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 influenced associated invertebrate macrofaunal communities. The subject of this study was to determine the effects of the annual vegetative cycle of Caulerpa on the composition of these animal communities. The different stations 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 that the densest macrofaunal populations in this meadow were at the intermediate Caulerpa density. In the period of greatest algal vegetative growth (September) the minima of diversity or species richness were found at the points of greatest biomass. Dense algal cover had a negative effect on the infauna, especially bivalves, because of anoxic conditions and/or physical impediment offered by the stolen structure, and on epifauna by space compactness and the dominance of species that are favoured by the existence of abundant surface area or organic enrichment. In May, when cover was lowest, the opposite phenomenon occurred with a positive correlation with algal biomass and organic matter. At this time, only two stations were vegetated areas, with numerous faunal species, especially crustaceans. The C, prolifera bed, even though it is not a system as rich and structured as a seagrass meadow, presents a heterogeneous environment with high structural complexity, in which 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.