Abstract
The development of an epibenthic community in the St. Lawrence Estuary (Quebec, Canada) was studied using artificial substrata. Community development was followed on series of panels immersed for periods ranging from 1-18 mo. Colonization and decolonization rates of algal and animal species were higher during summer than during winter. Intensity of settlement varied from year to year for a given species. In the long series (18 mo.), 2 early colonizers, the barnacle Balanus crenatus and the colonial hydroid Obelia longissima, dominated the community and determined much of its physical structure during most of the study period. Biogenic heterogeneity created by the dominant species was shown to increase the number of both individuals and new species. The mechanisms responsible for this attraction (increase in surface area, new types of substrata, creation of crevices, modification of water movements) are discussed. Subsequent disruption of the structure, due to high mortality of the 2 dominants, caused impoverishment of the assemblage. It is suggested that B. crenatus and O. longissima maintain their dominance using 3 strategies: dense and early colonization and/or rapid growth; greater attractiveness for other species than a flat substratum, which will eventually also cause the elimination of other species (epibionts) on the panels at the time of their own disappearance; and positive or neutral attractiveness to settling larvae of their own species, ensuring their rapid recolonization and maintenance of stable populations.