The Quagga Mussel Invades the Lake Superior Basin

Prior studies recognized the presence of a single dreissenid species in Lake Superior—the zebra mussel Dreissena polymorpha. However, taxonomic keys based on traditional shell morphology are not always able to differentiate dreissenid species with confidence. We thus employed genetic and morphological analyses to identify dreissenids in a major river-embayment of Lake Superior—the lower St. Louis River/Duluth-Superior Harbor—during 2005–2006. Our results revealed the presence of a second dreissenid species—the quagga mussel D. bugensis (alternatively known as D. rostriformis bugensis). Both species occurred in mixed clusters, in which zebra mussels outnumbered quagga mussels (20–160:1). The largest quagga mussel collected in 2005 was 26.5 mm long and estimated to be two years old, suggesting that the initial introduction occurred no later than 2003. Further monitoring is necessary to determine whether the quagga mussel will colonize Lake Superior. Our results indicate that the coupling of conventional morphological and molecular approaches is essential for monitoring dreissenid species.     

Multicomponent molluscicide mixtures for zebra mussel control

Intuitively, it is reasonable to expect enhanced control of the biofouling zebra mussel through multicomponent molluscicide cocktails. In this study, the potential of combined potassium chloride, polyDADMAC, niclosamide ethanolamine salt and 2-(thiocyanomethylthio)benzothiazole (TCMTB) for zebra mussel mitigation was investigated. A series of mixtures of varying compositions was tested. First, the combination was considered in its entirety, and the nature of the biocides' joint toxicity was elucidated by adopting a structured classification system previously defined. Then, a central composite experimental design was employed to detail the contribution of each ingredient to the blend performance and ultimately derive an empirical model of mixture effects to optimise the formulation composition. Whilst the action of some of the toxins was synergised, the blend does not appear promising for zebra mussel control. Overall, the chemicals acted less than additively and, under some circumstances, antagonistic effects were observed. Although these results do not immediately lead to a new approach to pest mitigation, the study highlights aspects that are of practical relevance for the design of combined chemical treatments. In particular, this work recalls the funnel hypothesis from the field of ecotoxicology (blends tend to be additive as the number of ingredients increases), which may provide key guidance in the mixture design process. Furthermore, the study shows that multiple biocides do not necessarily ensure improved zebra mussel mitigation, and therefore the nature of their combined effects should always be carefully examined. The systematic procedure proposed here to critically design biocide blends is useful in this context.     

Daphnia lumholtzi Sars a new alien species in Lake St. Clair

Daphnia lumholtzi Sars, an exotic tropical/subtropical cladoceran from Australia, southeast Asia, and Africa, was newly found in Lake St. Clair in a vertical tow sample taken at 3 m depth on 25 July 2007. The species was previously found in 1990/1991 in some reservoirs in the southern United States from where it colonized many waters north to the Great Lakes. In 1999, it was found in Lake Erie. This cladoceran had a density of 117 individuals/m³ when we collected it from Lake St. Clair and it was represented by both females (95.12 %) and males (4.88 %). It seems that D. lumholtzi will continue to expand its distribution area in the Great Lakes.     

Historical changes and current status of crayfish diversity and distribution in the Laurentian Great Lakes

Despite increasing recognition of the importance of invertebrates, and specifically crayfish, to nearshore food webs in the Laurentian Great Lakes, past and present ecological studies in the Great Lakes have predominantly focused on fishes. Using data from many sources, we provide a summary of crayfish diversity and distribution throughout the Great Lakes from 1882 to 2008 for 1456 locations where crayfish have been surveyed. Sampling effort was greatest in Lake Michigan, followed by lakes Huron, Erie, Superior, and Ontario. A total of 13 crayfish species occur in the lakes, with Lake Erie having the greatest diversity (n = 11) and Lake Superior having the least (n = 5). Five crayfish species are non-native to one or more lakes. Because Orconectes rusticus was the most widely distributed non-native species and is associated with known negative impacts, we assessed its spread throughout the Great Lakes. Although O. rusticus has been found for over 100 years in Lake Erie, its spread there has been relatively slow compared to that in lakes Michigan and Huron, where it has spread most rapidly since the 1990s and 2000, respectively. O. rusticus has been found in both lakes Superior and Ontario for 22 and 37 years, respectively, and has expanded little in either lake. Our broad spatial and temporal assessment of crayfish diversity and distribution provides a baseline for future nearshore ecological studies, and for future management efforts to restore native crayfish and limit non-native introductions and their impact on food web interactions.     

Salinity tolerance of the invasive round goby: Experimental implications for seawater ballast exchange and spread to North American estuaries

The Eurasian round goby (Neogobius melanostomus) invaded the freshwater North American Great Lakes in ~ 1990 via accidental introduction from ballast water discharge. Its genotypes in the Great Lakes traced to estuaries in the northern Black Sea, where the round goby flourishes in a variety of salinities to 22 parts per thousand (ppt). To prevent further introductions, U.S. and Canadian Coast Guard regulations now require that vessels exchange ballast water at sea before entering the Great Lakes. Since salinity tolerance of the invasive round goby population is poorly understood, we tested 230 laboratory-acclimated fish in three experimental scenarios: (1) rapid salinity increases (0–40 ppt), simulating ballast water exchange, (2) step-wise salinity increases, as during estuarine tidal fluxes or migration from fresh to saltwater, and (3) long-term survivorship and growth (to 4 months) at acclimated salinities. Almost all gobies survived experiments at 0–20 ppt, whereas none survived ≥ 30 ppt, and at 25 ppt only 15% withstood rapid changes and 30% survived step-wise increases. Ventilation frequencies were lowest at 10–15 ppt in step-wise experiments, in conditions that were near isotonic with fish internal plasma concentrations, reflecting lower energy expenditure for osmoregulation. Growth rates appeared greatest at 5–10 ppt, congruent with the larger sizes reached by gobies in Eurasian brackish waters. Thus, we predict that the Great Lakes round goby would thrive in brackish water estuaries along North American coasts, if introduced. However, oceanic salinities appear fatal to the invasive round goby, which likely cannot withstand complete seawater ballast exchanges or oceanic habitats.     

Early observations on an emerging Great Lakes invader Hemimysis anomala in Lake Ontario

Hemimysis anomala, a Ponto-Caspian littoral mysid, is an emerging Great Lakes invader that was discovered in Lakes Michigan and Ontario in 2006. Similar to the native mysid Mysis diluviana, Hemimysis exhibits a diel vertical migration pattern but generally inhabits shallower and warmer waters than M. diluviana. Because basic information on the distribution, habitat use, and biology of Hemimysis in the Great Lakes is scarce, the potential for food web disruption by Hemimysis cannot easily be predicted. Preliminary observations indicate widespread invasion of Hemimysis in Lake Ontario. In this study, we confirm the presence of Hemimysis at sites spanning the northern and southern shores of Lake Ontario and the presence of the individuals during winter months. In one horizontal tow in November 2007, over 26,000 individuals were collected with a length range of 4.4 to 9.0 mm and an average caloric density of 611 cal/g wet weight. The most effective methods for sampling Hemimysis were horizontal tows with either a zooplankton net in the water column or a benthic sled near the lake bottom. Although more quantitative data on the life history and distribution of this species is necessary, our preliminary observations support the prediction that the potential for Hemimysis to impact the nearshore food web in Lake Ontario appears high.     

Enhanced mortality of the biofouling zebra mussel, Dreissena polymorpha, through the application of combined control agents

Intuitively, cumulative and synergistic effects of combined biocides seem a promising avenue to explore in managing the biofouling zebra mussel. However, such an approach has not been comprehensively examined. In this study, the potential of a binary mixture of poly(diallyldimethyl ammonium chloride) and potassium chloride for zebra mussel control was investigated. The toxicity of the mixed biocides to both adults and veligers was evaluated in laboratory static bioassays. The combined toxicity of the chemicals was observed to depend on the life stage of the mussels. For adults, it was shown to vary with the magnitude of the response under consideration. When producing low lethal effects (below around 25% mortality), the chemicals acted synergistically on the mature organisms and tended to be additive, whilst at high mortality levels, they operated more than additively. In contrast, regardless of the response level under consideration, the toxins appeared to exert additive or less than additive effects on the veligers depending on the potassium chloride dosage. These results have direct practical implications for zebra mussel control. They suggest that the mixture under analysis is very promising for use in mitigation programmes targeted at adults, but its potential for use in proactive treatments to control veligers is not as definitive. The paper also includes a discussion on the contribution the ecotoxicological background on mixture toxicity may have to the development of combined chemical treatments for pest mitigation. Therefore, it may have further application in the setting of experimental protocols for designing control methods.     

Evaluating the growth potential of sea lampreys (Petromyzon marinus) feeding on siscowet lake trout (Salvelinus namaycush) in Lake Superior

Differences in the preferred thermal habitat of Lake Superior lake trout morphotypes create alternative growth scenarios for parasitic sea lamprey (Petromyzon marinus) attached to lake trout hosts. Siscowet lake trout (Salvelinus namaycush) inhabit deep, consistently cold water (4-6 °C) and are more abundant than lean lake trout (Salvelinus namaycush) which occupy temperatures between 8 and 12 °C during summer thermal stratification. Using bioenergetics models we contrasted the growth potential of sea lampreys attached to siscowet and lean lake trout to determine how host temperature influences the growth and ultimate size of adult sea lamprey. Sea lampreys simulated under the thermal regime of siscowets are capable of reaching sizes within the range of adult sea lamprey sizes observed in Lake Superior tributaries. High lamprey wounding rates on siscowets suggest siscowets are important lamprey hosts. In addition, siscowets have higher survival rates from lamprey attacks than those observed for lean lake trout which raises the prospect that siscowets serve as a buffer to predation on more commercially desirable hosts such as lean lake trout, and could serve to subsidize lamprey growth.     

The effects of dreissenid mussels on the survival and condition of burrowing mayflies (Hexagenia spp.) in western Lake Erie

Burrowing mayflies (Hexagenia limbata and H. rigida) are once again prominent members of the benthic community in western Lake Erie. However, this community is now dominated by dreissenid mussels. We conducted a laboratory experiment and field sampling to investigate whether survival and condition of Hexagenia were affected by the presence, density, and quality of dreissenid mussels. In a laboratory experiment, Hexagenia survival was higher in microcosms without dreissenid mussels. We also found Hexagenia density to be higher at field sites with low dreissenid density, suggesting that Hexagenia survival is higher in these areas as well. In microcosm treatments with low dreissenid density, Hexagenia survival was higher in treatments with live dreissenids than in treatments containing only dreissenid shells. These findings suggest that while dreissenid shells degrade the quality of soft sediments for Hexagenia, some of the negative effect is offset by the presence of live dreissenids. The positive effect of live dreissenids is likely due to additional food resources made available to Hexagenia by the filtering activity of dreissenids. Neither dreissenid density nor shell “type” (shells alone or live dreissenids in shells) had an effect on Hexagenia condition. Thus, the interactions between these dominant benthic invertebrates are complex. Recovery of Hexagenia populations in western Lake Erie is likely affected by both changing environmental conditions due to anthropogenic activities and the introduction of exotic species into the benthic community. The results are likely to be continued instability of the benthic food web and unpredictable consequences for human utilization of this ecosystem.     

The establishment of the nuisance cyanobacteria Lyngbya wollei in Lake St. Clair and its potential to harbor fecal indicator bacteria

Lyngbya wollei is a filamentous cyanobacterium which forms large nuisance mats and has infested eastern and southeastern U.S. Lakes and reservoirs for over 100 years. Lyngbya was recently identified in the Great Lakes system in the St. Lawrence River, and Western Lake Erie. Here we report on large deposits of L. wollei washing onshore at a popular recreational beach in Lake Saint Clair, part of the Great Lakes system. The amount of L. wollei deposited on shore was quantified and evaluated for the presence of fecal indicator bacteria (FIB). High concentrations of Escherichia coli, enterococci and Clostridium perfringens were found in the L. wollei in nearshore waters. The densities of E. coli (MPN), enterococci (MPN) and C. perfringens (CFU) attached to L. wollei averaged 3.5, 3.2 and 3.2 log/g, respectively. In contrast, nearshore waters contained nearly 10 times less FIB, averaging 2.6, 2.4 and 2.6 log/100 ml of E. coli (MPN), enterococci (MPN) and C. perfringens (CFU), respectively. DNA fingerprint analysis was used to examine the population structure of E. coli isolates obtained from L. wollei mats. The L. wollei-borne E. coli strains were genetically diverse, suggesting a causal relationship between E. coli and L. wollei. Results from this study indicate that in addition to the macroalga such as Cladophora, cyanobacteria like L. wollei also harbor FIB, potentially impacting water quality and human health in the Great Lakes.     

Distribution and abundance of freshwater polychaetes, Manayunkia speciosa (Polychaeta), in the Great Lakes with a 70-year case history for western Lake Erie

Manayunkia speciosa has been a taxonomic curiosity for 150 years with little interest until 1977 when it was identified as an intermediate host of a fish parasite (Ceratomyxa shasta) responsible for fish mortalities (e.g., chinook salmon). Manayunkia was first reported in the Great Lakes in 1929. Since its discovery, the taxon has been reported in 50% (20 of 40 studies) of benthos studies published between 1960 and 2007. When found, Manayunkia comprised < 1% of benthos in 70% of examined studies. In one extensive study, Manayunkia occurred in only 26% of 378 sampled events (1991–2009). The taxon was found at higher densities in one area of Lake Erie (mean = 3658/m²) and Georgian Bay (1790/m²) than in five other areas (mean = 60 to 553/m²) of the lakes. A 70-year history of Manayunkia in western Lake Erie indicates it was not found in 1930, was most abundant in 1961 (mean = 8039, maximum = 67,748/m²), and decreased in successive periods of 1982 (3529, 49,639/m²), 1993 (1876, 25,332/m²), and 2003 (79, 2583/m²). It occurred at 48% of stations in 1961, 58% in 1982, 52% in 1993, and 6% of stations in 2003. In all years, Manayunkia was distributed primarily near the mouth of the Detroit River. Causes for declines in distribution and abundance are unknown, but may be related to pollution-abatement programs that began in the 1970s, and invasion of dreissenid mussels in the late-1980s which contributed to de-eutrophication of western Lake Erie. At present, importance of the long-term decline of Manayunkia in Lake Erie is unknown.     

Contrasting phenotypic variation among river and lake caught cisco from Great Slave Lake: Evidence for dwarf and large morphs

Coregonids are among a wide array of northern freshwater fishes that have received attention in evolutionary studies as they show phenotypic and life history variation. This intraspecific divergence is commonly manifested as dwarf and large morphs. We assessed and contrasted cisco (Coregonus artedi) in the Great Slave Lake (Northwest Territories, Canada) basin from adfluvial versus lacustrine life histories. Using conventional geometric and linear morphometric methods in conjunction with other phenotypic and life history attributes, we tested the hypothesis that the cisco in the two different environments constituted a dwarf and large species pair. River populations were sampled and compared to lacustrine from Great Slave Lake. Cluster analysis provided the strongest evidence for two phenotypic groups and these two clusters generally characterized lake and river caught cisco based on assignment success from multivariate analyses. The river form was smaller, had a more fusiform body shape, anteriorly positioned paired fins. Larger cisco showed smaller gill rakers spacing indicating that this morph may be feeding at a lower trophic level. Comparisons within river spawning groups showed that the same life history type was present in multiple rivers suggesting that human exploitation was not driving the observed life history. This study provides preliminary evidence that C. artedi exists as a species pair in Great Slave Lake. Moreover, this study adds to a growing wealth of research suggesting that the level of coregonine diversity in Great Slave Lake may rival that of the Laurentian Great Lakes prior to stock collapses.     

Occurrence of the Great Lake's most recent invader, Hemimysis anomala, in the diet of fishes in southeastern Lake Ontario

The Ponto-Caspian mysid, Hemimysis anomala, was first observed in southeastern Lake Ontario in May 2006. During July and August 2007, gill nets were fished in 6 to 8 m of water at two locations of known Hemimysis colonization in southeastern Lake Ontario to determine if fish that consume macroinvertebrates were beginning to include this new invasive mysid in their diets. Of nine fish species captured in August, September, and October 2007, three species had consumed Hemimysis: alewife (Alosa pseudoharengus), rock bass (Ambloplites rupestris), and yellow perch (Perca flavescens); and six species had not: round goby Apollonia melanostoma, smallmouth bass Micropterus dolomieu, spottail shiner Notropis hudsonius, gizzard shad Dorosoma cepedianum, white perch Morone americana and log perch Percina caprodes. Diets of alewives from all samples were composed predominantly of Hemimysis (69.6% -100% frequency of occurrence, 46.0%–74.5% dry weight diet composition). Two of 6 rock bass stomachs sampled in August contained ≥ 98.9% Hemimysis (10 and 40 individuals each) and one of 61 yellow perch stomachs sampled in September contained 10.0% Hemimysis (6 individuals) and 90.0% fish. While Hemimysis were observed only sparsely in the diet of most nearshore fish, their predominance in alewife diets and their omnivorous feeding behavior indicated that they have the potential to alter energy flow in Great Lakes' foodwebs.     

Great Lakes Cladophora in the 21st century: same algae—different ecosystem

Nuisance growth of the attached, green alga Cladophora was considered to have been abated by phosphorus management programs mandated under the Great Lakes Water Quality Agreement. The apparent resurgence of nuisance growth in Lakes Erie, Michigan and Ontario has been linked conceptually to ecosystem alterations engineered by invasive dreissenid mussels (Dreissena polymorpha and Dreissenabugensis). Here, we apply contemporary modeling tools and historical water quality data sets in quantifying the impact of long-term changes in phosphorus loading and dreissenid-mediated changes in water clarity on the distribution and production of Cladophora. It is concluded that reductions in phosphorus loading in the pre-dreissenid period achieved the desired effect, as model simulations were consistent with the biomass declines reported from the early 1970s to the early 1980s. These declines were, however, largely offset by dreissenid-driven changes in water clarity that extended the depth of colonization by Cladophora, increasing total production. We were not able to isolate and quantify the significance of dreissenid mediation of phosphorus cycling using the historical database. Phosphorus management remains the appropriate mechanism for reducing nuisance levels of Cladophora growth. The development of action plans will require an improved understanding of nearshore phosphorus dynamics such as might be obtained through regular monitoring of soluble reactive phosphorus levels, internal phosphorus content and Cladophora biomass in impacted nearshore regions of the Great Lakes.     

Factors governing the distribution and fish-community associations of the round goby in Michigan tributaries of the Laurentian Great Lakes

The round goby (Neogobius melanostomus) is increasingly being reported in tributaries of the Laurentian Great Lakes where these fish have been shown to adversely impact native stream biota. Determining the characteristics and distribution of invaded streams are the first steps toward effective round goby management. We sampled 30 tributaries in the Great Lakes basin and characterized each in terms of nine physical reach-scale attributes. Round goby were detected in 14 streams where abundances ranged from 4% to 53% of the fish sampled in each stream. Round goby was the single most abundant fish species sampled, constituting 14% of all fish encountered across all sites, and 30% of individuals in round goby-present sites. Round goby-present sites were larger, had lower channel slopes, less large wood, and less canopy cover than round goby-absent sites, suggesting that these attributes may promote round goby establishment. Mottled sculpin, cyprinids, brook stickleback, white sucker and rainbow trout were associated with goby absence while centrarchids, percids, yellow bullhead, and mud minnow were associated round goby presence. Collectively these results demonstrate that round goby are widespread in eastern Michigan tributaries to the Great Lakes, present in streams with a range of physical habitat characteristics, and that round goby presence is associated with certain fish species.     

Occurrence and Food Habits of the Round Goby in the Profundal Zone of Southwestern Lake Ontario

Little is known about the ecology of round goby (Neogobius melanostomus), an invasive benthic fish, in the profundal zone of the Great Lakes. In April 2002–2005 we caught increasing numbers of round gobies with a bottom trawl in the 45–150 m depth range of southwestern Lake Ontario. In 2005, we examined gut contents of 30 round gobies from each of three depths, 55, 95, and 130 m, and qualitatively compared gut contents with density of benthic invertebrates determined by Ponar grabs. Round goby guts contained mostly Dreissena spp. and opposum shrimp, Mysis relicta (Mysis); the frequency of occurrence of dreissenids in guts decreased with depth, whereas the frequency of occurrence of Mysis in guts increased with depth. Abundance of these invertebrates in the environment followed the same pattern, although dreissenids of optimum edible size (3–12 mm) were still abundant (1,373/m²) at 130 m, where round gobies primarily consumed Mysis, suggesting that round gobies may switch from dreissenids to more profitable prey when it is available. Other food items were ostracods and fish, with ostracods generally eaten by smaller round gobies and fish eaten by larger round gobies. Occurrence and increasing abundance of round gobies in the profundal zone and predation on Mysis by round goby could have far-reaching consequences for the Lake Ontario fish community.     

Diet effects on lipid composition,somatic growth potential,and survival of the benthic amphipod Diporeia spp.

The benthic amphipod Diporeia represents a crucial trophic link that conveys vital nutrients and energy to predators at higher trophic levels. The current decline of Diporeia populations, mostly in the North American Great Lakes, may, in part, be related to concurrent declines in food quantity and/or quality. We hypothesized that somatic growth and survival of Diporeia would be positively related to dietary supply and subsequent retention of polyunsaturated fatty acids (PUFA); a class of chemicals known to affect diet quality. We examined how different algal PUFA concentrations in; a) Ankistrodesmus falcatus (Chlorophyta), b) a naturally occurring diatom assemblage from Lake Ontario, c) a non-toxic strain of Microcystis aeruginosa (Cyanophyta), and, d) fasting for 30 d, affected PUFA concentrations, somatic growth, and survival of Diporeia. Total PUFA concentrations were significantly higher in A. falcatus than in diatoms and Microcystis, but only diatoms contained considerable amounts of eicosapentaenoic (EPA) and docosahexaenoic acid (DHA). EPA, DHA, and arachidonic acid (ARA) were highly retained in Diporeia even in the absence of dietary supply with ARA being the most efficiently bioaccumulated PUFA. Survivorship of Diporeia ranged from 60% (diatom-fed), 68% (A. falcatus-fed), to 70% (fasting treatment), but was 0% in the M. aeruginosa diet treatment. Nucleic acid ratios (RNA:DNA), commonly used as proxies for somatic growth potential, were highest in Diporeia feeding on diatoms and lowest in fasting animals. We conclude that overall condition of Diporeia improved with dietary access to EPA and DHA, but survival was not related to this food quantity and/or quality.     

Genetic Analysis of the Chinese Mitten Crab (Eriocheir sinensis) Introduced to the North American Great Lakes and St. Lawrence Seaway

The Chinese mitten crab (Eriocheir sinensis) is an invasive organism of concern, with established non-native populations in Europe and California, USA. The species is thought to pose a risk to other North American waterways, including the Great Lakes and St. Lawrence Seaway. Since 1965, there have been sixteen confirmed adult E. sinensis caught in the North American Great Lakes or adjoining waterways. Analysis of their mitochondrial DNA sequence variation for part of the cytochrome c oxidase subunit I gene discerned three haplotypes among seven individuals (caught between 1973 and 2005), identical to common haplotypes in Europe. Analysis of mitochondrial haplotype frequencies and shipping patterns suggests that E. sinensis has been introduced to the Great Lakes from Europe, although we are unable to preclude native Asian populations as putative sources. The species is catadromous, migrating between salt and fresh water to complete its life cycle. This trait makes it unlikely that E. sinensis will establish a breeding population in the Great Lakes proper, which are separated from saltwater by a considerable distance and significant instream barriers such as waterfalls and navigation locks. However, the recent discovery of two confirmed mitten crabs in the St. Lawrence River, which could be more readily colonized, underscores the risk posed by the repeated introduction of this species into the Great Lakes and St. Lawrence Seaway.     

Bioenergetics and Prey Consumption of Breeding Double-crested Cormorants in the Beaver Archipelago,Northern Lake Michigan

Colonial waterbirds are an important component of Great Lakes ecosystems. In order to investigate the role these birds play in an aquatic food web, bioenergetics models, using allometric equations, were applied to breeding double-crested cormorants (Phalacrocorax auritus) and their offspring in the Beaver Archipelago, northern Lake Michigan. These models were parameterized using detailed information collected during the 2000 and 2001 breeding seasons, as well as literature values. Each breeding season was divided into stages in the models to reflect changes in cormorant diet and population size documented in the study area. The models estimated the total prey biomass consumed as 1,445 metric tonnes (mt) of prey in 2000, and 1,585 mt of prey in 2001. Each year, the majority of the prey biomass was alewife (Alosa pseudoharengus), with these fish comprising a greater percentage of prey biomass consumed in 2001. An increase in cormorant reproductive success in 2001 may be linked to this increase in alewife biomass consumed; the breeding bird population size, however, declined in 2001 as compared to 2000. The other prey items, which are not considered to be species of commercial or sport value, were also important contributors to bird diet and consumption of these species did tend to vary from year-toyear. Overall, the application of bioenergetics models allows for greater understanding of the role of cormorants as predators and as energy links in the system.     

Ecosystem changes and nuisance benthic algae on the southeast shores of Lake Huron

We conducted studies of algal fouling along the southeastern shore of Lake Huron to determine the kinds and spatial distribution of benthic algae, the spatial extent and timing of beach fouling, and the possible influences of biological changes to Lake Huron. There was no change in the physical texture of the substratum, but coverage by algal turf increased from 11% of sites in 1977 to nearly 90% in 2007. Shoreline surveys showed that Chara was most common on flat rocky substrata at depths of 0.15 to 0.20 m. Algae stranded on beaches consisted of 62% periphyton turf, 30% Chara and 8% Cladophora and were not evenly distributed; the largest accumulations were found where shoreline irregularities interrupted longshore flow. Quantities of stranded algae partially reflected the height and duration of waves directed onshore. Macroinvertebrate densities were not correlated with benthic algal abundance in 2010 and were lower with fewer large grazers than in 1980. Densities of Dreissena spp. increased with depth, and small tufts of Cladophora were found on larger individuals. The proliferation of algae in the nearshore zone of central eastern Lake Huron appears to be the result of several recent changes. Phosphorus management and filtering by dreissenid mussels have reduced phytoplankton abundance, improving the light regime. Changes in land use may have increased loadings of phosphorus through shallow groundwater and tributary streams. Dreissenids have also redirected nutrients to the lakebed, further enhancing benthic primary production, and predation by round goby has reduced the numbers of grazing benthic invertebrates.