Jérôme Marty

Distribution and ecology of Hemimysis anomala, the latest invader of the Great Lakes basin.

Since 2006, the known distribution of Hemimysis anomala has greatly expanded in the Great Lakes ecosystem, with, to date, 45 sites of occurrence among 91 monitored sites, located in four of the Great Lakes and the upper St. Lawrence River. By means of carbon and nitrogen stable isotopes, a first assessment of the feeding ecology of Hemimysis was completed. The δ13C values of 18 individuals collected in Lake Erie (Port Mainland) on a single date (Sept. 23, 2008) ranged from −30.2 to −24.5‰, indicating that Hemimysis could feed on multiple carbon sources including pelagic and littoral autochthonous and terrestrial carbon. In Lake Erie, variation in δ13C was related to δ15N, indicating the importance of food source for determining the trophic position of Hemimysis. The δ15N signatures of individuals were strongly related to their C/N ratios, suggesting that variations in the nutritional value of Hemimysis may depend on trophic position. Isotopic variation among individuals in Lake Erie was complemented by temporal variation in Lake Ontario. Monthly changes (from June to December 2008) in carbon isotope signatures were observed and related to changes in water temperature, highlighting the variations in the baseline prey signatures that fuel Hemimysis diets. The observed variation in stable isotope signatures occurring among individuals within a localized Hemimysis assemblage and temporally should be considered as a key design feature in further studies attempting to identify the possible effects of Hemimysis on nearshore food webs in the Great Lakes.

Assessing the fish consumption beneficial use impairment in the Bay of Quinte

The state of contamination in Bay of Quinte fish was assessed to determine whether delisting criteria have been met, and to recommend further studies/actions to be undertaken. We examined fish contaminant data collected by the Ontario Ministry of the Environment between 1975 and 2008 for seven sites in Lake Ontario including the Bay of Quinte. Where sufficient data was available, we tested for differences in recent years by examining the post-1998 data for Walleye, Smallmouth Bass, Yellow Perch and Brown Bullhead. Our analysis specifically focused on known contaminants of concern within the Bay of Quinte: polychlorinated biphenyls (PCBs), mercury (Hg), as well as Mirex which is known to originate from Lake Ontario. Insufficient data was available for the examination of total TEQs (dioxins, furans and dioxin-like PCBs). When appropriate, we used the general linear model (GLM) to compare contaminant concentrations among sites as a function of fish length. When no significant relationship between contaminant concentration and fish length was found, mean values among sites were compared using analysis of variance. While there were no significant differences for the majority of contaminants among sites, some species and contaminant combinations at one or more of the Bay of Quinte sites had elevated fish concentrations compared to some reference sites. For instance, mercury concentrations in Yellow Perch and Brown Bullhead at Quinte sites exceeded those from some reference sites. Current consumption restrictions for Brown Bullhead and Yellow Perch are more severe in the Upper Bay of Quinte compared to the other sites, indicating impacts of local sources. As a result, the fish consumption beneficial use impairment continues to be classified as impaired for the Bay of Quinte. As many sport fish such as Walleye and Smallmouth Bass are large, long-lived and potentially wide-ranging species, it is difficult to link contaminant concentrations to local sources. To investigate the impact of sources within the Upper Bay of Quinte, comparison of contaminants in sentinel fish collected on the same scale as the source of the contamination is recommended.

The effects of flow regulation on food-webs of Boreal Shield Rivers

Alteration of flow regimes is a major threat to the functioning of lotic food-webs and is responsible for a wide range of ecological responses, including biodiversity loss (BUNN & ARTHINGTON 2002), reduction of food-chain length at lower trophic levels (MARKS et al. 2000), or diversion of energy flow from top consumers (WOOTTON et al. 1996). Despite growing recognition of the effects of flow disturbances on biota, quantitative understanding and/or predictive models of biotic responses to altered flow regimes are lacking. Consequently, environmental regulations that help to sustain lotic ecosystem ecological integrity are weakened. Such difficulty may stem from ignoring the complexity of flow as a combination of many variables including magnitude, frequency, timing, duration, or rate of change (ARTHINGTON et al. 2006), which have differing consequences on the biota (POWER et al. 1996). We applied a stable isotope (SI) approach to determine the impacts of a flow perturbation on food-web structure in rivers. The carbon and nitrogen isotopic compositions of organisms (δC and δN) are useful to characterize main sources of carbon and positions in the food-web because of the consistent fractionation between consumers and diet (FRY & SHERR 1984, FRANCE 1996, VANDER ZANDEN & RASMUSSEN 2001). In natural streams, the application of SI techniques revealed the importance of flow as a key variable driving the variation in δC of primary producers (FINLAY et al. 1999, MCCUTCHAN & LEWIS 2001, TRUDEAU & RASMUSSEN 2003). The controlling effect of flow at the base of the food-web has been further detected at higher trophic levels based on cross-ecosystem studies showing relationships between the carbon isotopic composition of consumers and basin characteristics such as drainage area (MCNEELY et al. 2006) and geochemistry (JEPSEN & WINEMILLER 2007). Stable isotope techniques have also been successfully applied to study the response of food-web structure to anthropogenic perturbations such as nutrient loading (ANDERSON & CABANA 2006) or contaminant accumulation (CABANA & RASMUSSEN 1994). Despite the great potential of SI techniques to identify impoundment and flow-related perturbations, they are rarely used to quantify food-web structure in regulated systems. We report on the effect of flow regulation on carbon sources and food-web structure of boreal streams based on a large-scale in situ experiment. We related variations in the flow regime to the carbon and nitrogen stable isotope composition of aquatic vegetation, invertebrates, and fish. This study aimed to determine the effects of (1) impoundment and (2) variation in the ramping rate (RR – or rate of change) regime on the food-web of a regulated stream.

From the Great Lakes flows a Great River: overview of the St. Lawrence River ecology supplement

The articles gathered together in this special issue of Hydrobiologia stem from a two year conference series (2008 & 2009) co-hosted by the St. Lawrence River Institute of Environmental Science at Cornwall, ON and the Great Rivers Center at Clarkson University, of Potsdam, NY. The conference commemorated what have been arguably the most significant ecological impacts on this river since the Wisconsin Glacial Episode, namely, the damming of the St. Lawrence River to create an hydroelectric power dam and the concomitant creation of the St. Lawrence Seaway lock system that allowed oceangoing vessels to enter the furthest reaches of the Laurentian Great Lakes. Studies on the St. Lawrence River ecosystem in the past have varied in scope and generally focused on the river reaches downstream from the power dam at Cornwall, ON and Massena, NY. In contrast, the International Section of the St. Lawrence River, from the headwaters at Lake Ontario to the entry of the river fully into Canada, has been relatively under-studied (Twiss, 2007). Notable publications documenting the St. Lawrence River ecosystem are provided by Patch & Busch (1984), the St. Lawrence Centre (1996), a special issue published in the Canadian Journal of Fisheries and Aquatic Science (Lean, 2000, and references cited therein), an analysis by Vincent & Dodson (1999), and a recent report by Talbot (2006). We count this special issue among these milestones as a contribution to our understanding of the ecological functioning of a large river that, like most large rivers globally, is under marked ecological stress from a variety of sources, Guest editors: M. Power, J. Marty, M. R. Twiss, J. Ridal, Y. de Lafontaine, J. M. Farrell / St. Lawrence River–Great Lakes Ecosystems: An Ecological Overview