Recovery potential of mutualistic anemone and anemonefish populations

Many anemone and anemonefish populations have been depleted by environmental disturbance and over-fishing. However, little is known about recovery potential of these populations, limiting the ability of resource managers to optimise recovery strategies. Depleted populations of multiple anemone and anemonefish species were monitored for ten years after commencement of a species-specific fishing moratorium at the Keppel Islands (Australia), which have recently been impacted by several environmental disturbances including flooding, mass bleaching and a cyclone. Although the moratorium was found to have positive effects on populations of Entacmaea quadricolor (anemone) and Amphiprion melanopus (anemonefish), rates of recovery were very slow, potentially due to Allee effects (depensation), reduced habitat quality, and (or) demographic constraints associated with obligate mutualism. Contemporary densities of E. quadricolor and A. melanopus appeared to be much lower than historical densities, suggesting that ten years without fishing was insufficient to facilitate population recovery in an era punctuated by environmental disturbances. Anemone and anemonefish species that were excluded from the moratorium either declined slightly in density (Amphiprion akindynos) or became so rare that they were not seen again during later surveys (Heteractis crispa and Amphiprion clarkii). We conclude that anemone and anemonefish populations can only support relatively light fishing pressure and likely require extended timeframes to recover from over-exploitation and disturbance. Strong precautionary management, including harvest limits with broad safety margins as insurance against future environmental disturbances, is therefore warranted.