Development of a subtidal epibenthic community: factors affecting species composition and the mechanisms of succession.

Macroinvertebrate grazers and temporal variability were found to strongly influence species composition of communities that developed subtidally on plexiglas panels. On panels exposed to the naturally high densities of sea urchins and sea stars, only grazer-resistant algal crusts, a diatom/blue-green algal film and short-lived filamentous algae became abundant. On those panels protected from grazers, however, other algae and sessile invertebrates were also common. Both the effects of grazing and the abundance of individual taxa differed on panels immersed at different times of the year.Resident species also affected subsequent recruitment. Some colonists were found more frequently on panels with established communities than on recently immersed plates. Others became more abundant on younger than on older panels. Considerable small-scale spatial variation in the abundance of species was also found among panels within treatments and appeared to persist throughout the 13 months of the study.I suggest that since the interactions that determine which mechanisms are important in succession occur between individuals (generalized here to species), not between successional stages, factors such as those examined that can determine which species will interact, indirectly determine the mechnaisms that are important in the development of a community. Models that deal with interactions between successional stages may lack the detail neccessary to predict or explain changes in species composition in diverse communities.