Edge effects and succession dynamics in Brachidontes mussel beds

Abstract

Succession dynamics in natural communities can be influenced both by interactions among recruiting species and by characteristics of the gaps created by disturbances such as the perimeter:area (P:A) ratio. We carried out experiments on 2 subtropical shores in SE Brazil to investigate the influence of gap size (P:A ratio and area variable) and shape (P:A ratio constant and area variable) on the succession of mussel beds dominated by Brachidontes solisianus and B. darwinianus. Small gaps harbored more herbivorous gastropods (mainly the limpet Collisella subrugosa) and were more rapidly preempted by lateral migration of the surrounding mussels than larger gaps. The larger gaps had higher densities of the barnacle Chthamalus bisinuatus and sheltered more limpets in the edges, while the core areas had more Brachidontes recruits. Gaps with different areas but constant P:A ratios had similar succession trends. Although the processes that influence gap closure in other mussel bed species are similar to the studied one, the closure rate in Brachidontes was lower, possibly due to bed structure. However, there were differences between both mussel species, with a faster response to gap formation by B. darwinianus in comparison to B. solisianus, suggesting that disturbances can influence the distribution of these species. The relative influence of edge effects on succession processes may differ among communities dominated by different organisms, and generalizations are possibly restricted to communities composed of functionally similar species.