Structure of intertidal and subtidal assemblages in Arctic vs temperate boulder shores
Several studies suggest that assemblages in intertidal zones that experience frequent physical extremes (e.g. wave-impacts) should be highly dependent on the regional input of propagules. Therefore with higher disturbance in the intertidal zone, higher dependence on the species pool from nearby assemblages (e.g. subtidal) should be observed. Here we examine adult Community structure to investigate levels of similarity among marine assemblages of Arctic intertidal zones compared with those in adjacent subtidal areas. Additionally we compare Arctic results with similar data from a temperate area. We selected boulder fields as a model habitat and we predicted that subtidal and intertidal diversity would change differently under varying disturbance regimes. Multivariate analysis of data from Arctic and temperate North Atlantic indicates that in the Arctic, intertidal and subtidal assemblages were more similar to each other than were temperate intertidal and subtidal assemblages. We suggest this is not because of species differences but that the temperate areas are less disturbed. The wave and ice battered, highly disturbed intertidal assemblages of the Arctic were composed of a subset of nearby subtidal assemblages with similar dominance structure. Intertidal specialist species were not found in the Arctic samples. In contrast, temperate intertidal boulder-field assemblages had a completely different dominance structure to the adjacent subtidal. Furthermore, temperate intertidal assemblages were composed of different (specialist) species often not found in the subtidal zone. We conclude that more disturbed environments, such as our Arctic study sites, are more dependent on Outside sources of recruitment.