Anemonefish aggressiveness affects the presence of Dascyllus trimaculatus co-existing with host anemones

Abstract

One of the most well-known symbiosis of coral reefs is the relationship between host anemones and anemonefish. Host anemones are used not only by anemonefish but also by other species such as the immature phase of the three spot damsel (Dascyllus trimaculatus). Anemonefish can be a superior competitor to D. trimaculatus, which shares host anemones as shelter resources. Interspecific competition for shelter resources is considered to be an important factor affecting community structure in coral reef fish. In this study, we investigated the factors affecting host anemone utilization of D. trimaculatus around Okinawajima Island. Among 296 colonies, D. trimaculatus inhabited 52 (= 17.6%) host anemones. Decision tree analyses (CHAID) using five independent variables (species of host anemone and anemonefish, presence/absence of adult anemonefish, numbers of immature anemonefish, and size of host anemone) revealed that D. trimaculatus rarely occupied the anemones Entacmaea quadricolor and Stichodactyla haddoni, and seldom cohabited with Amphiprion frenatus and A. polymnus. We experimentally presented a clay model of D. trimaculatus to colonies of six species of anemonefish and compared the duration of aggressive behavior. The aggressive behaviors of A. frenatus and A. polymnus were significantly longer and more intense than that of the other four species. Our findings demonstrate that species composition in anemone symbioses may be affected by coexisting anemonefish as aggressive behavior toward intruders differs among species.