Warming overcomes dispersal-limitation to promote non-native expansion in Lake Baikal

Non-native species and climate change pose serious threats to global biodiversity. However, the roles of climate, dispersal, and competition are difficult to disentangle in heterogeneous landscapes. We combine empirical data and theory to examine how these forces influence the spread of non-native species in Lake Baikal. We analyze the potential for Daphnia longispina to establish in Lake Baikal, potentially threatening an endemic, cryophillic copepod Epischurella baikalensis. We collected field samples to establish current community composition and compared them to model predictions informed by flow rates, present-day temperatures, and temperature projections. Our data and model agree that expansion is currently limited by dispersal. However, projected increases in temperature reverse this effect, allowing D. longispina to establish in Lake Baikal’s main basin. A strong negative impact emerges from the interaction between climate change and dispersal, outweighing their independent effects. Climate, dispersal, and competition have complex, interactive effects on expansion with important implications for global biodiversity.     

Current state of the sponge fauna (Porifera: Lubomirskiidae) of Lake Baikal: Sponge disease and the problem of conservation of diversity

The spatial distribution of healthy and diseased sponges in Lake Baikal was investigated. The endemic sponges were studied in May ? June 2015 at 11 transects within the depth range of 0 to 40 m. More than 500 sponge specimens were collected, and 29 taxa including 12 species and 17 morphospecies (sp. taxa) were identified. Among the 29 taxa, only B. martinsoni specimens and 14 morphospecies were healthy, whereas specimens of the other 11 species and 3 morphospecies were diseased, making up 35% of the total number of specimens (512). The different body forms of sponge found among the specimens were encrusting (66%), globulous (21%), and branched (13%). Sponges with necrosis signs, discolored specimens or covered with violet film or brown spots, were found in all transects under study (37 stations of 68). The percent cover of the bottom (per m²) by various body forms of sponges was evaluated with a sponge faunal state assessment test. Changes in the diversity and abundance of sponges due to their disease may jeopardize the functioning of the entire ecosystem of Lake Baikal which is a World Heritage Site. This baseline data on patterns of sponges, including their spatial distribution and percent cover, will be utilized to support future management and monitoring of Lake Baikal. Data on the current state of Baikal endemic sponge fauna are essential for understanding the causes and prognosis of disease processes of freshwater sponges.     

Measurement of Diporeia respiration rate for Lake Superior

The freshwater amphipod Diporeia is a dominant macroinvertebrate species in Lake Superior’s benthic community and an important prey item for many fish. A capacity to predict growth and production rates of Diporeia using a bioenergetics model requires information on physiological processes of the species. The objective of this study is to quantify oxygen consumption of Lake Superior Diporeia and to determine if respiration rate changes with body length. Diporeia were collected from Lake Superior and kept over natural sediment maintained at 4 °C. Dissolved oxygen levels for groups of immature (2 mm), juvenile (4 mm), and adult (6 mm) Diporeia in 20 ml microcosms were measured using a polarographic microelectrode. Mass-specific respiration rates for Lake Superior Diporeia ranged from 32.0 to 44.7 mg O₂ g DW^− 1 day ⁻¹. A significant relationship between body length and mass-specific respiration rate (p > 0.1) was not found. The estimate of Diporeia respiration presented here is significantly higher (p < 0.05) than previous findings from populations in Lakes Michigan and Ontario. This study provides new data on respiration rates of Lake Superior Diporeia and compares findings to studies for other connecting Great Lakes.     

Recent changes in the offshore crustacean zooplankton community of Lake Ontario

Crustacean zooplankton communities in the offshore of Lake Ontario have undergone substantial changes between 1997 and 2011. A shift was apparent in 2004 from an initial assemblage dominated by cyclopoid copepods (mostly Diacyclops thomasi), Daphnia retrocurva and bosminids, and with Cercopagis pengoi (which invaded the lake in 1998) the dominant predatory cladoceran, to one characterized by reduced numbers of cyclopoids, a more varied predatory cladoceran community, and increased biomass of calanoid copepods. These changes represented a shift from a community which has been relatively stable in the offshore of the lake for at least 40 years. A further change was seen in 2008, marked by increased biomass of Leptodiaptomus sicilis, Bythotrephes longimanus and Daphnia mendotae. Unlike the somewhat similar changes seen recently in the zooplankton communities of Lakes Huron and Michigan, the shifts in Lake Ontario have not been accompanied by a trend towards increased oligotrophy. A more likely explanation for the observed shifts in Lake Ontario is decreased vertebrate predation, likely due to alewife declines, and changes in the predatory invertebrate community.     

Ice–water heat exchange during ice growth in Lake Baikal

Using a custom-made thermistor chain frozen into the ice cover we obtained the first detailed information on distribution of temperature within ice and structure of the ice–water boundary layer during ice growth in Lake Baikal. A mathematical model of the heat transport in a multilayer ice–water system (Stefan problem) was developed and verified on results of in situ measurements. Effective coefficients of thermal diffusivity and ice–water heat fluxes were estimated from the inverse solution of the model and compared with direct flux estimates from the flux-gradient method. Both estimations agreed on flux values of 1–10 W m^− 2 and demonstrated strong synoptic variability in ice–water heat exchange. We estimated the thickness of viscous laminar sublayer under ice, as well as the thickness of the transitional layer on top of the turbulent water column. The thickness of the viscous sublayer of 1–1.5 cm in Lake Baikal was several times smaller than values reported previously from small lakes, suggesting high magnitudes of convective velocities and/or of the under-ice currents in Lake Baikal. Significant growth of the thermal diffusivity coefficient with increasing distance from the ice bottom was detected: its value at the top of the transition layer of under ice water was 10–40 times higher compared with its value in viscous laminar sublayer. This is also significantly higher than previous estimations in smaller freshwater lakes.     

Diets,population structure,and seasonal activity patterns of mudpuppies (Necturus maculosus) in an urban,Great Lakes coastal habitat

Freshwater species native to the Laurentian Great Lakes region face numerous environmental stressors, and the conservation status and ecological relationships of many remain poorly understood. One such species, the mudpuppy (Necturus maculosus), is declining, but better information on their natural history and development of more effective population monitoring techniques is needed. We assessed seasonal variation in capture success, biases in capture techniques, and feeding ecology of mudpuppies in Wolf Lake, a highly perturbed and urban former estuarine wetland complex to Lake Michigan. Trapping periods of ≥ 3 consecutive nights occurred from January to May 2015, and October 2015 to March 2016. Overall trapping success differed among trapping periods (p = 0.01) and declined precipitously at water temperatures above 14.1 °C (p < 0.001). Mudpuppies in traps (mean 26.9 ± 0.5 cm) were larger than those caught with hand nets (mean 14.7 ± 0.8 cm, p < 0.0001), suggesting that multiple methods may be needed to accurately assess demographics. Stomach contents obtained through gastric lavage included mollusks, leeches, insects, isopods, amphipods, crayfish, fish, a frog, and a juvenile conspecific. Invasive species, including rusty crayfish (Orconectes rusticus), round gobies (Neogobius melanostomus), and zebra/quagga mussels (Dreissena spp.) were present in guts, suggesting mudpuppy foraging has changed along with aquatic communities in the region. Prey community analyses revealed differences in overall diet among size classes of mudpuppies (p = 0.001), but relatively weak similarity within size classes. Results suggest that mudpuppies in lake ecosystems occupy a broad niche that changes as they grow.     

Modelling of nearshore microbial water quality at confluence of a local tributary in Lake St. Clair

Microbial water quality, measured as Escherichia coli (E. coli) concentration, at beaches along the southern shore of Lake St. Clair in Canada, often exceeds public safety guidelines. Belle River, located near a public beach and a drinking water intake, is one of the several smaller tributaries of the lake whose contribution to nearshore microbial water quality is currently unknown. A flexible mesh 3D coupled TUFLOW-FV and Aquatic Ecodynamic (AED2+) model was used to simulate the hydrodynamics and microbial water quality in Lake St. Clair. A higher resolution nested model was developed within the lake-wide TUFLOW-FV model for better spatial and temporal resolution in the local region surrounding Belle River. Regular and up to a factor of four difference in predicted E. coli concentrations were observed with the nested and lake-wide models at the public beach next to Belle River, whereas the difference was marginal at the drinking water intake about a kilometre away from the shore. While the E. coli loading to Lake St. Clair from Belle River is considered negligible, >90% of the predicted daily E. coli concentration at the beach and > 50 % at the water intake were attributed to Belle River from amongst all watershed sources to Lake St. Clair considered in the model. The model results also show that the construction of a new 150 m jetty in 2018, replacing the older 25 m jetty separating Belle River from the public beach, is expected to significantly reduce E. coli concentrations observed at the beach.     

Precision of Ages Determined from Scales and Opercles for Yellow Perch Perca flavescens

Scales and opercles were used to age yellow perch Perca flavescens collected in 1989 from Lake Madison (South Dakota), Dauphin Lake (Manitoba), and southern Lake Michigan (Indiana). Three readers aged fish from Lake Madison and Dauphin Lake once and two readers aged fish from Lake Michigan twice. The coefficient of variation (CV) was calculated to compare precision. Ages determined from opercles were as precise as those from scales for fish from Lake Madison (CV = 0 for both structures), and more precise than ages from scales for fish from Dauphin Lake (CV_opercle = 14.0, CV_scale = 27.4, p < 0.001) and Lake Michigan (CV _opercle = 10.6, CV_scale = 13.9, p < 0.001). The high precision of scale and opercle ages for yellow perch from Lake Madison can be attributed to the fast growth rate of fish from that lake and also that only age 1 and 2 fish were aged. The greater precision of opercle ages in comparison to scale ages for Dauphin Lake and Lake Michigan yellow perch can be attributed to ease of recognition of false annuli on opercles as well as to difficulty in distinguishing between false and true annuli crowded on the edge of scales from mature, slower growing fish. Because true annuli are more easily recognized on opercles, ages determined from opercles may be more accurate than ages determined from scales for yellow perch growing at slow or moderate rates.     

Energy Density of Three Fishes from Minnesota Waters of Lake Superior

Energy densities of three salmonine prey species in Lake Superior were determined by bomb calorimetry to examine seasonal trends, differences due to gender and to establish a relation with percent dry weight. These results from April through October for 1992 and 1993 were compared with other studies from the Great Lakes region. Across the 2-year sampling period rainbow smelt Osmerus mordax energy density decreased from April to June and July then significantly increased into September. Lake herring Coregonus artedii energy density was highest in June, decreased significantly by August, and remained stable through October. Bloater C. hoyi energy density was lowest in July, then increased in August and early September before decreasing in late September. There were no significant differences in energy density between males and females for rainbow smelt and lake herring collected on the same date across sampling dates. However, bloater energy density was significantly higher for females than for males on two dates. Energy density estimates for bloater in Lake Superior were lower than those reported from Lake Michigan. Energy density values of rainbow smelt and lake herring fell within the range reported in Lake Michigan and Lake Ontario (rainbow smelt), and from two inland lakes in Minnesota and Lake Mendota, Wisconsin (lake herring). Percent dry weight was a good predictor of energy density (P < 0.001, r² = 0.92–0.99) for all three species for both years. Percent dry weight vs energy density was significantly different between years for bloater and lake herring, and was significantly different for all three species compared with populations in other lakes in the Great Lakes Region.     

Rapid Increase and Subsequent Decline of Zebra and Quagga Mussels in Long Point Bay,Lake Erie: Possible Influence of Waterfowl Predation

Distribution and density of two introduced dreissenid species of mollusks, the zebra mussel Dreissena polymorpha and quagga mussel D. bugensis, were monitored in the Inner Bay at Long Point, Lake Erie, 1991–1995. Since populations of certain waterfowl species have been reported to alter their dietary intake and migration patterns in response to the ready availability of zebra mussels, the percent occurrence of zebra mussels in the diet of 12 duck species (552 birds) was studied concurrently, and several spring and fall aerial waterfowl surveys were flown between 1986 and 1997 (n = 75), to document changes in duck populations at Long Point. The first reproductive population of zebra mussels on the bay most likely appeared in 1990. After an initial rapid increase in density and colonization of the Inner Bay, zebra mussels began to steadily and consistently decline in absolute numbers, density per station and occupied area. Mean density per station in 1995 was 70% less than in 1991, the first year of rapid colonization, and 67% less than in 1992, the year of peak abundance in the bay (P < 0.05). Occupied area peaked in 1992, with 80% of sampling stations supporting mussels; the following 3 years showed consistent declines in the proportion of stations supporting mussels: 1993 = 75.9%, 1994 = 63.2% and 1995 = 57.1% (P < 0.05). Mussels in size class 0 to 5 mm were most abundant in 1991, 1993 and 1995, whereas those in size class 6 to 10 mm predominated in 1992 and 1994 (P < 0.05). Very few mussels over 15 mm were found. Lesser Scaup Aythya affinis (75.4 to 82.5 % occurrence), Greater Scaup A. marila (66.7 to 81.5 % occurrence), and Bufflehead Bucephala albeola (46.7 to 60 % occurrence) were the only three waterfowl species that consistently incorporated zebra mussels in their diet, and the mussel decline coincided with a substantial increase in the populations of these species at Long Point. Waterfowl days for Lesser and Greater Scaup combined increased rapidly from 38,500 in 1986 (prior to the zebra mussel colonization of Long Point) to 3.5 million in 1997 (P = 0.012). Bufflehead days increased from 4,700 to 67,000 during the same period (P = 0.001). Oligotrophication of Lake Erie, through reduced plankton and chlorophyll concentrations, has occurred since the invasion of zebra mussels, probably a result of filtering activities of introduced mussels. While a reduction in plankton availability may have contributed to the zebra mussel decline, high rates of waterfowl predation probably had the most substantial effect on mussel densities at Long Point. Waterfowl predation also probably influenced the size structure of the zebra mussel population, since waterfowl are size-selective foragers, and increased water clarity would have facilitated their ability to select preferred medium and large size classes of mussels. Quagga mussels, which were first detected in 1993, experienced a decline in both density and area occupied over the next two years. Quagga mussels rarely attached to soft substrates, and their decline is possibly related to the decline of suitable hard substrates, such as zebra mussels, as well as to predation by waterfowl.     

Smelt (Osmerus eperlanus): Glacial relict,planktivore, predator,competitor, and key prey for the endangered Arctic char in Lake Vättern,southern Sweden

Smelts are crucial forage prey for many piscivorous fish species and have, as such, been frequently introduced outside their indigenous ranges, a management measure causing controversy, as smelts are also efficient predators and competitors. In Lake Vättern, relict Arctic char, fourhorn sculpin, smelt and seven species of crustaceans form a deep-water food-web, and interact closely as competitors, predators and prey. Here, we analyzed new and archived data back to the late 1960s in order to understand and relate observed life-history shifts in the smelt population, to concurrent adverse life-history changes observed in the endangered Arctic char population. Smelt growth was sigmoidal and the size frequency distribution dominated by fish up to 110 mm and age 0–4, although smelt occasionally reached 250 mm. Smelt diet shifts as the fish grow, from zooplankton, to Mysis relicta, to piscivory for individuals larger than 150 mm. Recruitment commonly demonstrates regular inter-annual pulses of YOY abundance although strong year classes produced during years with higher spring temperature cause post-annual irregularity of year class strength. Young smelt reside in surface water and older fish in deeper water. This ontogenetic shift in distribution depends on temperature occupied, prey availability and risk of inter- and intra-specific predation. Interestingly, even though very small Arctic char feed on smelt, most small Arctic char are found in deep water together with large smelt, and most large Arctic char are found in shallow water with small smelt.     

Lake Herring (Coregonus artedi) and Rainbow Smelt (Osmerus mordax) Diets in Western Lake Superior

We describe the diets of lake herring (Coregonus artedi) and rainbow smelt (Osmerus mordax) in western Lake Superior during the summers of 1996 and 1997. Both species consumed predominantly (> 71% by number) zooplankton, showing a preference for larger taxa. Diet overlap between the two species was low (Schoener's index = 0.42). Mysis was most important in rainbow smelt diets, whereas Diaptomus sicilis was most important in lake herring diets. Rainbow smelt selected larger taxa, and larger individuals within a taxon when compared to lake herring, although rainbow smelt tended to be smaller fish. Fish diets have changed relative to previous studies and may be reflecting changes in the zooplankton community. Continued changes in the fish and zooplankton community will alter predatorprey and energetic pathways, ultimately affecting growth and production of the ecosystem.     

Food of Trout and Salmon in Lake Ontario

Stomachs of trout and salmon (n = 1,904) were collected from fish registered at fishing tournaments held in New York State waters of Lake Ontario between April and September 1983 and 1984. Numbers of adult-sized fish containing identifiable food items were 323 lake trout (Salvelinus namaycush), 289 brown trout (Salmo trutta), 24 rainbow trout (S. gairdneri), 164 coho salmon (Oncorhynchus kisutch), and 63 chinook salmon (O. tschawytscha) Proportional similarity in diet between pairs of species was high and normally exceeded 0.70; diet composition of individual species was similar between years. Alewives (Alosa pseudoharengus) were the main prey of all species during all months and were normally 110–149 mm in standard length. Rainbow smelt (Osmerus mordax) was the second most common prey eaten but was generally found in fewer than 20% of the stomachs examined during any month. Diet diversity was generally higher during April-May than during July-September for coho salmon, lake trout, and brown trout. Larger brown trout ate larger alewife in 1983 but not in 1984. Results suggest that the five trout and salmon species in Lake Ontario are potential competitors.     

Benthic Macroinvertebrates as Indicators of Environmental Degradation in the Southern Nearshore Zone of the Central Basin of Lake Erie

The benthic macroinvertebrates of the central basin of Lake Erie were sampled with a Ponar grab in the summers of 1978 and 1979 along a 155-km reach of the nearshore zone (≤ 12 km offshore) in Ohio, U.S.A., at depths of less than 20 m. The major groups and their most abundant species were, in order of overall abundance, Oligochaeta (Limnodrilus hoffmeisteri, L. cervix-L. claparedeianus group, L. maumeensis), Sphaeriidae (Pisidium casertanum, P. henslowanum, Sphaerium corneum, Musculium transversum), and Chironomidae (Procladius sp., Chironomus spp.). The average abundance of oligochaetes in the harbors was 21,000 individuals m^?2 in 1978 and 12,700 m^?2 in 1979, compared with 1,500 m^?2 and 1,200 m^?2, respectively, in the areas outside of harbors. Comparison of the macrobenthic assemblages with those in other regions of the Great Lakes, using several numerical indices as well as indicator species distributions, indicated that the general area of the nearshore zone outside of harbors possesses a moderate degree of organic enrichment, with a gradient of decreasing pollution in an offshore direction. The harbors appeared to be severely degraded, as reflected by the high densities of oligochaetes and the almost complete absence of all but the most pollution-tolerant species. The documentation of species distributions will enable future assessments of changes in the nearshore benthic communities.     

Temporal trends of phytoplankton and zooplankton stable isotope composition in tropical Lake Malawi

Stable isotope ratios of three seston size classes (20–100 μm, 2–20 μm, and 0.2–2 μm) and zooplankton species were analyzed to determine the plankton food web structure of Lake Malawi. Over an annual cycle, seston δ¹³C varied between ?20.41‰ and ?27.43‰ with a mean value of ?24.27‰ ± 1.2 while δ¹³C values for zooplankton fluctuated between ?22‰ and ?25‰ with a mean of ?23.84‰ ± 0.77. Seston δ¹³C fluctuations appeared to be related to changes in physical and meteorological conditions in the lake that ultimately control nutrient availability. The highest seston δ¹³C values observed during the rainy and mixed seasons likely result from high phytolankton growth rates. δ¹⁵N of plankton was temporally variable, suggesting short term changes in N cycling dynamics that control the supply of N to phytoplankton. Very low seston δ¹⁵N values recorded during the mixing season suggest excess NO₃^? availability resulting from upwelling and vertical mixing. In contrast to expectations the calanoid Tropodiaptomus cunningtoni appeared to feed at a trophic level higher than that of all other zooplankton species, including the cyclopoid, Mesocyclops aequatorialis aequatorialis. δ¹⁵N values indicate that zooplankton were nearly 2 trophic levels above seston in the early stratified season. This implies that adult zooplankton could be utilizing forms of food other than phytoplankton during this period, such as nauplii or protozoans. This extra step in the food web, and the trophic positions of large zooplankton species, may alter estimates of food web efficiency and potential fish production for Lake Malawi.     

A socioeconomic analysis of habitat restoration in the Muskegon Lake area of concern

As part of the 2009 American Recovery and Reinvestment Act (ARRA), a $10 million grant was awarded to restore wetlands and stabilize shoreline along the south shore of Muskegon Lake (MI), a Great Lakes Area of Concern. A socioeconomic analysis was conducted as part of this award, which included a travel cost survey for lake recreation and a hedonic housing valuation to estimate return on investment. The value of a trip to Muskegon Lake was estimated to be $39.76; when applied to the anticipated increase in post-restoration recreational trips to Muskegon Lake, and using a conservative 7% discount rate, the Net Present Value over 20 years is $38.1 million. The hedonic analysis examined values for houses between 100 and 800 m from the shoreline, using both the current shoreline distances and the new shoreline distances after restoration; this resulted in a predicted $11.9 million in additional housing value as a result of the improved shoreline features. Summing the hedonic value and travel cost estimates, along with the original $10 million spent, the result is that over 20 years, the total value generated for the local region is nearly six times the initial ARRA spending. In other words, of the $60 million of value created on the Muskegon Lake restoration, $50 million is increased environmental value over the 20 year period.     

Stable Carbon and Oxygen Isotope Records From Lake Erie Sediment Cores: Mollusc Aragonite 4600 BP–200 BP

We present the first δ¹⁸O and δ¹³C data from mollusc aragonite from Lake Erie for the 4.6–0.2 ka (4600 BP to 200 BP ¹⁴C yrs) time interval and describe single and composite species isotope trends. Composite species δ¹⁸O data show an almost 2.0%o increase from 3.3 to 3.0 ka followed by a nearly 2.5%o decrease at 2.8 ka. Oxygen isotope values then fluctuate by < l‰ until 0.2 ka. This trend in oxygen values is also evident in single species analyses of Sphaerium striatinurn. The most dramatic changes in isotope values, which occur from 3.3–2.8 ka, may reflect a pattern of water level changes in Lake Erie which occurred during the Nipissing flood and its lower water aftermath. Carbon isotope data show progressively more ¹³C enriched values from 4.6 ka (averaging–6.5‰ PDB) to the present (–0.57‰). This trend may reflect the dilution of isotopically light CO₂ from the oxidation of organic matter due to rising lake levels. The short-term increase in δ¹⁸O values is coupled with a corresponding decrease in δ¹³C values. A similar pattern for Lake Erie prior to 10.5 ka was also associated with a lowering of water levels in the lake.     

Evidence of Natural Reproduction by Planted Lake Trout in Lake Michigan

Lake trout (Salvelinus namaycush) fry were captured in southeastern Lake Michigan for the first time since the species was reintroduced from hatchery stocks in 1965. Spawning apparently occurred in fall 1979 on newly placed limestone riprap covering recently constructed power plant intake and discharge pipelines. Eggs presumably hatched in late February–March, 1980, and 57 fry (22–43 mm total length) were collected April–June, 1980, and three fry (55–62 mm) were collected in August, 1980.     

Analysis of the correlations between environmental factors and rare cranes in the Poyang Lake region of China

Using survey data during 2001–2013 from a total of 38 lakes in the Poyang Lake region of China, we analyzed the inter-annual change in crane populations and the spatial distribution of crane species. Across the study sites, the total crane population was 6400 ± 2620 individuals during the period 2001–2013. Crane populations varied widely across the study sites: the largest crane population was observed on Bang Lake with an annual average of 2373, followed by Qi Lake, Dacha Lake, and Zhu Lake. The four main crane species, which were active on 50–80% of study lakes during the period of investigation, were G. leucogeranus, G. monacha, G. vipio, and G. grus. In particular, G. leucogeranus, G. monacha, and G. vipio were observed mainly in Poyang Lake National Nature Reserve and nearby lakes. G. grus was mostly observed in Poyang County. The largest populations of G. leucogeranus, G. vipio, and G. monacha were observed on Bang Lake, with annual averages of 1229, 985, and 88 birds, respectively. The largest G. grus population was observed on Qi Lake, with an annual average of 756 birds. We found that habitats for G. leucogeranus, G. monacha, and G. vipio were defined by similar environmental factors. In particular, increasing distance from roads had a positive impact on populations of these three species. By contrast, sedimentary total phosphorus content showed negative correlations with populations of all four main crane species, which implied that eutrophication could pose a threat to these rare crane species.     

Ecological Significance of Upwelling Events in Lake Ontario

Upwelling events in Lake Ontario were studied to determine (1) their significance as mechanisms to provide nutrients from the hypolimnion to the epilimnion and (2) their impact on resident plankton communities of the nearshore zone. It was concluded that such events did not result in sufficient mixing to recharge nutrient stocks of these areas. Upwellings were characterized as being temporal displacements of nearshore water masses which returned at the end of each event. Plankton communities of the nearshore area were displaced with the water mass and therefore received little or no benefit from the upwelled nutrient rich hypolimnetic waters. Evidence is provided to suggest that diatom species such as Asterionella formosa Hass and Fragilaria crotonensis Kitton were able to grow in the upwelled hypolimnetic water, and upwellings might be a mechanism to inoculate these species into the epilimnion of deep lakes prior to the autumn overturn. Upwelling events also caused rapid shifts in the species composition of zooplankton communities. Such shifts were particularly pronounced within 1 km of the shoreline.