Effect of the vegetative cycle of Caulerpa prolifera on the spatio-temporal variation of invertebrate macrofauna

Caulerpa prolifera cover fluctuated on a small spatio-temporal scale and in fluenced associated invertebrate macrofaunal communities. The subject of th is study was to determine the effects of the annual vegetative cycle of Cau lerpa on the composition of these animal communities. The different station s studied were distributed on a gradient based on the density of Caulerpa, but the fauna seemed capable of discriminating between only wide degrees of vegetation cover (high, intermediate and low). Rank analysis indicated tha t the densest macrofaunal populations in this meadow were at the intermedia te Caulerpa density. In the period of greatest algal vegetative growth (Sep tember) the minima of diversity or species richness were found at the point s of greatest biomass. Dense algal cover had a negative effect on the infau na, especially bivalves, because of anoxic conditions and/or physical imped iment offered by the stolen structure, and on epifauna by space compactness and the dominance of species that are favoured by the existence of abundan t surface area or organic enrichment. In May, when cover was lowest, the op posite phenomenon occurred with a positive correlation with algal biomass a nd organic matter. At this time, only two stations were vegetated areas, wi th numerous faunal species, especially crustaceans. The C, prolifera bed, e ven though it is not a system as rich and structured as a seagrass meadow, presents a heterogeneous environment with high structural complexity, in wh ich a great variety of animal relationships is produced, mainly in response to the spatio-temporal variation of the vegetative cycle of the alga. (C) 2001 Elsevier Science B.V. All rights reserved.