Effects of ephemeral algae on coralline recruits in intertidal and subtidal habitats

Abstract

Coralline algae are an abundant and conspicuous component of intertidal and shallow subtidal algal turfs, and are among the first type of algae to recruit into these assemblages. Initial experiments found the size and abundance of coralline recruits to be negatively correlated with the percentage cover of ephemerals at each of three times. Cover of ephemeral algae was, however, also correlated with habitat (greater covers in intertidal than in subtidal habitats). These experiments evaluate the model that the cover of ephemerals negatively affects the sizes and abundances of corallines. It was predicted that the sizes and abundance of corallines would be greater where the cover of ephemerals is reduced, relative to where it is great. This hypothesis was tested in a field experiment that manipulated the cover of ephemerals in intertidal and in subtidal habitats (thus, unconfounding habitat from cover of ephemerals). It was found that in intertidal and in subtidal habitats, recruits were more abundant and grew larger where there was a great cover of ephemeral algae. In addition, in intertidal habitats, a great cover of ephemeral algae decreased mortality of coralline algal recruits. Thus, particularly in intertidal habitats, ephemeral algae have marked positive effects on the growth and survival of coralline recruits. These results are discussed in terms of their implications for traditional models of succession.