Benthic composition influences habitat use and toxicity of coral-dwelling fishes

Abstract

The distribution and abundance of habitat specialists is often associated with the availability of preferred habitat; however, other environmental features can also influence habitat selection. Coral-dwelling gobies are habitat specialist fishes that depend on the availability of a few key species of coral for their survival and rely on skin toxins to reduce predation risk. This study investigated the influence of benthic substratum around coral colonies on patterns of habitat use and toxicity of two species of coral-dwelling gobies (Gobiodon erythrospilus and Gobiodon histrio) that compete for access to the coral, Acropora nasuta. Field surveys demonstrated that the benthic substratum around A. nasuta coral colonies differed between colonies occupied by G. histrio and G. erythrospilus. Juvenile, single adult and breeding pairs of G. erythrospilus mostly inhabited A. nasuta colonies surrounded by branching corals. In contrast, juvenile and single adult G. histrio associated with A. nasuta coral colonies that had adjacent epilithic algal matrix and G. histrio breeding pairs inhabited colonies surrounded by sand/rubble. Habitat choice experiments demonstrated that both goby species prefer A. nasuta coral colonies with benthic substratum mainly composed by epilithic algal matrix and sand; suggesting that competition for coral colonies in preferred locations could influence patterns of habitat use observed in the field. The substratum around preferred coral colonies also influenced the toxicity levels of associated fishes. Gobies inhabiting A. nasuta coral colonies surrounded by epilithic algal matrix and sand showed higher levels of toxicity than gobies collected from colonies surrounded by branching corals. Given the potential for toxicity level to reduce the risk of predation, this could explain why gobies would compete for access to colonies of the preferred coral species surrounded by epilithic algal matrix and sand. These results show that the habitat use of coral habitat specialist fishes can be affected by the benthic composition around preferred coral colonies and demonstrate how competition for important secondary resources can influence patterns of habitat use.