Abstract

We evaluated the contribution of beta (β) diversity of macroalgal assemblages in subtropical rocky reefs of the Gulf of California. Seasonal samplings of macroalgae were taken in six sites from 2005 to 2008. We identified 157 species, with a local richness [alpha (α) diversity] between 8 and 38 species, with the lowest values in fall. Additive partitioning of species diversity show that β diversity contributed between 61% and 70% of gamma diversity, without differences among seasons. The temporal β diversity (measured as the qualitative dissimilarity between consecutive seasons of the year) was between 49% and 94% dissimilarity, with higher values in the seasonal transition from fall to winter. Increased macroalgal mortality by severe environmental conditions during middle summer are probably the most important driver of seasonal variability in α diversity, whereas high levels of β diversity are probably maintained through environmental and biotic variability in space and time and the stochastic processes of mortality and settlement of species. These findings indicate that β diversity is a key diversity component of macroalgal assemblages in subtropical rocky reefs in the Gulf of California.