Scales of substratum heterogeneity, and the early establishment of a community* structural complexity, marine epibenthic

This study examines experimentally, in situ, the influence of four scales of heterogeneity (0, 1, 10, 100 mm) and the hierarchical combination of those scales of heterogeneity (0 + 1 + 10, 0 + 1 + 100, 0 + 10 + 100, 0 + 1 + 10 + 100 mm) on the early establishment of a sessile marine littoral epibenthic community. The study was carried out in St. Andrews, New Brunswick (Canada) from July to October 1989. Flat panels without and with crevices of various depths (1, 10, 100 mm) alternating with adjoining flat areas were moored according to a random design in the surface 2 m in the sublittoral zone. Species diversity and total percent cover increased from August to October. However, the ANOVA showed no significant effect of substratum heterogeneity nor complexity (the hierarchical combination of various scales of heterogeneity) on overall diversity (H’) in August and October nor on percent cover on the whole panels in August. However, one type of complex panel out of eight types tested did show a significantly lower percent cover than the others in October. Small scale patterns of distributions varied significantly among the different types of surfaces within each panel, however. In general, percent cover of organisms were greater in 1 mm crevices in August and in 10 mm crevices 2 months later, than on other types of surfaces. Local hydrodynamics and active larval choice may be involved. Our study shows that both substratum heterogeneity and complexity did not influence much the overall northern sessile community characteristics (diversity and abundance), but structured strongly the small scale distribution of its species during the early phases of development.