Canopy–understorey relationships are mediated by reef topography inEcklonia radiatakelp beds

There is a growing body of literature that demonstrates that distributions of macroalgal species are heavily influenced by local-scale processes, such as species competition and small-scale variability in the physical environment. Macroalgal assemblages on shallow temperate reefs in Australia are structured by the presence or absence of kelp canopies. Here we test if the negative influence of a canopy of Ecklonia radiata differs among reefs with different topographies. Reefs, with complex topography have higher irradiance and greater water motion than topographically simple, horizontal reefs and these physical differences may affect the extent that the canopy shades the understorey. In this study, we quantified the relationship between understorey assemblage structure and the density of the kelp canopy on reefs of different topographies. We also measured sub-canopy irradiance on each reef type and kelp morphology. The kelp canopy had a greater effect on the understorey on reefs with simple, planar topogra...