STRUCTURE AND DYNAMICS OF CODIUM VERMILARA COMMUNITY IN THE COSTA BRAVA (WESTERN MEDITERRANEAN)

Abstract

Codium vermilara community occurs in rocky bottoms around 8-20 meters depth in some places of the Catalan Coast (Northwestern Mediterranean). Species composition is dominated by sciaphilic algae such as Codium vermilara, Halopreris Jilicina and Sphaerococcus coronopifolius, Encrusting algae (e.g. Mesophyllum lichenoides, Neogoniolirhon mamillosum?) cover all the substrate and represent a high percentage of the whole biomass. Turf-algae are also very abundant and thallus of Codium vermilara are entirely covered by epiphytes in spring. Biomass ranges between 1.500 and 2.000 g dwt m^-2 (including calcareous algae) and percentage coverage ranges between 180 and 410%. Species richness is extraordinarily high (up to 129 species in 1.024 cm²). Species diversity (Shannon's index) ranges between 1.6 and 2.7 bits (calculated from biomass values) or between 2.8 and 4.3 bits (calculated from coverage values). Pattern diversity is relatively high, so that areas of 600 cm² are recommended in order to pick up representative samples of this community. Community dynamics can be included in the model described by BALLESTEROS (1984) for Mediterranean phytobenthic communities. Production phase occurs in spring-summer, while diversification phase occurs in autumn-winter. Production of Codium vermilara seems to be mainly limited by light since period of maximum growth occurs in spring and summer. Nevertheless, nutrient availability seems to play an important role in production cycle of this species, slightly displacing production to spring, when irradiance has not reached its maximum values but nutrient concentration in seawater is still detectable. Mean annual production of Codium vermilara ranges between 0.15 and 0.30 g C m^-2 day^-1, and community production ranges between 0.3 and 0.4 g C m^-2 day^-1 that represents an amount of organic matter higher than that produced by phytoplankton. In comparison with other Mediterranean communities these values are lower than those estimated from other infralittoral communities, but higher than those estimated from circalittoral, strongly light-limited, communities.