Coral reefs are widely appreciated for their beauty and spectacular biodiversity, which rivals that of tropical rainforests. Unfortunately, coral reefs are in decline worldwide due to both natural and human impacts. These impacts have had particularly adverse effects on hard corals, which are the major architects responsible for building reefs. Because there is a strong relationship between coral-generated structure and the abundance and diversity of other reef-dwelling organisms, maintaining healthy corals is the key to conserving the biodiversity of reef communities.

 

Project Objectives

  • Develop and test hypotheses explaining the diversity of reef corals
  • Quantify the role of key Caribbean reef herbivores in maintaining coral-dominated reefs
  • Determine the relative importance of herbivory versus corallivory on tropical reefs


A corallivorous butterflyfish

(Photo by J. Idjadi)

Coral reef diversity

(Photo by R. Rotjan)

Coral Reef Diversity

Understanding the ecological processes that promote and maintain coral species diversity is increasingly essential as coral reefs continue to be threatened. We have been using experiments and modeling to test hypotheses of coral species coexistence on the reefs of French Polynesia. As the primary frame builders on reef, corals create habitat that countless other marine invertebrates rely upon for refuge and settlement space. Using surveys, we have been examining the relationship between coral-generated habitat features and the abundance and diversity of the associated reef fauna.

Coral Reef Herbivory

Urchins are key algal grazers whose loss in the Caribbean preceded a huge decline in coral cover and increases in the abundance of algae. In Discovery Bay, Jamaica, the decline of urchins in part led to massive coral die-offs and algae-dominated reefs. Now that these urchins are returning, we have demonstrated increases in coral growth, settlement and survivorship in Jamaica, which indicate the importance of these urchins for reef resilience.

 

The Herbivory-Corallivory Balance

Parrotfish are colorful and charismatic reef fish, and they are thought to contribute to the maintenance of healthy coral reefs by grazing seaweeds (herbivory) that could otherwise overgrow corals. However, coral reefs are complicated ecosystems, and although parrotfish benefit corals, they may sometimes cause unexpected damage. Parrotfish use their beak-like jaws to feed not only on seaweeds, but also on living corals (corallivory). Parrotfish scars on corals are highly conspicuous and can range from a few small bites to total colony destruction. Research we have conducted on Belizean and Bahamian reefs shows that in some areas, nearly 20 percent of coral colonies are killed by parrotfish grazing, and these corals do not recover. In spite of the complex role played by parrotfish grazing in maintaining reef communities, this aspect of coral reef ecology has received little scientific attention.