Variations In Zooplankton Community Structure Research Articles

Joint seasonal dynamics of phytoplankton and zooplankton in the sub-Arctic White Sea

The seasonal succession of phytoplankton species composition and biomass plays a pivotal role in driving the seasonal variations in zooplankton community structure and biomass. Our study focused on the seasonal dynamics of planktonic communities in the Chupa Inlet (Kandalaksha Bay, White Sea) to determine if there are distinct complexes of phyto- and mesozooplankton species associated with different seasons, and whether these complexes are interconnected. Four seasonal groups of phyto- and zooplankton samples were revealed, each characterized by a specific composition of typical species. The winter and spring groups of phytoplankton and zooplankton corresponded to each other in their temporal span. Later in the year, this temporal correspondence was disrupted as early copepodite stages of Calanus glacialis dominated the community briefly in late spring, forming the basis of a separate seasonal group. From July until the end of the study period, warmer-water species constituted the community core, shaping the summer-autumn seasonal group. The role of smaller species in both phyto- and zooplankton communities increased during summer and autumn. The size structure and motility of the phytoplankton were found to significantly influence the seasonal succession of the zooplankton. This apparently contributes to better trophic coupling between phyto- and zooplankton throughout the seasonal cycle.

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

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

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.

Seasonal Changes in Zooplankton Community Structure and Distribution Pattern in the Yellow Sea, China

Changes in zooplankton community and distribution have significant influences on fishery resources due to their vital role in the marine food web. Seasonal variations in zooplankton community structure, abundance and biomass of major taxa and distribution pattern in the Yellow Sea, China were analyzed to obtain the current status of secondary production. A total of 73 taxa (mostly at the species level) were recorded with the highest species richness in summer and lowest in spring. The most abundant zooplankton species in all seasons were copepods Oithona similis, Paracalanus sp. and Calanus sinicus. The mean total zooplankton abundance was the highest in spring and followed a declining trend till winter. Cluster analysis identified two distinct zooplankton assemblages geographically found in the deep (> 50 m depth) and shallow regions. Zooplankton in the shallow region had higher abundance and species richness with the exception of winter season. Small copepods exhibited higher biomass in the shallow region but few abundance differences between the two domains. Large copepods (LC) and giant crustaceans (GC) usually had higher biomass in the deep region with the exceptions of LC in spring and GC in summer. Both the abundance and biomass of chaetognaths were significantly higher in the shallow region, where cnidarian abundance was also higher from spring to autumn. Water currents contributed to the transport of zooplankton between the two domains. The high abundance of copepods in the shallow region satisfied the requirements for the larval fish survival from spring to autumn. However, the high abundance of carnivorous zooplankton in summer–autumn may compete with larval fish for prey, and may directly feed on fish larvae.

Inter-annual and seasonal variations in zooplankton community structure in the Yellow Sea with possible influence of climatic variability

Inter-annual and seasonal variations in zooplankton community structure in the Yellow Sea, China were studied in relation to climatic events and local environment from 2014 to 2018. Three zooplankton assemblages were identified based on cluster analysis, which were associated with seasonal temperature changes. Group 1 composed spring stations with moderate water column temperatures. The spring zooplankton assemblage had the highest mean total abundance with crustaceans, including euphausiids, amphipods and copepods dominating samples. Stations in the basin area during summer–autumn and all stations in winter composed Group 2, with low bottom water temperatures being a prominent feature. Zooplankton assemblage of Group 2 mainly consisted of a mixture of low-temperature species and some tropical species that were transported into the region by the Yellow Sea Warm Current. Coastal stations with high water temperature during summer–autumn made up Group 3. Zooplankton was characterized as summer–autumn neritic assemblage with high jellyfish abundance. Some meroplankton and brackish water species, i.e. Labidocera euchaeta, were indicator species confirming the influence of the river discharge. Both PDO (from positive to negative) and ENSO (from negative to positive) reversed their signs in 2016/2017. The abundances of total zooplankton, Noctiluca scintillans, Calanus sinicus and small copepods were much higher in spring of 2017–2018 compared to spring 2015 due to the warmer conditions. In addition, zooplankton community of summer 2017 was characterized by high abundances of copepods and gelatinous zooplankton, Diphyes chamissonis and Doliolum denticulatum. This was influenced by a strong river runoff and warm current transport, and differed from 2014 and 2016 summers. Our results suggest that a regime shift occurred in 2016/2017, which was supported by sharp changes in physical settings as well as zooplankton community structure in the Yellow Sea. However, a longer time series is required to uncover detailed processes and response mechanisms of environmental conditions of the Yellow Sea to climate change.

Evaluation of spatial and temporal variations in zooplankton community structure with reference to water quality in Teluk Bahang Reservoir, Malaysia

The patterns of zooplankton community structural attributes were evaluated with reference to water quality in Teluk Bahang Reservoir, Penang, Malaysia over an annual cycle (March 2014–March 2015) and spatial gradients. Four sampling stations located at the lacustrine (Stations 1, 2 and 3) and riverine (Station 4) zones of the reservoir were designated to gather data. Samples were collected vertically at 5 m, 10 m and 15 m depth. Zooplankton samples were collected by filtering forty litres of lake water using plankton net with 30 µm mesh size. A total of 28 taxa from three major groups of zooplankton (Rotifera, Cladocera and Copepoda) were recorded. Pearson’s correlation showed that the abundance of zooplankton is directly correlated with most environmental variables including water transparency, temperature, dissolved oxygen, conductivity, total dissolved solids, pH, chlorophyll a, ammonium-nitrogen, nitrite-nitrogen and rainfall. In a similar vein, the Canonical Correspondence Analysis (CCA) also revealed that zooplankton abundances were influenced by the combined effects of water quality variables. This was further proven by the fact that the zooplankton diversity, when measured by Shannon-Weiner index, was low probably due to short water retention time and fluctuations in water levels. The results of this study indicated that the occurrence of zooplankton was characterised by the reservoir water conditions based on the value of species-environment correlations (0.66–0.84) in CCA analysis.

Damming interacts with the flood pulse to alter zooplankton communities in an Amazonian river

Abstract Flow modification of lotic ecosystems is one of the main threats to global freshwater biodiversity. Commonly, and in the river studied here, modification results from hydroelectric dam installation. We evaluated the impacts of damming on zooplankton communities in the Amazonian floodplain of the Madeira River (Porto Velho, Rondônia, Brazil) following construction in 2012 of the run‐of‐river dam of Jirau Hydroelectric Power Plant. Using data sampled between 2009 and 2015, we tested for discontinuities in zooplankton community composition attributable to damming and the naturally occurring flood pulse. The flood pulse remained the main predictor explaining variation in zooplankton community structure even with the installation of the dam on the Madeira River. Despite this, discontinuities for the entire zooplankton community and for the main compositional groups (testate amoebae, rotifers, cladocerans, and copepods) were detected in relation to the dam (pre‐/post‐dam periods), mainly in ebb and low water, and with weaker evidence of dam effects during flood and highwater hydrological periods. A multivariate regression tree explained 9.6% of the variation in zooplankton communities and identified four groups: (1) flood and high‐water periods; (2) low water post‐dam; (3) low water pre‐dam; and (4) ebb hydrological periods. The deviance in each multivariate regression tree node was attributable to variation in eight rotifer, three testate amoeba, and three copepod taxa. Our study demonstrates that the flood pulse, dam construction, and interaction between both of these factors affect zooplankton community structure in the Madeira River. While for many zooplankton community variables, effects occurred mainly during ebb and low‐water periods, some effects were also observed during high water and flood periods. We thus recommend the establishment of a permanent environmental monitoring programme during all hydrological periods in tropical floodplain rivers and the addition of sampling sites downstream from dams. Many rivers in the world are increasingly disrupted by multiple dams, yet little is known of their effects, especially for run‐of‐river dams. Our study identified short‐term impacts of only one run‐of‐river dam on zooplankton communities. More research is needed on the effects of multiple run‐of‐river dams on zooplankton and other biota, especially in tropical floodplain rivers, so that negative effects can be understood and ameliorated.

Spatial variations in zooplankton community structure along the Japanese coastline in the Japan Sea: influence of the coastal current

Abstract. This study evaluates spatial variations in zooplankton community structure and potential controlling factors along the Japanese coast under the influence of the coastal branch of the Tsushima Warm Current (CBTWC). Variations in the density of morphologically identified zooplankton in the surface layer in May were investigated for a 15-year period. The density of zooplankton (individuals per cubic meter) varied between sampling stations, but there was no consistent west–east trend. Instead, there were different zooplankton community structures in the west and east, with that in Toyama Bay particularly distinct: Corycaeus affinis and Calanus sinicus were dominant in the west and Oithona atlantica was dominant in Toyama Bay. Distance-based redundancy analysis (db-RDA) was used to characterize the variation in zooplankton community structure, and four axes (RD1–4) provided significant explanation. RD2–4 only explained < 4.8 % of variation in the zooplankton community and did not show significant spatial difference; however, RD1, which explained 89.9 % of variation, did vary spatially. Positive and negative species scores on RD1 represent warm- and cold-water species, respectively, and their variation was mainly explained by water column mean temperature, and it is considered to vary spatially with the CBTWC. The CBTWC intrusion to the cold Toyama Bay is weak and occasional due to the submarine canyon structure of the bay. Therefore, the varying bathymetric characteristics along the Japanese coast of the Japan Sea generate the spatial variation in zooplankton community structure, and dominance of warm-water species can be considered an indicator of the CBTWC.

Spatio-temporal variations in zooplankton community structure and water quality in a Chinese eutrophic river

To collect information about the community structure of zooplankton and to study how zooplankton respond to environmental conditions, zooplankton samples were collected from seven stations in a heavily polluted river (the Nanfei River, China). Samples were collected in March (spring) and June (summer) 2014, September (autumn) and December (winter) 2013. A total of 275 species of zooplankton belonging to 79 genera were identified, the total zooplankton abundance was 193 040 ind./L. Protozoa and rotifer comprised a high proportion of species number and abundance of zooplankton. The upper reaches had higher greater species number and lower abundance than those in middle and lower reaches, and at the entrance of Chaohu Lake. The species number and abundance of zooplankton were the highest in autumn, and the lowest in winter. The habitats of Nanfei River had high spatiotemporal heterogeneity, revealed by unweighted pair-group method using arithmetic averages (UPGMA) clustering analyses on environmental factors and detrended correspondence analysis (DCA) clustering analyses on zooplankton abundance. In addition, water quality of upper reaches was better than the middle and lower reaches, and the entrance; and better in autumn than in other three seasons in terms of species number, abundance, Shannon-Wiener index, and Pielou evenness index. Results of canonical correspondence analysis (CCA) indicate that the combination of water temperature, total phosphorus, total nitrogen, pH, chemical oxygen demanded, soluble phosphate, and conductance rate were responsible for the variations in zooplankton community structure. Results of the present study indicated that zooplankton communities of the Nanfei River had obvious spatial and temporal heterogeneity, and the environmental factors played an important role in the changes in zooplankton community in Nanfei River.

The vertical distribution and abundance of copepod nauplii and other micro- and mesozooplankton in the seasonal ice zone of Lützow-Holm Bay during austral summer 2009

The Antarctic seasonal ice zone (SIZ) is an ecologically important region of the Southern Ocean. However, the abundance and vertical distribution of micro- and mesozooplankton in this zone, in particular the contribution of nauplii of smaller copepod taxa, are poorly understood. We investigated the vertical distribution, abundance, and species composition of micro- and mesozooplankton in the SIZ of Lutzow-Holm Bay, East Antarctica, in January 2009. Zooplankton samples were collected using a 60-µm mesh closing net (appropriate to estimate the quantitative abundance of copepod nauplii) vertically hauled from three depth layers (0–100, 100–200, 200–500 m). Small calanoid copepods, Oithonidae, and Oncaeidae were dominant among the zooplankton communities in this region. Cluster analysis revealed that the communities were separated by depth into epipelagic (0–200 m) and mesopelagic (>200 m) groups. Distribution patterns in the 0- to 100-m layer changed at the sea ice edge, but showed no clear relationship with frontal structures. Nauplii of copepods including Oithona spp., Oncaea spp., and Calanoida were major contributors to total zooplankton abundance. The abundance of these nauplii in the surface layer was high in open water and the marginal ice zone but low in the pack ice zone where chlorophyll a concentrations were high. Low water temperature associated with sea ice, rather than food availability, may have caused the low copepod nauplii abundance observed in the surface layer within the pack ice zone. These findings provide valuable background information to monitor variations in zooplankton community structure in response to changing environmental conditions.

Changes in zooplankton community structure in Sanmen Bay, China

Seasonal variations in zooplankton abundance, biomass, species diversity and community structure were investigated in the Sanmen Bay, China. Samples were collected from 15 stations, on the seasonal basis, in April (spring), July (summer) and October 2005 (autumn) and January 2006 (winter), respectively. The results show that zooplankton species number, abundance and biomass varied widely and had distinct spatial heterogeneity in the Sanmen Bay. A total of 72 species of zooplankton belonging to 56 genera and 17 groups of pelagic larvae were identified. The zooplankton species richness was strongly related to salinity. Based on hierarchical cluster analysis, zooplankton in this study area were classified into three groups: coastal, neritic and pelagic groups, which corresponded to the upper, middle and lower portion of the Sanmen Bay, respectively. The coastal low-saline species were dominant in the study area. The zooplankton abundance and biomass reached a peak in summer, moderate in spring and autumn, and the lowest in winter. Zooplankton abundance decreased from the upper to lower portion of the bay in April, when the highest biomass occurred in the middle portion of the bay. There were the same spatial distribution patterns for the biomass and abundance in July, with the maximum in the middle of the bay. However, zooplankton abundance was the highest in the middle of the bay in October, when maximum biomass occurred near the lower of the bay. Zooplankton abundance and biomass were evenly distributed in the Sanmen Bay in January. Spatial and temporal variations in zooplankton and their relationship with environmental factors were also analyzed. The BIOENV results indicate that the combination of chlorophyll a (Chl-a), salinity, dissolved inorganic nitrogen (DIN), dissolved oxygen (DO) and silicate (SiO3) was responsible for the variations in zooplankton community structure in the Sanmen Bay. The environmental changes played an important role in changes in the zooplankton community structure in the Sanmen Bay.

Variations in zooplankton community structure and water quality conditions in three habitat types in northern Lake Victoria

AbstractLake Victoria is vulnerable to increasing eutrophication, which has become manifested in ecological changes not yet fully understood. From October 2009 to January 2010, the influence of water quality on zooplankton community structure in three habitats in northern Lake Victoria, including sewage lagoons at the lake shores, Napoleon Gulf (NG) and the interface between the lake and the Nile River (also known as Source of the Nile River), was examined. Selected physico‐chemical parameters (dissolved oxygen concentration; water temperature; electrical conductivity; water depth) were measured in‐situ, while water samples were collected for chlorophyll‐a determinations. Zooplankton was sampled with conical plankton net (mesh size 60 μm; 0.25‐m mouth diameter). The NG and Source of the River Nile (SN) sampling sites exhibited significantly higher species richness, relative to the Sewage Lagoons (SL) site (F2,69 = 68.533; P < 0.05). Higher mean densities and dry biomass of zooplankton was generally a characteristic of the SL site (8715 ± 3241 ind L−1; 1862 ± 451 μg L−1), compared to the NG (119 ± 24 ind L−1; 53 ± 8 μg L−1) and SN sites (151 ± 26 ind L−1; 58 ± 9 μg L−1). Copepoda constituted a high numerical composition of the zooplankton at the NG and SN sites (>90% for both sites), while Rotifera dominated the zooplankton community at the SL site (97%). The mean values (±SE) of soluble reactive phosphorus (4060.7 ± 776.6 μg L−1) and nitrate–nitrogen (2121.7 ± 355.5 μg L−1) were much higher for the SL site, compared with the SN (8.2 ± 1.1 μg L−1; 28.6 ± 5.3 μg L−1, respectively), and NG site (7.8 ± 0.8 μg L−1; 32.7 ± 5.4 μg L−1, respectively). This study indicated the nutrient‐rich conditions observed at the SL site suppress the zooplankton species diversity, but favour species‐specific abundance and biomass. These study results indicate the zooplankton community structure can be used as a biological indicator of water quality in the Lake Victoria region.

Estuarine mesozooplankton dynamics on a short-term time scale: role of semidiurnal tidal cycle

Wageningen University Hydrology and Quantitative Water Management, Environmental Sciences Group (Atlas, Droevendaalsesteeg 4, 6708 PB, Wageningen, The Netherlands) Descriptors: Mesozooplankton, Acartia tonsa , Tidal variability, Estuaries, Argentina. Descritores: Mesozooplancton, Acartia tonsa , Ciclo de marea, Estuario, Argentina. In estuaries and coastal areas, planktonic organisms are subject to tidal, diurnal and seasonal environmental changes (MARQUES et al., 2009). Knowledge of the variability of zooplankton communities on different spatial and temporal scales is a prerequisite for the understanding of ecosystem dynamics. Tidal currents and estuarine circulation are well known phenomena that contribute to both vertical and horizontal redistribution of planktonic organisms (MORGADO et al., 2003. Moreover, biological mechanisms may also account for a significant part of the temporal variation in zooplankton community structure (MARQUES et al., 2009). Planktonic communities have presumably developed adaptations in order to compensate for or resist dispersive losses (LAM-HOAI et al., 2006), thus resulting in recurrent patterns of zooplankton distribution. The Bahia Blanca Estuary constitutes a mesotidal system with a semidiurnal tidal cycle, the tides being one of the most important sources of energy (PERILLO; PICCOLO, 1991). The temporal and spatial dynamics of the mesozooplankton in this estuary have been extensively investigated (e.g. HOFFMEYER 2004; HOFFMEYER et al., 2008) but none of these studies has considered the short-term variability associated with tidal cycles. The objectives of the present study were to describe the influence of the tidal cycle on mesozooplankton variability and to compare the mesozooplankton distribution of two zones in the main channel of the estuary: its northern margin and the deeper central zone. The Bahia Blanca Estuary is a coastal plain system (38°45´S; 62°22´W) on the Atlantic coast of Argentina (Fig. 1). It is formed by several NW to SE tidal channels separated by extensive intertidal flats, low marshes and islands (PICCOLO; PERILLO, 1990). The tides and winds have been considered the main factors controlling the water turbulence processes (PICCOLO; PERILLO, 1990), especially in the inner zone where the tidal height is maximal (tidal range of up to 3.6 m). Tidal currents are reversible with maximum surface velocities of about 1.3 m s

Inter-annual variation in summer zooplankton community structure in Prydz Bay, Antarctica, from 1999 to 2006

Inter-annual variations in zooplankton community structure in Prydz Bay were investigated using multivariate analysis based on samples collected with a 330-μm mesh, 0.5-m2 Norpac net during the austral summer from 1999 to 2006. Two distinct communities, an oceanic and a neritic community, were consistently identified in all surveys. Oceanic communities had higher diversity and were indicated by species such as Haloptilus ocellatus, Heterorhabdus austrinus, Thysanoessa macrura, Rhincalanus gigas, Scolecithricella minor and Oikopleura sp.. Neritic communities were indicated by Euphausia crystallorophias and Stephos longipes and were characterized by fewer but more abundant species. In 1999 and 2006, a transitional community was also distinguished near the continental shelf edge, where ice coverage was more extensive than either the oceanic or neritic regions. Significant inter-annual variations in community structure (mainly involving species abundance rather than species composition) were found in both oceanic and neritic communities, being more obvious in the latter. The timing and amplitude of sea ice retreat (polynya appearance), and its effect on food availability, had strong influences on zooplankton community structure. In oceanic communities during years with earlier ice retreat, the extra time available for phytoplankton blooms to accumulate resulted in a higher proportion of large copepods (Calanoides acutus, Calanus propinquus, Metridia gerlachei) (especially the younger copepodites) in the zooplankton assemblage. In neritic communities, zooplankton such as the ice krill E. crystallorophias, and large copepods (C. acutus, C. propinquus, M. gerlachei), also showed higher abundance and earlier developmental stages in years with larger polynya. On the other hand, in years with later ice retreat, smaller polynya, and less time for phytoplankton blooms to form, the abundance of large copepods was lower and older age classes were more common.

Spatial variation in zooplankton community structure is related to hydrologic flow units in the Missouri river, USA

AbstractZooplankton are a vital link in the food webs of large rivers, and their communities are shaped by both local environmental features and advection. In the Missouri River, flow characteristics naturally change along its length, but human modifications to facilitate commercial transport have altered natural flow in many sections of the river. We evaluated the effect of flow on zooplankton community structure at multiple spatial scales, and used multivariate analyses to evaluate the relative importance of flow and local abiotic environment on these communities. During July–September 2005, zooplankton samples and physico‐chemical measures were collected from the Missouri River main channel at 78 sites over a 2831 km range (Montana to Missouri). We identified a total of 30 cladoceran species, 22 copepod species and 27 rotifer genera, and we detected highly significant differences in zooplankton community structure among hydrologically distinct flow units and larger spatial zones. At the local scale, crustacean zooplankton and rotifers responded differently in the analyses. For copepods and cladocerans, distance from the nearest upstream reservoir explained more of the overall community pattern of the river than any other combination of environmental factors, reflecting the influence of dams on the zooplankton community of the Missouri River. For rotifers, a combination of flow characteristics due to impoundment and channelization and local environment (temperature) was important. Our study indicates that, because of the overwhelming effect of flow on zooplankton communities, hydrology must first be taken into account before zooplankton can be used as bioindicators of other environmental stresses. Copyright © 2009 John Wiley & Sons, Ltd.

Invasibility of plankton food webs along a trophic state gradient

Biological invasions are becoming more common, yet the majority of introduced exotic species fail to establish viable populations in new environments. Current ecological research suggests that invasion success may be determined by properties of the native ecosystem, such as the supply rate of limiting nutrients (i.e. trophic state). We examined how trophic state influences invasion success by introducing an exotic zooplankter, Daphnia lumholtzi into native plankton communities in a series of experimental mesocosms exposed to a strong nutrient gradient. We predicted that the attributes of nutrient‐enriched communities would increase the likelihood of a successful invasion attempt by D. lumholtzi. Contrary to our original predictions, we found that D. lumholtzi was often absent from mesocosms that developed under high nutrient supply rates. Instead, the presence of D. lumholtzi was associated with systems that had low nutrients, low zooplankton biomass, and high zooplankton species diversity. Using generalized estimating equations (GEE) and multivariate species data, we found that the presence–absence of D. lumholtzi could be explained by variations in zooplankton community structure, which was itself strongly influenced by nutrient supply rate. We argue that the apparent invasion success of D. lumholtzi was inhibited by the dominance of another cladoceran species, Chydorus sphaericus. These results suggest that the interaction between trophic state and species identity influenced the invasion success of introduced D. lumholtzi.

ZOOPLANKTON METACOMMUNITY STRUCTURE: REGIONAL VS. LOCAL PROCESSES IN HIGHLY INTERCONNECTED PONDS

Local communities can be structured by both local interactions (competition, predation, environmental variables, etc.) and by regional interactions (dispersal of individuals between habitats). Using data from a three-year study on 34 neighboring ponds in an interconnected pond system, we tested whether zooplankton communities show a metacommunity structure, how much variation in zooplankton community structure is related to local environmental factors vs. spatial configuration (taking into account the dispersal pathways), and what environmental variables are the locally structuring forces. In three different years, we found evidence for a metacommunity structure. We also found that spatial and environmental components act independently of each other due to the small geographic area and the high dispersal rates in this system. Despite these homogenizing forces, local environmental variables (associated with alternative equilibria in shallow lakes) were strongly related with zooplankton community structure ...

Distribution of the non-indigenous Cercopagis pengoi in the coastal waters of the eastern Gulf of Finland

Abstract We studied the distribution and population structure of the immigrant predaceous cladoceran species Cercopagis pengoi and its role in the zooplankton community during a 1-week cruise at the beginning of September 1997. Samples were collected at 20 stations within a coastal area of 500 km2 in the Gulf of Finland. Temperature above the thermocline was about 16–18°C. Phytoplankton was dominated by filamentous blue-green algae, metazooplankton by rotifers, cladocerans, cyclopoids, and calanoids. Ciliates (maximum density 2 × 105 L −1) were dominated by oligotrich ciliates and Mesodinium rubrum. The maximum density of different metazoan taxa varied from a few (Cercopagis) to a thousand (rotifers) per litre. Most of the Cercopagis population consisted of maturing parthenogenic females with a low percentage of males and gametogenic females. On the basis of population structure, we suggest that the population was still in the growth phase, parthenogenesis being the dominant reproduction strategy. Variation in zooplankton community structure and density was associated with differences in salinity, the stations nearest to the coast favouring cladocerans and cyclopoids. Rotifers and ciliates were most abundant at the eastern stations. Since density of Cercopagis was also highest at the eastern stations, this predator may have been an important factor in the structure of the zooplankton community. The potential effects of Cercopagis on the pelagic community structure and dynamics in the Gulf of Finland are discussed.

Seasonal and spatial variation in zooplankton community structure and their relation to possible controlling variables in Lake Okeechobee

1. Lake Okeechobee is a large (1732 km2), shallow (mean depth 2.7 m), eutrophic, subtropical lake located in southern Florida. Approximately 25% of the lake surface area is occupied by an extensive littoral zone. From August 1988 to June 1992, ≈ 2000 zooplankton samples were collected throughout the lake.2. During the study period, a severe drought lowered lake levels more than 1 m. At low and normal lake stage, the average lake‐wide abundance of rotifers (c. 2000 l–1) was greater than during high water periods (c. 1600 l–1). The average abundance of adult crustaceans (cladocerans and copepods) (c. 30 l–1) varied little regardless of lake stage.3. Although only minor differences were apparent when lake‐wide means in rotifers and adult crustaceans for each lake stage were compared, pronounced differences were evident in the distribution of zooplankton communities within Lake Okeechobee. During high and normal lake stage, both rotifer and adult crustacean populations were more uniformly distributed throughout the lake. At low lake stage, the densest zooplankton populations were concentrated in the transition area between the central lake and the littoral fringe. The abundance of all zooplankton groups was inversely correlated with lake stage, but the relationship was much stronger for rotifers than crustaceans. Both rotifer and crustacean zooplankton population densities were positively related to increased phytoplankton biomass (as measured by chlorophyll a) but the relationship was much stronger for rotifers than crustaceans.

Short-term temporal variation in coastal zooplankton communities: the relative importance of physical and biological mechanisms

Drogues were deployed off the coast of Northumberland (north-east England), as they were tracked zooplankton were collected, by four vertical hauls of a UNESCO WP-2 net (200 μm), adjacent to the drogue at hourly intervals Sampling covered a full tidal cycle, at least once each month from February to April, and in July and August 1993. Short-term changes in the community structure (in terms of species composition and abundance) were investigated with respect to the local wind field and tidal advection. It was observed, from a cluster analysis that during horizontal transport, the zooplankton maintained the same community structure for at least three consecutive hours on each sampling occasion [Pearson correlation (r) ≥0.70; P≤0.01] even during periods of high turbulent mixing, driven by wind stress Multiple regression models including parameters of the wind field and the rate of horizontal transport only accounted for a maximum of 52% of the temporal variation in zooplankton community structure. The unaccounted for variation provides the basis for the consideration of the zooplankton as ‘active drifters’ rather than ‘passive particles’, this is discussed.