Diadema Grazing Experiments

Overgrazing of macrophytes is an increasing ecological threat to coastal ecosystems, that occurs due to overfishing of top predators and/or to rapid tropicalization of temperate systems. Recently, the expanding invasion of the sea urchin Diadema setosum may further increase this threat to Mediterranean reef ecosystems. In 2017 it was discovered along the Israeli coast where it formed small patchy aggregations. The arrival of this new sea urchin created a knowledge gap regarding its potential ecological impacts. The aim of this study was to test these impacts utilizing lab and field experiments. We used an outdoor mesocosm facility to test grazing rates on turf-covered boulders under ambient and elevated temperatures, and a caging experiment to test grazing impacts in the field. In both experiments, all or most rock algal cover was grazed within a few weeks, leaving bare rock. The results are highly important for marine management, and call for policy action around the Mediterranean, for example, the implementation of extensive removal campaigns for this grazer across the region.