Differences in the sea urchin Diadema aff. antillarum population structure, which have been attributed to removal of predatory fish through over fishing, are observed throughout the Canary Islands. Low urchin abundances and a "desired conservation state" are currently found in Mar de Las Calmas Marine Protected Area and nearby. shed areas (FAs) in El Hierro Island, in contrast to the occurrence of high urchin densities and the "undesired conservation state" in the highly FAs (HFAs) of Tenerife Island. Under these different levels of fishing pressure, we consider a set of ecological variables potentially affecting urchin populations (settlement, recruitment, adult urchin densities, predation rates, and abundance of urchin fish predators) to infer their magnitude and relative importance in addressing community-wide changes. No differences in settlement and recruitment rates were found, but predation pressure was higher in El Hierro, where adult density was low and predation rates were high. The combination of these factors provides evidence of a top - down control of sublittoral reef communities. Although the effect of protection was less clear, we demonstrate the positive effects of reduced fishing effort in enhancing trophic cascade processes and reducing the establishment of barren grounds.
