UC San Diego

Herbivory is an essential component to maintaining ecosystem structure and function in both terrestrial and marine systems. Benthic fleshy algal production on coral reefs is controlled by both bottom-up influences via nutrient availability and top-down control by herbivorous fishes, urchins, and invertebrate microherbivores. Anthropogenic impacts have modified reefs around the world, shifting their composition from dominance by reef builders to increased dominance by fleshy algae and non-coral invertebrates. This dissertation is an examination of herbivory on coral reefs, exploring the contributions of individual herbivore species as well as the herbivore community as a whole to the consumption of reef algal production. I explored the functional redundancy of the diverse community of herbivorous fish at Kahekili Herbivore Fisheries Management Area (KHFMA) on West Maui, Hawaii, finding that herbivorous fish across guilds on the reef largely consume turf algae, though these turf communities may vary in composition. However, herbivorous fish are consuming different types of macroalgae, turf algae, and other substrates selectively based on benthic composition. I further developed a model for calculating benthic fleshy algal production and herbivorous fish consumption at Kahekili. Through this model, I determined benthic fleshy algal production exceeded fish community consumption by three-fold, although larger size classes of herbivores in more recent years were contributing more to the consumption budget. I then applied this model to a diverse set of reefs around Maui to determine the relative balance of algal production and fish consumption, seeing a handful of reefs with a balanced budget. I further found that consumption rates were a better predictor of benthic community structure than fish biomass. I further determined that more herbivorous fish biomass would be required to reduce algal cover on a reef than maintain low algal cover on an already high coral cover reef. Finally, I examined the relative role of the herbivorous fish community and sea urchins on reef community composition and algal biomass. I found that herbivorous fish contributed more to macroalgal removal while urchins contributed more to turf grazing and exposure of bare limestone. Herbivorous fish may be also be facilitating further urchin grazing. The results of these four chapters support the potential for herbivore management to aid in recovery of degraded reefs