MORPHOLOGICAL VARIATIONS IN THE MEDITERRANEAN-SEA FAN EUNICELLA-CAVOLINI (COELENTERATA, GORGONACEA) IN RELATION TO EXPOSURE, COLONY SIZE AND COLONY REGION

We quantified the phenotypic variation in weight and architectural par ameters of fan-like colonies of the gorgonian Eunicella cavolini. For the quantification of the morphological plasticity with fan size, we d eveloped a method for the precise determination of colony size with fa n-like growth forms. The cortex mineralization as well as the percenta ge by weight of the architectural parameters axis, sclerites and organ ic content increased towards the base of the colonies. Compared to the center the periphery of colonies is characterized by longer, thinner and less ramified branches and by a higher distance between branches ( branch distance). With increasing colony size the branch distance incr eases in the periphery and decreases in the center. This results in mo re or less constant branch distances (and thus porosity values) at any given fan size. When colonies are getting larger, the end branches in the periphery get longer and less ramified, whereas in the center the branch length increases and ramification density remains constant. Ge nerally, branches become thicker, longer and less ramified, and increa se in width becomes more important as colonies increase in size. Becau se flow velocity increases with the distance from the substratum, the variation in architectural parameters in different regions of a colony and in colonies of different size is probably a morphological adaptat ion to reduce drag forces. This study corroborates data from the liter ature showing that colonies from extremely sheltered and very exposed habitats have very porous branching networks with long branches and fe w ramifications compared to colonies from intermediate habitats, which are characterized by strongly ramified branches with low porosity val ues. Differential growth and ramification rates were shown to be the m ajor reasons for the variations of growth forms in relation to colony region and colony size. The intensity of water movement is discussed a s a potential force influencing growth and ramification rates.