Assemblages on limestone and siltstone boulders diverge over six years in a primary-succession transplant experiment

ABSTRACT: Transplant experiments have been used to test for associations between different rock types and developing assemblages during succession in intertidal boulderfields, with all previous experiments of this type concluding within 1 yr. Therefore, differences in colonisation and recruitment on different rocks have been well established but any late-successional associations remain unknown. To remedy this, a previous transplant experiment contrasting limestone and siltstone was extended so that the assemblages that developed on transplanted bare boulders were investigated over 6 yr. The structure and richness of the later-successional assemblages differed between rocks, with limestone assemblages on both upper and lower surfaces being characterised by more species, and higher abundances of some species, than siltstone. These assemblage differences were most strongly correlated with rock-related differences in surface rugosity and microhabitat density. The later-successional assemblages sampled after 5 and 6 yr were generally similar to earlier-successional assemblages sampled after 11 mo. However, the subtle successional changes that transpired were such that all rock-related differences after 5 and 6 yr were unique to later-successional assemblages only. These rock-related differences, that appear to take multi-year time scales to manifest, would have remained unknown had this experiment concluded within the typical timeframe of <1 yr.