Interactive effects of interspecific competition and microhabitat on early post-settlement survival in a coral reef fish

Microhabitat type and the competition for microhabitats can each influence patterns of abundance and mortality in coral reef fish communities; however, the effect of microhabitat on the intensity and outcome of competition is not well understood. In Kimbe Bay, Papua New Guinea, surveys were used to quantify microhabitat use and selectivity in two live-coral specialist damselfishes (Pomacentridae), Chrysiptera parasema, and Dascyllus melanurus. A patch reef experiment was then conducted to test how intra- and interspecific competition interacts with two types of microhabitat to influence survival of recently settled C. parasema. Surveys demonstrated that C. parasema and D. melanurus recruits utilized similar coral microhabitats; 72% of C. parasema and 85% of D. melanurus used corymbose and bottlebrush growth forms of Acropora. One microhabitat type, Pocillopora sp. coral, was commonly used by D. melanurus but rarely by C. parasema. The patch reef experiment revealed that both microhabitat and interspecific competition influence abundance of recently settled C. parasema. Microhabitat had the strongest influence on survival of C. parasema. In the absence of interspecific competitors, ~85% of C. parasema survived for 5 days after transplantation to high-complexity bottlebrush Acropora reefs when compared to only 25% survival of Pocillopora reefs. In both microhabitats, interspecific competition with D. melanurus, but not intraspecific competition, significantly decreased the survival of C. parasema. Taken together, these results suggest that the observed distribution of C. parasema results from specialized microhabitat requirements and competition for space in those microhabitats. This study demonstrates that interspecific competition and microhabitat type can interact to influence early post-settlement survival in coral reef fishes, though, whether and how these factors influence survival will depend on the behavioural attributes and strength of habitat associations among potential competitors.