Towards the development of an ecosystem model for the Hamilton Harbour, Ontario, Canada

Our main objective is to undertake a synthesis of the Hamilton Harbour ecosystem and to elucidate the relative importance of the underlying trophic relationships using the mass-balance modeling software Ecopath with Ecosim (EwE). We present a conceptual model comprising all the essential food web components of the system, which was parameterized using both local and literature-based information. Among the trophic relationships considered by the Hamilton Harbour ecosystem model, our analysis highlights the central role of round goby demonstrating a wide range of effects on a number of functional groups at both higher and lower trophic levels. Several ecosystem attributes (e.g., primary production/biomass, biomass/total throughput, system omnivory index, amount of recycled throughput, and Finn's cycling index) provide evidence that the Hamilton Harbour is an immature and fairly simple system with linear food chain structure, although the internal redundancy and the system overhead estimates indicate that the Harbour possesses substantial reserves to overcome external perturbations. The aggregation of the ecosystem into discrete trophic levels suggests that most of the trophic flows are concentrated within the first two trophic levels, while flows were practically insignificant at the higher trophic levels of the food web. The fairly low ecotrophic efficiency values for both carnivorous and herbivorous cladocerans are indicative of low zooplanktivory levels in the system. Finally, our study identifies knowledge gaps and critical next steps to rigorously assess the credibility of the model and to consolidate its use for predictive purposes.