Examining the effect of different grazers on algal biomass
Herbivory drives ecosystem dynamics in both terrestrial and marine habitats, controlling type and biomass of vegetation. In tropical coral reefs, herbivorous fishes and invertebrates feed on benthic macroalgae, resulting in decreased algal biomass and increased hard substratum available for coral growth and recruitment, providing for increased levels of biodiversity. In 1983, the long-spined sea urchin, Diadema antillarum, suffered mass mortality in the Caribbean, resulting in dramatic changes to ecosystem dynamics such as decreased coral cover and increased macroalgal cover. This study aimed to examine the impact of various grazers on algal biomass in areas with and without D. antillarum in Bonaire, Dutch Caribbean, from late February to early April, 2012, using herbivore exclusion cages with varying levels of exclusion. Grazer categories were established based on cage type and proximity to D. antillarum. It was hypothesized that algal biomass would decrease with increased herbivore access. At locations with D. antillarum, there was a general increase in algal biomass with increased exclusion, whereas at locations without D. antillarum, the opposite trend was observed. Algal biomass generally decreased with increased grazer access; however, differences were not statistically significant. Herbivorous fishes removed the highest amount of algae, followed by D. antillarum, and large invertebrates. This study shows the importance of multiple herbivores in maintaining low algal biomass in Bonaire.