Associate Professor Université du Québec à Montréal Montréal, Quebec, Canada
Exotic invasive species have altered food web structure and trophic pathways in freshwater ecosystems. The round goby (Neogobius melanostomus) is a significant invader in the Great Lakes-St. Lawrence River system. Round gobies can feed on dreissenid mussels which rely on pelagic production and can accumulate essential fatty acids differently from other macroinvertebrates. The round goby can therefore potentially shift energy pathways and transfer previously unavailable nutrients and contaminants to higher trophic levels. However, since invasive species impacts on food webs can be modulated by spatial variation in environmental conditions, it is still unclear as to what extent the round goby can modify energy production. This study aimed to determine spatial patterns in the round goby trophic role across environmental gradients in an invaded heterogenous ecosystem. Round gobies and its associated prey were collected from 24 sites in the Upper St. Lawrence River. Food web tools like stomach content, stable isotopes and fatty acids were used in a concomitant way. Bayesian mixing model (MixSiar) was used to assess the importance of the round goby benthic and pelagic diet proportions in relation to covariates, and mixing models were compared using WAIC and LOO criteria to identify the best fit model.
Preliminary results for the stomach content data showed that the round goby diet is comprised of both benthic and pelagic sources with the predominance of crustacean zooplankton, dreissenid mussels, ostracods, gastropods, and chironomids. An ontogenetic shift was observed in the frequency of occurrence and abundance of prey; larger fish ( >60 mm) had more frequently dreissenid mussels in stomachs. Preliminary Bayesian stable isotopes mixing models comparison indicated that the model with site and conductivity as covariates was preferred. Round gobies occupying low conductivity sites were characterized by a larger proportion of benthic diet whereas round gobies living in higher conductivity habitats were relying on a more important pelagic diet proportion. However, while not the most preferred, the model including site and substrate type could not be ruled out. Environmental characteristics can therefore have impacts on round goby feeding patterns and in turns influence essential fatty acids or contaminants transfer to higher trophic levels. This study is the first to address the round goby trophic role in the St. Lawrence River using three trophic indicator methods. It highlights the importance of how environmental heterogeneity within a freshwater ecosystem can influence diet patterns of an exotic predator, and effects on food webs.