Kelp forests collapse reduces understory seaweed β-diversity.

Although the loss of the kelp canopy affected the composition of the macroalgal understory, none of the conventional indicators of α-diversity detected significant differences between healthy and degraded reefs. In contrast, small-scale spatial β-diversity decreased significantly as a result of deforestation, suggesting that the loss of kelp canopy may not significantly affect the number of species but still have an effect on their spatial arrangement. Our results suggest that small-scale β-diversity may be a good proxy for a more comprehensive assessment of the consequences of kelp forest decline.