Examining the Impact of Diadema antillarum and Herbivorous fish Populations on Coral Reef Health on a Honduran Reef System

Abstract

Coral reefs are some of the most diverse ecosystems on the planet. One source of the biodiversity and resilience of coral reef ecosystems is the wide range of symbioses and biological interactions that reefs facilitate and in which they participate. One of these involves Diadema antillarum and herbivorous fish. D. antillarum and herbivorous fish are the primary herbivores in Caribbean reef systems and are responsible for regulating microalgae biomasses. In the absence of both herbivores, algae biomasses grow to unpalatable levels and result in phase shifts on the reef, from coral-dominated to algae dominated systems. The D. antillarum mortality of 1983 caused a severe reduction in sea urchin populations in the Caribbean. Herbivorous fish would normally have been able to continue effective grazing and algae regulation, but overfishing has resulted in their loss from several Caribbean reefs as well. As such many reef systems in the Caribbean have been deprived of both their primary herbivores. In this study I examine the role of D. antillarum and herbivorous fish in determining coral reef health in a reef system off the coast of Honduras, in the Caribbean. I use Linear Mixed-effects Models to describe the reef system and assess the importance of, primarily, D. antillarum and herbivorous fish, and also depth and habitat complexity to coral reef health. I show that in the Honduran reef system, algae populations are regulated by D. antillarum and that herbivorous fish occur in low population densities and so do not have a significant effect on coral reef health. I also compare two common marine data collection protocols, the use of quadrats and the use of transects, and find that depending on resources, time, equipment and funding each data collection protocol has its own region of applicability.