Effects of larger heterospecifics and structural refuge on the survival of a coral reef fish,Thalassoma hardwicke

Structural refuge and competition can influence the survival of coral reef fishes; however, the effect of structural refuge on the outcome of competition remains unclear. In Moorea, French Polynesia, surveys were used to quantify habitat association for juvenileThalassoma hardwickeand 7 sympatric labroid species. Having identified the 3 species most similar to focalT. hardwickein habitat association, a field assay was used to determine if the presence of larger individuals of these species adversely affected the survival of focal individuals. Finally, a field experiment was used to test how competition with larger residents and structural refuge interact to influence survival of transplantedT. hardwicke. Surveys demonstrated thatGomphosus varius,Pseudocheilinus hexataenia, andT. quinquevittatumwere most similar toT. hardwickein habitat association. In the field assay, the presence ofT. quinquevittatumhad the greatest negative effect on survival ofT. hardwicke. The field experiment revealed that competition withT. quinquevittatumand structural refuge both alteredT. hardwickesurvival, although their effects were not interactive. Survival ofT. hardwickewas 2.3 times greater in treatments withoutT. quinquevittatumrelative to those withT. quinquevittatum, and 2.8 times greater in treatments with structural refuge relative to those without structural refuge. The additive effect may have occurred via the establishment of social dominance hierarchies between transplantedT. hardwickeand residentT. quinquevittatumindependently of structural refuge, suggesting that it is important to account for interactions occurring independently of resources when examining resource competition.