Autecology of shallow-water Octocorallia from Mediterranean rocky substrata, I. The Banyuls area

The autecology of eleven mediterranean octocoral species (3 Stolonifera, 4 Alcyonacea, 4 Gorgonacea) was studied near Banyuls-sur-Mer (southern France). Field observations were carried out by means of SCUBA-diving in forty underwater stations. The ecological amplitude of each species was determined for a number of abiotic factors, viz. water temperature, submarine irradiance, water movement, slope of substratum and sediment. In this way the ecological niche for the different species was defined. The niches of several species partly overlap: the survival “strategy” of these species was defined as “competitivity”. Other species display “specialization”, a strategy by which they avoid competitive situations. A third survival mechanism is “opportunism”, encountered in species which are extremely tolerant with respect to their environment. Although experimental work is needed to determine how niche selection occurs, larval and juvenile stages are considered to be critical in this respect.