2010 Volume 3 Issue 2 Pages 81-92
Ecological impacts of Diadema species on benthic communities in the warm temperate waters of Northern Hemisphere, Japan in the Northwest Pacific and Macaronesian in the Northeast Atlantic, were reviewed in a concerted way as a result of two independent research groups. In Japan, two species D. setosum (known since early 1800's) and D. savignyi are distributed from southern to central Japan (up to 38°N in the Sea of Japan and 36°N on the Pacific coast) and causing locally patchy or zoned urchin barrens. In D. setosum, sexual maturity occurs only in summer; its grazing on macroalgae is highly dependent on water temperature and the algal size; mass mortality was recorded during cold temperatures in winter of 2002 (<12°C). In Macaronesian Archipelagos, Diadema antillarum-b, which is genetically separated from the western Atlantic population (D. antillarum-a), is widespread on rocky bottoms. D. antillarum-b matures throughout the year and seems to be much more voracious than D. setosum by means of feeding larger species of macroalgae and causing patchy or extensive urchin barrens. Besides elevation of water temperature, a variety of anthropogenic factors (e.g., increase of artificial structures in Japan, overfishing in Canary Islands) should be considered for the cause of the recent increase of Diadema barrens. In both areas, removal of Diadema has resulted in the establishment of macroalgal beds, but the implementation of long-term sustainable fisheries management, including the declaration of effective MPAs as well as the enactment of mitigation programs such as sea urchin control campaigns and/or predators restocking, should be considered as appropriate measures to control the population demography of Diadema and, consequently, to recover sound and balanced trophic structures on rocky bottoms. The combined effects of these actions may enhance the return of healthy marine vegetation in shallow coastal areas, which are considered at the base of the trophic chain in coastal ecosystems.
