Ingestion of Small-Bodied Zooplankton by Zebra Mussels (Dreissena polymorpha): Can Cannibalism on Larvae Influence Population Dynamics?

The zebra mussel Dreissena polymorpha established populations in western Lake Erie in 1986 and achieved densities exceeding 3.4 × 105 individuals∙m−2 during 1990. We assessed apparently incidental predation on Lake Erie and Erindale Pond zooplankton by adult mussels. Dreissena larvae and small rotifers (Polyarthra spp., Keratella spp., Trichocerca) sustained moderate to high predatory mortality whereas larger taxa (Bosmina, Scapholeberis) were invulnerable to predation. Larval Dreissena almost always sustain \u3e 99% mortality in European lakes. While mortality has been ascribed primarily to lack of suitable settling substrate and unfavourable environmental conditions, it may be confounded by larval predation by adults. We demonstrate using STELLA™-modelling that with a larval mortality rate of 99%, settled mussel densities observed in western Lake Erie during 1990 would not be achieved until at least 1994. A model that combines a lower rate (70%) of abiotic mortality with larval predation by adult mussels c..., Les populations de dreissena polymorphe (Dreissena polymorpha) déjà établies dans la partie ouest du lac Érié en 1986 atteignaient des densités supérieures à 3,4 × 105 individus par mètre carré au cours de 1990. Nous avons évalué Ta prédation du zooplancton du lac Érié et de l\u27étang Erindale par les dreissenas adultes. Les larves des dreissenas et les petits rotifères (Polyarthra spp., Keratella spp., Trichocerca) présentaient une mortalité par prédation variant de moyenne à élevée tandis que les plus gros taxons (Bosmima, Scapholeberis) résistaient à toute prédation. Les larves de Dreissena des lacs européeens présentent presque toujours un taux de mortalité supérieur à 99%. La mortalité a surtout été attribuée à l\u27absence d\u27un substrat de fixation adéquat et à des conditions environnementales défavorables, mais elle peut être confondue avec celle découlant de la prédation des larves par les adultes. Nous avons montré, à l\u27aide d\u27un modèle STELLAmd, que les densités de dreissenas fixées notées en 1990 n\u27..

The relevance of seabird ecology to great lakes management

Seabirds are an integral part of Great Lakes ecosystems. However, most species are of no economic importance to humans and, therefore, they receive little direct management attention. Because many species of seabirds on the Great Lakes rely on fish as their primary food, factors that alter fish availability will also affect seabird populations. This paper examines how management practices may indirectly affect Great Lakes seabirds leading to changes in population sizes, diet composition, and destruction of breeding habitat. Consideration of the impacts of management actions on non-target groups, such as seabirds, will require the application of an ecosystem approach to management. Although the ecosystem approach philosophy has been widely accepted from a theoretical perspective, little tangible evidence exists that it has been routinely applied

Surfing the biomass size spectrum: some remarks on history, theory, and application

Charles Elton introduced the ‘pyramid of numbers’ in the late 1920s but this remarkable insight into body-size dependent patterns in natural communities lay fallow until the theory of the biomass size spectrum was introduced by aquatic ecologists in the mid-1960s. They noticed that the summed biomass concentration of individual aquatic organisms was roughly constant across equal logarithmic intervals of body size from bacteria to the largest predators. These observations formed the basis for a theory of aquatic ecosystems, based on the body size of individual organisms, that revealed new insights into constraints on the structure of biological communities. In this review we discuss the history of the biomass spectrum and the development of underlying theories. We indicate how to construct biomass spectra from sample data, explain the mathematical relations among them, show empirical examples of their various forms, and give details on how to statistically fit the most robust linear and nonlinear models to biomass spectra. We finish by giving examples of biomass spectrum applications to production and fisheries ecology, and offering recommendations to help standardize use of the biomass spectrum in aquatic ecology.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Evaluation of the responsiveness of the crustacean zooplankton community size spectrum to environmental change and an exotic invader in a sample of Canadian Shield lakes

We evaluated the crustacean zooplankton size spectrum as an indicator of lake characteristics and ecosystem change. First, we used time series from seven Canadian Shield lakes to identify the factors associated with among-lake and among-year variability in the spectrum slope (relative abundance of small and large zooplankton) and centered height (total abundance). Second, we used time series from an invaded and three control lakes to assess change in mean and variability in slope and height due to a Bythotrephes invasion. We found that the slope and height reflected among-lake predictors related to morphometry. The slope was responsive to long-term declining lake phosphorus levels, whereas the height reflected both increases in dissolved organic carbon and decreases in ice duration. We detected a significant increase (i.e., flattening) in mean slope and substantial (up to 120%) increases in the CV of height after Bythotrephes invaded Harp Lake. Thus, the zooplankton size spectrum was responsive to long-term environmental change, and a strong top-down perturbation can be detected through regular and frequent monitoring programs.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Calibration of the zooplankton community size spectrum as an indicator of change in Canadian Shield lakes

Developing the crustacean zooplankton community size spectrum into an indicator of change in lakes requires quantification of the natural variability in the size spectrum related to broad-scale seasonal, annual, and spatial factors. Characterizing seasonal patterns of variation in the size spectrum is necessary so that monitoring programs can be designed to minimize the masking effects that seasonal processes can have on detecting longer-term temporal change. We used a random effects model to measure monthly, annual, and interlake variability in the slope (i.e., relative abundance of small and large organisms) and centered height (i.e., total abundance) of the crustacean zooplankton normalized abundance size spectrum from 1981 to 2011 among eight Canadian Shield lakes. Consistent with theoretical predictions, the slope was a relatively stable characteristic of the zooplankton community compared with the height, which varied significantly among lakes. We identified a seasonal signal in height and slope and used a mixed effects model to characterize the linear rate of change from May to October; there was an overall decline in height and an overall increase in slope. Seasonal variance was greater than annual variance for both the height and the slope, suggesting that long-term monitoring of lakes and interlake comparisons using zooplankton size spectra should be based on temporally standardized sampling protocols that minimize the effects of seasonal processes. We recommend sampling the zooplankton community in midsummer because this results in size spectrum estimates close to seasonal mean values.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Size spectra analysis of a decade of Laurentian Great Lakes data

Size spectra analysis (SSA) is used to detect changes in food webs by simplifying complex community structures through abundance-versus-biomass considerations. We applied SSA to 10 years (2006-2015) of data on Great Lakes organisms ranging in size from picoplankton to macrozooplankton. Summer pelagic size spectra slopes were near the theoretical value of -1.0, but spring slopes were steeper, reflecting seasonal differences in abundance of small and large individuals. Pelagic size spectra slopes were relatively stable over the time period we examined. Height (the predicted number of organisms at the spectra midpoint) varied among lakes and was slightly higher in summer than spring in more productive basins. Including benthic data led to shallower slopes when combined with pelagic data, suggesting benthic organisms may increase food web efficiency; height was less affected by benthic data. Benthic data are not routinely included in SSA, but our results suggest they affect slopes and therefore SSA-based predictions of fish abundance. The ability of SSA to track changes in trophic energy transfer makes it a valuable ecosystem monitoring tool.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author