Green Zones on the Great Barrier Reef do more than just give fish a place to grow larger and more abundant. They also protect the reef itself and help it recover.
Last year the Great Barrier Reef suffered the largest and most widespread of the three mass bleaching events of the past two decades. The bleaching event affected reefs all over the world. When it hit Australia, it evolved very rapidly. Eventually over 93% of reefs were affected by bleaching. The northern section of the Great Barrier Reef was most badly damaged, with between 50 and 90% of corals dying.
One of the great benefits of green zones is that they allow large herbivorous fishes to survive in abundance. Those fish consume algae that would otherwise dominate corals and other reef building species. In a 2006 experiment led by scientist Terry Hughes, large fish were excluded from reefs damaged by bleaching. Large cages were constructed in green zones that would allow small fish to enter but prevent the large ones coming in. Over a period of three years the reefs were dominated by seaweed up to three metres in length and the survival rate of corals declined significantly compared with areas control sites without cages.
This study provides clear evidence that green zones help the reef recover from coral bleaching. With the likelihood of increased bleaching due to global warming it is time we began to look more closely at the management of our marine ecosystems and whether we need more than the current 30% green zones in the Great Barrier Reef.
(Phase Shifts, Herbivory, and the Resilience of Coral Reefs to Climate Change by Hughes et al, Current Biology 17, 360–365, February 20, 2007)
