Ecosystem approach of artificial reef through trophic web modelling

Abstract

Along the French coast of the Atlantic and English Channel in a high tidal regime, only a limited number of Artificial Reefs (ARs) had been immerged in very few localities in the aim to increase the local production of fisheries of such hard artificial substratum. Moreover, ARs design have been planned to increase the diversity, abundance and biomass of benthic species associated to hard-bottom. Does the deployment of such artificial structure improve the production and ecological functioning on such equipped areas? Trophic models describing the interaction between species at different trophic levels and based on the quantification of energy flow and matter in ecosystems are able to respond to this question. They allow the application of numerical methods for the characterization of emergent properties of the ecosystem, also called Ecological Network Analysis (ENA). Usually, these indices have been proposed as ecosystem health indicators as they have been demonstrated to be sensitive to different impacts on marine ecosystems. Here, Ecopath ecosystem models composed of 23 compartments, from phytoplankton to mammals, are built to describe the situation “Before” and “After” the implantation of ARs in two areas: the Rade of Cherbourg in the central part of the English Channel along the French coast, and in the south of the Bay of Biscay along the Landes coast. In addition, ENA indices are calculated for the two periods, “before” and “after” the implantation of artificial reefs to compare network functioning and the overall structural trophic web properties. In both areas, increase of benthic and fish compartments insure an increase of the system maturity; nevertheless, the high surge of planktinovorous fishes on the Landes AR showed a protection role of such AR than changes of planktonic preys.