An offshore buoy as a small artificial island and a fish-aggregating device (FAD) in the Mediterranean

Abstract

The ODAS Italia 1 oceanographic buoy is moored in the Ligurian Sea, 37 nm from Genoa, along the Genoa-Cape Corse transect (43° 48.90′ N-09° 06.80′ E), over a 1270 m deep sea bottom. The underwater portion of the buoy is 37 m long and 0.60 m in diameter, acting as a small island for colonization of fouling organisms and as a fish-aggregating device (FAD). The role of the buoy in attracting and maintaining fish assemblages was investigated by visual censuses in different seasons at depths of 0–40 m. Fish from seven families, comprising 12 species, of which three are benthic, were recorded with maximum abundance in summer. Fouling was studied from samples collected on the buoy and on immersed panels. The fouling community of the buoy consisted of 34 algae and 100 animal species, including three fish. The settlement processes of the fouling community on the panels, in particular on those exposed for over 70 months at 12 m and 33 m depth, are described based on counts of settled organisms, the covering index of each taxa and biomass assessments. On the panels, 63 species were identified. The fouling biomass, on the panel submerged for 70 months, assessed as wet weight, reached 2.8 kg/m² at 12 m depth and 4.8 kg/m² at 33 m depth.

Observations of benthic organisms settled directly on the buoy were made between 1988 and 1989 and when the buoy was retrieved and brought back to shore on April 15, 1991 after 52 months at sea. At this time, the fouling community along the full 37 m length of the buoy was sampled, and 91 taxa, including 83 species, were identified. Several of the species present on the buoy are shallow, coastal species, some with a very short larval period. Possible ways of colonization by such species are discussed. Despite seasonal changes, the pelagic fish community was more stable over the period of 11 years of study than the benthic community settled on the buoy (that is still developing).