Zooplankton Body Size Research Articles

Seasonality of zooplankton active flux in subtropical waters

AbstractThe biological carbon pump (BCP) is the mechanism by which the ocean transports organic matter below the mixed layer, exporting or sequestering it for years to millennia. Physical transport of dissolved and particulate organic carbon, the sinking of particles, and the carbon transported by diel and seasonal vertical migrants are the three main mechanisms of the BCP. In the study of active flux, seasonality is almost unknown and changes in ocean productivity during the annual cycle could promote differences in this transport. Here, we show the results of a cruise performed during spring in the Canary Current System, where we studied zooplankton active flux in two transects from the coastal zone off Northwest Africa toward the ocean. We measured biomass and the enzymatic activity of the electron transfer system (ETS) as a proxy for respiration in the water column down to a depth of 900 m. Compared with a previous survey during fall, we found higher values of specific ETS activity in the mesopelagic zone, promoting a higher active flux. Our results showed that the seasonality of active flux is driven not only by differences in biomass but also by differences in respiration rates in the mesopelagic zone, mainly due to differences in zooplankton body size. A review of the zooplankton active flux values around the Canary Islands showed a fourfold increase during spring compared with other seasons. This small window of higher flux should be considered in models of active carbon export in the ocean.

Contrasting resistance and resilience trajectories of zooplankton communities in restored fishless alpine lakes

AbstractCatastrophic state changes often occur in ecosystems as consequences of shifts in the dominant life forms, such as in the case of sportfish introduction into naturally fishless mountain lakes. While the pronounced ecological displacement of native communities by these novel predators (i.e., weak resistance) is well documented, few studies have also examined the dynamics of their recovery rates (i.e., “engineering resilience”) following stressor removal. We addressed this knowledge gap by quantifying the taxonomic and species trait‐based ordination trajectories of crustacean zooplankton communities in stocked alpine lakes, which differed in how they were restored to a natural fishless state over a period of six decades. Resilience and resistance trajectories differed in each lake as the ecological importance of trait‐based species recolonization potential (e.g., asexual vs. sexual reproduction) replaced that of tolerance of size‐selective predation by fish (e.g., body size, pigmentation, motility). As a result, re‐establishment of large‐bodied zooplankton following the elimination of fish restored annual secondary production. In contrast, a more gradual unidirectional ordination trajectory toward smaller zooplankton body size and a decline in total zooplankton biomass occurred in a nearby alpine lake containing a protected native bull trout population. Although recovery trajectories returned via routes that differed from those of earlier resistance trajectories (i.e., hysteresis), we discovered that full taxonomic and functional recovery was realized in all the restored fishless lakes within three decades, regardless of the approach used to achieve ecosystem restoration.

Zooplankton community size structure across lakes within a semi-arid landscape: the effect of temperature and salinity

AbstractBody size is a master trait controlling biological communities and ecosystem functioning. Mean population size not only depends on the size of individuals, but also on the size distribution of individuals within the population. Mean community size is additionally influenced by the composition of species (larger- or smaller-sized species). Shallow lakes within semi-arid landscapes are prone to experience large changes in temperature and salinity, which affect the zooplankton size structure. Higher temperatures are expected to result in smaller average body size, while the effect of salinity appears to depend on the range under study. Here we analyze zooplankton body size patterns across shallow lakes from the semi-arid central region of Argentina. All community size descriptors point to decreasing size and a narrow size range at higher temperatures. On the other hand, the maximum average community body size occurred at intermediate (~30 gL−1) salinity levels. The combined effect of both variables resulted in a bell-shaped pattern, with maximum community body size toward lower temperatures and intermediate salinities. Based on future temperature scenarios, one may anticipate an overall decrease in community body size. But such prediction is strongly conditioned by regional and local trends in salinity.

Mass spectrometry imaging reveals the spatial distribution of essential lipids in Daphnia magna – potential implications for trophic ecology

ABSTRACT Lipids and fatty acids are key dietary components for the nutrition of organisms at all trophic levels. They are required to build cellular structures such as cell membranes, serve as energy storage, and take part in signal transduction cascades. For decades, ecological research investigated how dietary fatty acid availability contributes to the fitness of individuals and their populations. The omega-3 polyunsaturated fatty acid eicosapentaenoic acid (EPA) is of particular interest because its dietary availability determines the fitness of many aquatic consumers. Because of the small body size of zooplankton, only bulk tissue fatty acid analysis was previously performed, and thus the tissue-specific importance of EPA for zooplankton remained elusive. We used matrix-assisted laser desorption/ionization–mass spectrometry imaging (MALDI-MSI) to reveal the tissue-specific distribution of functional phospholipids in the herbivorous zooplankton Daphnia magna. We demonstrate several lipid species for heart, egg, gut, gonad, somatic, and neurological tissues of D. magna, including the compound eye as well as the optical and cerebral ganglion. The compound eye revealed a large diversity in lipid species containing EPA, which were also found in other neurological tissues and eggs. Such knowledge of tissue-specific fatty acid requirements is essential to investigate how selective allocation of dietary fatty acids within this key grazer affects processes on a functional and molecular level from the individual to food web scales. This methodological advancement will facilitate investigations on how invertebrate physiology and behaviour adjust to changing environmental conditions and potentially affect food web structures, including the trophic transfer of dietary fatty acids.

Biogeochemical shifts and zooplankton responses in post-CAAA northeastern lakes: The success of acid recovery, complexity of biological recovery, and value of long-term monitoring

Lakes in the northeastern U.S., as in other regions, experienced significant declines in water quality and ecosystem health in the mid to late 20th century as atmospheric deposition from industrial emissions caused surface waters to acidify. After the Clean Air Act Amendments of 1990 enhanced regulations to limit emissions of sulfur and nitrogen, many lakes in the Northeast recovered from acidification. The organisms that inhabit lakes are susceptible to these shifts, and zooplankton can serve as valuable indicators of lake ecosystem responses to shifts due to their position as primary consumers in the food web. We evaluated a large historical dataset from the U.S. Environmental Protection Agency (EPA) Eastern Lake Survey (ELS) of 143 lakes throughout the northeastern U.S. to understand how recovery from acidification and subsequent chemical changes influenced zooplankton body size and community composition. We observed significant changes in chemistry; surface water sulfate concentrations decreased by 22% in the ELS lakes between the two sample years of 1986 and 2004. Increasing concentrations of DOC are common from the combined influence of deacidification and climate change, and the ELS lakes experienced a 26% increase in DOC. Notably, in the more developed regions of our study area, chloride concentration in lakes tripled, likely due to increased use of road deicers, and this is related to a subsequent increase in calcium and magnesium base cations. Zooplankton body size increased significantly between 1986 and 2004 across all taxa, and body size of Daphnia species, which require higher amounts of calcium than other zooplankton taxa, was positively associated with high calcium lakes. Shifts in zooplankton community structure, however, were most strongly influenced by variation in ANC, sulfate, and DOC. Our findings indicate that, while surface water acidity has a strong influence on zooplankton community structure, zooplankton populations are likely on a different trajectory than a simple recovery due to multiple chemical changes, such as increased chloride, occurring in lakes undergoing acid recovery. These, along with changes in climate and land-use, elicit multiple simultaneous responses in zooplankton communities.

Plankton growth dynamic driven by plankton body size in deterministic and stochastic environments

In this paper, we establish a new phytoplankton–zooplankton model by considering the effects of plankton body size and stochastic environmental fluctuations. Mathematical theory work mainly gives the existence of boundary and positive equilibria and shows their local as well as global stability in the deterministic model. Additionally, we explore the dynamics of V‐geometric ergodicity, stochastic ultimate boundedness, stochastic permanence, persistence in the mean, stochastic extinction, and the existence of a unique ergodic stationary distribution in the corresponding stochastic version. Numerical simulation work mainly reveals that plankton body size can generate great influences on the interactions between phytoplankton and zooplankton, which in turn proves the effectiveness of mathematical theory analysis. It is worth emphasizing that for the small value of phytoplankton cell size, the increase of zooplankton body size can not change the phytoplankton density or zooplankton density; for the middle value of phytoplankton cell size, the increase of zooplankton body size can decrease zooplankton density or phytoplankton density; for the large value of phytoplankton cell size, the increase of zooplankton body size can increase zooplankton density but decrease phytoplankton density. Besides, it should be noted that the increase of zooplankton body size cannot affect the effect of random environmental disturbance, while the increase of phytoplankton cell size can weaken its effect. There results may enrich the dynamics of phytoplankton‐zooplankton models.

Dynamics of interacting plankton induced by plankton body size in deterministic and stochastic environments

In this paper, we study the dynamics of a nutrient–phytoplankton–zooplankton model incorporating the factor of plankton body size in deterministic and stochastic environments. The value of this paper lies in two aspects: Mathematically, for the model without stochastic environmental fluctuations, we give the existence of boundary and positive equilibria, show the local and global stability of these equilibria, and prove the existence of Hopf bifurcation. For the model with stochastic environmental fluctuations, we provide the results related to the stochastic extinction and persistence in the mean, as well as the existence of ergodic stationary distribution. Ecologically, via numerical simulations, we find that plankton body size plays a key role in regulating the dynamics of interacting plankton in the deterministic and stochastic environments. It is worth emphasizing that the increase of phytoplankton cell size can stabilize the model by excluding the periodic solution induced by nutrient removal rate, while the increase of zooplankton body size can remain such periodic phenomena. Additionally, it should be noted that the very small phytoplankton cell size or zooplankton body size has a negative effect on the plankton growth in the stochastic fluctuation environments. These results may help to understand the complex dynamics of plankton models.

Zooplankton assemblage and body size responses to severe lake eutrophication from agricultural activities near mink farms in Nova Scotia, Canada

Abstract Mink fur farming was once a widespread agricultural activity in southwestern Nova Scotia. Freshwaters near to and downstream of several mink fur farm operations have experienced severe water quality issues, including eutrophication and recurring algal blooms. Here, we use dated lake sediments to examine trends in primary producers and primary consumers from a hypereutrophic lake to assess how cladoceran assemblages have responded to extreme eutrophication. Shifts in the dominant pelagic cladoceran taxa began in the early 1900s, coinciding with an increase in sedimentary chlorophyll-a concentrations. Notably, small-bodied bosminids decreased, while taxa such as Chydorus brevilabris and Daphnia pulex spp. dominated assemblages in recent decades. Bottom-up ecological factors, such as decades of greater primary production, were the likely drivers of assemblage shifts of primary consumers. Consistent body sizes of bosminids throughout the sedimentary record suggested that pelagic cladocerans were not influenced solely by predation pressure from macroinvertebrates or fish. This study provides evidence of large-scale ecological shifts occurring at multiple trophic levels in a hypereutrophic temperate lake with mink farming operations in its catchment.

The wind‐driven distribution of nearshore zooplankton in a stratified lake varies with their body size

Abstract Wind‐driven forces are expected to concentrate zooplankton along downwind shores in lakes and provide food subsidy to nearshore food webs, but the bathymetric complexity of nearshore areas could result in high spatial variability. Here we test: (1) whether zooplankton accumulate downwind on windy days, and whether the magnitude of accumulation varies with zooplankton body size and with nearshore bathymetric slope; and (2) whether nearshore zooplankton are more spatially variable than offshore zooplankton, and whether their spatial variability is related to wind conditions and to zooplankton body size. This study focuses on zooplankton distribution at the whole‐lake basin and at intermediate (10 m–1 km) spatial scales. Zooplankton were sampled repeatedly along four c. 1 km transects at each of the upwind and downwind ends of a 22.1‐km2 stratified lake basin. Two transects were oriented perpendicular to shore and two were parallel, one close to shore and the other further offshore. Zooplankton were sampled along each transect using an optical plankton counter morning and afternoon over 3 consecutive days, under a range of wind conditions, during early stratification (early June), mid‐stratification (mid‐July) and late stratification (late September). A 3D‐hydrodynamic model was used to help interpret the results. Small‐bodied zooplankton accumulated downwind during windy periods, reaching 8%–34% higher biomass than the basin‐wide average. This downwind accumulation of biomass was best explained by a partial (metalimnetic) upwelling displacing the epilimnion to the downwind end of the lake basin. Active upward movement of zooplankton is required to explain near‐surface biomass accumulation in this displaced water mass. Large‐bodied zooplankton accumulated in nearshore areas, regardless of wind conditions. Higher nearshore accumulation of large zooplankton was observed along transects following a shallow (1.9%) bathymetric slope but not along a steep (6%) slope. Large‐bodied zooplankton are more patchily distributed than small‐bodied zooplankton, both nearshore and offshore. The spatial variability of large zooplankton declined with increasing wind speed, but only at upwind sites. The patchy distribution of large‐bodied zooplankton is driven, or at least strongly influenced, by biological processes. The spatial distribution and patchiness of zooplankton varies with wind speed, zooplankton body size and nearshore bathymetry. Planktonic organisms are not passive drifters, and their patchiness and influx to certain parts of the lake during windy periods are both expected to affect the efficiency of trophic transfers in lake food webs.

The impact of plankton body size on phytoplankton-zooplankton dynamics in the absence and presence of stochastic environmental fluctuation

In this paper, we study the dynamics of a stochastic phytoplankton-zooplankton (PZ) model with phytoplankton cell size and zooplankton body size. In the case of PZ model without stochastic environmental fluctuations, we provide the positivity and boundedness of the solutions, investigate the dissipativity and permanence of the model, prove the existence of Hopf bifurcation, and give the local and global stability of the boundary and positive equilibria. In the case of PZ model with stochastic environmental fluctuations, the stochastic dynamics including a unique ergodic stationary distribution, stochastic permanence, stochastic extinction and persistence in the mean are explored in detail. Based on the theoretical analysis above, via numerical simulations, we find that the increase of environmental capacity can not only destabilize the deterministic model via Hopf bifurcation and induce periodic solutions, but can also stabilize the deterministic model by rejecting the periodic solutions. Interestingly, the increase of phytoplankton cell size or zooplankton body size can stabilize the deterministic model by excluding the periodic solutions induced by environmental capacity. Additionally, it is worth emphasizing that the small phytoplankton cell size can lead to the inability of plankton to survive in both deterministic and random environments, while the small zooplankton body size can destabilize the deterministic model and induce periodic solutions. Furthermore, it should be noted that the large phytoplankton cell size can weaken the effect of random environmental disturbance, but large zooplankton body size can not. These results may provide new insights in understanding the complex dynamics of phytoplankton-zooplankton models.

Zooplankton body size is filtered by a thermo‐oxygenic niche at the regional scale

AbstractAimThere is ongoing debate regarding the extent to which body size is selected by the environment. To address this issue, we assessed how thermo‐oxygenic conditions select body size of rotifer species composing a regional species pool.LocationApproximately 600 different water bodies in Sweden.TaxonRotifers (188 species).MethodsData were acquired from previously published studies. For the environmental parameters, we conducted principal component analysis (PCA) to recognize the pattern among the species‐specific thermal and oxygenic preferences of rotifers of different ecology. We assigned a standard body length to each species. We performed phylogenetically correlated analyses to evaluate the relationships between body length and the parameters that were selected as PCA drivers.ResultsThermal and oxygenic tolerance ranges, designated by the differences between the minimum and maximum of species occurrence, were grouped separately from the optima designated by the conditions referring to the highest species abundance, according to PC1 versus PC2. The parameters representing temperature and oxygen occupied opposite positions on the PC2 axis. Body size selection was driven by both temperature and oxygen, but the cues for this selection differed; species with higher thermal optima were smaller, while species with wider oxygen tolerance ranges were larger.Main conclusionThe body sizes of rotifer species are filtered by both thermal and oxygenic conditions. Selection is driven by tolerance ranges and optima. Oxygenic conditions are as important as thermal conditions in body size selection within a species assemblage.

Density‐dependent modulation of copepod body size and temperature–size responses in a shelf sea

AbstractBody size is a fundamental trait in ecology, and body size reduction with increasing temperature has been termed the third universal response to climate warming. Although effects of temperature and food on phenotypic plasticity of zooplankton adult body size have been investigated, density‐dependent effects have been neglected. We measured seasonal changes in the prosome length of 7098 adult females of 7 dominant copepod species in 13 yr spanning a 27‐yr period of warming at the L4 time series off Plymouth, UK. The seasonal temperature–size (T–S) response varied greatly among species, from reductions of 2.93% of carbon mass °C−1 for Paracalanus parvus to 10.15% of carbon mass °C−1 for Temora longicornis. Evidence for a long‐term T–S response was detected in at least two species, supporting the hypothesis that climatic warming leads to smaller adult sizes. April was a crucial month for determining the strength of the T–S response. During this month, body size related negatively to total zooplankton abundance. We suggest that the mechanism for this density dependence is via competition for food and/or intraguild predation, since spring was also the period when the ratio of food biomass to zooplankton biomass was at its lowest. Our study is among the first in situ demonstrations of density‐dependent effects on the body size of marine zooplankton and shows the need to consider the effect of top‐down as well as bottom‐up factors on body size in a warming climate.

Is Zooplankton Body Size an Indicator of Water Quality in (Sub)tropical Reservoirs in China?

Is Zooplankton Body Size an Indicator of Water Quality in (Sub)tropical Reservoirs in China?

Evaluating the Potential for Rearing Walleye in Lined Ponds Filled with Well Water

Walleye (Sander vitreus) fingerlings (30 to 35 mm) are commonly reared in ponds filled with surface (i.e., lake) water, but the use of ground (i.e., well) water would provide increased biosecurity. We assessed the potential for using well water to rear walleye by comparing plankton and water quality over 30 days between organically fertilized lined ponds that were filled with either unfiltered lake or well water. All ponds were inoculated with plankton that originated from Blue Dog Lake, filled by May 15, 2020, and remained fishless. Zooplankton density and body size were consistently reduced in well ponds suggesting that fry survival and growth would be reduced. Initially, well ponds exhibited higher ammonia-nitrogen and alkalinity, but lower pH owing to the inherent chemistry of the well water. Later, reduced ammonia-nitrogen combined with increased dissolved oxygen and pH suggest that decomposition of the organic fertilizer occurred slower in well ponds. A phytoplankton bloom was successfully initiated but was difficult to maintain despite consistently lower zooplankton density in well ponds. While the use of well water would enhance biosecurity, these data suggest that walleye fingerling production would be reduced relative to lined ponds filled with productive, lake water. Increasing organic fertilizer, supplementing with liquid 28N:0P:0K, and/or filling ponds earlier (e.g., 30 days) may provide a more favorable environment for walleye culture in lined ponds filled with well water.

Body size and stable isotope composition of zooplankton in the western tropical Atlantic

Abstract Size-based approaches are paramount tools for the study of marine food webs. Here, we investigated the relationship between zooplankton body size, stable isotope composition and trophic level (TL) along a large-scale onshore-offshore gradient in the western tropical Atlantic. Samples were obtained on the Brazilian continental shelf, slope and in oceanic waters (off Fernando de Noronha archipelago and Rocas Atoll) in September and October 2015. Zooplankton was sieved into five size fractions. Zooplankton was dominated by copepods, except for the largest (>2000 μm) size fraction, that showed a high biovolume of chaetognaths, decapods, and fish larvae. Maximum zooplankton abundance and biovolume was found at the continental slope. POM showed consistently lower δ13C than zooplankton, indicating a selective use of 13C-rich primary food sources by zooplankton. Particulate organic matter (POM) was more 13C-enriched in shelf areas (average: −22.8, −23.6 and − 24.3‰ at the shelf, slope and oceanic islands, respectively), probably due to the higher abundance of diatoms nearshore. POM had δ15N values between 2.5 and 6.9‰ (average: 4.0, 4.9 and 4.2‰ at the shelf, slope and oceanic islands, respectively). Zooplankton δ15N and TL increased with body size. The δ15N of the 200–500 μm size fraction was used as baseline for TL estimation. Oceanic areas (average baseline δ15N = 5.8‰ ± 0.52, n = 14) showed a higher baseline δ15N than the shelf (average = 3.9‰ ± 0.69, n = 9) and the slope areas (average = 3.1‰ ± 0.93, n = 9). In spite of differing baselines, the δ15N data produced a consistent pattern of log-linear increase in TL with increasing size, in all areas. The choice of input trophic enrichment factor (TEF) values only slightly changed the log10 (body size) vs TL slopes, but this choice had a considerable effect on the estimates of predator/prey size ratio (PPSR) and predator/prey mass ratio (PPMR). Using a TEF above 2.3 leads to unrealistic PPSR and PPMR estimates. Overall average slope was 0.59 ± 0.08 TL μm−1 with TEF = 2.3 and 0.42 ± 0.07 TL μm−1 with TEF = 3.2.

Predators drive community reorganization during experimental range shifts.

Increased global temperatures caused by climate change are causing species to shift their ranges and colonize new sites, creating novel assemblages that have historically not interacted. Species interactions play a central role in the response of ecosystems to climate change, but the role of trophic interactions in facilitating or preventing range expansions is largely unknown. The goal of our study was to understand how predators influence the ability of range-shifting prey to successfully establish in newly available habitat following climate warming. We hypothesized that fish predation facilitates the establishment of colonizing zooplankton populations, because fish preferentially consume larger species that would otherwise competitively exclude smaller-bodied colonists. We conducted a mesocosm experiment with zooplankton communities and their fish predators from lakes of the Sierra Nevada Mountains in California, USA. We tested the effect of fish predation on the establishment and persistence of a zooplankton community when introduced in the presence of higher- and lower-elevation communities at two experimental temperatures in field mesocosms. We found that predators reduce the abundance of larger-bodied residents from the alpine and facilitate the establishment of new lower-elevation species. In addition, fish predation and warming independently reduced the average body size of zooplankton by up to 30%. This reduction in body size offset the direct effect of warming-induced increases in population growth rates, leading to no net change in zooplankton biomass or trophic cascade strength. We found support for a shift to smaller species with climate change through two mechanisms: (a) the direct effects of warming on developmental rates and (b) size-selective predation that altered the identity of species' that could colonize new higher elevation habitat. Our results suggest that predators can amplify the rate of range shifts by consuming larger-bodied residents and facilitating the establishment of new species. However, the effects of climate warming were dampened by reducing the average body size of community members, leading to no net change in ecosystem function, despite higher growth rates. This work suggests that trophic interactions play a role in the reorganization of regional communities under climate warming.

Micro- and mesozooplankton successions in an Antarctic coastal environment during a warm year.

The rapid increase in atmospheric temperature detected in the last decades in the Western Antarctic Peninsula was accompanied by a strong glacier retreat and an increase in production of melting water, as well as changes in the sea-ice dynamic. The objective of this study was to analyze the succession of micro- and mesozooplankton during a warm annual cycle (December 2010-December 2011) in an Antarctic coastal environment (Potter Cove). The biomass of zooplankton body size classes was used to predict predator-prey size relationships (i.e., to test bottom-up/top-down control effects) using a Multiple Linear Regression Analysis. The micro- and mesozooplanktonic successions were graphically analyzed to detect the influence of environmental periods (defined by the degree of glacial melting, sea-ice freezing and sea-ice melting) on coupling/uncoupling planktonic biomass curves associated to possible predator-prey size relationship scenarios. At the beginning of the glacial melting, medium and large mesozooplankton (calanoid copepods, Euphausia superba, and Salpa thompsoni) exert a top-down control on Chl-a and microzooplankton. Stratification of the water column benefitted the availability of adequate food-size (Chl-a <20) for large microzooplankton (tintinnids) development observed during fall. High abundance of omnivores mesozooplankton (Oithona similis and furcilia of E. superba) during sea-ice freezing periods would be due to the presence of available heterotrophic food under or within the sea ice. Finally, the increase in microzooplankton abundance in the middle of spring, when sea-ice melting starts, corresponded to small and medium dinoflagellates and ciliates species, which were possibly part of the biota of sea ice. If glacier retreat continues and the duration and thickness of the sea ice layer fluctuates as predicted by climate models, our results predict a future scenario regarding the zooplankton succession in Antarctic coastal environments.

Long-term Variation Characteristics of Zooplankton Community Structure in Meiliang Bay, Lake Taihu

Zooplankton, as an important part of the water food chain, plays an important role in lake ecosystems. It is an important monitoring indicator for water bodies. However, due to the lack of long-term monitoring data of zooplankton community structure, there is a lack of understanding about its long-term characteristics. Based on monthly monitoring data from 1997 to 2017 of Meiliang Bay in Lake Taihu, the long-term trends of zooplankton community structure and its relation to the environment were examined. The results showed that the abundance and biomass of zooplankton in Meiliang Bay significantly decreased from 1997 to 2017 (P<0.05). In particular, the abundance and biomass of rotifer and copepod slowly declined, and the abundance of cladocerans fluctuated but its biomass presented a significant decreasing trend (P<0.05). The cladocerous biomass contributed the most to the zooplankton biomass in Meiliang Bay. The dominance of smaller cladocerans and copepods increased with decreasing rotifer density, significantly decreasing the average body size of zooplankton (P<0.05). This study indicated that zooplankton were becoming smaller, potentially weakening the top-down control on phytoplankton. In addition, zooplankton abundance and biomass showed an upward trend in spring and decreased in autumn and winter, and reached maximum values of 1406.70 ind.·L-1 and 25.64 mg·L-1, respectively, in September. In the summer, their changes were the opposite. Pearson correlation analysis showed that zooplankton community structure was significantly related to water physical characteristics (alkalinity, electrical conductivity, water depth, suspended substance, and water temperature), chlorophyll a, and nitrogen (P<0.05). This indicated that the eutrophication of Meiliang Bay in Lake Taihu had a significant impact on the community structure of zooplankton.

Temperature‐mediated changes in zooplankton body size: large scale temporal and spatial analysis

Climate warming has been linked with changes in the spatiotemporal distribution of species and the body size structure of ecological communities. Body size is a master trait underlying a host of physiological, ecological and evolutionary processes. However, the relative importance of environmental drivers and life history strategies on community body size structure across large spatial and temporal scales is poorly understood. We used detailed data of 83 copepod species, monitored over a 57‐year period across the North Atlantic, to test how sea surface temperature, thermal and day length seasonality relate to observed latitudinal‐size clines of the zooplankton community. The genus Calanus includes dominant taxa in the North Atlantic that overwinter at ocean depth. Thus we compared the copepod community size structure with and without Calanus species, to partition the influence of this life history strategy. The mean community body size of copepods was positively associated with latitude and negatively associated with temperature, suggesting that these communities follow Bergmann's rule. Including Calanus species strengthens these relationships due to their larger than average body sizes and high seasonal abundances, indicating that the latitudinal‐size cline may be adaptive. We suggest that seasonal food availability prevents high abundance of smaller‐sized copepods at higher latitudes, and that active vertical migration of dominant pelagic species can increase their survival rate over the resource‐poor seasons. These findings improve our understanding of the impacts that climate warming has on ecological communities, with potential consequences for trophic interactions and biogeochemical processes that are well known to be size dependent.

Responses of zooplankton body size and community trophic structure to temperature change in a subtropical reservoir.

Understanding the effects of global warming on trait variation and trophic structure is a crucial challenge in the 21st century. However, there is a lack of general patterns that can be used to predict trait variation and community trophic structure under the ongoing environmental change. We investigated the responses of body size and community trophic structure of zooplankton to climate related factors (e.g., temperature). Isotopic niche breadth was applied to investigate the community trophic structure across a 1‐year study from a subtropical reservoir (Tingxi Reservoir) in southeastern China. Body size and community isotopic niche breadth of zooplankton were larger during water mixing than stratification periods and correlated significantly with water temperature change along the time series. The contributions of intra‐ and intertaxonomic components to body size and community trophic structure variation showed significant relationships with the temperature change going from the mixing to stratification periods. Water temperature imposed direct effect on body size, while direct and indirect effect on the community trophic structure of zooplankton occurred through trophic redundancy along time series. Water temperature and community properties (e.g., body size, trophic redundancy, or trophic interaction) showed complex interactions and integrated to influence community trophic structure of zooplankton. Our results can expand the knowledge of how elevated temperature will alter individual trait and community trophic structure under future climate change.