Algal turf negatively affects recruitment of a Caribbean octocoral

Abstract

Algal cover has increased and scleractinian coral cover has steadily declined over the past 40 years on Caribbean coral reefs, while octocoral abundance has increased at sites where abundances have been monitored. The effects of algal cover on recruitment may be a key component in these patterns, as upright octocoral recruits may escape competition with algae by growing above the ubiquitous algal turfs. We used laboratory and field recruitment experiments to examine impacts of algal turf on recruitment of the common, upright, and zooxanthellate Caribbean octocoral Plexaura homomalla. Laboratory recruitment rate was significantly higher in lower turf cover treatments. The survival of recruits in the field was significantly reduced by increased turf cover; for every 1% increase in turf cover, polyps died 1.3% faster. In a model parameterized by the observed field survival, polyps exposed to 100% turf cover had a 2% survival rate over 51 days, while polyps exposed to no turf cover had a 32% survival rate over the same time. We found that high densities of turf algae can significantly inhibit recruitment of octocorals. Experimentally obtained octocoral survival rates were higher than those published for Caribbean octocorals. The factors that influence recruitment are critical in understanding the dynamics of octocorals on Caribbean reefs as continuing declines in scleractinian cover may lead to more octocoral-dominated communities.