Study areas

In Catalonia, the purple sea urchin, Paracentrotus lividus, is the most abundant species and is considered the most important herbivore controlling the macroalgal dynamics on shallow reefs. Although the black sea urchin, Arbacia lixula, is also common, it is approximately one order of magnitude less abundant than P. lividus on the Catalan coast. In this region, the dramatic increase of sea urchins due to the depletion of predatory fish (mainly seabreams) represents one of the major causes of degradation of benthic coastal assemblages. Long term monitoring of sea urchin populations has been performed, showing more abundance and variability outside the MPAs, and a higher recovery trend of P. lividus abundance. These results suggest subtle predation effects inside the MPAs Cap de Creus and Medes Islands, with a positive indirect trophic effect of protection, increasing the cover of some forest-forming macroalgae. Outside the MPAs sea urchin fisheries are regulated within the region using different quotas along the coast. 

In Sardinia, the local market of edible sea urchins has significantly developed during the last decades as a result of the increased demand of gonads, driving P. lividus populations close to collapse across the majority of the region. Sea urchins’ fishery is regulated on a regional scale, allowing harvesting also inside the partially protected zone of the MPA Capo Caccia-Isola Piana, which borders with one of the most exploited areas of North-West coast of Sardinia. In contrast, the MPA Tavolara-Punta Coda Cavallo is considered a well-enforced area, with strict limitations for sea urchins harvesting and well-preserved sea urchin populations. Outside the MPAs sea urchin fisheries are regulated using fixed quotas along all the coasts. Long term monitoring of sea urchin populations shows a significant decrease of the sea urchins especially along the West Coast. Actions of restocking and the recent ban on the harvesting in specific areas were implemented to counteract this negative trend.