Zooplankton Abundance Research Articles

Zooplankton of the Eastern Kara Sea: Response to a Short Ice-Free Period

—A characteristic feature of the eastern Kara Sea, which is separated from its central part by the shallow Central Kara Rise, is a later ice breakup, a shorter ice-free period, and lower water temperature. Zooplankton in this part of the sea is virtually unstudied. The first data on the composition, spatial distribution of zooplankton, age structure and feeding of the dominant species, and their grazing impact on phytoplankton were obtained in the cruise 125 of the R/V Professor Shtokman (September 2013) and cruise 63 of the R/V Akademik Mstislav Keldysh (September 2015) to the eastern Kara Sea. 2015 was a typical year in terms of the ice regime for this region, while in 2013, seasonal ice coverage lasted longer than usual. Zooplankton biomass (17–112 mg dry weight m–3), to which copepods Calanus glacialis contributed the main portion, were close to the values in the central Kara Sea in September. The seasonal development of the C. glacialis population began much later than in the central Kara Sea, but development of Metridia longa was not influenced by the specifics of the ice regime and hydrophysical conditions in the eastern Kara Sea. The interannual differences in the timing of ice retreat had almost no effect on the zooplankton abundance, seasonal development of the dominant copepod populations, feeding activity, and grazing impact on phytoplankton.

Plankton Community Composition and Water Quality in Gili Ketapang, Probolinggo Regency, East Java

Gili Ketapang is an area with quite high fisheries potential, reaching 40% of the resource production in East Java. The catch season is often associated with the presence of plankton as the main source of food availability in marine ecosystems, influenced by season, weather, temperature, and water quality. The aim of this research is to report water quality results and analysis of phytoplankton and zooplankton composition in the coastal waters of Gili Ketapang, East Java. The method used in this research is quantitative descriptive to describe plankton composition and water quality in Gili Ketapang, East Java. In this study, 26 phytoplankton genera and 35 zooplankton genera were found. The abundance of phytoplankton and zooplankton measured in the West Season was lower compared to the abundance in Transition Season I. The phytoplankton and zooplankton diversity index showed moderate diversity (1<H'<3). In general, the results of water quality measurements obtained in the West Season were temperature 32.8 , pH 8.54, dissolved oxygen 6.72 mg/L, salinity 32.66 ppt, Secchi depth 13.11 m, and nitrate 1.39 mg/L. Meanwhile, the water quality in Transition Season I was respectively temperature 30.26 , pH 7.8, dissolved oxygen 8.24 mg/L, salinity 31.47 ppt, Secchi depth 10.92 m, and nitrate 1.21 mg/L.

Zooplankton as ecosystem indicators and their effects on eutrophication in Lake Arekit (Ethiopia) – implication for freshwater habitat management

This paper examines the zooplankton abundance and composition along with various environmental factors in Lake Arekit – a shallow freshwater habitat in Ethiopia’s rift valley system. Zooplankton samples and specific environmental data were collected by a seasonal campaign (rainy season: June to August) and dry season: March to May 2023) from three sites: inlet area (IA), pelagic area (PA), and macrophyte area (MA). In total, 11 zooplankton taxa from four different groups – rotifera (7 taxa), cladocera (2 taxa), copepod (1 taxa), and ostracoda (1 taxa) – were identified in Lake Arekit. Large-bodied copepoda and cladocera comprised 90% of the zooplankton density in the lake, but small-bodied rotifers dominated the zooplankton diversity. The most noticeable zooplankton in the lake were Mesocyclops aequatorialis, Daphnia barbata, and Cypridopsis vidua. Seasonal difference in the total zooplankton abundance was evident (p < 0.01): being high during the rainy season which was accompanied by an increase in the lake’s water temperature and nutrient levels. At MA, where D. barbata predominated, chlorophyll a was relatively low. Chlorophyll a had a strong negative correlation with the abundance of grazing zooplankton, especially with D. barbata (r = −0.563) and C. vidua (r = −0.518). The zooplankton composition and abundance of Lake Arekit reveal a low Shannon diversity index (H’) (1.03) and a predominance of a few species, indicating heavy contamination of the lake’s water. Moreover, Lake Arekit was determined to be hypertrophic (TSI > 70) using Carlson’s trophic index (TSI), which took into account the lake’s water transparency, total phosphorus, and chlorophyll a. Our results indicated that high densities of Daphnia should be the goal of biomanipulation since they can achieve filtration potentials high enough to enhance the water’s clarity in hypereutrophic lake. Even though high D. barbata concentrations cannot address the underlying cause of eutrophication, grazing can assist by lengthening the clear-water stages in a hypertrophic lake – Lake Arekit. The sources of pollution for the lake are the discharge of wastewater from nearby water bottling companies and possibly high nutrient levels from the lake’s geological history. Stopping the discharge of wastewater from the nearby commercial industries (the major source of contaminant) into heavily washed open areas and establishing a buffer zone may help manage the water quality of Lake Arekit.

Ecological changes in subtidal macrobenthic communities of the Taean coast following the Hebei Spirit oil spill: A 10-year longitudinal study

We examined long-term response (2008–2017) of the macrobenthos to the Hebei Spirit oil spill that occurred around the Taean coast, Korea, in December 2007. Oil concentrations were below the Korea/US environmental standards as of January 2008. Organic matter, chlorophyll-a, and zooplankton abundance dominated by Noctiluca scintillans were higher after the spill. Macrobenthic diversity recovered to pre-incident (2007) level in 2011. Biomass exceeded that level in 2011 and the increase prolonged for 5 years. Cross-correlation and regression analyses showed that chlorophyll-a at year t and zooplankton abundance at t-2 had a significant relationship with macrobenthic biomass at t (p < 0.05 for both), suggesting the transfer of increased organic matter (transformed from crude oil within the pelagic ecosystem) into the benthic ecosystem. Coastal wetlands around the incident area, vulnerable to oil pollution and slowly remobilizing accumulated oil, seemed to affect pelagic ecosystem processes and the unexpectedly increased and sustained biomass.

Space-time multi-level modeling for zooplankton abundance employing double data fusion and calibration

An important objective for marine biologists is to forecast the distribution and abundance of planktivorous marine predators. To do so, it is critically important to understand the spatiotemporal dynamics of their prey. Here, the prey we study are zooplankton and we build a novel space-time hierarchical fusion model to describe the distribution and abundance of zooplankton species in Cape Cod Bay (CCB), MA, USA. The data were collected irregularly in space and time at sites within the first half of the year over a 17 year period, using two different sampling methods. We focus on sea surface zooplankton abundance and incorporate sea surface temperature as a primary driver, also collected with two different sampling methods. So, with two sources for each, we observe true abundance or true sea surface temperature with measurement error. To account for such error, we apply calibrations to align the data sources and use the fusion model to develop a prediction of daily spatial zooplankton abundance surfaces throughout CCB. To infer average abundance on a given day within a given year in CCB, we present a marginalization of the zooplankton abundance surface. We extend the inference to consider abundance averaged to a bi-weekly or annual scale as well as to make an annual comparison of abundance.

Zooplankton biodiversity and temporal dynamics (2005-2015) in a coastal station in western Portugal (Northeastern Atlantic Ocean).

Long-term monitoring of zooplankton assemblages provides essential knowledge to assess key factors impacting marine ecosystems. Despite the importance of this type of data, monitoring stations worldwide are spatially and temporally limited due to the difficulty of maintaining them. In the northeastern Atlantic area, Cascais-Watch is one monitoring site operating since 2005, despite some constraints throughout the years, and has allowed the collection of important data on the zooplankton communities of the area. The present work summarizes the knowledge collected until 2015 on the biodiversity and dynamics of zooplankton in the site. The results showed a year-round high productivity of the zooplankton abundance, biomass and diversity for the area, with no significant general trends or periodicity, despite the relatively lower winter and higher spring values. The results revealed two main transition periods with marked changes in species composition and dominance of the most abundant taxa. This shift was tentatively attributed to the extended annual dry season verified in Portugal after 2011, the low values of upwelling and precipitation, and the warmer waters. The zooplankton abundance presented an interannual increase for spring periods, and the proportion of Copepoda, the dominant taxa, was lower during summer months, corresponding to increased abundances of Mollusca, Diplostraca (Cladocera) and Cnidaria. In particular, the study shows an increasing abundance of the gelatinous species (particularly Cnidaria) for spring/summer months in recent years, suggesting changes in primary production and prey dynamics. Other relevant tendencies were the higher abundance of meroplankton, such as Bivalvia and fish larvae/eggs, and the decreasing trend in the abundance of the meroplanktonic coastal crustaceans, Decapoda and Cirripedia taxa, highlighting possible changes in the benthic coastal populations in the study region. The present study highlights probable changes and trends in the zooplankton community that should be monitored in the following years.

Seasonal variation in plankton abundance and diversity of Tanga coastal waters, Tanzania

Several studies have reported on seasonal patterns in plankton (phytoplankton and zooplankton), in different ecoregions. However, information on these plankton along the coastal waters of Tanga is limited. This study attempts to uncover and describe information related to abundance, distribution, and diversity of phytoplankton and zooplankton in the coastal waters located in the western side of the Pemba Channel, Tanzania, during the southeast monsoon (SEM) and the northeast monsoon (NEM) seasons. The samples of phytoplankton, zooplankton and environmental variables were collected in the coastal waters of Tanga, from June 2019 to January 2021. A total of 199 species of phytoplankton and 32 genera of zooplankton were identified. Although the abundance varied between the SEM and the NEM seasons, Bacillariophyceae were the most abundant among the phytoplankton groups, while Copepods were the most abundant zooplankton in both seasons. The abundance variation in phytoplankton and zooplankton could be attributed to environmental variables, which varied significantly between seasons. The results suggest that high nutrients concentration during the SEM season influences high plankton abundance, richness, and diversity.

The Structure of the Zooplankton Communities in Sukhoe More Bay, Southeastern White Sea

This paper presents the results of our investigation of the zooplankton communities from Sukhoe More Bay, located in the southeastern part of Dvina Bay of the White Sea, in July−August, 2018. The species composition, quantitative characteristics and spatial distribution of zooplankton were studied. The zooplankton communities are composed of 34 species of hydrobionts. Copepods were the dominant group in the entire study area. The zooplankton communities were characterized by high quantitative indicators. Juvenile stages of copepods were a significant contribution to the formation of the total number of zoocenoses. During high water level, the abundance of zooplankton was 37 000 ind./m3, biomass, 0.6 g/m3 (wet weight). During low water level these parameters were 210 000 ind./m3 and 1.7 g/m3 (wet weight), respectively. The structure, abundance and spatial distribution of zooplankton in the bay are determined by the morphometric features of the reservoir (shallow water), the influence of a complex of environmental factors (temperature and salinity), as well as tidal phenomena.

Dynamics of Zooplankton Consumption by the Three-speed Stickleleback &lt;i&gt;Gasterosteus aculeatus&lt;/i&gt; (Linnaeus, 1758) at Different Densities of the Predator

An experiment was set up to estimate the rate of zooplankton consumption by the three-spined stickleback Gasterosteus aculeatus (Linnaeus, 1758) at different predator densities. A differential equation describes the dynamics of zooplankton abundance depending on duration of predator feeding. The derived function accurately characterizes the rate of zooplankton consumption by stickleback in the experiment, demonstrating a good agreement between the theoretical prerequisites and the experimental results. The relationship between changing a number of prey during predation, its mortality and consumption rate was revealed. The hypothesis of consumption rate proportional to the number of predators was tested. A comparative analysis of ingestion rate as a function of time and a function of prey density was performed.

Multiple island effects shape oceanographic processes and zooplankton size spectra off an oceanic archipelago in the Tropical Atlantic

Pelagic ecosystems around tropical oceanic islands are considered oases of high plankton biomass in the middle of oligotrophic “blue deserts”. To understand the dynamics of such a pelagic ecosystem, we used CTD and ADCP data and zooplankton samples taken from the waters off the remote Fernando de Noronha Archipelago (FNA), Tropical Atlantic. We analyzed how the flow and island topography interactions influence the spatial variability of chlorophyll-a fluorescence and zooplankton abundance, biovolume, and normalized biovolume size spectra (NBSS). We used a 500-μm mesh bongo net to obtain plankton samples in July and August 2010 in areas upstream and downstream of FNA. Zooplankton samples were analyzed with a ZooScan device. Chlorophyll-a peaks and a rise in thermocline indicated a topographic uplift and turbulence downstream of the island, i.e., the “Island Mass Effect”. The NBSS presented a mean slope of −1.19 ± 0.28, and a mean intercept of 3.98 ± 0.87. There were no significant differences in NBSS slopes and intercepts between upstream and downstream areas. Nevertheless, zooplankton and decapod community structures were significantly different between areas: meroplanktonic communities showed higher abundances and biovolumes downstream (p < 0.05). Zoeae of stenopodid cleaner shrimps, anomuran and brachyuran crabs, and fish eggs were significantly more abundant downstream, indicating a “Larval Island Effect”. Distinct peaks in size spectra due to teleost eggs and decapod larvae, downstream of FNA, also indicated a Larval Island Effect. Upstream of the island, there was a higher abundance of gelatinous organisms, holoplanktonic decapods, and advanced stages of brachyuran crabs (“Upstream Island Effect”). Also, copepods, gelatinous organisms, large-sized “other crustaceans” (e.g., euphausiids, amphipods, stomatopod larvae, mysids, etc.), teleost eggs, and stenopodids caused abundance peaks in the size spectra upstream. Our study highlights the need for careful management and conservation of parental spawning stocks of fishes and macroinvertebrates surrounding tropical oceanic islands.

Analisis Komposisi Jenis dan Kelimpahan Zooplankton di Perairan Kampung Nafri, Kota Jayapura

This study aimed to determine the type, composition, and abundance of zooplankton in the waters of Kampung Nafri. Zooplankton were identified using zooplankton sample identification guidelines, and zooplankton abundance analysis was performed using the Sedgewick Rafter. Purposive sampling was used in this study. Zooplankton sampling was carried out horizontally on the surface of the water using a plankton net which was carried out in the morning around 08:00 - 10:30 WIT at 3 stations. Sampling at each station was done 2 times repetition and the water parameters were done 3 times repetition. In situ measurement of water quality parameters, such as salinity, pH, current speed, and temperature Based on the identification results, there are 11 types of zooplankton that inhabit the waters of Kampung Nafri. The highest value of zooplankton species composition in Nafri Waters was Naplius sp., which was 63%, and the lowest was Temora sp. and Corycaeus sp. by 1%. The highest abundance of zooplankton species in Nafri Waters was Nauplius sp. (Copepoda larvae), with a total abundance of 9,900 ind/l, and the lowest was Corycaeus sp. and Temora sp., with a total abundance of 200 ind/l.

Zooplankton as an indicator of hydrological connectivity of the main channel and the floodplain in a large river system

AbstractThe connectivity of the river–floodplain system during floods plays a decisive role in organisms/matter contribution to the ecosystems of large lowland rivers. We hypothesized that the direction of water-level trends during flood was crucial for zooplankton release from the floodplain into the river channel. The seven-year study of zooplankton in the large plain Ob river suggest that at the inundated floodplain even a slight water level fall brings to plankton release from the floodplain into the river thus causing its abundance boom in the main channel. At water-level stabilization or rise, zooplankton communities of floodplain become isolated from the channel that ceases the recruits’ inflow from the floodplain and brings to a sharp drop in number of river zooplankton. Therefore, it is necessary to take into account dynamics trends (i.e., fall or rise) in river water level when assessing zooplankton density in large lowland rivers. The analysis of such trends should become the basis for predicting of river zooplankton abundance and assessing changes in feeding conditions of fish during the growing season.

Vertical changes in zooplankton abundance, biomass, and community structure at seven stations down to 3000 m in neighboring waters of Japan during the summer: Insights from ZooScan imaging analysis

The imaging device ZooScan is used to examine net-collected zooplankton samples. ZooScan has been applied to regional and seasonal changes in the zooplankton community, but it has rarely been used to characterize vertical changes, especially down to the deep sea. In this study, we report a ZooScan analysis of vertically stratified zooplankton samples collected by collected by Vertical Multiple Plankton Sampler down to 3000 m at seven stations near Japan in the Okhotsk Sea, Japan Sea, East China Sea, and subarctic, transitional, and subtropical North Pacific. Throughout the region, both abundance and biomass, as indicated by aggregate zooplankton volume decreased with increasing depths. ANCOVA analysis revealed that factors linked to vertical changes varied with location. Depth and region were the primary determinants of abundance and biomass, respectively. Cluster analysis based on abundance delineated 8 distinct zooplankton community groups. The occurrence of each group varied regionally and 3–5 groups were vertically stratified at each station. Across all stations, Normalized Biomass Size Spectra (NBSS) and size diversity showed pronounced change around 150–500 m depths. At shallower depths, the NBSS slope was steep, the intercept was high, and size diversity was low while, at deeper depths the opposite was true for each of those parameters. Generalized additive models showed that depth, temperature, and salinity had a significant effect on NBSS and size diversity. This study indicates that the ZooScan imaging approach may be useful in the analysis of deep-sea zooplankton communities.

Positive and negative impacts of flue gas desulfurization (FGD) gypsum on water quality

Flue gas desulfurization (FGD) gypsum, a by-product of carbon-based energy sources, has typically been incorporated as a component of concrete mixes and wallboard and beneficially used as an agricultural amendment to enhance terrestrial crop production and improve the quality of runoff. These various uses for the by-product aid in reducing the amount that is ultimately landfilled. Limited studies have investigated its benefits when used directly in aquatic settings, such as ponds and lakes, to increase hardness and potentially mitigate eutrophication. A 36-day field mesocosm experiment tested a larger range of FGD gypsum concentrations (500–2000 mg/L) than those previously tested in the literature to investigate its desired and potentially undesired impacts on water quality, including the algal community. High FGD gypsum concentrations, 1000 and 2000 mg/L, were found to have more undesired impacts than the 500 mg/L treatment, including an initial spike in cyanobacteria, a decrease in total zooplankton abundance, and an increase in certain trace metals in the highest treatment. Ultimately, the 500 mg/L FGD gypsum treatment was found to have fewer undesired impacts while still resulting in significant desired effects, including those on hardness and pH, as well as moderate reductions in algal abundance. This experiment provides a better understanding of the effects of FGD gypsum when directly used in an aquatic setting, determines an optimal dose for future field experiments, and helps provide the groundwork for developing an upper threshold on FGD gypsum so as to not have the negative effects outweigh the positive.

Habitat and food habits of the endemic fish Oryzias eversi in Tana Toraja, South Sulawesi, Indonesia

Abstract. Lamba T, Ambeng, Andriani I. 2023. Habitat and food habits of the endemic fish Oryzias eversi in Tana Toraja, South Sulawesi, Indonesia. Biodiversitas 24: 5137-5145. The population of the medaka fish species, Oryzias eversi, was categorized as Near Threatened by the International Union for Conservation of Nature (IUCN) 2019 due to its restricted distribution and occurrence in a single threatened location. One way to protect this species from extinction is through captive breeding, which requires understanding its habitat conditions and food habits. Therefore, this research aimed to analyze the habitat conditions and food habits of Oryzias eversi (Hadiaty &amp; Nolte, 2012) in Tilanga Pool, Tana Toraja. Purposive random sampling was used to obtain fish samples, while habitat conditions were determined by measuring environmental parameters, and the abundance and diversity of plankton. Food habits were analyzed by calculating the Index of Preponderance (IP) and Relative Gut Length (RGL). The results indicated that O. eversi inhabited a highly polluted habitat with dissolved oxygen content that ranged from 3.95 to 4.16 mg/L. The abundance of phytoplankton and zooplankton ranged from 185-435 cells/L and 10-25 ind/L, respectively. Phytoplankton diversity was in the moderate category, while zooplankton was low, with average values of Diversity Index (H’) ranging from 1.61-1.93 and 0.69-024, respectively. IP and RGL showed that O. eversi was an omnivore-carnivore fish. The average IP of zooplankton and phytoplankton ranged from 0.35-61.11% and 0.69-1.04%, respectively. Meanwhile, the RGL ranged from 0.48 to 0.62, respectively. Cyclops sp. larvae were identified as the primary food source for O. eversi with IP above 40% and Eurycercus sp. with IP range of 4-40% as additional food.

Composition and distribution of the zooplankton community along the west coast of Baja California peninsula and its relationships with the environment variables

The year 2014 is between one of the coldest La Niña events (2011−2012), and one of the most intense warming events between (2013–2016) in the California Current System (CCS). The information provided in this work documents part of the missing information about zooplankton and oceanographic features for the year 2014 along the southern portion of the CCS off the western Coast of Baja California Peninsula (WBCP). The statistical analysis of environmental variables during the summer of 2014 distinguished three regions off the WBCP (north, transitional, and south), in coincidence with changes in zooplankton groups composition. Thermal and saline oceanic fronts off the central region coincided with an increasing abundance of gelatinous zooplankton, where two cold core eddies were present. These mesoscale structures represent physical barriers that seem to determine the distribution limits of planktonic communities. Since no day/night statistical differences in zooplankton composition were found, zooplankton community changes seem more related to the latitudinal environmental changes and mesoscale semi-permanent structures in the middle peninsula.

Integrating hydrological connectivity and zooplankton composition in Arctic ponds and lakes

Abstract Arctic landscapes are characterised by their numerous ponds and lakes. With increased climate warming and consequent changes in hydrological connectivity, the ecology of many of these waterbodies is expected to change. We sampled 13 ponds and 22 lakes for zooplankton and various limnological and physical environmental variables in the vicinity of Cambridge Bay, Nunavut (69.1169° N, 105.0597° W), with the aim of testing how well the degree of hydrological connectivity explained patterns in species composition and abundance and contributed to crustacean production. Ponds were hydrologically isolated while the lakes were arranged in four lake chains and ranged from the headwaters to highly inter‐connected lakes receiving water from one to 768 upstream lakes. In all sites combined, 77 zooplankton species were found, including 56 rotifers, six copepods, 11 cladocerans, two fairy shrimp species, a mysid, and a tadpole shrimp. We show that the zooplankton communities differed between hydrologically isolated (ponds) and connected (lakes) systems, with 17 species unique to ponds and 20 to lakes. Furthermore, the communities were more similar within lake chains and hence in lakes closer to each other. In ponds, distances between waterbodies had no impact on community similarity. Zooplankton abundance was higher in lakes (255 ind/L) than in ponds (65 ind/L) due to the higher number of rotifers that accounted for nearly 80% of the zooplankton abundance in lakes. In ponds, rotifers, cladocerans, and copepods were equally abundant. In terms of biomass, cladocerans represented 65% of total biomass in all waterbodies except for a chain of deep lakes that had abundant fish communities. In these lakes, cladoceran abundance and biomass were low and probably limited by fish predation. Zooplankton production was higher in ponds (4.6 mgC m−3 day−1) than in lakes (1.7 mgC m−3 day−1), and within lakes was lowest in the chain composed of large lakes (1.3 mgC m−3 day−1). The high production in ponds was closely linked to high zooplankton biomass and further explained by high gross primary production supported by relatively high nutrient concentrations in these shallow systems. Our study emphasises that hydrological connectivity is key to shaping zooplankton communities, although fish presence also appears to affect them. It shows that isolated ponds (that currently account for c83% of all waterbodies on southern Victoria Island) are hotspots of aquatic biological productivity that probably play an essential role in Arctic freshwater landscapes. Finally, our study provides critical baseline information on the current composition of Arctic zooplankton communities important for estimating climate change impacts.

Long-Term Trends in Seasonality and Abundance of Three Key Zooplankters in the Upper San Francisco Estuary

Zooplankton provide critical food for threatened and endangered fish species in the San Francisco Estuary (estuary). Reduced food supply has been implicated in the Pelagic Organism Decline of the early 2000s, and further changes in zooplankton abundance, seasonality, and distribution may continue to threaten declining fishes. While we have a wealth of monitoring data, we know little about the abundance trends of many estuary zooplankton species. To fill these gaps, we reviewed past research and then examined trends in seasonality and abundance from 1972 to the present of three key but understudied zooplankton species (Bosmina longirostris, Acanthocyclops spp., and Acartiella sinensis) that play important roles in the estuary food web. We fit Bayesian generalized additive mixed models of each taxon’s relationship with salinity, seasonality, year, and geography on an integrated database of zooplankton monitoring in the upper estuary. We found marked changes in the seasonality and overall abundance of each study species. Bosmina longirostris no longer peaks in abundance in the fall months, Acanthocyclops spp. precipitously declined in all months and lost its strong relationship with salinity, and A. sinensis adult abundance has become more strongly related to salinity while juveniles have developed wider seasonal abundance peaks. Through these analyses, we have documented the relationship of each species with salinity and seasonality since the beginning of monitoring or their introduction, thus increasing our understanding of their ecology and importance in the estuary. These results can inform food-web models, be paired with fish data to model the contributions of these species toward fish abundance trends and be mirrored to elucidate other species’ trends in future studies.

Within‐lake variatiability in predation risk shapes the spatio‐temporal structure of the zooplankton community

Abstract While it is well‐accepted that predation plays a key role in shaping both size structure and species composition in natural ecosystems, fine‐scale variation in predation risk within ecosystems has been largely neglected. The objective of this study was to use normalised size spectra (NSS) to investigate whether small‐scale spatial variation in predation risk (by fish) can modulate zooplankton community structure at the within‐lake level in a small temperate lake. We tested the difference in the NSS between two hydrologically well‐connected basins of a lake exhibiting contrasting thermal regimes. The first is a well‐mixed shallow basin (max. depth 2.5 m) that is inaccessible to brook charr (Salvelinus fontinalis) during summer because the temperature is too warm. The second is a deeper basin (max. depth 18 m) offering a thermal refuge during summer because of lake stratification. As a consequence of these differences in fish accessibility, the fishless basin should contain larger and more abundant zooplankters, inducing a change in NSS slope and height. Our results showed that both the zooplankton size structure and taxonomic composition were distinct in the two basins, with a higher proportion of small individuals and a higher abundance of zooplankton in the shallow basin compared to the deep one. Furthermore, following cooling of the epilimnion in late summer, the zooplankton communities of both basins exhibited a clear shift in size structure and species composition: in autumn, there were smaller individuals and larger proportions of Bosminidae and Daphniidae compared to colonial rotifers than in summer. These results suggest a potential effect of the change in the spatial distribution of brook charr which feed preferentially on large individuals, reducing the average body size of the zooplankton community. Our results show that predation risk by fish can induce a spatial and temporal variation in zooplankton community structure within small temperate lake ecosystems exhibiting contrasted thermal regimes. Other potential predators also influenced the zooplankton community structure, creating a complex interplay that has to be taken into account to disentangle ecological processes and predict their future changes.

Contrasting effects of river inflow and seawater intrusion on zooplankton community structure in Jiaozhou bay, the Yellow Sea

Environmental changes associated with river inflow and seawater intrusion are known to affect zooplankton communities in coastal systems, but how zooplankton respond to these environmental changes remains unclear at present. Here we explored the effects of river inflow and seawater intrusion on zooplankton community structure in Jiaozhou Bay. The results showed that the river inflow and seawater intrusion are key in driving zooplankton dynamics, but with contrasting effects. According to the distinct hydrographic conditions, the sampling area could be geographically divided into the river inflow area with low-salinity and high-nutrient conditions (i.e., EIZ) and the seawater intrusion zone with high-salinity and low-nutrient conditions (i.e., SIZ). There were significant differences in zooplankton communities (e.g., abundance and species composition) between the two regions with seasonal changes. For example, the zooplankton abundance was significantly higher in the SIZ than in the EIZ during spring, whereas an opposite pattern was observed for the summer season. In contrast, the species richness was higher in the EIZ than in the SIZ in spring, while an opposite variation trend was observed during summer. These results together suggested that the river inflow and seawater intrusion had contrasting effects on zooplankton community structure in different seasons. According to the canonical correspondence analysis, we observed that the zooplankton community structure was mainly driven by temperature, chlorophyll a (Chl a), and nutrients in the EIZ, but it was largely affected by salinity in the SIZ. The implication is that changes in temperature, Chl a, and nutrients as a result of river inflow and changes in salinity as a consequence of seawater intrusion are key in driving the dynamics of zooplankton communities in Jiaozhou Bay.