Structure and dynamics of the Cystoseira caespitosa Sauvageau (Fucales, Phaeophyceae) community in the North-Western Mediterranean
Enric Ballesteros

Research on community structure and dynamics was carried out in a Cystoseira caespitosa community from Tossa de Mar (North-Western Mediterranean). Cystoseira caespitosa occurs on rocky coasts, always in sheltered, shallow and unpolluted waters from the Gulf of Lions and the Costa Brava. Species composition is dominated by C. caespitosa, C. compressa and Halopteris scoparia, with a large number of small photophilic species such as Polysiphonia fruticulosa, Sphacelaria cirrosa and Corallina granifera as epiphytes. A cespitose layer mainly constituted by turfs of Gelidium pusillum and Corrallina elongata is always present. Encrusting calcareous algae belonging to Corallinaceae and Peyssonneliaceae occur in the basal stratum of the community, together with the cnidarian Aiptasia diaphana. Algal biomass ranges between 900 and 2250 g dwt m-1 (including calcareous algae) and percentage coverage ranges between 260 and 1000%. Species richness, species diversity and pattern diversity are very high in relation to other Mediterranean phytobenthic communities; mean number of species per sample (784 cm2) amounts to 105 species and Shannon's diversity index ranges between 2.0 and 4.5 bits. Diversity/area curves always become stabilized at surfaces of 250 cm2 but areas of 500 cm2 are recommended to pick up representative samples of the community both from a qualitative and a quantitative point of view. There is great structural and functional variation during the year, as it has been indicated for most Mediterranean photophilic algal communities. The production phase occurs in winter-spring, reaching a biomass maximum in June. Highest growth of Cystoseira occurs in March-April with a daily production of 4-10 g dwt m-1. Growth seems to be mainly limited by nitrogen availability. Annual production of Cystoseira caespitosa depends on the density of individuals, and it has been estimated at 460-800 g dwt m-2. A mean daily production of 0.5-0.8 g C m-2 supposes a rather high value for aquatic ecosystems with strong depletion of nutrients from waters such as those of the Mediterranean. Nevertheless, these values are much lower than production values found in Cystoseira mediterranea, a species which replaces C. caespitosa in exposed places. Structural and functional differences between both Cystoseira communities are attributed to hydrodynamism. The Cystoseira caespitosa community, characteristic of sheltered places, has a higher species richness and diversity, but its production is lower, as corresponds to a system with a lower input of energy. Auxiliary energy is emphasized as an essential point to understand the structure and dynamics of Mediterranean phytobenthic communities.

Keywords: Phytobenthos, Cystoseira, structure, production, North-Western Mediterranean
Contents of this volume Sci. Mar. 54(2) : 155-168 Back PDF
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