Effect of temperature on settlement and postsettlement survival in a barrens-forming sea urchin

Large populations of the sea urchin Diadema aff. antillarum occur in the east Atlantic archipelagos. The origin and stability of these large herbivorous populations are not well known. Variability in settlement, recruitment and adult urchin density were quantified and compared over a 7 yr period (2002 to 2008) within the Canary Islands. Variables that potentially affect urchin settlement such as gonad index, temperature and primary productivity (phytoplankton) were measured. Settlement was found to be high during warm years; temperatures >24°C induced important settlement pulses. Postsettlement survival in barren areas of Tenerife was exponentially and positively correlated with seawater temperature changes, while very low to 0 survival was found at macroalgal beds off El Hierro. Assuming that climate change predictions are correct, the strong positive relationship between thermal history and postsettlement survival of this ecologically important species suggests that barren grounds will persist as seawater warms up if no mass mortality occurs. This future scenario will have important implications for the stability of algal beds and coastal ecosystems as a whole.