Ecological succession and the climax community on a marine subtidal rock wall

Persistence and development of an epibiotic community occupying a temperate, marine.subtidal rock wall was studied for 4.5 yr.Composition and abundance of the biota of unmanipulated control quadrats remained remarkably constant.Fleshy red algae fluctuated seasonally, and other taxa fluctuated aperiodically, but abundances of all taxa remained within rather narrow limits.To determine the repeatability of succession, quadrats were cleared of all residents in summer and in winter in each of 2 yr.The encrusting bryozoans and annelids that occur commonly in other areas heavily grazed by sea urchins quickly colonized the cleared quadrats but within 1 to 3 yr gave way to the assemblage that characterizes uncleared areas.With minor variations, all quadrats had nearly converged quantitatively to the control condition by about 3 yr after clearing.A thlrd set of quadrats was caged to exclude all macropredators (1 starfish and 3 grazing fishes).Density of the epibiotic mat increased and some changes in the growth forms of some organisms occurred, but no major, lasting changes in abundances were observed over 3 yr.These and other observations suggest that the high local taxonom~c divers~ty here must arise mainly not from external disturbances but from interactions between the sessile epibiotic species themselves.