Zooplankton Community Composition Research Articles

Influence of ocean alkalinity enhancement with olivine or steel slag on a coastal plankton community in Tasmania

Abstract. Ocean alkalinity enhancement (OAE) aims to increase atmospheric CO2 sequestration in the oceans through the acceleration of chemical rock weathering. This could be achieved by grinding rocks containing alkaline minerals and adding the rock powder to the surface ocean where it dissolves and chemically locks CO2 in seawater as bicarbonate. However, CO2 sequestration during dissolution coincides with the release of potentially bioactive chemicals and may induce side effects. Here, we used 53 L microcosms to test how coastal plankton communities from Tasmania respond to OAE with olivine (mainly Mg2SiO4) or steel slag (mainly CaO and Ca(OH)2) as alkalinity sources. Three microcosms were left unperturbed and served as a control, three were enriched with olivine powder (1.9 g L−1), and three were enriched with steel slag powder (0.038 g L−1). Olivine and steel slag powders were of similar grain size. Olivine was added in a higher amount than the steel slag with the aim of compensating for the lower efficiency of olivine to deliver alkalinity over the 3-week experiment. Phytoplankton and zooplankton community responses as well as some biogeochemical parameters were monitored. Olivine and steel slag additions increased total alkalinity by 29 and 361 µmol kg−1, respectively, corresponding to a respective theoretical increase of 0.9 % and 14.8 % of the seawater storage capacity for atmospheric CO2. Olivine and steel slag released silicate nutrients into the seawater, but steel slag released considerably more and also significant amounts of phosphate. After 21 d, no significant difference was found in dissolved iron concentrations (>100 nmol L−1) in the treatments and the control. The slag addition increased dissolved manganese concentrations (771 nmol L−1), while olivine increased dissolved nickel concentrations (37 nmol L−1). There was no significant difference in total chlorophyll-a concentrations between the treatments and the control, likely due to nitrogen limitation of the phytoplankton community. However, flow cytometry results indicated an increase in the cellular abundance of several smaller (∼<20 µm) phytoplankton groups in the olivine treatment. The abundance of larger phytoplankton (∼>20 µm) decreased much more in the control than in the treatments after day 10. Furthermore, the maximum quantum yields of photosystem II (Fv/Fm) were higher in slag and olivine treatments, suggesting that mineral additions increased photosynthetic performance. The zooplankton community composition was also affected, with the most notable changes being observed in the dinoflagellate Noctiluca scintillans and the appendicularian Oikopleura sp. in the olivine treatment. Overall, the steel slag used here was more efficient for CO2 removal with OAE than the olivine over the 3-week timescale of the experiment. Furthermore, the steel slag appeared to induce less change in the plankton community than the olivine when comparing the CO2 removal potential of both minerals with the level of environmental impact that they caused.

Anthropogenic Eutrophication Drives Major Food Web Changes in Mwanza Gulf, Lake Victoria

AbstractDiscerning ecosystem change and food web dynamics underlying anthropogenic eutrophication and the introduction of non-native species is necessary for ensuring the long-term sustainability of fisheries and lake biodiversity. Previous studies of eutrophication in Lake Victoria, eastern Africa, have focused on the loss of endemic fish biodiversity over the past several decades, but changes in the plankton communities over this same time remain unclear. To fill this gap, we examined sediment cores from a eutrophic embayment, Mwanza Gulf, to determine the timing and magnitude of changes in the phytoplankton and zooplankton assemblages over the past century. Biogeochemical proxies indicate nutrient enrichment began around ~ 1920 CE and led to rapid increases in primary production, and our analysis of photosynthetic pigments revealed three zones: pre-eutrophication (prior to 1920 CE), onset of eutrophication with increases in all pigments (1920–1990 CE), and sustained eutrophication with cyanobacterial dominance (1990 CE–present). Cladoceran remains indicate an abrupt decline in biomass in ~ 1960 CE, in response to the cumulative effects of eutrophication and lake-level rise, preceding the collapse of haplochromine cichlids in the 1980s. Alona and Chydorus, typically benthic littoral taxa, have remained at relatively low abundances since the 1960s, whereas the abundance of Bosmina, typically a planktonic taxon, increased in the 1990s concurrently with the biomass recovery of haplochromine cichlid fishes. Overall, our results demonstrate substantial changes over the past century in the biomass structure and taxonomic composition of Mwanza Gulf phytoplankton and zooplankton communities, providing a historical food web perspective that can help understand the recent changes and inform future resource management decisions in the Lake Victoria ecosystem.

Secondary production at the Barents Sea polar front in summer: contribution of different size classes of mesozooplankton

The Barents Sea polar front is characterized by high primary production following the retreat of the ice edge during spring. However, secondary production estimates of mesozooplankton across the front are scarce, despite being essential for understanding energy flow through the food web. We investigated mesozooplankton community composition and production across the Barents Sea polar front (75°-78°N) in June, covering both Atlantic and Arctic water masses with high spatial and taxonomic resolution. We highlight the contribution of small and large groups of mesozooplankton and estimate secondary production by comparing and evaluating 4 commonly used growth rate models. The zooplankton community composition and size distribution changed across the polar front. In the Atlantic region, Rotifera, Chaetognatha and Appendicularia were common, while copepods and their nauplii contributed most across the polar front and in Arctic water masses. Mesozooplankton secondary production took place mainly in the surface and was highest south of the front, declining towards Arctic waters. Considering production by copepods alone, highest values were found in the northern sector of the polar front and in the Arctic region. Young developmental stages (CI-CIV) of Calanus spp. and small-sized taxa contributed most to copepod production in Atlantic waters, while calanoid copepod nauplii contributed considerably to copepod production in Arctic waters. We emphasize that the production estimates were strongly influenced by the growth rate model and conclude that copepod secondary production in a summer situation with non-limiting food concentration was best described using a model that solely considers water temperature and copepod body weight.

Indication of feeding ground inside the Manta Ray's cleaning station by investigation of the zooplankton community composition in Raja Ampat Islands, Indonesia

Abstract. Widiastuti, Borumei D. 2024. Indication of feeding ground inside the Manta Ray's cleaning station by investigation of the zooplankton community composition in Raja Ampat Islands, Indonesia. Biodiversitas 25: 1239-1245. Raja Ampat Islands, Indonesia, hosts reef manta ray (Mobula alfredi) and oceanic manta ray (Mobula birostris). Studies reported that these areas have functioned as manta ray cleaning and nursery sites. However, food availability is also the main attraction for manta ray aggregation. Thus, this study investigated the zooplankton community composition and abundance in the Manta Sandy Spot, a manta's cleaning station, to indicate its other role as the manta ray's feeding ground. Three sampling sites were located around the cleaning station bordered by mooring. A plankton net collected samples with a 100 µm mesh size, a mouth diameter of 30 cm, and a 1 m length horizontally towed from a boat for 5-10 min at a speed of ~2 knots. Manta ray's behavior was observed by snorkeling in the surface waters. Results demonstrated that the zooplankton was only composed of Copepod, consisting of three orders: Calanoida, Cyclopoida, and Harpacticoida. Among these orders, Calanoids dominated the zooplankton composition (93%). These genera were further grouped according to their body sizes, whereas three genera in Calanoids (Eucalanus, Calanus, and Undinula) were categorized as large-bodied zooplankton. The presence of the large-bodied zooplankton in the water samples, Calanoids, and Cyclopoids, which have been reported as the manta rays' preferred prey, indicates the area's role as the manta ray's feeding ground. This finding is supported by studies that found these zooplankton in the water where manta rays' feeding activity occurred and were absent in areas with no feeding activity. More indications were demonstrated by the manta ray's behavior, which followed the feeding activity criteria.

Факторы зональности и их влияние на зоопланктон озёр Среднего Поволжья

We analyzed the results of studies of 176 different types of lakes in the Middle Volga region (Russia). The impact of various environmental factors (morphometric parameters of lakes, physical and chemical indicators of water) on the lakes’ zooplankton communities of two landscape-geographical zones (forest and forest-steppe) was studied. The aim of the work was to identify the biodiversity of pelagic zooplankton and to assess the role of environmental factors in the development of zooplankton communities. Statistical studies included the calculation of the Spearman and Pearson correlation coefficients, data analysis using linear and logistic regression methods. We identify 230 species of zooplankton, including Rotifera – 107 (45.6%), Cladocera – 76 (33.6%), Copepoda – 47 (20.8%). Forest lakes show more species in the sample and higher quantitative indices compared to the forest-steppe lakes. The values of these indicators are determined by a complex of factors, the most important of which are the morphometric parameters of the lakes, the content of mineral nitrogen, oxygen, water mineralization and its determining ions. The depth of the reservoir can increase in the number of species in the sample or decrease them. Zooplankton quantification decreases as maximum depth increases. In deep-water lakes they are usually lower than in wellwarmed high-trophic and shallow ones. High mineralization and higher content of nutrients reduce the number of species in the sample and quantitative indicators of zooplankton. The increase in mineral nitrogen concentration and average ranking index is negatively related to zooplankton abundance, which is due to the occurrence of negative effects associated with anthropogenic eutrophication. Local conditions determine the composition and structure of zooplankton communities within the landscape-climatic zones, which determine the ionic composition of water and the concentration of major ions.

Trophic impact of an invasive mysid shrimp depends on zooplankton community composition: A mesocosm experiment

Abstract Invasive species are a major threat to the structure and functioning of freshwater ecosystems, yet their functional roles in the invaded habitats are often poorly understood, especially in omnivores. Their impact on the invaded ecosystems may be strongly dependent on local species composition, but so far there is little evidence to support this. We ran a mesocosm experiment to test whether the top‐down effect of the widespread omnivorous mysid shrimp of Ponto‐Caspian origin, Limnomysis benedeni, is the function of community composition of the invaded community. Zooplankton communities with different initial composition, dominated by either Cladocera or Copepoda, were crossed with the presence/absence of L. benedeni. We found that the effect of L. benedeni depended on community composition by suppressing zooplankton biomass only in communities dominated by Cladocera. This is presumably related to the differences in predator avoidance abilities, specifically that the dominant Daphnia species were less efficient in escaping predation by L. benedeni compared to Copepoda. While the elimination of such large planktonic grazers may cascade down to the level of primary producers, we did not find clear evidence for this, as phytoplankton biomass was mostly unaffected during the 2‐week experimental duration. Based on our results, we urge further proof‐of‐principle experiments coupled with field observations to be able to better predict the effects of invaders on different local communities.

Temporal variation and spatial factors affecting zooplankton communities in freshwater rock pools

Most ecological studies have focused on one snapshot in a single location and the same taxonomic group. However, relatively few studies have explored different taxonomic groups over multiple periods, particularly in ephemeral Neotropical ecosystems. This study investigates the seasonal dynamics of zooplankton communities and their responses to environmental variables in temporary pools in the Seasonally Dry Forest Ecosystem, Pernambuco, Brazil. We examined the seasonal fluctuations in species abundance, diversity, and evenness of Cladocera, Copepoda, and Rotifera in five temporary rock pools. Although these pools are meters apart, they vary considerably in size and drought sensitivity, leading to distinct seasonal dynamics mediated by water availability. We asked (i) how do species abundance, diversity, and evenness vary seasonally? (ii) Do these seasonal shifts differ between Cladocera, Copepoda, and Rotifera? And (iii) How do water environmental variables and spatial distance of pools influence zooplankton species composition? We hypothesized that Cladocera and Copepoda are positively affected by the rainy season, but Rotifera is mostly common in the dry season. Our findings underscore seasonality as the primary driver influencing the abundance and composition of zooplankton communities. We observed higher abundance of Cladocera and Rotifera during the post-rainy season, but Copepoda was dominant in the rainy season, leading to a strong seasonal variation in species evenness. These differences among groups highlight the importance of considering biological differences when understanding the ecological drivers of temporary freshwater ecosystems.

Declining calcium concentration drives shifts toward smaller and less nutritious zooplankton in northern lakes.

Zooplankton community composition of northern lakes is changing due to the interactive effects of climate change and recovery from acidification, yet limited data are available to assess these changes combined. Here, we built a database using archives of temperature, water chemistry and zooplankton data from 60 Scandinavian lakes that represent broad spatial and temporal gradients in key parameters: temperature, calcium (Ca), total phosphorus (TP), total organic carbon (TOC), and pH. Using machine learning techniques, we found that Ca was the most important determinant of the relative abundance of all zooplankton groups studied, while pH was second, and TOC third in importance. Further, we found that Ca is declining in almost all lakes, and we detected a critical Ca threshold in lake water of 1.3 mg L-1 , below which the relative abundance of zooplankton shifts toward dominance of Holopedium gibberum and small cladocerans at the expense of Daphnia and copepods. Our findings suggest that low Ca concentrations may shape zooplankton communities, and that current trajectories of Ca decline could promote widespread changes in pelagic food webs as zooplankton are important trophic links from phytoplankton to fish and different zooplankton species play different roles in this context.

Zooplankton in northern lakes show taxon‐specific responses in fatty acids across climate‐productivity and ecosystem size gradients

AbstractNorthern lakes are facing rapid environmental alterations—including warming, browning, and/or changes in nutrient concentrations—driven by climate change. These environmental changes can have profound impacts on the synthesis and trophic transfer of polyunsaturated fatty acids (PUFA), which are important biochemical molecules for consumer growth and reproduction. Zooplankton are a key trophic link between phytoplankton and fish, but their biochemical responses to environmental change are not well understood. In this study, we assess the trends in fatty acid (FA) composition of zooplankton taxa among 32 subarctic and temperate lakes across broad climate‐productivity and ecosystem size gradients. We found that genus‐level taxonomy explained most FA variability in zooplankton (54%), suggesting that environmental changes that alter the taxonomic composition also affect the FA composition of zooplankton communities. Furthermore, the FA responses and their underlying environmental drivers differed between cladocerans and copepods. Cladocerans, including widespread Bosmina spp. and Daphnia spp., showed pronounced responses across the climate‐productivity gradient, with abrupt declines in PUFA, particularly eicosapentaenoic acid and arachidonic acid in warmer, browner, and more eutrophic lakes. Conversely, calanoid copepods had high and relatively stable PUFA levels across the gradient. In addition, all zooplankton taxa increased in stearidonic acid levels in larger lakes where PUFA‐rich cryptophytes were more abundant. Overall, our results suggest that climate‐driven environmental alterations pose heterogeneous impacts on PUFA levels among zooplankton taxa, and that the negative impacts of climate warming are stronger for cladocerans, especially so in small lakes.

Plankton Diversity and Hydro-biological Parameters at Wazirabad Barrage in Yamuna River

This study conducted a comprehensive investigation into the qualitative and quantitative analysis of plankton diversity and Physico-chemical water quality parameters in the Yamuna River. Samples were collected from the Wazirabad barrage from June 2022 to November 2022, revealing a diverse phytoplankton community consisting of 50 genera distributed across five major classes. The abundant classes were Bacillariophyceae, with 18 genera, followed by Chlorophyceae with 20 genera, Cyanophyceae with 9 genera, Euglenophyceae with 2 genera, and Dianophyceae represented by a single genus. The qualitative analysis uncovered a zooplankton community with 20 genera from Protozoa and Rotifera, Copepoda, and Cladocera. Protozoa were represented by two genera, Copepods exhibited eight genera, Cladocera included five genera, and Rotifera featured four genera. The most abundant class of phytoplankton is Chlorophyceae and Zooplankton is Copepods. Physico chemical water quality parameters more fluctuation during the study period. These findings offer valuable insights into the biodiversity and composition of phytoplankton and zooplankton communities in the Wazirabad Barrage ecosystem.

Common bully (Gobiomorphus cotidianus) and mosquitofish (Gambusia affinis) shift littoral zooplankton community composition to smaller bodied taxa

ABSTRACT We investigated the effects of native common bully (Gobiomorphus cotidianus) and non-native western mosquitofish (Gambusia affinis) on zooplankton assemblages in an outdoor mesocosm experiment. Twenty-one 100 L mesocosms containing zooplankton were assigned either four G. cotidianus, four G. affinis, or were left as a control group (i.e. with no fish) and monitored for 14 days. Zooplankton community composition in the fish treatments was significantly different from the control tanks by day 14, but did not differ from one another. Both G. cotidianus and G. affinis reduced crustacean abundances, including Bosmina meridionalis, Daphnia pulex and Mesocyclops australiensis, relative to the controls. This reduced the effects of predation, competition, and physical interference by the crustaceans on rotifers, allowing rotifers to reach numerical dominance in the fish treatments. In contrast, zooplankton assemblages in the control mesocosms became dominated by cladocerans, indicating that these had a competitive advantage in the absence of the zooplanktivorous fish species. Our results suggest that G. cotidianus and G. affinis have similar preferences for zooplankton taxa and that G. affinis can alter littoral zooplankton assemblages in a comparable manner to G. cotidianus.

The role of fish predators and their foraging traits in shaping zooplankton community structure.

Differentiation of foraging traits among predator populations may help explain observed variation in the structure of prey communities. However, few studies have investigated the phenotypic effects of predators on their prey in natural communities. Here, we use a comparative analysis of 78 Greenlandic lakes to examine how foraging trait variation among threespine stickleback populations can help explain variation in zooplankton community composition among lakes. We find that landscape-scale variation in zooplankton composition was jointly explained by lake properties, such as size and water chemistry, and the presence and absence of both stickleback and arctic char. Additional variation in zooplankton community structure can be explained by stickleback jaw protrusion, a trait with known utility for foraging on zooplankton, but only in lakes where stickleback co-occur with arctic char. Overall, our results illustrate how trait variation of predators, alongside other ecosystem properties, can influence the composition of prey communities in nature.

Zeta Diversity Reveals the Small Wetland Complex Promotes Biodiversity

Small wetlands provide crucial ecosystem services but are facing widespread loss and degradation. At present, small wetland complexes provide an alternative avenue for conservation; we used a dataset to illustrate how zeta diversity can be assessed in a small wetland complex. The small wetland complex studied consisted of nine hydrologically connected ponds, and all the ponds were connected by narrow ditches. Data collected included the composition of both zooplankton and phytoplankton communities, water physicochemical parameters, and hydrological connectivity. Two ways in which connectivity affects biodiversity, dispersal filtration (path distance-controlled biological diffusion) and environmental filtration (environment-selected species), were quantified. As a result, (1) 46 zooplankton and 119 phytoplankton species were identified, with species richness distribution significantly affected by water properties (explained variances of 68% and 39%, respectively), reflecting significant environmental filtration, and (2) both zooplankton and phytoplankton showed zeta diversity distance decay (p < 0.001), reflecting significant dispersal filtration, and (3) relatively rare species dominated community turnover, in which environmental filtration was far stronger than dispersal filtration. Overall, the small wetland complex in this study was characterized by hydrological connectivity, which not only allowed moderate biological connectivity but also promoted the coexistence of diverse habitats and communities. We emphasize the applicability of zeta diversity for assessing small wetland complexes, further demonstrating the value of small wetland complexes in promoting biodiversity such as species richness and species turnover.

Distribution pattern of zooplankton assemblages in the eutrophic Hangzhou Bay, China

To reveal the distribution pattern of the zooplankton community in the typical eutrophic Hangzhou Bay in the northern East China Sea, we investigated the zooplankton community. The study was conducted in 2019 during the summer. A total of 57 species of zooplankton belonging to 6 phyla and 52 genera were identified. During the sampling period, the abundance of zooplankton in Hangzhou Bay was 26.7–497.2 ind/m3, with an average of 179.58 ind/m3. The abundance of zooplankton increased from west to east, and the abundance of zooplankton in most waters of the offshore area was higher than that in the coastal waters of Hangzhou Bay. The top dominant species, Tortanus vermiculus, was distributed in Hangzhou Bay, whereas Paracalanus aculeatus was mainly distributed in the mouth of Hangzhou Bay, and Acartia (Odontacartia) spinicauda and Centropages dorsispinatus were distributed between Zhoushan Island and Hangzhou Bay. The spatial distribution of the ShannonWiener index and evenness index of the zooplankton in Hangzhou Bay and its adjacent waters showed that the community structure of zooplankton was stable in the estuary of Hangzhou Bay and eastern part of the Zhoushan Islands. In addition to salinity and water temperature, eutrophication-related water quality parameters were also crucial to zooplankton species number, Margalef species richness and the abundance of the dominant species Tortanus vermiculus. The zooplankton dominant species and community composition were affected or restructured by eutrophication-related factors, especially for phosphate (PO4), nitrate nitrogen (NO3), dissolved inorganic nitrogen (DIN) and the eutrophic index (EI).

Temporal Changes in Zooplankton Community Composition and Abundance in Chemical and Organic Rice Fields in Buri Ram Province, Thailand

Temporal Changes in Zooplankton Community Composition and Abundance in Chemical and Organic Rice Fields in Buri Ram Province, Thailand

Combined effects of climate warming and pharmaceuticals on a tri-trophic freshwater food web

Multiple anthropogenic stressors influence the functioning of lakes and ponds, but their combined effects are often little understood. We conducted two mesocosm experiments to evaluate the effects of warming (+4 °C above ambient temperature) and environmentally relevant concentrations of a mixture of commonly used pharmaceuticals (cardiovascular, psychoactive, antihistamines, antibiotics) on tri-trophic food webs representative of communities in ponds and other small standing waters. Communities were constituted of phyto- and zooplankton and macroinvertebrates (molluscs and insects) including benthic detritivores, grazers, omnivorous scrapers, omnivorous piercers, water column predators, benthic predators, and phytophilous predators. We quantified the main and interactive effects of warming and pharmaceuticals on each trophic level in the pelagic community and attributed them to the direct effects of both stressors and the indirect effects arising through biotic interactions. Warming and pharmaceuticals had stronger effects in the summer experiment, altering zooplankton community composition and causing delayed or accelerated emergence of top insect predators (odonates). In the summer experiment, both stressors and top predators reduced the biomass of filter-feeding zooplankton (cladocerans), while warming and pharmaceuticals had opposite effects on phytoplankton. In the winter experiment, the effects were much weaker and were limited to a positive effect of warming on phytoplankton biomass. Overall, we show that pharmaceuticals can exacerbate the effects of climate warming in freshwater ecosystems, especially during the warm season. Our results demonstrate the utility of community-level studies across seasons for risk assessment of multiple emerging stressors in freshwater ecosystems.

Assessing the Seasonal and Spatial Dynamics of Zooplankton through DNA Metabarcoding in a Temperate Estuary.

Zooplankton are key components of estuarine trophic networks. However, routine monitoring is hindered by the difficulty of morphology-based identification. DNA-based methods allow us to circumvent some of these hurdles, providing precise species identifications regardless of the taxonomic expertise of the investigator or the developmental stage of the specimens. However, the process is dependent on the completeness of the reference libraries. In this study, we sought to evaluate the potential of DNA metabarcoding to assess the seasonal (summer, autumn, and early spring) and spatial dynamics of zooplankton (four locations spanning ca. 6 km) in the Lima estuary (NW Portugal). Two genetic markers were used: the cytochrome c oxidase subunit I and the V4 hypervariable region of the ribosomal 18S rRNA genes. Overall, 327 species were recovered, and both markers displayed minute overlap (7% were detected with both markers). Species richness, composition, and taxonomic distinctness were majorly influenced by the season, with a declining tendency from summer (highest number of exclusive species, n = 74) to spring. Second to season, the taxa composition was influenced by spatial variation where the most downstream site displayed the highest number of exclusive species, n = 53. A total of 16 non-indigenous species were detected using metabarcoding, but only one (Austrominus modestus) has been documented out in the estuary. In conclusion, both the seasonal and spatial gradients influenced the recovered richness, composition, and taxonomic distinctness, confirming the great aptitude of DNA metabarcoding for providing higher density monitoring and shedding new light on the composition and dynamics of complex zooplankton communities.

Nested Patterns of Phytoplankton and Zooplankton and Seasonal Characteristics of Their Mutualistic Networks: A Case Study of the Upstream Section of the Diannong River in Yinchuan City, China

The Diannong River, a valuable river and lake resource of the northern Ningxia Yellow River Irrigation Area, plays an instrumental role in regional flood control, drought resistance, climate regulation, and biodiversity conservation. Phytoplankton and zooplankton, as crucial elements of the aquatic ecosystem, have their distribution patterns evaluated and potential influencing factors identified, thereby enhancing the understanding of community distribution patterns. Nested structures and interspecies interaction relationships bear significant implications for community distribution patterns, functions, and stability. The upstream section of the Diannong River in Yinchuan City was chosen as the study object. Water samples were collected in January, April, July, and October 2021, and the community composition of phytoplankton and zooplankton was analyzed using relative abundance, density, and biomass. The distribution matrix temperature and bipartite network methodologies were deployed to investigate their nested pattern and interaction network seasonal characteristics. The findings indicate that the water environment of the Diannong River’s upstream section displays pronounced spatiotemporal heterogeneity, characterized by weak alkalinity and high fluoride content. The plankton community composition and relative abundance showed marked differences among the distinct sampling periods. The temperature of the random distribution matrix shows a significant difference compared to the zero-sum model, revealing a notable nested pattern in plankton in the Diannong River’s upstream section. The bipartite network suggests that the plankton composition was the simplest in January and the most complex in July, with the fiercest species competition observed in January and the lowest levels of species specificity, vulnerability, and generality. Water temperature (WT), dissolved oxygen (DO), total phosphorus (TP), available phosphorus (AP), CODCr, F−, and Cl− constitute the environmental parameters influencing the overall structure of the phytoplankton community in the Diannong River’s upstream section, whereas zooplankton did not present a significant correlation with water environmental factors.

Spatial Density, Biomass, and Composition of Crustacean Zooplankton on Lake Michigan Beaches

Ecosystem alterations to Lake Michigan (LM), such as the invasion of dreissenid mussels, have decreased the abundance of phytoplankton and, subsequently, zooplankton, which has implications for Great Lake fisheries. The community composition of zooplankton has also been altered over the past 20 years in LM, shifting the summer dominance from cladoceran to calanoid taxa. However, most of our information on zooplankton community dynamics is from deeper pelagic zones. The nearshore beach (≤1 m) habitat, which serves as a critical nursery for some larvae and juvenile fish, is composed of different zooplankton taxa than deeper zones, but limited data are available for comparison. We conducted a standardized summer sampling campaign to characterize the zooplankton community across 32 beaches in LM. We found the lowest crustacean zooplankton density and biomass on northern LM beaches and a higher zooplankton density and biomass on Greater Green Bay and central LM beaches, which had warmer water temperatures. Smaller-bodied cladocera (mainly Bosmina) and cyclopoid taxa were the most abundant groups on beaches. Our results provide the first comprehensive characterization of zooplankton on beaches in the Great Lakes, with applications for other lake systems. These results may help identify potential “hot spots” of fish recruitment for management.

Zooplancton del Río Paraná Medio: variaciones temporales y distribucionales en el área de confluencia con el Río Paraguay

The distribution, composition and numeric density of zooplankton communities at the first reach of Middle Paraná River were studied at the crosssection “Corrientes-Resistencia", about 30 km downstream its confluence with Paraguay River, by means of monthly samplings from April/76 to December/79.
 Samples were obtained one meter deph, fíltering 100 1 water with a 53 np mesh size sieve, at three stations: two located about 50 m from the margins (left at Corrientes and right at Chaco próvinces), and thé third at the centre of the section. Several Imnological parameters were recorded and water samples were taken to carry out current physical analysis at the laboratory.
 The numeric density of zooplankters and its specific composition, though very variable, resutted quite elevated (between 1 and 195 ind/l, with a total of 127 species), becoming both valúes more elevated towards the right margin. This river skle is very influenced by Paraguay River, wbile the left one, practically receive only Paranean waters. In spite of that, most zooplanktonic characteristic species in numerosity and frequence were generaüy similar in both margins.