Development and Stability of the Fouling Community at Beaufort, North Carolina

Community development was followed for 2 1/2 to 3 1/2 years on unglazed ceramic tile plates (232 cm2), suspended horizontally beneath the Duke University Marine Laboratory dock, in Beaufort, North Carolina. Series of 3 or 4 plates were submerged at approximately the 1st of each month from May—November 1971 and from April—November 1972. Percentage cover for each species that settled and grew on the lower surface was estimated at 6— to 8—week intervals, using 75 points randomly positioned over the plate area. Samples were nondestructive; plates were resubmerged after each census. Larval recruitment was estimated at 1— to 3—week intervals on newly submerged plates. Temperature and salinity were also measured. Initial community development was relatively unpredictable. Larval recruitment patterns varied markedly from year to year and as a result, different patterns of initial community development were observed both within and between years. Instead of preparing the way for subsequent arrivals, most resident adults strongly inhibited the recruitment and growth of other species. Species varied in their ability to resist subsequent invasion as adults and in their ability to invade occupied substrate as larvae. After an unpredictable initial developmental phase, subsequent changes in species composition depended in part on the degree to which larvae were able to invade existing adult assemblages. This in turn depended on the identity of the resident adults and the identity of the invading larvae. As a result, the direction and rate of community development, dependent on the order of initial invasion and subsequent recruitment, were difficult to predict although an equilibrium number of 8—10 species/plate was often observed. Adult residence time was generally <1 year and the mortality and/or disappearance of these adults produced 20—60% free space on an approximately annual basis. This free space was usually occupied by recruits of a different species than the original occupant. The combined addition of species through larval recruitment and subtraction of species as a result of adult mortality produced dramatic changes in community structure each year. There is no reason to believe these changes will ever cease. We conclude that succession in the classical sense (Odum 1969) does not occur in this system because initial development was variable, residents impeded subsequent development instead of enhancing it, and there was no stable climax. There is good reason to believe similar processes occur in other temperate and subtropical fouling communities. We believe these communities are fundamentally different from terrestrial plant communities, where succession may occur, for 3 reasons: (1) the organisms do not alter the substrate they occupy, i.e., “prepare” it for later arrivals, (2) there is no possibility of “storing” dormant “seeds” of successional species. Colonization of free space is generally by animals which have a short—lived, even nonfeeding larvae, (3) most adults are extremely short—lived. An emerging paradigm of marine benthic community organization postulates the existence of competitive hierarchies in which 1 or a few species win in the absence of disturbances. The fouling community appears to lack such dominants.