Estructura y dinámica de la comunidad infralitoral de Codium Vermilara (olivi) delle chiaje de la Costa Brava (Mediterráneo Occidental

Abstract

Se analiza la composición específica, la estructura y la dinámica de la comunidad de Codium vermilara propia de los fondos rocosos de la Costa Brava situados entre los 8 y los 20 metros de profundidad. Esta comunidad, dominada por especies esciáfilas es extraordinarimante rica en especies, posee una elevada diversidad y el motivo estructural se alcanza para superficies cercanas a los 600 cm2 . La variación del recubrimiento a lo largo del año permite describir la dinámica de la comunidad. Esta se ajusta al modelo general descrito para las comunidades bentónicas del Mediterráneo Occidental. La fase de producción tiene lugar en primavera-verano y la fase de diversificación ocurre en otoño-invierno, como corresponde a una comunidad de tránsito entre las zonas infralitoral y circalitoral. El crecimiento de Codium vermilara está gobernado por la disponibilidad de luz y nutrientes aunque la irradiancia parece ser el factor principal. La producción anual media de Codium vermilara se ha estimado en 0.15-0.30 g C m-2 día- l y la producción global de la comunidad en 0.3-0.4 g C m-2 día- l, valores inferiores a la producción de otras comunidades infralitorales pero superiores a la de comunidades circalitorales, fuertemente limitadas por la luz.

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 al1 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-Z (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 spnng and summer. Nevertheless, nutrient availability seems to play an important role in production cycle of this species, slightly displacing production to spnng, 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- ', and community production ranges between 0.3 and 0.4 g C m-2 day-l 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.