Zooplankton Composition Research Articles

Кормление личинок судака (Sander lucioperca Linnaeus, 1758) при их подращивании в установке замкнутого водоснабжения

The article presents materials on optimizing the conditions for growing pike-perch during the larval period of development in an artificially created environment. The problems associated with the complexity of embryonic and post-embryonic development, the transition of larvae from endogenous to exogenous food, their rearing on artificial feed, and the causes of cannibalism have been described. The goal was to obtain and analyze the results of growing pike-perch larvae in conditions of closed water supply using living organisms as starter feed. The results of a study of the reproduction of pike-perch in industrial conditions of the aqua complex of the Coastal Scientific Expeditionary Base “Kagalnik” of the SSC RAS (Rostov Region, Azov District) are presented, describes the results of rearing pike-perch larvae in a recirculating aquaculture system. The values of the main hydrochemical parameters of the environment in fish tanks, necessary to ensure the normal growth and development of pike-perch larvae, as well as the characteristics of growth and survival during the experiments, are given. As a result, biotechnical standards for the reproduction of pike-perch by the intensive method have been developed. For high survival of pike-perch larvae, it is necessary to ensure timely feeding of larvae – after filling the swim bladder and switching to active feeding. The diet should be varied in terms of species composition of zooplankton. To prevent cannibalism among farmed fish, it is important to maintain the hydrochemical parameters at an optimal level, and the presence of food organisms in the fish tank is also necessary.

Zooplankton composition and structure in the Indus River Estuary, Sindh, Pakistan

In this study abundance and composition of zooplanktons in the Indus River Estuary was conducted to examine habitat characteristics and its impact on tiny organisms. Overall 30,656 individuals were identified and segregated into seven major groups including Copepods, Cnidarians, Decapods, Mollusk, Pisces, Amphipods and Chaetognaths. For better understanding they were further divided into eighteen planktonic categories. Among them Lucifer spp. comprises of 52.21% was the most abundant group with a peak appeared in March whereas Chaetognaths were rarely observed in the entire study period. Species diversity exhibited a mixed trend with the highest values (0.776) of dominance observed in spring (March). The results of Canonical Correspondence Analysis (CCA) indicate (60.2% and 39.79%) variability among first II axis. On this basis of the result it is obvious that water turbidity is trigger of the abundance and distribution whereas total dissolved solids (TDS) showed minimal influence deduced from CCA analysis.

СОСТОЯНИЕ ПЛАНКТОННЫХ СООБЩЕСТВ НИКОЛЬСКОГО УСТЬЯ РЕКИ СЕВЕРНАЯ ДВИНА В ОСЕННИЙ ПЕРИОД 2022 ГОДА

The work is part of the environmental monitoring of the Nikolskaya estuary. Severnaya Dvina, carried out in 2022, with the aim of comprehensive research of aquatic biological resources and their environment. Information was obtained on the species diversity and structure of plankton communities of the studied object belonging to the drainage basin of the Severnaya Dvina River. The taxonomic composition of phytoplankton and zooplankton in the navigation period of 2022 is shown. Species diversity was assessed using the Shannon index, based on the relative abundance of species, the Menhinik, index, which determines species richness, the average abundance and biomass of phytoplankton of the Nikolsky Estuary were determined. The Pantle-Bukka saprobity index was calculated to assess the pollution of natural waters. According to observations, 53 algae taxa with a rank below the genus and 21 zooplankton organisms have been registered. It was found that the basis of algoflora was diatoms. Copepoda copepods formed the basis of the zooplankton community. New data on the state of phytoplankton and zooplankton communities can serve as an informational and methodological basis for the development of environmental monitoring programs for aquatic ecosystems in the region.

Diversity and seasonal development of large zooplankton along physical gradients in the Arctic Barents Sea

Due to ongoing climate change, a new Arctic Ocean ecosystem is emerging. Within the framework of the Nansen Legacy project, we investigated the community composition of the large zooplankton and its seasonal development along a latitudinal gradient in the northern Barents Sea. Total biomass was maximal in summer and early winter, and minimal in spring, with copepods contributing considerably in all seasons. Euphausiids represented a minor fraction of the biomass, whereas chaetognaths and other gelatinous zooplankton contributed substantially to the sampled zooplankton at all stations, particularly in winter. Amphipod biomass was high in early winter, but otherwise low. Temperature in the water column interior and bottom-depth had the highest explanatory power for the community composition of the large zooplankton, both revealing the same distinct Atlantic and Arctic domains along the studied section. The continental shelf of the northern Barents Sea had an Arctic signature and was in terms of biomass characterized by a dominance of cold-water species, such as Themisto libellula, and Calanus glacialis. The copepod Calanus hyperboreus was the dominant over the continental slope. Locations at the southern and northern end of the studied section were influenced by Atlantic Water (at intermediate depth at the northern stations), and contained a mixture of temperate species, deep-water species, and sympagic amphipods in northern ice-covered waters. In the northern Barents Sea, a seasonal change was observed in the biomass fractions of different zooplankton feeding guilds, with dominance of herbivores in summer and carnivores in winter. This suggests switching between bottom-up and top-down control through the year. On the continental slope, species that are typically considered omnivores seemed to increase in importance. The role of seasonally changing food preferences to bridge periods outside of the main primary production season is discussed in light of ecosystem resilience to the expected changes in the Arctic Ocean.

Effects of microplastic ingestion on feeding activity in a widespread fish on the southwestern Atlantic coast: Ramnogaster arcuata (Clupeidae)

The presence of microplastics (MPs) in the fish gastrointestinal tract has been documented in several studies. However, it is unclear whether this ingestion is active or passive and whether it affects feeding activity in natural environments. In this study, three sites with different anthropogenic pressure were selected from the Bahia Blanca estuary, Argentina, and the small zooplanktivorous pelagic fish Ramnogaster arcuata was used to evaluate MP ingestion and its effect on specie's trophic activity. We analyzed the zooplanktonic composition, levels, and types of MPs in both the environment and the stomach contents of R. arcuata. Moreover, we assessed the trophic behavior of R. arcuata to determine electivity, stomach fullness, and vacuity indexes. The results showed that despite the availability of prey in the environment, 100 % of the specimens ingested MPs, and their levels and characteristics were different according to the site. Stomach contents at sites related to harbor activities presented the lowest MPs concentrations, most of them were paint fragments, with the smallest sizes and a low diversity of colors. The highest MP ingestions were found near the principal sewage discharge, being mostly microfibers, followed by microbeads, and with a greater variety of colors. Electivity indices showed that R. arcuata has a passive or active ingestion according to the size and shape of MPs. In addition, the lowest stomach fullness index and the highest vacuity index values were associated with the highest level of MP ingestion near the sewage discharge. Altogether, these results demonstrate a negative effect of MPs in the feeding activity of R. arcuata and help to elucidate some mechanisms by which these particles are ingested by a bioindicator fish used in South America.

Assemblages of pelagic thaliaceans in oceanographic features at the tropical-temperate transition zone of a western boundary current.

Mesoscale oceanographic features influence the composition of zooplankton. Cyclonic eddies can promote upwelling and production of gelatinous zooplankton, which play critical roles in ocean biogeochemical cycling. We examined variation in assemblages of thaliaceans (salps, doliolids and pyrosomes) among mesoscale oceanographic features at the tropical-temperate boundary of the East Australian Current (EAC) in Spring 2019 and Autumn 2021. The influence of cyclonic eddies was examined in a large offshore cyclonic eddy in 2019 and a newly formed frontal eddy in 2021. Pyrosomes were most abundant in the offshore EAC jet, and salps and doliolids were most abundant in coastal features, including within eddies that were transported offshore. In 2019, Salpa fusiformis increased 4-fold over 8 days in the large cyclonic eddy, and in 2021, doliolids increased > 50-fold over 2 weeks in a chlorophyll-rich coastal eddy while abundances of other thaliaceans remained unchanged or decreased. Correlations between abundances of thaliaceans and chlorophyll-a concentrations across the 102 samples collected during both voyages revealed that doliolids occupy a wider range of chlorophyll-a concentrations than salps. Our observations indicate that doliolids thrive in productive shelf environments, salps occur in less productive shelf waters and pyrosomes are most abundant in oligotrophic waters of the south Coral Sea.

Timing of Ice Retreat Determines Summer State of Zooplankton Community in the Ob Estuary (the Kara Sea, Siberian Arctic)

In the estuaries of large Siberian rivers, ice coverage and the timing of ice retreat have varied in recent decades under the ongoing climate change. The seasonal development and functioning of the mesozooplankton community depend to a great extent on the timing of ice retreat. In the Arctic estuaries, the response of zooplankton to the timing of ice melt remains unclear. An earlier ice retreat was suggested to result in an advanced seasonal development of zooplankton, and higher biomass and feeding rates. Zooplankton composition, biomass, demography and grazing (assessed with the gut fluorescent approach) were studied in the Ob Estuary in July 2019 (“typical” ice retreat time). The obtained results were compared with the published data for July 2016 (ice retreat three weeks earlier). Zooplankton biomass in 2019 was considerably lower than in 2016, while species composition was similar; dominant populations were at an earlier stage of development. Herbivorous feeding of the dominant copepod, Limnocalanus macrurus, was also lower in 2019. The consequences of an earlier ice melt and increased temperature on seasonal population dynamics of the dominant brackish-water species are discussed. Our findings demonstrate that zooplankton communities in the Arctic estuaries are highly sensitive to the environmental changes associated with early sea-ice reduction.

Assessing the Composition and Diversity of Zooplankton in Bhosga Lake, Kalaburagi District, Karnataka, India: Implications for Water Quality and Conservation

Assessing the Composition and Diversity of Zooplankton in Bhosga Lake, Kalaburagi District, Karnataka, India: Implications for Water Quality and Conservation

Flow and plankton availability control young‐of‐the‐year fish diet in two floodplain nurseries

AbstractIn large river floodplains, the availability of trophic resources to the fish fauna is highly variable as a consequence of seasonal environmental change and habitat diversity. Young‐of‐the‐year fishes (YOY) must find suitable habitats to settle, feed and survive. However, very few in‐depth studies are available about the food preferences of the young fishes during their first growing season. Here, we investigated the composition of planktonic assemblages and the YOY diet of three generalist fish species Alburnus alburnus (Linnaeus, 1758), Squalius cephalus (Linnaeus, 1758) and Pseudorasbora parva (Temminck & Schlegel, 1846) from four floodplain sites of the French Upper Rhône River. More specifically, we studied their temporal and spatial variations in relation to five environmental variables: hydrology, dissolved oxygen, primary production, water temperature and conductivity. Stable flow conditions and the associated temperature and conductivity strongly structured the phytoplankton community in the floodplain channels, whereas water movements within channels and dissolved oxygen concentrations were significantly correlated to the zooplankton composition. A zooplankton density above ≈100 ind L−1 allowed the initiation of a YOY diet mainly based upon zooplankton for the three fish species. When zooplankton densities were insufficient, all three species used phytoplankton as their main food resource. Finally, the diet overlaps between species, differed significantly between sites. The study highlights the need to examine the diet of juvenile fishes and environmental variables in the floodplains.

Zooplankton assemblages and indicator species in the Changjiang river estuary and its adjacent waters

Zooplankton is a vital biological indicator in estuarine ecosystems. In this study, the Changjiang River Estuary (CRE) was investigated in the dry (March) and wet seasons (July) of 2019 for spatial and temporal fluctuations of zooplankton based on the indicator value (IndVal) index method. A total of 172 zooplankton taxa (146 adult taxa and 26 larvae) were identified. Zooplankton composition, abundance, biodiversity, grouping, and indicator species all showed substantial seasonal changes. The hydrological environment of the CRE was affected by diluted water and current intrusions. Compared to the dry season, the wet season had a higher abundance and biodiversity of zooplankton. Zooplankton communities from the inside-mouth fresh-brackish, intermediate transition, and offshore neritic regions were distributed in a three-segment pattern (fresh-brackish, transitional and neritic) and were significantly impacted by Changjiang River discharge. In general, freshwater and brackish species shifted toward the ocean during the wet season, whereas during the dry season, when river flow decreased, marine species shifted toward the estuary. Sinocalanus sinensis and Mesocyclops spp. were indicators of the Changjiang Diluted Water. Temora turbinata and Flaccisagitta enflata were good indicators of Taiwan Warm Current invasion, while Calanus sinicus may represent the effect of the Yellow Sea Coastal Current in the northern CRE. This research contributes to a thorough understanding of pelagic ecosystem dynamics and seasonal succession patterns in the CRE, which has a complicated hydrological environment.

Роль солоноватоводной фауны и состояние биоресурса экосистемы гипергалинного озера Кулундинское в фазе трансгрессии (Алтайский край)

The results of ecological monitoring of the hypergaline lake Kulundinskoye of the Altai Territory in the period 2021-2022 are presented. The research was carried out in the form of a comprehensive study of abiotic factors of the reservoir (climatic features of the lake, temperature regime, salinity of water), biological factors (species composition of brackish-water zooplankton, its abundance), production and structural indicators of the gill-legged crustacean Artemia Leach, 1819. Desalination of water during the transgressive period of water content caused successional speciation processes. There was a change of the gill-legged crustacean as a dominant and monovid to a complex of brackish-water fauna. The artemia population developed under the influence of unfavorable salinity of water with a fluctuation in the lake from 1.9 (April) to 99.0 mg/dm3.
 The influence of the transgressive phase of water content on the biota and the extraction (catch) of a biological resource - artemia (at the stage of cysts), as well as the importance of the formation of their commercial accumulations of abiotic environmental factors, is shown. Studies have shown that the prevailing combination of factors during the transgression period – tense climatic conditions, low salinity of water (less than 100 mg/dm3), low number of artemia crustaceans, was the absence of commercial accumulations of biological resources.

Изучение состояния зоопланктона, ихтиопланктона и зообентоса в акватории Азовского моря в позднеосенний период 2021 года

The article presents the results of hydrobiological monitoring of the water area of the Sea of Azov in the late autumn period of 2021. The characteristics of the taxonomic composition and quantitative indicators of zooplankton and zoobenthos are given, the distribution of hydrobionts by dominant species is shown, and saprobity indicator species are noted.

Drivers of spatial and temporal micro- and mesozooplankton dynamics in an estuary under strong anthropogenic influences (The Eastern Scheldt, Netherlands)

The Eastern Scheldt estuary in the Netherlands has been anthropogenically changed by the construction of a storm surge barrier about 30 years ago, affecting abiotic conditions as well as phytoplankton and zooplankton (ZP). As the ZP communities have not been sampled in the last decades, it is unclear to what extent they have changed during the last 30 years. We analyzed the micro- and mesoZP composition and background parameters at eight stations in the Eastern Scheldt in spring, summer, and autumn 2018. Additionally, we conducted dilution experiments to estimate phytoplankton growth and microZP grazing rates. Seasonal variability of ZP was higher than spatial variability, but there were differences between stations. In agreement with data from the 1980s, we identified salinity and chlorophyll a as the most important factors in explaining the ZP community. Suspended particulate matter and water retention time were additionally identified for mesoZP, as well as dissolved inorganic nitrogen and phosphate concentration for microZP. We observed some changes in ZP composition with respect to the 1980s, most of which could be explained by the changes induced by the barrier construction. However, increased abundances of the cyclopoid copepod Oithona sp. were likely related to changes in phytoplankton composition due to large-scale bivalve cultivation in the estuary. Phytoplankton growth and microZP grazing rates were variable between seasons, which could be explained by changes in the phytoplankton community during the annual plankton succession. Overall, the observed alterations in the ZP community due to changed background parameters and intense bivalve filtration could affect the microbial loop as well as consumers of mesoZP and thus the functioning of the pelagic food web.

Особливості росту дволіток веслоноса (Polyodon spathula Walbaum, 1792) в умовах ставового господарства Лісостепу України

Purpose. To investigate the peculiarities of growth of age-1+ paddlefish depending on water temperature and quantitative parameters of zooplankton development in ponds of the forest-steppe zone of Ukraine. Methodology. Age-1+ paddlefish, a North American zooplanktophagus were reared in polyculture with cyprinids in a 72-hectare pond using semi-intensive technology. The stocking density of age-1 paddlefish with an average weight of 86.5 g was 59 fish/ha, with a total stocking density of 2,402 fish/ha for all objects of polyculture. The intensification measures included fertilization of ponds with traditional organic fertilizers and feeding of carp with feed mixtures based on waste from the processing of agricultural raw materials of plant origin. The study of the intensity of development of the natural food supply and physicochemical parameters of water was carried out according to the methods generally accepted in hydrobiology and hydrochemistry. Determination of piscicultural parameters and growth characteristics of age-1+ paddlefish was carried out using methods common in ichthyology based on the dynamics of body weight gains in absolute and relative values. Findings. The conditions of the pond environment during most of the period of rearing of age-1+ paddlefish met the biological requirements of this species. A periodic decrease in the content of oxygen dissolved in water to 3.3-3.5 mgO2/dm3 was noted, which could negatively affect the growth of fish. Water temperature during the fish breeding period varied between 9.8-26.5oC. The average seasonal biomass of phytoplankton and zooplankton of the pond was 16.49 mg/dm3 and 3.92 g/m3, respectively, with a predominance of Cladocera and Copepoda (respectively, 61.0 and 34.5% in the average seasonal biomass) in the quantitative composition of zooplankton. As a result, age-1+ paddlefish reached an average weight of 1318.3 g with a fish productivity of 45.6 kg/ha and a total pond fish productivity of 1162.6 kg/ha. Maximum relative weight gains of paddlefish of 4.25–4.37% per day were observed during the first half of the growing season (mainly in June) at a water temperature of 22–25oC during the period of increase in zooplankton biomass from 3.79 to 10.11 g/m3. Originality. New data were obtained on the growth characteristics of paddlefish depending on environmental conditions of the ponds of the Forest-Steppe zone of Ukraine. Practical value. The study results can be used in the process of improving pond aquaculture technologies in Ukraine. Key words: pond aquaculture, paddlefish, growth, zooplankton, water temperature.

Parasite ecology of Carassius gibelio (Bloch, 1782) in Jandari Lake (Georgia)

The aim of the investigation was to study the current structure of the parasitic fauna of the gibel carp (Carassius gibelio) population in the Georgian part of Jandari Lake. In total, 423 young gibel carp collected during 2014-2018 years from Jandari Lake have been subject to parasitological examination. The 20.3% (n=86) of examined fish were invaded by 11 species of parasites belonging to 5 taxonomic groups. The dominant taxonomic groups were discovered to be Protozoa and Monogenea. The eight species were registered for the first time in the gibel carp of freshwater reservoirs in Georgia. In general, young fish were more invaded by the monoxenic species of the direct life cycle. None of the revealed parasites were specific to gibel carp. The parasitic fauna of Jandari Lake is relatively poor, though it is comparatively rich and diverse in spring. Trichodina sp. from Protozoa, Ancyrocephalus sp., Dactylogyrus vastator, Gyrodactylus elegans from Monogenea, and Contracaecum sp. from Nematoda were revealed as the species most sensitive to annual changes. The main factor determining the parasite fauna of gibel carp in Lake Jandari is anthropogenic eutrophication, which changes the qualitative and quantitative composition of zooplankton, the main food source of juvenile fish and intermediate hosts of helminths. The difference in invasion indices between female and male gibel carp was insignificant. The synergetic relationship between some parasitic protozoans and monogeneans was marked.

Mutual links between microcystins-producing cyanobacteria and plankton community in clear and brown northern lakes

This work studies the composition and abundances of phytoplankton and zooplankton and their relationships during cyanobacteria bloom (mainly Dolichospermum lemmermannii) in two subarctic oligotrophic lakes, a clear deep lake (Krivoe) and a brown shallow lake (Krugloe). Cyanobacteria bloom (D. lemmermannii) was observed four times during 7–10 days in both lakes: late July, late August, September 2019, and late September 2020. The toxicity of cyanobacteria was determined by the presence of cyanotoxins in water and plankton biomass. Microcystins (mostly LR, RR, and other structure variants) were found in every case of visible blooms (July–September of 2019–2020) in the shallow lake and only once in the deep lake. Despite the nutritious food items (cryptomonads), the presence and dominance of colony-forming microalgae (Botryococcus brauni) and filamentous cyanobacteria in both lakes consisted of a low-efficient food base for grazers. A high abundance of toxic microcystins in the shallow lake with dystrophic features led to the specific composition of zooplankton with the prevalence of the selective grazers, copepod Eudiaptomus graciloides, and cladoceran Ceriodaphnia pulchella adapted to cyanotoxins. In a clear deep lake, where toxic variants of microcystins were low or not detected during the cyanobacteria bloom, the omnivorous rotifer Asplanchna priodonta and small grazer Bosmina longirostris reached high abundance. This study confirms close relationships between cyanobacteria and zooplankton communities.

Feeding of sunbleak (Leucaspius delineatus Heckel, 1843) from the pond of Noginsky district of Moscow region in February 2023

The nutrition of sunbleak (Leucaspius delineatus) from the pond of Noginsk district of Moscow region in February 2023, owned by GNP “Yakor”, was studied. The aim of the study was to investigate the nutrition of sunbleak. To achieve this aim, the following tasks were performed: the age of the caught fish, their average length and weight were determined, the quantitative and qualitative composition of zooplankton in the reservoir was studied, the food boluses of the fish were considered in order to establish the frequency of occurrence of food objects in them, the intestinal filling index and the selection index. The study of the sunbleak nutrition seems relevant for establishing links in the ecosystem of a fishery reservoir, with the aim of further optimal selection of fish multiculture, based on the analysis of the state of the natural food supply. As part of the zooplankton community of the reservoir, 11 taxa were identified: 4 species of rotifers, 4 species of branchous and 3 taxa of copepods. In the course of the study, it was found that the sunbleak from the reservoir in question fed on almost all the species encountered except rotifers. With age, the fullness of the fish intestines decreased. The species composition of the consumed crustaceans differed depending on the age of the fish. Younger fish preferred the smaller size species of crustaceans, older fish preferred larger size and more nutritious species of crustaceans. Crustaceans of the Daphnia genus turned out to be the most preferable food for the sunbleak of all ages, and with age, the fish more and more preferred this food object. The most abundant crustaceans of the Bosmina genus in the water body were avoided by the fish, even the underyearlings, the only age category of the sunbleak that fed on these organisms.

Ionic adjustments do not alter plankton composition in low salinity Penaeus vannamei intensive nursery with synbiotic system

ABSTRACT The aim of this study was to test the effect of different ionic adjustments in low salinity water on the composition and temporal variation of plankton from intensive shrimp nurseries with a synbiotic system. For this, a Penaeus vannamei nursery (35 days) was carried out with three treatments: T1 – diluted seawater (control; salinity ∼2.5 g L−1), T2 – salinity ∼2.5 g L−1 with K+ adjustment to approximate the seawater equivalent concentration, and T3 – salinity ∼2.5 g L−1 with Ca:Mg:K ratio adjusted to 1:3:1. Rice bran processed by probiotic microorganisms was used as an organic carbon source. Phytoplankton and zooplankton were sampled weekly and analysed using standard methods. The temporal variation of phytoplankton and zooplankton composition were more pronounced than differences among treatments indicating that the ionic adjustment had little effect on these communities. During the experimental time, the dominant phyla in phytoplankton were Ochrophyta, Cyanophyta and Chlorophyta, whereas zooplankton’s dominant phyla were Ciliophora, Amoebozoa, and Cercozoa. Cyanophyta’s relative abundance was lower than traditional biofloc systems, suggesting a higher control of these microorganisms in synbiotic systems. Ionic adjustments have then a low potential to affect plankton, likely because limitation by these ions was not achieved under the ionic manipulations tested.

Research on the seasonal variation of zooplankton community in Daya Bay, South China Sea

Changes in zooplankton composition, abundance, and some species in response to environmental variation were investigated over four seasons (2020) in Daya Bay. In total, 129 taxa of zooplankton (16 groups of planktonic larvae and 20 indeterminate species) were identified. Zooplankton communities exhibited a significant seasonal shift in abundance and taxonomic composition. The maximum number of zooplankton species was recorded in winter (72 species) and the lowest in spring (42 species). However, the abundance was highest in spring (1,372.01 ± 1,071.14 individuals/m³) and lowest in autumn (50.93 ± 34.05 individuals/m³). Pearson correlation analyses demonstrated that the zooplankton abundance and the variations of indicator species were obviously correlated with environmental parameters (e.g., salinity, temperature, pH, and chlorophyll-a). Based on specificity and occupancy analysis, a total of eight species were selected as indicator species. It is noteworthy that some kollaplankton (such as Dolioletta gegenbauri and Doliolum denticulatum) could potentially cause disaster to the nuclear power plant cooling system because of their relatively large body size and huge blooms in spring. In addition, Centropages tenuiremis blooms in spring and Penilia avirostris blooms in summer could attract assemblages of larval or adult pelagic fish, which would also threaten the cooling system security in Daya Bay. In conclusion, our results suggest that zooplankton communities and some species may be considered as favorable indicators of the marine environment.

Zooplankton community structure in relation to environmental variables in a tropical endorheic Soda Lake Shala, Ethiopia

Lake Shala, endorheic Soda Lake in the Ethiopian Riftvally Lake, supports an enormous biodiversity, with a large human population and economic development. However soda lakes are under several ecological changes, with unexpected shifts in biodiversity composition and physicochemical changes. This study focuses on assessing the community structure of zooplankton in Lake Shala. Samples were taken at monthly intervals from January to December 2018. A total of 32 zooplankton species were identified, of which 23 species were Rotifers and followed by Copepoda (6) and Cladocera (3). The community was dominated by Brachionus dimidiatus, B. dimidiatus inermis, B. plicatilis and B. calyciflorus. Their abundance exhibit significant seasonal and vertical variations (ANOVA, p < 0.05). Zooplankton community structure of Lake Shala has changed over time, benthic harpacticoids (Nitocra lacustris) have become replaced by small-bodied and generalist-feeder rotifers (genus Brachionus). Such ecological shifts may be driven mainly by partial atelomixis in this deep tropical lake. Overall, zooplankton species distribution and abundance are influenced by various environmental factors such as conductivity, salinity, Chl-a and nutrients. This study concludes that the composition and community structure of zooplankton in Lake Shala has changed over time with the change in physicochemical and internal limnological dynamics (atelomix).