish. Zooplankton communities are diverse with a patchy distribution at different spatial scales, influenced by oceanographic processes. The continental shelf of eastern South Africa is narrow and exposed to the western-boundary Agulhas Current, with some shelter against strong directional flow provided by the broader KwaZulu-Natal Bight, a coastal offset adjacent to an estuary. We compared zooplankton species richness, diversity and relative abundance of key taxa among sheltered and exposed shelf areas using metabarcoding and community analysis, to explore the ecological role of the bight in a highly dynamic ocean region. Metabarcoding recovered higher richness and diversity at a finer resolution than could previously be achieved with traditional microscopy. Of 271 operational taxonomic units (OTUs) recovered through metabarcoding, 63% could be matched with >95% sequence similarity to reference barcodes. OTUs were dominated by malacostracan crustaceans (161 spp.), ray-finned fishes (45 spp.) and copepods (28 spp.). Species richness, diversity and the relative abundance of key taxa differed between sheltered and exposed shelf areas. Lower species richness in the bight was partly attributed to structurally homogeneous benthic habitats, and an associated reduction of meroplanktonic species originating from local benthic-pelagic exchange. High relative abundance of a ray-finned fish in the bight, as observed based on fish eggs and read counts, confirmed that the bight is an important fish spawning area. Overall, zooplankton metabarcoding outputs were congruent with findings of previous ecological research using more traditional methods of observation.

Seasonal and spatial occurrence of plankton and environmental variables in Ogun coastal water on the Bight of Benin

The influence of environmental variables on the seasonal and spatial distribution of plankton was studied for 24 months between February 2015 and January 2017 in the marine coastal water of Ogun State, Nigeria. The coastline was stratified into three sampling stations, and surface water samples were collected monthly per station for physico-chemical and plankton analyses. Mean values of physico-chemical parameters were: temperature (28.60±0.27°C), salinity (29.25±0.45‰), pH (7.38±0.07), electrical conductivity (42.13±0.33μS/l), total dissolved solids (29.59±0.30mg/l), dissolved oxygen (6.48±0.07mg/l), phosphate (1.36×10-2±0.39mg/l) and nitrate (2.25×10-2±0.65mg/l). The dominant phytoplankton and zooplankton groups were Diatomaceae (42.06%) and Calanoids (25.42%), respectively. Spatial diversity analysis of plankton in the study area showed that the highest (19, 35) species richness and abundance (5703, 12,452) for phytoplankton and zooplankton, respectively occurred in Site 3. Seasonal species richness of phytoplankton and zooplankton was higher in the wet (27, 40) than the dry (23, 38) season. Canonical correspondence analysis explained 77.8% of the influence of environmental variables on plankton distribution. Water temperature, dissolved oxygen, salinity, phosphate, pH, TDS and nitrate were the most marked factors that affected the distribution and abundance of plankton.