Algal Turf Recruitment and Early Growth did not Differ Across Sites that Varied Greatly in Herbivore and Coral Community Structure.

Worldwide losses of coral with accompanying phase shifts to algae have been attributed to human alterations of major ecological processes, especially top down (herbivory) and bottom up (nutrients) forces. While positive effects on macroalgae have received some attention, less is known about turf algae. Closely cropped turf algae (< 1cm) are a major component of pristine coral reefs, providing trophic support, aiding in nutrient cycling, and providing high rates of photosynthesis. We hypothesized that enhanced nutrient supplies from developed watersheds and reduced herbivory from overfishing would result in longer turf, and possibly development of macroalgae. The goals of this study were to quantify top down and bottom up forces in conjunction with assessments of turf algae recruitment and growth on a fringing reef in Mo’orea French Polynesia. While this study will continue for 2 years, data here are for 5 weeks. We chose 3 sites in Cooks Bay that likely varied in nutrients and 3 along the north shore, presumably higher in herbivory. At each site 10 recruitment tiles were deployed. Turf communities accumulated over five-weeks while benthic and herbivorous fish communities were quantified at each site. Herbivorous fish communities consisted of juveniles and adults from the families Acanthuridae and Scaridae with both adult and juvenile acanthurids, comprising > 50% of all herbivorous fish. Sites within the bay, however, contained at least 66.7% less fish than sites along the north shore. In contrast benthic surveys portrayed little difference between sites, with turf making up > 70% of total hard bottom cover. Similarly, there was little difference among sites in the recruitment and growth rate (~0.2-0.3 mm/week) of turf on tiles. While turf recruitment and early development appeared to be unaffected by herbivory or nutrients over the short time, we predict that longer-term effects will occur as this community develops.