The influence of white seabream (Diplodus sargus) production on macrobenthic colonization patterns

The present work evaluates the influence of fish production on macrobenthic colonization over large areas (approximately 700 m²), where the colonizing populations are not nearby the disturbed area. Sampling was undertaken within newly created aquaculture earthen ponds under two contrasting conditions: white seabream (Diplodus sargus) production and no production (control). Macrobenthic and geochemical samples were collected 7, 23, 54, 93 and 180 days after filling the earthen ponds with seawater pumped from a water reservoir for the first time. The water reservoir was also sampled, and is used as a reference for the colonizing populations. Macrobenthic colonization rate in the ponds was low, probably due to the isolation of the disturbed habitat, to the large size of the defaunated area, and possibly to geochemical constraints. Initial colonization was by insect larvae (mainly chironomids), the bivalves Cerastoderma spp., the polychaetes Pseudopolydora paucibranchiata and Hydrodoides elegans, and nemerteneans. The number of species was similar in control and production ponds, even though under production higher total abundance values were observed. Although well represented in the water reservoir, the amphipod Microdeutopus gryllotalpa was only observed within the new ponds after 6 months. Preliminary results suggest that macrobenthic colonization patterns were influenced by fish production, as assemblages were significantly different among ponds. Higher food availability due to fish production may explain the results obtained, but ecological reasons, such as predation, may also contribute for shaping the macrobenthic communities.