白洋淀浮游动物生物多样性及水生态评价

为研究白洋淀浮游动物生物多样性和水生态状况,2012年6月和10月对浮游动物进行了采样调查。结果表明:白洋淀共鉴定出浮游动物37种,其中枝角类最多,占总数的51.4%;各监测站点浮游动物密度为2480~7580ind/L,平均密度4160 ind/L;生物量为0.46~1.81 mg/L,平均生物量1.24 mg/L。Margalef多样性指数为1.83~3.51。浮游动物损失指数表明,整个白洋淀地区浮游动物状况相对于历史数据均有不同程度变差。用浮游动物多样性指数评价水质状况,白洋淀处于中度污染水平;综合浮游动物生物量评价水体营养级别标准,考虑到富营养化指示物种的存在,综合评价白洋淀水体处于富营养状态。     

Zooplankton partitioning in a tropical alkaline–saline endorheic Lake Nakuru,Kenya: Spatial and temporal trends in relation to the environment

Spatial and temporal zooplankton variations were studied for 1 year in tropical alkaline–saline Lake Nakuru to determine how they partition in the habitat, relative to environmental variables. Monthly samples were collected at 10 sampling sites, with subsurface tows, using 33.5‐μm mesh plankton nets. Physicochemical parameters displayed clear seasonal variations associated with precipitation patterns. Nine species, belonging to two main zooplankton taxonomic groups (ciliates; rotifers), were identified in the samples. Brachionus dimidiatus dominated the samples, accounting for 80% of the total zooplankton abundance. Kruskall–Wallis tests indicated significant (P < 0.05) temporal and spatial variations among all taxonomic groups. Different zooplankton species displayed a clear succession throughout the year. The total abundance of the rotifers and ciliates peaked at sampling sites near inlets during the long rainy seasons, while those in the inshore sites displayed variable succession patterns. Spatiotemporal structure of the zooplankton assemblages, and its correlation with environmental variables, indicated each species displayed distinct niche‐based partitioning. The ciliates niche was associated with increasing soluble reactive phosphorus, total phosphorus and nitrite–nitrogen (NO₂–N) concentrations. Niche partitioning in rotifers was associated with nitrate–nitrogen (NO₃–N), conductivity and pH. These results indicate physical niche separation, even in a small, relatively homogenous lake among species of rotifers and ciliates, providing information from which future changes in their abundance and spatial distributions can be predicted, given continuous water quality changes.     

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

Lake 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 (F_2,69 = 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.     

Relationship of sediment influx to ostracode populations on the variably deforested Luiche and Mahale platform coasts of Lake Tanganyika,Tanzania

We investigated the hypothesis that ostracode populations are sensitive to variations in sediment discharge related to watershed differences at Lake Tanganyika. Many ostracode species are documented to be sensitive to high turbidity which increases during runoff from strong rainfall events and changes in ostracode populations can impact organisms higher in the food web. We compared surficial death assemblages of ostracodes around two sites with extensive shell beds, the highly deforested Luiche Platform area, heavily populated since the 20th Century, and the less deforested Mahale Platform area, with recent population increases, to understand the impacts of increasing sedimentation within and between sites. The study found that whereas the Mahale Platform area is less disturbed, the faunal differences between sites is not large. The data showed high species richness and abundance of ostracodes at 10–20 m depth at both sites, within shell bed zones, with no statistical difference in raw species richness between the sites. The Mahale Mountain area ostracode populations were however statistically more diverse (Shannon H) than at Luiche. We conducted a multi-response permutation procedure and found that the sites are statistically different, but with very small differences in species richness and ostracode abundance. Non-metric multidimensional scaling ordination of species assemblages shows that most samples overlap on both major axes. This study synthesized with ongoing research about shell bed communities in less disturbed regions of the lake will give insights into how conservation projects can be optimized to preserve the lake’s benthic ecosystem from the effects of deforestation.     

Ecological implications of artificial mixing and bottom-sediment removal for a shallow urban lake, Lake Sheldon, Colorado

This paper describes the results of the investigation of a shallow urban lake before, and a second year after, restoration to determine the effects of aeration and bottom‐sediment removal on the trophic state and environmental variables controlling the lake's phytoplankton, macrovertebrates and zooplankton compositions. The anthropogenic eutrophic process of the lake is characterized by increased nutrient concentrations from urban run‐off inputs. This addition triggers a chain of events that start with a massive increase in the growth of primary producers, as these are generally growth‐limited by nutrients in freshwater ecosystems. Although the lake was artificially mixed, nuisance cyanobacteria were dominant as primary producers the second year after restoration, during the summers of 2004 and 2005, until this population collapsed and were replaced by diatoms after periods of high winds, rainfall and a decreased temperature. The absence of macrophytes in the main basin because of the removal of bottom sediment had a major effect on macroinvertebrates and zooplankton. Daphnia sp. was the dominant zooplankton species before restoration, being replaced by Bosmina sp., possibly because of the lack of refuge by macrophytes. As an alternative, Bosmina sp. used the surface blooms of cyanobacteria in summer as refuge from grazing by planktivorous fish. The greatest disturbance on the macroinvertebrate community richness and evenness was the decline of scrapers and shredders, because of the lack of macrophytes after removal of the lake bottom sediment.     

Effect of Spatial Heterogeneity on Zooplankton Diversity: A Multi‐Scale Habitat Approximation in a Floodplain Lake

Environmental heterogeneity is an essential quality of ecosystems as it has important implications in community structure. Macrophytes are a main component of environmental heterogeneity in floodplain lakes, and their dynamics are highly influenced by water level changes. In this context, we analysed at different spatial scales the relationship among hydrological variations, environmental heterogeneity associated to macrophytes and zooplankton regional diversity (γ diversity) in a South American floodplain lake adjacent to the Paraná River, and we also compared the local zooplankton diversity (α diversity) among the different environments that comprised the lake heterogeneity. At very low waters, the environmental heterogeneity was reduced as the lake was mainly limited to open water areas with low zooplankton diversity. At high waters, the profuse vegetation development (emergent and free‐floating), in mixed or homogeneous patches, determined a higher lake environmental heterogeneity with enhanced regional zooplankton diversity; littoral species increased over limnetic ones. Zooplankton α diversity was higher in environments with free‐floating macrophytes than in those without these plants. The structural complexity in the water column provided by plant roots would be closely related to the enhanced diversity found under free‐floating mats. This study contributes to the knowledge on the effects of strong water level variations on environmental heterogeneity, which is strongly associated to macrophytes and on zooplankton diversity, and highlights the role of free‐floating plants as diversity hosts and ‘key structures’ in floodplain lakes. Copyright © 2013 John Wiley & Sons, Ltd.     

Contrasting zooplankton communities of two bays of the large,shallow, eutrophic Lake Taihu,China: Their relationship to environmental factors

Zooplankton are an important link in aquatic food webs of lakes serving as consumers of algae, bacteria, and other microorganisms and as prey for fish and invertebrates. Despite their importance, little is known about the structure of the zooplankton communities of subtropic, large, shallow, eutrophic freshwater lakes. Our investigation of zooplankton communities in Lake Taihu, a subtropic, shallow, eutrophic lake and the third largest lake in China provides new information on this subject. Zooplankton, phytoplankton, and water chemistry samples were collected monthly from July 2006 to June 2007 in Meiliang and Gonghu Bays of Lake Taihu. Thirty zooplankton species were identified in Meiliang Bay with small-bodied cladocerans Bosmina coregoni and Ceriodaphnia cornuta contributing 21% and 11%, respectively to total zooplankton abundance which averaged 459 ind/L. Thirty-five species were identified in Gonghu Bay with the rotifers Polyarthra trigla and Brachionus calyciflorus the dominant species, contributing 21% and 11% respectively to total zooplankton abundance which averaged 467 ind/L. Predation by lake anchovy (Coilia ectenes taihuensis) and ice fish (Neosalanx tangkahkeii taihuensis) likely accounted for the dominance of both bays by small-bodied species. Community structure and community patterns were correlated with differences in Microcystis blooms and organic matter levels (chemical oxygen demand) in the two bays. Based on canonical correspondence analyses dissolved total nitrogen, orthophosphate, Cyclotella and Pinnularia also contributed to variability in zooplankton community composition.     

Zooplankton dynamics in a Great Lakes connecting channel: Exploring the seasonal composition within the St. Clair-Detroit River System

The connecting channels linking the Laurentian Great Lakes provide important migration routes, spawning grounds, and nursery habitat for fish, but their role as conduits between lakes for zooplankton is less understood. To address this knowledge gap in the St. Clair–Detroit River System (SCDRS), a comprehensive survey of crustacean zooplankton was performed in both riverine and lacustrine habitats from spring to fall 2014, providing the first system-wide assessment of zooplankton in the SCDRS. Zooplankton density and biomass were greatest in northern reaches of the system (southern Lake Huron and the St. Clair River) and decreased downstream towards Lake Erie. The composition of zooplankton also changed moving downstream, transitioning from a community dominated by calanoid copepods, to more cyclopoids and cladocerans in the Detroit River, and to cladocerans dominant in western Lake Erie. Coincidentally, species richness increased as sampling progressed downstream, and we estimated that our single-year sampling regime identified ~88% of potential taxa. Other species assemblages have responded positively to recent water quality and habitat restoration efforts in the SCDRS, and this survey of the zooplankton community provides benchmark information necessary to assess its response to continued recovery. In addition, information regarding the lower trophic levels of the system is integral to understanding recruitment of ecologically and economically valuable fish species targeted for recovery in the SCDRS.     

Zooplankton sampling in large riverine systems: A gear comparison

Large river systems create challenges when sampling zooplankton. The dynamics of large rivers, spatial heterogeneity of biota, and behaviours of zooplankton can all contribute to large variation in estimation. The gear utilized for zooplankton collections may also be a factor, and there is not a well‐studied gear, nor industry standard, for collection in riverine systems. The lack of consistent sampling methods makes it difficult to compare zooplankton within and across systems. A standard method for zooplankton collection would be valuable for comparison among studies. To optimize zooplankton assessment in large river habitats, we tested how community estimations varied between four common zooplankton sampling devices across three river habitat types. We tested four gears: the Schindler–Patalas trap, integrated tube sampler, powered water pump, and horizontal tow net. Each device was used to collect samples in thalweg, channel border, and backwater river habitats within Pool 8 of the Upper Mississippi River in June, July, and August of 2017. Our results support that there are qualitative and quantitative differences in zooplankton estimates among gear in different habitats. The powered pump most often yielded highest abundances of total and individual zooplankton taxa allowing for more reliable community comparisons. With some modification, the pump is recommended as the most appropriate sampling gear when performing quantitative studies of zooplankton composition and abundance in large river habitats.     

Planktonic indicators of water quality: A case study in the Amacuzac River Basin (State of Morelos,Mexico)

Planktonic organisms are good indicators of water quality but are rarely used in Mexican riverine studies in spite of the high level of contamination in these lotic waters. In this study, we focused on the plankton of the river Amacuzac in Mexico and a large saline waterbody, Lake Tequisquitengo, which is located in the Amacuzac river basin. We collected samples at three sites in the River Amacuzac and one at Lake Tequisquitengo from May 2015 to March–April of 2016. We analysed the physicochemical variables, coliform bacteria, and biological oxygen demand levels. We also quantified phytoplankton and zooplankton. Our results indicate that the study sites are mesotrophic with high densities of diatoms and cyanobacteria. Among the zooplankton, the dominant organisms were rotifers. The constancy of planktonic taxa was high in the lake but low in the river. The Descy index ranged from 2.9 to 4.5 in the river and from 4.0 to 5.0 in the lake. The saprobic index shows that the system is β‐mesosaprobic. The species diversity was higher in the river than in the lake. Our study shows that plankton can efficiently be used to evaluate the water quality in rivers and lakes.     

Nearshore Community Characteristics Related to Shoreline Properties in the Great Lakes

Successful protection and restoration of Great Lakes nearshore ecosystems will likely rely on management of terrestrial resources along Great Lakes shorelines. However, relationships between biological communities and changing shoreline environmental properties are poorly understood. We sought to begin understanding the potential roles of shoreline geomorphological and land cover properties in structuring nearshore biological communities in the Laurentian Great Lakes. Despite high variability in densities (benthic macroinvertebrates and zooplankton) and catch per unit effort (CPUE, shallow water and nearshore fish) within and among lake areas, several biological community patterns emerged to suggest that nearshore aquatic communities respond to shoreline features via the influences of these features on nearshore substrate composition and stability. Benthic macroinvertebrate densities were not different between shoreline types, although they were generally lower at nearshore sites with less stable substrates. Shallow water fish CPUE and zooplankton densities were generally lower for nearshore areas adjacent to developed mid-bluff shorelines and sites characterized by less stable substrates. Larger fish CPUE appeared to be unresponsive to local shoreline and substrate properties of nearshore zones. The emergence of these patterns despite significant ecological differences among lake areas (e.g., productivity, community composition, etc.) suggests that shoreline development may have comparable influences on nearshore ecosystems throughout the Great Lakes, providing a terrestrialbased indicator of relative nearshore biological and ecological integrity.     

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

Zooplankton 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.     

Dreissena veligers in western Lake Superior – Inference from new low-density detection

The notion that Lake Superior proper is inhospitable to dreissenid mussel survival has been challenged by recent finds on shipwrecks and rocky reefs in the Apostle Islands region. Motivated by concerns surrounding these finds, we conducted an intensive sampling campaign of Apostle Islands waters in 2017 to understand Dreissena prevalence and distribution. The 100-site effort combined random and targeted sites and collected zooplankton, benthos, video, environmental DNA, and supporting water quality data. We did not find settled Dreissena in any video footage or benthos samples, and quantitative PCR applied to eDNA samples was negative for Dreissena. Dreissena veligers were found in almost half the zooplankton samples but at orders of magnitude lower densities than reported from other Laurentian Great Lakes. Veligers were most prevalent around the western islands and associated with shallower depths and slightly higher phosphorus and chlorophyll, but did not spatially match known (still very localized) settled Dreissena colonies. This is the first study to conduct veliger-targeted sampling in western Lake Superior and the first to report consistent detection of veligers there. We speculate that these Apostle Islands veligers are not a new locally-spawned component of the zooplankton community, but instead are transported from an established population in the St. Louis River estuary (~100 km away) by longshore currents; i.e., low-density propagule pressure that may have been present for years. Small-mesh zooplankton data collected along a gradient from the Apostle Islands to the St. Louis River estuary and enumerated with thorough veliger searching would help elucidate these alternatives.     

Effects of environmental factors on seasonal and spatial changes in surface zooplankton in Golden Horn Estuary (Istanbul,Turkey)

The abundance and spatial distribution of zooplankton at monthly intervals were studied in polluted Golden Horn Estuary (Istanbul, Turkey), from July 2006 to December 2007. Selected water quality parameters also were measured. The zooplankton community was characterized by the presence of freshwater, estuarine and marine species, with a total of 59 taxa. Rotifers were the most important fraction of the total zooplankton, comprising 36.52% of all the samples. The zooplankton exhibited seasonal patterns, with the highest abundance occurring in the summer (979 ind. L^?1) and the lowest in the spring (856 ind. L^?1). Rotifera was the most abundant group in the upper and middle estuary, whereas Copepoda usually reaches the maximum densities in the higher salinity waters in the lower estuary. The study results indicated that both the sampling time (seasons) and sampling sites jointly had significant effects on the zooplankton densities (manova P < 0.05), and horizontal patterns were related to electrical conductivity, water temperature, dissolved oxygen, suspended particulate matter, pH and chlorophyll a measured in the estuary.     

Underestimation of microzooplankton is a macro problem: One size fits all zooplankton sampling needs alterations

Microzooplankton (rotifers, copepod nauplii, and dreissenid veligers) are an important but overlooked part of zooplankton communities and aquatic food webs, particularly in the Great Lakes. Most studies that do include microzooplankton data are not describing the full picture due to inappropriate sampling methodology. We compared the traditional macrozooplankton sampling method (64-μm mesh plankton net) to a microzooplankton method using a 20-μm mesh screen in various habitats in Lake Michigan. The macrozooplankton method significantly underestimated total rotifer density by an order of magnitude, veliger density by nearly an order of magnitude, and copepod nauplii density by threefold. Combining macrozooplankton method estimates for cladocerans and copepods with estimates of rotifer, nauplii, and veligers from the microzooplankton method samples showed rotifers contributed 51% of total mean zooplankton biomass, refuting the past notion that rotifers contribute little to overall zooplankton biomass. Our study demonstrates that the traditional one-size fits all sampling approach used in the majority of zooplankton monitoring studies in the Great Lakes significantly underestimates microzooplankton abundance and its relative importance. Biassed information on Great Lakes zooplankton community composition has ramifications beyond a basic understanding of Great Lakes food webs. The lack of accurate data on microzooplankton abundance suggests that prey resources available to Asian carp in Lake Michigan have been greatly underestimated along with the likelihood these invasive species could become established. The dual sampling approach must become the norm rather than the exception for zooplankton research in the Great Lakes and other freshwater systems.     

A COMPARISON OF TWO ELECTROFISHING PROGRAMMES USED TO MONITOR FISH ON THE ILLINOIS RIVER,ILLINOIS, USA

The Illinois River Biological Station monitors fish communities in the Illinois River using two different electrofishing programmes, one using three‐phase alternating current [AC; The Long Term Illinois Fish Population Monitoring Program or long‐term electrofishing (LTEF)] and the other pulsed direct current [DC; The Long Term Resource Monitoring Program (LTRMP)]. In 2001, we replicated three‐phase AC sampling sites with pulsed‐DC electrofishing gear to test for differences between the two collection methods and programmes. Electrofishing runs at each site were standardized by length and time, with 48 samples collected for each gear. Our objective was to test for differences in fish catch rates using total catch, species richness, fish size ranges, and sample composition and structure. Total catch was significantly greater for LTRMP electrofishing (4368 total fish, mean = 91.0 fish per sample) compared with LTEF electrofishing (1423 total fish, mean = 29.6 fish per sample). Species richness also was significantly greater for LTRMP electrofishing (50 total species, mean = 12.9 species per site) compared with LTEF electrofishing (38 total species, mean = 7.9 species per site). Size ranges of fishes, composed of 100‐mm‐length groups, showed higher total catches for the LTRMP within all length groups. Although our analyses suggest that collections from the LTRMP were significantly greater in most instances, a consistent pattern of species composition between the two programmes was not evident. Our results suggest that caution must be taken when attempting to compare fish community composition and structure information between these programmes. Copyright © 2011 John Wiley & Sons, Ltd.     

Nearshore-offshore trends in Lake Superior phytoplankton

Changes in phytoplankton community composition and structure can have broad-scale ecosystem effects; however, drivers of species diversity in planktonic systems are not well understood. In lakes, a common but not thoroughly tested assumption is that shallow, nearshore waters are much more diverse and productive, and contribute considerably more material and energy to pelagic food webs than deeper waters farther offshore. Lake Superior is a large, cold, oligotrophic freshwater system which can provide insight into community organization under oligotrophic conditions. We used epilimnion and deep chlorophyll layer phytoplankton data from a lake-wide sampling program conducted in 2011 and 2016 to test whether assemblage composition, total algal biovolume, cell concentrations, diversity, and richness vary with depth. Although lake depth was an important factor in structuring assemblage composition, there were no clear nearshore-offshore gradients in cell density or biovolume despite the exposure of nearshore areas to higher concentrations of watershed-derived nutrients. Shannon diversity increased slightly with increasing depth, whereas richness was uncorrelated. Understanding of the nearshore-offshore patterns in phytoplankton community characteristics in the Great Lakes has implications for designing monitoring strategies and for considering how further changes in climate and nutrient deposition would affect the base of the food web.     

Distribution and Abundance of Zooplankton in the U.S. Waters of Lake St. Clair, 1973

Zooplankton were obtained in the U.S. waters of Lake St. Clair at 28 stations sampled monthly from July through September 1973. Distribution and abundance of zooplankton were compared with physicochemical data collected concurrently and with previous studies on Lake St. Clair zooplankton.Sixty five species of Rotifera were recorded. Brachionus angularis, Conochilus unicornis and Synchaeta stylata were the three most abundant species. Total rotifers, averaging 47.1 individuals per liter over the study period, were about 30 times more abundant than the micro-crustaceans. The Cladocera were represented by 28 species, while five species of cyclopoids, seven calanoids and four harpacticoids were recorded from the Copepoda. Bosmina longirostris was the predominant micro-crustacean.Spatial distribution of zooplankton was hypothesized to be primarily dependent on current patterns generated by prevailing winds. The Canadian portion of the lake has a persistent eddy structure which apparently allows build-up of nutrient levels encouraging high zooplankton biomass. The U.S. side, however, experiences more rapid flow-through of St. Clair River water which accounts for lower zooplankton abundance. Despite the fast flushing rate on the U.S. side, a localized patch of high zooplankton density and a community structure indicative of eutrophic situations was consistently observed off the Clinton River Cutoff Canal. This is presumably due to nutrient loading from the Clinton River watershed.     

Long-term patterns in Lake Champlain's zooplankton: 1992–2010

We examined patterns in Lake Champlain zooplankton abundance from 1992 to 2010 using summer data from five study sites. Rotifer abundance (#/m³) for many common taxa such as Polyarthra, Kellicottia, and Keratella declined lakewide in the mid-1990s which coincided with the invasion of zebra mussels (Dreissena polymorpha) into Lake Champlain. The only rotifer to increase in density following zebra mussel invasion was Conochilus which is a colonial species. Long-term shifts in copepod and cladoceran community composition can be attributed to the arrival of another invasive species in 2004–2005, the alewife (Alosa pseudoharengus). Our results support previous findings that alewife predation can impact larger bodied zooplankton within temperate lake systems. Following alewife invasion into Lake Champlain, body length of Leptodiaptomus and Daphnia retrocurva decreased to a size at or below known alewife feeding preferences. In addition, smaller bodied copepods (primarily Diacyclops thomasi) have increased in abundance since alewife invasion while juvenile copepods have declined. Our results suggest that post-alewife zooplankton patterns are most likely due to alewife size-selective feeding strategies. Observed long-term changes in zooplankton community structure have potential implications for the lake's food web dynamics, particularly recent declines in large bodied zooplankton which may release smaller plankton from top-down control.     

Results from the U.S. EPA's Biological Open Water Surveillance Program of the Laurentian Great Lakes: III. Crustacean Zooplankton

Open water zooplankton communities were sampled across all five Laurentian Great Lakes during spring and summer 1998. Spring communities were characterized by relatively low species numbers and densities. Crustacean communities in all lakes except Lake Ontario were dominated by diaptomid copepods in spring. During summer, both abundance and species richness increased, the latter owing largely to the appearance of populations of cladocerans. Crustacean communities in the upper lakes were dominated by diaptomid copepods, cyclopoid copepodites, and Daphnia galeata mendotae (codominant with Holopedium gibberum in Lake Superior), and showed a high degree of spatial homogeneity. Lake Erie supported a notably more species rich community, and also exhibited a high degree of spatial heterogeneity. Lake Ontario differed from the other lakes by its relative lack of calanoid copepods, being dominated instead by cyclopoid copepods, along with Bosmina and Daphnia. There was a clear distinction between community composition in the western and eastern portions of the lake, though the reasons for this are unclear.