Microcystis aeruginosa, a planktonic colonial cyanobacterium, was not abundant in the 2-year period before zebra mussel (Dreissena polymorpha) establishment in Saginaw Bay (Lake Huron) but became abundant in three of five summers subsequent of mussel establishment. Using novel methods, we determined clearance, capture, and assimilation rates for zebra mussels feeding on natural and laboratory M. aeruginosa strains offered alone or in combination with other algae. Results were consistent with the hypothesis that zebra mussels promoted blooms of toxic M. aeruginosa in Saginaw Bay, western Lake Erie, and other lakes through selective rejection in pseudofeces. Mussels exhibited high feeding rates similar to those seen for a highly desirable food alga (Cryptomonas) with both large (>53 m m) and small (<53 m m) colonies of a nontoxic and a toxic laboratory strain of M. aeruginosa known to cause blockage of feeding in zooplankton. In experiments with naturally occurring toxic M. aeruginosa from Saginaw Bay and Lake Erie and a toxic isolate from Lake Erie, mussels exhibited lowered or normal filtering rates with rejection of M. aeruginosa in pseudofeces. Selective rejection depended on "unpalatable" toxic strains of M. aeruginosa occurring as large colonies that could be rejected efficiently while small desirable algae were ingested. Résumé: Mycrocystis aeruginosa, une cyanobactérie qui forme des colonies planctoniques, s'est multipliée dans la Baie de Saginaw (Lac Huron) durant trois des cinq étés qui ont suivi l'établissement de la Moule zébrée (Dreissena polymorpha), alors qu'elle n'était pas abondante durant les deux années qui ont précédé cet établissement. Des méthodes inédites ont permis de déterminer les taux de clearance, de capture et d'assimilation de Moules zébrées alimentées de souches naturelles et de souches de laboratoire de M. aeruginosa, présentées seules ou en combinaison avec d'autres algues. Nos résultats s'accordent avec l'hypothèse qui veut que les Moules zébrées favorisent, par des rejets sélectifs dans leurs pseudofèces, la formation de fleurs d'eau à M. aeruginosa de souche toxique dans la baie de Saginaw, dans la région occidentale du lac Érié et dans d'autres lacs. Nourries de grandes (>53 m m) et de petites (<53 m m) colonies d'une souche non-toxique et d'une souche toxique de laboratoire de M. aeruginosa, qui inhibent l'alimentation chez le zooplancton, les moules maintiennent des taux élevés d'alimentation, semblables à ceux que l'on observe lorsqu'on les nourrit d'une algue très recherchée (Cryptomonas). Dans des expériences d'alimentation utilisant des souches naturelles de M. aeruginosa toxiques de la baie de Saginaw et du lac Érié et un isolat toxique du lac Érié, les moules présentent des taux de filtration réduits ou normaux et rejettent M. aeruginosa dans leurs pseudofèces. Ce rejet sélectif dépend de la présence de grandes colonies de souches toxiques «à goût désagréable» de M. aeruginosa qui peuvent être éliminées facilement, alors que les petites algues appétissantes sont ingérées...
We describe, explain, and "predict" dispersal and ecosystem impacts of six Ponto-Caspian endemic species that recently invaded the Great Lakes via ballast water. The zebra mussel, Dreissena polymorpha, and quagga mussel, Dreissena bugensis, continue to colonize hard and soft substrates of the Great Lakes and are changing ecosystem function through mechanisms of ecosystem engineering (increased water clarity and reef building), fouling native mussels, high particle filtration rate with selective rejection of colonial cyanobacteria in pseudofeces, alteration of nutrient ratios, and facilitation of the rapid spread of their Ponto-Caspian associates, the benthic amphipod Echinogammarus ischnus and the round goby, Neogobius melanostomus, which feeds on zebra mussels. The tubenose goby,Proterorhinus marmoratus, which does not feed on zebra mussels, has not spread rapidly. Impacts of these benthic invaders vary with site: in some shallow areas, habitat changes and the Dreissena [Formula: see text] round goby [Formula: see text] piscivore food chain have improved conditions for certain native game fishes and waterfowl; in offshore waters, Dreissena is competing for settling algae with the native amphipod Diporeia spp., which are disappearing to the detriment of the native deep-water fish community. The predatory cladoceran Cercopagis pengoi may compete with small fishes for zooplankton and increase food-chain length.
Herein, we document changes in the Lake Michigan food web between 1970 and 2000 and identify the factors responsible for these changes. Control of sea lamprey (Petromyzon marinus) and alewife (Alosa pseudoharengus) populations in Lake Michigan, beginning in the 1950s and 1960s, had profound effects on the food web. Recoveries of lake whitefish (Coregonus clupeaformis) and burbot (Lota lota) populations, as well as the buildup of salmonine populations, were attributable, at least in part, to sea lamprey control. Based on our analyses, predation by salmonines was primarily responsible for the reduction in alewife abundance during the 1970s and early 1980s. In turn, the decrease in alewife abundance likely contributed to recoveries of deepwater sculpin (Myoxocephalus thompsoni), yellow perch (Perca flavescens), and burbot populations during the 1970s and 1980s. Decrease in the abundance of all three dominant benthic macroinvertebrate groups, including Diporeia, oligochaetes, and sphaeriids, during the 1980s in nearshore waters ([Formula: see text]50 m deep) of Lake Michigan, was attributable to a decrease in primary production linked to a decline in phosphorus loadings. Continued decrease in Diporeia abundance during the 1990s was associated with the zebra mussel (Dreissena polymorpha) invasion, but specific mechanisms for zebra mussels affecting Diporeia abundance remain unidentified.
We determined the clearance rates of the profunda morph of the quagga mussel (Dreissena bugensis) using seston and Cryptomonas ozolini, a high-quality algal food, for the temperature range 1-7°C, which is the full temperature range this morph is likely to experience during isothermal conditions or in the hypolimnion of deep lakes. Experiments at 3°C with the shallow-water morph of the quagga and the zebra mussel provided very similar results. The clearance rates were combined with dreissenid abundance in 0-30 m, 30-50 m, 50-90 m, and N 90 m depth zones of the southern basin of Lake Michigan to calculate a maximum (using Cryptomonas) and minimum (using seston) fraction of the water column cleared (FC) per day in the different depth zones at 3°C to determine dreissenid impact on the spring phytoplankton bloom from 1994 to 2008. Starting in 2003 or 2004 with the replacement of zebra mussels by quagga mussels in shallow water and expansion of quagga mussel biomass in deep water, FC began to exceed likely phytoplankton growth in the 30-50 m zone. In 2007-2008, FC greatly exceeded likely phytoplankton growth by a factor of about 5 in the 30-to 50-m depth zone, where dreissenids were extremely abundant. Low FC in the offshore region led to the hypothesis of a mid-depth carbon (C) and phosphorous (P) sink caused by mussel uptake of seston-associated C and P that affected not only the mid-depth region, but also the offshore region "downstream" of the mid-depth zone.Published by Elsevier B.V.
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