Community structure and functioning in intertidal rock pools: effects of pool size and shore height at different successional stages

Rock pools are dynamic and intermittently isolated habitats in the rocky intertidal. They can be used as model systems to provide a more general insight into the ecology of patchy habitats, which are less amenable to experimentation, such as islands and wildlife reserves. In the present study, a range of pools of differing sizes was selected at 2 vertical levels on the shore to assess the importance of habitat size and shore height on the structure and functioning of rock pool macroalgal communities. Half of these pools were denuded of biota by scraping and chiselling, while the other half were left unmanipulated, to compare the effect of patch size on communities at different successional stages. Pool depth was shown to be markedly more important than area in determining community structure of rock pools, although its effect varied with shore height. The diversity, abundance of some macroalgal morphological groups, and algal gross primary productivity in some circumstances were correlated with pool size, whereas total algal cover generally was not. There was evidence that, even within the same morphological group, species responded differently to the influence of pool size, thus emphasising the importance of species identity when predicting responses to changes in environmental conditions (e.g. temperature stress). This study revealed the importance of pool depth over area in dictating macroalgal community structure, but also highlights the existence of various other effects of rock pool size that were more idiosyncratic.