Low density populations of anemonefish with low replenishment rates on a reef edge with anthropogenic impacts

Abstract

The population dynamics of anemonefish are expected to have unique patterns because of the symbiotic relationship with host anemones. Recent anthropogenic impacts may affect the abundance of anemones, which may also affect population dynamics of anemonefish. However, long-term field studies and demographic data on reproduction, immigration, and mortality rates are deficient. Here, we investigated the dynamics of anemonefish for 3 years on the reef edge with anthropogenic impacts of Okinawa-jima Island, southern Japan. During the study period, six species of host anemone were used as spawning grounds by four species of anemonefish, and as nurseries by six species of immature anemonefish. The density of breeding pairs was low (0.21–1.46 /ha), which may have been restricted by the abundance of host anemones. Survival rates were different among species; from 0.21 to 1.00 over 3 years. Ten cases of dissolution of breeding pairs were observed during the 3 years, and only five pairs were replenished. Through the study period, 215 individuals of six species of immature fish immigrated into the study site, and this number was skewed due to higher numbers of Amphiprion clarkii (77.7%). Demographic patterns differed among species, and requirements for conservation will therefore be different among species on the reef edges of Okinawa-jima Island under anthropogenic impact.