Status and Trends of Benthic Populations in a Coastal Drowned River Mouth Lake of Lake Michigan

Muskegon Lake was designated an Area of Concern because of severe environmental impairments from direct discharge of industrial and municipal wastes. Since diversion of all municipal and industrial wastewater in 1973, few studies have assessed ecological changes associated with improved water quality. We examined distributions and long-term changes in the benthic macroinvertebrate community at 27 sites. Distributions were evaluated relative to distance from the river mouth, water depth, grain size, and known areas of sediment contamination. Temporal changes were assessed relative to wastewater diversion. Oligochaeta and Chironomidae dominated the community, and the oligochaete trophic condition index indicated that, in 1999, the lake was generally mesotrophic to eutrophic. Cluster analysis resulted in four distinct site groupings. A cluster of sites near the river mouth had the highest total density (9,375 m⁻²) and lowest diversity (Shannon Weaver Index 1.05) suggesting an enriched habitat. A site cluster in the south central region had the lowest oligochaete density (2,782 m⁻²), lowest oligochaete trophic condition index scores (1.00), and highest diversity (2.24), suggesting the best habitat. The chironomid community in this site cluster was dominated by predatory species, possibly resulting from high concentrations of heavy metals at some sites. Densities of all major taxonomic groups increased significantly between 1972 and 1999. Decreasing proportions of oligochaetes (0.85 to 0.68) and increasing diversity suggest improved environmental conditions over this period. Evidence suggests that changes in Muskegon Lake's benthic community were more a result of wastewater diversion than Dreissena invasion.     

Spatial and temporal trends in invertebrate communities of Great Lakes coastal wetlands,with emphasis on Saginaw Bay of Lake Huron

The shallow-sloping coastal bathymetry of Saginaw Bay (Lake Huron) supports broad fringing wetlands. Because benthic invertebrates form an important forage base for fish, wading birds, and waterfowl that utilize these habitats, understanding the drivers of invertebrate community structure has significant management implications. We used Great Lakes basin-wide data from 2002 to place Saginaw Bay wetland invertebrate communities and their environmental drivers into a basin-wide context. Various aspects of community structure were highly correlated with fetch and watershed agriculture across the basin. Saginaw Bay wetlands had relatively high fetch and watershed agriculture and supported unique invertebrate communities, typified by high abundances of many insect taxa. Wetlands from other regions around the basin tended to have more crustaceans and gastropods than the Saginaw Bay wetlands. A 1997–2012 time series from three representative Saginaw Bay wetlands revealed substantial shifts in community structure throughout the period, especially from 2001 through 2004. These years followed a 1-m decline in Lake Huron water levels that occurred between 1997 and 2000. Major community changes included decreasing insect abundance, especially chironomids, and increasing crustacean abundances, especially Hyalella azteca (Amphipoda). While factors in addition to water levels were likely also important, our time series analysis reveals the marked temporal dynamics of Saginaw Bay wetland invertebrate communities and suggests that water level decline may have influenced these communities substantially. Both the spatial and temporal community patterns that we found should be considered in future bio-assessments utilizing wetland invertebrates.     

Current Status and Trends in Muskegon Lake,Michigan

A long-term monitoring program was initiated in 2003 to determine the ecological status of Muskegon Lake, a Great Lakes Area of Concern. This paper presents data generated from the first 3 years of the monitoring program, discusses how the data are being used to establish and justify lake restoration targets, and assesses how water quality conditions have changed over time. Between 1972 and 2005, lake-wide averages of total phosphorus and soluble reactive phosphorus from the water surface have declined from 68 to 27 μg/L and from 20 to 5 μg/L, respectively. In addition, average chlorophyll a concentrations have declined from 25 to 6 μg/L over this period, while Secchi disk depths have increased from 1.5 to 2.2 m. Wastewater diversion, and perhaps dreissenid filtering activity, is most likely responsible for these changes. However, nitrate concentrations have increased from 70 to 270 μg/L over the same time period. During 2003–2005, phytoplankton abundance and fish catch were lower in the spring compared to the summer and fall. Microcystis was the most abundant phytoplankton genus; the fish community generally was dominated by round goby (Neogobius melanostomus) in spring and summer, and sunfishes (Centrarchidae) in the fall. Dreissenid abundance was highly variable over time, but densities were low relative to Saginaw Bay. Approximately 65% of the Muskegon Lake shoreline has been hardened (i.e., physically altered). Overall, the water quality of Muskegon Lake has improved over the past 30 years, but environmental challenges still exist, including contaminated sediments, loss of natural habitat, and invasive species.     

Temporal shifts in the biodiversity of nearshore small fishes in Lake Simcoe

Nearshore small fish species represent a large proportion of fish biodiversity in Lake Simcoe, a large inland lake in southern Ontario, Canada. Over the past 30 years, Lake Simcoe has experienced several changes to its aquatic habitat, benthic invertebrate communities and predatory fish populations. This study compared samples of the nearshore small fish community in three geographic areas of Lake Simcoe. Fish community data were grouped into two time periods: a contemporary period (2007–2009) and a historical period (1982–1995). The fish community was compared across time periods for each area to assess if observed ecological changes had an impact on the small fish community. Species richness significantly declined between time periods in two areas (Cook's Bay and the southeast shoreline), the number of individuals captured declined between time periods in one area of the lake (Kempenfelt Bay) and Simpson's diversity index declined between time periods in one area of the lake (southeast shoreline). There were no significant differences in the Shannon–Weiner evenness index between time periods in any of the study areas. Additional analyses of intra- and inter-annual variation in fish sampling results generally supported the findings that shifts in the fish community occurred between time periods. Overall, this study suggests that the nearshore small fish biodiversity of Lake Simcoe has shifted over time but these shifts are not clearly related to recent increases in water clarity, macrophyte growth and nearshore benthic invertebrate densities.     

Cold and wet: Diatoms dominate the phytoplankton community during a year of anomalous weather in a Great Lakes estuary

As sentinels of climate change and other anthropogenic forces, freshwater lakes are experiencing ecosystem disruptions at every level of the food web, beginning with the phytoplankton, a highly responsive group of organisms. Most studies regarding the effects of climate change on phytoplankton focus on a potential scenario in which temperatures continuously increase and droughts intersperse heavy precipitation events. Like much of the conterminous United States in 2019, the Muskegon River watershed (Michigan, USA) experienced record-breaking rainfall accompanied by unusually cool temperatures, affording an opportunity to explore how an alternate potential climate scenario may affect phytoplankton. We conducted biweekly sampling of environmental variables and phytoplankton in Muskegon Lake, a Great Lakes Area of Concern that connects to Lake Michigan. We compared environmental variables in 2019 to the previous eight years using long-term data from the Muskegon Lake Observatory buoy, and annual monitoring excursions provided historical phytoplankton data. Under cold and wet conditions, diatoms were the single dominant division throughout the entire growth season – an unprecedented scenario in Muskegon Lake. In 10 of the 13 biweekly sampling days in 2019, diatoms comprised over 75% of the phytoplankton community in the lake by count, indicating that the spring diatom bloom persisted through the fall. Additionally, phytoplankton seasonal succession and abundance patterns typically seen in this lake were absent. In a world experiencing reduced predictability, increased variability, and regional climate anomalies, studying periods of extreme weather events may offer insight into how natural systems will be affected and respond under future climate scenarios.     

东太湖不同人为干扰程度区域植物多样性研究

水产养殖等人为活动会影响水生植被群落结构、群落动态和生物多样性。为具体分析人为活动对水生植被群落的影响,2013~2014年,在东太湖人工干扰严重的网围养殖区和人工干扰较轻的非养殖区选取11个样点进行了8次实地采样分析。分析结果表明,东太湖现有双子叶植物16科21属23种,主要有3种植物群落类;在人为干扰严重的围栏养殖区域,植物多样性较轻度人为干扰的湖区有明显下降;但植物多样性在2010年退渔还湖后较2002~2008年有较为明显的提高。     

Lake Champlain offshore benthic invertebrate community before and after zebra mussel invasion

Benthic invertebrates are important bio-indicators of water quality and play a significant role in aquatic systems. Lake Champlain has limited benthic invertebrate data which hinders development of food web models, assessment of invasive species impacts, and evaluation of management actions. In June 2016, we assessed benthic invertebrates along three transects in the main basin of Lake Champlain ranging from 5 to 100?m, and then compared results to densities from a limited survey in 1991 prior to the zebra mussel (Dreissena polymorpha) invasion. In 2016, total biomass and density were 1–2 orders of magnitude greater at 5?m than at 20–100?m. Zebra mussels, chironomids, oligochaetes, and gastropods were dominant at 5?m, and oligochaetes and sphaeriids were dominant at 20–100?m. Total density at the 5-m site was 94% lower in 2016 compared to 1991, but similar at the 100-m site. Diporeia, while abundant in many freshwater bodies, is historically rare in Lake Champlain and was not detected in our sampling. Because Lake Champlain benthic invertebrate densities are low and display dissimilar distributions to the Great Lakes, we hypothesize the offshore fish community is likely much more reliant on pelagic rather than benthic production. Although the current composition and biomass suggest the benthic community in Lake Champlain may not be greatly impacted by an invasion of quagga mussel (D. rostriformis bugensis), the potential for quaggas to re-route energy from pelagic to benthic habitats, as it has in the Great Lakes, could limit the Lake Champlain offshore fish community.     

Contemporary genetic structure of walleye (Sander vitreus) reflects a historical inter-basin river diversion

River diversions can have unexpected biological consequences. In the mid-20th century, the upper Ogoki River in northern Ontario was diverted from its original Hudson Bay drainage to flow into the Great Lakes. Although walleye were present in both systems prior to the diversion, the Hudson Bay and Great Lakes watersheds had previously been separated since the early Holocene (7500–8500 years ago). We assessed the effects that this inter-basin diversion has had on the genetic structure of two formerly allopatric populations. We assessed the genetic structure and diversity of walleye in the Ogoki and Little Jackfish river systems and Lake Nipigon (number, distribution, and divergence of identified genetic groups) and quantified the contribution of fish from the historical population (Hudson Bay drainage Ogoki River) and Lake Nipigon to walleye in the Ogoki and Little Jackfish Rivers. Walleye from Ogoki Lake, the Ogoki River diversion through the Little Jackfish River, Lake Nipigon and Nipigon Bay were genotyped at 10 microsatellite loci. Significant genetic differences were detected among sampling locations: walleye from Ogoki Lake, presumably representing fish originally from the historical Ogoki River gene pool, were genetically similar to but statistically distinct from walleye within the diversion. Walleye from sample sites within the diversion and Ombabika Bay appear to form a single genetic group that is largely derived from the Ogoki watershed and differs significantly from walleye in Lake Nipigon and Nipigon Bay. Our findings confirm that the historical river diversion has had long-term effects on the genetic composition of contemporary walleye populations.     

Economic benefits of remediating the White Lake and Muskegon Lake Areas of Concern

This study uses hedonic modeling to estimate the property value benefits of remediation in the White Lake and Muskegon Lake, MI Areas of Concern (AOC). Both sites had long histories of industrial contamination; in the case of White Lake, this included tannery waste, and in the case of Muskegon Lake, this included oil spills. Several remediation projects in White Lake led to its delisting as an AOC in 2014. In contrast, remediation in Muskegon Lake is ongoing and this study focuses on the benefits of several projects that removed contaminated sediment and debris by 2018. Spatial Difference-in-Difference (DiD) approaches are used after Euclidean distance-based matching to estimate benefits, comparing housing price differences pre- and post-remediation between homes near the AOC (the treated group) and homes further away (the control group). Results reveal that without remediation homes near the White Lake AOC lose 12.4 percent of their value, with remediation mitigating losses to 4.5 percent. This implies a 64 percent recovery of housing values which amounts to $5.3 million in total benefits. Similarly, homes near the Muskegon Lake AOC lose 10.3 percent of their value with remediation reducing losses to 3.3 percent. This implies a 68 percent recovery of housing values and $11.2 million in total benefits. These findings reveal the property value benefits that can result from remediated AOCs.     

Changes in Lake Erie benthos over the last 50 years: Historical perspectives,current status,and main drivers

During the last 50 years the ecosystem of Lake Erie has experienced major environmental changes, from anthropogenic eutrophication in 1930–1960s, to nutrient and pollution abatement in the 1970s, and then the introduction of exotic dreissenids in the 1980s. We used multivariate statistical techniques to examine long-term changes in the zoobenthic community, comparing contemporary collections (2009, 2011–2012) and historical data (1963–1965, 1978–1979, 1993, and 1998). The Lake Erie benthic community underwent significant changes during each decade examined, showing signs of recovery following ecosystem restoration in the 1970s, but then experiencing major structural and functional changes after dreissenid (Dreissena polymorpha and D. r. bugensis) introductions. There was a significant temporal trend in community composition changes from 1963 to 2012, and the largest difference was found between pre- and post-dreissenid invasion communities. Currently the lake-wide benthic community is dominated by dreissenids both in density (41%) and total wet biomass (97%), followed by oligochaetes and chironomids. The largest benthic density was found in the central basin, and the greatest biomass in the eastern basin. The number of exotic species found in benthic surveys increased every decade, from 1 in 1963 to 10 in 2009–2012, and the majority of the invaders were molluscs. Whereas the role of benthic invaders in community diversity is still low, their impact has had enormous consequences for the whole ecosystem.     

The influence of environmental conditions and hydrologic connectivity on cyanobacteria assemblages in two drowned river mouth lakes

We evaluated the temporal and spatial variability of cyanotoxins, water chemistry, and cyanobacteria communities in two lakes of different trophic status. Bear Lake is a hypereutrophic system that flows into mesotrophic Muskegon Lake. Total microcystins (MC) in Bear Lake (mean, 1.66 μg/L) were composed of multiple structural analogs: 43% MC-LR, 50% MC-RR, and 7% MC-YR. Total microcystins in Muskegon Lake (mean, 0.52 μg/L) consisted of MC-LR (76%), MC-RR (14%), MC-YR (6%), and MC-LA (3%). The lakes were dominated by the cyanobacteria Microcystis spp., which accounted for 75% of phytoplankton biovolume in Bear Lake and > 90% in Muskegon Lake. Total microcystin concentration was positively correlated with cyanobacteria biovolume and turbidity (Muskegon Lake) and total phosphorus (Bear Lake), while negatively correlated with ammonia (Bear Lake) and nitrate (both lakes). The relationships between microcystins and environmental factors differed between lakes, despite hydrologic connectivity, suggesting that local conditions have a greater influence on toxin production than regional effects. Cylindrospermopsis raciborskii was found in both systems; however, the assemblage does not appear to be capable of producing cylindrospermopsin due to the absence of the PKS gene. Although the Bear Lake discharge appears to be the source of C. raciborskii, the physical/chemical properties of Muskegon Lake (lower turbidity and temperature, higher nitrate) may constrain the growth of this invasive species. Thus, local conditions in each lake are important in determining which species are capable of maintaining a viable population.     

Long-term dynamics of Lake Erie benthos: One lake,three distinct communities

Lake Erie has experienced multiple anthropogenic-driven changes in the past century, including cultural eutrophication, phosphorus abatement initiatives, and the introduction of invasive species. The benthos of Lake Erie has been studied infrequently over nine decades and can provide not only insights into the impact of environmental changes but can also be used to examine ecosystem recovery through time. We used multivariate analyses to examine temporal changes in community composition and to assess the major drivers of long-term changes in benthos. Eutrophication, water quality improvement, and dreissenid introduction were the major drivers of changes in benthos in the western basin, while hypoxia was a major factor in the central basin, and dreissenid introduction was most important in the eastern basin. Non-dreissenid community composition of the western basin has changed dramatically over 90 years from benthic species indicative of good water quality in the 1930s, with a diverse community dominated by Hexagenia, to one of low diversity dominated by oligochaetes and other pollution-tolerant species in the 1960s, followed by recovery in the early 2000s to a state similar to that reported in 1930. In contrast, the non-dreissenid benthic community of the central basin over 60 years was consistently dominated by low oxygen-tolerant taxa, signifying the persistence of hypoxia, the major community driver in this basin. The eastern basin community also changed dramatically, including the disappearance of Diporeia after the introduction of Dreissena in the 1990s and more recent declines in oligochaetes, amphipods, gastropods, sphaeriid clams, and leeches.     

白洋淀底栖动物群落影响因子研究

基于2016年春、夏、秋3季的调查采样,采用典范对应分析(canonical correspondence analysis,CCA)研究底栖动物群落结构和分布对水环境因子和底泥环境因子的响应,识别影响底栖动物群落分布的关键环境因子。CCA结果显示,水环境因子中透明度、叶绿素a、水深、水温、溶解氧、氨氮、硝氮和氧化还原电位是影响底栖动物分布的主要因子;底泥环境因子中底质中值粒径、沉水植物生物量和氨氮含量是影响底栖群落分布的主要因子。优势物种摇蚊科和颤蚓科对高污染物浓度环境适应性更好。水体中氮、磷对底栖动物影响显著,而底泥中氮、磷的影响较小,可以通过氮磷的吸附转移降低水体污染对底栖动物的胁迫。     

Drivers of revitalization in Great Lakes coastal communities

Sediment remediation and habitat restoration projects have been increasingly employed along the coast of the Great Lakes to improve environmental quality since the designation of 43 highly degraded Areas of Concern (AOCs) by the 1987 Great Lakes Water Quality Agreement between the U.S. and Canada. Improvements in water quality, habitat, and other environmental conditions can also support community wellbeing and revitalization; however, the mechanisms that support these connections are relatively unclear. We address this gap through a case study of three AOCs near Lake Michigan: 1) Grand Calumet River; 2) White Lake, and 3) Muskegon Lake. By analyzing secondary data and planning documents, we found that alongside environmental cleanup, anchor institutions, housing and economic development, and local events drive revitalization. Our research also illustrates that, rather than acting as discrete processes, environmental cleanup and revitalization drivers overlap in time and space. Finally, our research reveals a high level of variation within and across AOCs in terms of diverse socioeconomic contexts, planning capacities, and existing partnerships. Together, our findings point to the need for collaborative and inclusive planning processes that account for the heterogeneity present within and across AOCs to simultaneously support remediation, restoration, and revitalization and to sustain continued revitalization in AOC communities after delisting.     

The Nearshore Benthic Invertebrate Community of Southern Lake Michigan and its Response to Beach Nourishment

The nearshore benthic environment of Lake Michigan represents a dynamic and little studied habitat. To explore the biology and response of this community to beach nourishment, Ponar samples were taken at 1.5, 3, and 6 m depths at 10 transects along the southern shore of Lake Michigan before and after beach nourishment. Forty taxa were identified, and two of these, Chaetogaster diastrophus and Nematoda, made up over 81% of all organisms collected. Shallow sites (≤ 3 m) were generally dominated by C. diastrophus and Nematoda, and these sites represent communities adapted to constant wave induced sediment disturbance. Deep (6 m) sites were generally dominated by Nematoda, but fair numbers of C. diastrophus, Amphichaeta leydigi, Paracladopelma spp., and other less abundant taxa were identified. Greater diversity at deeper sites may be related to the stability resulting from reduced wave disturbance. A notable decrease in mean invertebrate density (P < 0.01) from 2001 to 2002 downdrift from the site of beach nourishment suggests that sand placement affected invertebrate populations, although a more thorough understanding of this community's response to environmental variables is required to further support this conclusion.     

Benthic Macroinvertebrate Communities in Southwestern Lake Ontario Following Invasion of Dreissena: Continuing Change

Benthic macroinvertebrate communities were compared and quantified at natural cobble and artificial reef sites in Lake Ontario in 1983 (pre-Dreissena invasion), and in both 1991–1992 and 1995 (1 to 2 and 5 years post-Dreissena invasion, respectively). Diversity and abundance of non-dreissenid macroinvertebrates generally rose from 1983 to 1991–1992, but returned to 1983 levels or lower by 1995. Although community similarity (excluding Dreissena from analysis) remained high across study years, the 1995 invertebrate community more closely resembled the pre-Dreissena community of 1983 than the initial post-Dreissena community of 1991–1992 because of recent declines in the absolute abundance and diversity of macroinvertebrates. In particular, gastropods responded negatively to Dreissena or to associated benthic habitat or community changes that occurred from 1991–1992 to 1995. These results suggest that short- and long-term effects of Dreissena on other organisms may be quite different, and illustrate the need for long-term monitoring of biological communities in order to more fully determine effects of invasive species or other environmental perturbations on ecosystems.     

Delivery of nutrients and seston from the Muskegon River Watershed to near shore Lake Michigan

Drowned river mouth lakes are major features of coastal Great Lakes habitats and may influence nutrient and organic matter contributions from watersheds to near shore coastal zones. In May through October 2003, we measured loads of nutrients, surficial sediment, and seston to track the delivery of riverine-derived materials from the lower Muskegon River Watershed (MRW) into the near shore area of southeast Lake Michigan. Nutrient flux data indicated that seasonal loads of 1800 metric tons (MT) of particulate organic carbon, 3400 MT of dissolved organic carbon, and 24 MT of total phosphorus were discharged from the lower Muskegon River, with approximately 33% of TP load and 53% of the POC load intercepted within the drowned river mouth terminus, Muskegon Lake. Carbon: phosphorus molar ratios of seston in Muskegon River (C:P = 187) and Muskegon Lake (C:P = 176) were lower than in Lake Michigan (C:P = 334), indicating phosphorus limitation of phytoplankton in near shore Lake Michigan. Isotopic signatures of seston collected in Muskegon Lake were depleted in δ¹³C (− 30.8 ± 1.6‰) relative to the isotope signatures of seston from Lake Michigan (− 26.2 ± 1.3‰) or the mouth of the Muskegon River (− 28.1 ± 0.5‰), likely due to the presence of biogenic methane in Muskegon Lake. Seston δ¹⁵N increased on a strong east-to-west gradient within Muskegon Lake, indicating significant microbial processing of nutrients. The extent of nutrient uptake in Muskegon Lake altered the chemical and isotopic characterization of seston flowing into Lake Michigan from Muskegon River.     

Phenology and species diversity in a Lake Huron ichthyoplankton community: Ecological implications of invasive species dominance

Ichthyoplankton communities are dynamic and vary spatiotemporally based on factors such as wind, water currents, and phenology. Nonetheless, ichthyoplankton are an indicator of spawning success in fish populations and examining their community diversity and composition can serve to provide information on ecosystem integrity. Although some ichthyoplankton species may be transient, understanding their distribution in space and time provides information on species composition, abundance, and habitat use during critical early life stages. We sampled the spring-summer ichthyoplankton community during 2008 and 2009 in northern Lake Huron to determine species succession, abundance, and species diversity along physical and environmental gradients. Seasonal succession of species was similar during both years, indicating well-defined patterns in spawning by northern Lake Huron fish populations. Invasive alewife, rainbow smelt, and round goby were the dominant species during both years, with native stickleback species also abundant. Shannon Entropy (H′) increased with increasing water temperature until late summer when H′ declined. H′ decreased with increasing bottom depth and distance to tributary mouth indicating the important ecological role of these habitat features during early life stages. Although ichthyoplankton diversity was comparable to or higher than that reported for other areas of the Great Lakes, the prominence of invasive species in our study is reflective of the disturbed state of the Lake Huron fish community, despite large reductions in invasive planktivorous fish since 2004. Continued monitoring of ichthyoplankton communities will be important for measuring the impacts of species invasions or other ecosystem stressors on fish community structure in the Great Lakes.     

Invertebrate response to impacts of water diversion and flow regulation in high‐altitude tropical streams

Water supply systems are critical infrastructure that provides food and energy security for developed societies. The operation of reservoirs (flow regulation) and water intakes (water diversion) has known negative impacts on aquatic ecosystems; however, quantification of ecological impacts and examination of these two types of flow alteration remain a developing area of research. We investigated the individual and combined impact of flow regulation and water diversion on stream ecosystem integrity, the freshwater macroinvertebrate community, and the population structure of flow‐sensitive insects. For 2 years, we monitored quarterly discharge, physical and chemical stream conditions, and benthic invertebrates of four high‐altitude tropical streams that are part of the water supply system of Quito, Ecuador. Flow regulation caused a loss of the hydrological seasonality of these streams, including a decrease in stream depth and biotic quality. Water diversion caused a decrease in dissolved oxygen and overall ecosystem integrity. Freshwater invertebrate density and richness decreased as a result of water diversion and flow regulation. The combined flow alteration in these streams decreased the density of nymphal stages of the widely distributed mayfly Andesiops peruvianus. Given the societal needs for food and energy security, water management for diversion (e.g., irrigation) and in‐line storage practices (e.g., hydroelectric dams) are anticipated to increase. This research suggests that the negative environmental impacts of flow alteration could be mitigated with discharge releases designed to approximate the natural hydrologic regime of undisturbed streams.     

Changes in Benthic Invertebrate Communities of South Bay,Lake Huron Following Invasion by Zebra Mussels (Dreissena polymorpha), and Potential Effects on Lake Whitefish (Coregonus clupeaformis) Diet and Growth

In this study we evaluated changes in benthic invertebrate communities of South Bay, Lake Huron following the invasion of zebra mussels (Dreissena polymorpha) and considered the implications for diets and growth of whitefish (Coregonus clupeaformis), a commercially important fish in the Great Lakes. Of the ten benthic invertebrate groups identified prior to invasion (1980–81), only densities of Diporeia and Oligochaeta have changed since the appearance of the zebra mussel, and only Diporeia and Chironomidae changed in relative abundance. These changes are similar to those observed in other areas of the Great Lakes, with the exception of an increase in Oligochaeta density. Post-invasion (2002–03) shallow-water communities appear to be more homogeneous, dominated by zebra mussels and Isopoda, whereas deep-water sites are more heterogeneous due to the loss of Diporeia. Additional data on Diporeia density for several years between 1959 and 2004 indicated that current low densities are not typical of South Bay. Based on changes in the benthic communities and published literature on whitefish diets, we predict that unless whitefish are able to switch to Mysis as an alternative to Diporeia, post-invasion whitefish diets will only contain a maximum of 57 to 84% of their former energy content. These predictions are likely underestimates, as they do not take into account increased energy costs associated with reductions in total invertebrate density at historical foraging depths.