Abstract
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.
