How to determine the likely indirect food-web consequences of a newly introduced non-native species: A worked example

In this paper we demonstrate through a worked case-study that it is possible to make an assessment of the indirect food-web consequences that might occur as a result of the arrival of a hither-to not observed non-native species. We also explore implications for commercial fisheries catches, through the application of a suite of complimentary ecosystem modelling tools. aria commersonii is a lessepsian migrant (introduced via the Suez Canal) that was first recorded in the Mediterranean in January 2000. It has since spread throughout the basin and has been described as ‘the fastest and farthest spreading lessepsian fish migrant ever recorded’. We have used a Rank Proportion Algorithm (RPA) model to predict the theoretical diet composition of F. commersonii in the Bay of Calvi, Corsica. We did so based on potential prey abundances, as well as morphological and behavioural characteristics of both the prey and this novel predator. redicted’ diet composition of F. commersonii derived from the RPA analysis was then used as input to an Ecopath with Ecosim (EwE) model. This model was used to simulate possible consequences of introducing this invasive species, assuming different rates of expansion of F. commersonii populations in the region. Increases in the F. commersonii population resulted in a marked decline in certain prey types (notably planktivorous fish, Mullus surmuletus and Symphodus tinca). By contrast, seabirds and piscivorous fish were suggested as possible beneficiaries, although this depended heavily on model and scenario assumptions. Overall fisheries catches were projected to increase, and this reflected an anticipated ‘bottom up’ increase in piscivorous fish that are the main target of the commercial fishery in the Bay of Calvi region.