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Marty J.,St Lawrence River Institute | Marty J.,University of Waterloo | Ives J.,University of Waterloo | de Lafontaine Y.,Environment Canada | And 3 more authors.
Journal of Great Lakes Research | Year: 2012

This study is providing the first insight on the food sources supporting Hemimysis anomala in a lotic ecosystem where food webs differ from those of lentic ecosystems. Using carbon and nitrogen stable isotopes, the diet of Hemimysis was evaluated in multiple sites of the St Lawrence River where higher density swarms have been recently reported. We found that Hemimysis may feed on multiple food sources, including benthic and pelagic production, and from multiple trophic levels. Results from a mixing model applied to evaluate the importance of benthic versus pelagic food sources revealed site specific variations in diet. At the low flow sites located in the Montréal Harbour, Hemimysis fed primarily on pelagic production compared to the more open sites exposed to higher flow located outside of the harbor. This study indicates that Hemimysis may adapt its feeding behavior to environmental conditions and/or food source availability, potentially increasing its impacts on food web structure. © 2012 Elsevier B.V.

Walsh M.G.,U.S. Geological Survey | Boscarino B.T.,The Harvey School | Marty J.,St Lawrence River Institute | Johannsson O.E.,Canada Center for Inland Waters
Journal of Great Lakes Research | Year: 2012

Mysis diluviana and Hemimysis anomala are the only two species of mysid shrimps in the order Mysidacea that are present in the Laurentian Great Lakes of North America. M. diluviana has inhabited the deep, cold waters of this region since Pleistocene-era glacial retreat and is widely considered to have a central role in the functioning of offshore food webs in systems they inhabit. More recently, the Great Lakes were invaded by the Ponto-Caspian native Hemimysis, a species that inhabits warmer water and shallower depths relative to M. diluviana. Hemimysis has rapidly expanded throughout the Great Lakes region and has become integrated into nearshore food webs as both food for planktivorous fish and predators and competitors of zooplankton. This special issue is composed of 14 papers that represent the most recent advances in our understanding of the ecological importance of both species of mysids to lake and river ecosystems in the Great Lakes region of North America. Topics discussed in this special issue will inform future research in all systems influenced by mysid ecology. © 2012.

Ives J.T.,University of Waterloo | Marty J.,University of Waterloo | Marty J.,St Lawrence River Institute | Marty J.,Genivar Inc. | And 4 more authors.
Journal of Plankton Research | Year: 2013

Invasive species are a known stressor on aquatic ecosystems, particularly in the waters of the Great Lakes basin. A recent invader, Hemimysis anomala, has had significant impacts on food webs in Europe, where it invaded previous to its spread to North America. This study used carbon and nitrogen stable isotopes to characterize and compare the diet of Hemimysis from 13 sites in the Great Lakes basin. Results indicated that: (i) Hemimysis relied predominantly on pelagic carbon sources at the majority of sites, and isotopic differences between life-stages existed at two of the 13 sites examined, (ii) the trophic offset and reliance on pelagic food sources did not differ significantly between lotic and lentic sites, and (iii) the isotopic niche width of Hemimysis was spatially heterogeneous, varying by an order of magnitude among sites, but was unrelated to the degree of isotopic variation in the basal food web at each site. Observed ranges in trophic offset and the pelagic fraction of dietary carbon indicate that Hemimysis derives carbon from both benthic and water column sources, as well as at multiple trophic levels. Our results support the view that Hemimysis is an opportunistic omnivore that displays significant dietary flexibility. © 2013 The Author.

Smokorowski K.E.,Canadian Department of Fisheries and Oceans | Metcalfe R.A.,Ontario Ministry of Natural Resources | Finucan S.D.,Ontario Ministry of Natural Resources | Jones N.,Ontario Ministry of Natural Resources | And 4 more authors.
Ecohydrology | Year: 2011

Although dams have impounded the majority of the world's altered watercourses, there is a growing awareness of the importance of mitigating or reversing some of the negative effects on aquatic ecosystems and the related services they provide. We used an ecosystem approach, including detailed studies on hydrology, geomorphology, invertebrates, fish, and food web dynamics on a river altered by waterpower production and a natural flowing river to assess system responses to a change in the altered flow regime (specifically the ramping rate or rate of change of flow). Although there was significant alteration in the flow and sediment regimes under the original restricted ramping rate regime, differences in many biotic variables in the two rivers were not significant including total invertebrate abundance and diversity, fish biomass, fish condition, and food web length. However, significant differences in the abundance and distribution of some sensitive invertebrate taxa and fish diversity were observed between the altered and natural flowing rivers as was the energy base of the food web, measured with stable isotopes. The altered river had lower overall abundance of Odonata, Ephemeroptera and Plecoptera, and Diptera, Trichoptera, Ephemeroptera, and Coleoptera increase in abundance towards the deeper and higher velocity thalweg. On average, δ 13C values were lighter in altered sites compared to unaltered sites, likely due to carbon export from the upstream reservoir. Results will inform Canadian federal and provincial policy concerning the efficacy of ramping rate restrictions as a tool to mitigate the environmental impacts associated with peaking waterpower dam operations. © 2010 John Wiley & Sons, Ltd. and Crown in the right of Canada.

Ricciardi A.,McGill University | Avlijas S.,McGill University | Marty J.,St Lawrence River Institute
Journal of Great Lakes Research | Year: 2012

The bloody red mysid shrimp Hemimysis anomala is the most recent Ponto-Caspian invader of the Great Lakes. At present, there is a paucity of data that can be used to forecast its ecological impacts in North America; however, published studies of other invasive freshwater mysids (i.e. Mysis diluviana introduced to North American lakes and Mysis relicta introduced to Scandinavian lakes) reveal potentially valuable predictive information. A frequent impact of Mysis introductions is a drastic decline in zooplankton (particularly cladoceran) abundance, which can release phytoplankton populations from grazer control and alter the abundance and growth of pelagic fishes. Other impacts include enhanced bioaccumulation of contaminants, new pathways of parasite transmission to fishes, and altered nutrient cycling. Like Mysis spp., H. anomala has the potential to affect all trophic levels in lakes. It has reduced the abundance and diversity of zooplankton in European reservoirs, where it achieved mean densities higher than those recorded for other introduced mysids elsewhere. It can colonize a broader range of habitats than Mysis throughout the year, including the nearshore areas of lakes and large rivers. Within river systems, the impacts of H. anomala will likely be most pronounced in backwater lakes, impounded areas and reservoirs. Understanding the environmental factors that limit the local abundance of H. anomala and mediate its species interactions is essential for developing predictive models of its impact. © 2011 Elsevier B.V.

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