NCEAS

Coral reef ecosystems are among the most diverse and highly productive ecosystems on the planet yet are currently threatened by a number of natural and anthropogenic factors. Regardless of the cause, reef degradation generally results in an irreversible phase-shift from dominance by reef-building coral to dominance by fleshy macroalgae. These shifts are believed to be irreversible and lead to communities that are less diverse and much less complex. While a number of natural disturbances can cause localized coral mortality, reduced top-down control (caused by overfishing) and increased bottom-up control (caused by nutrient pollution) are the most frequently implicated causes of anthropogenic reef degradation. Past research has focused on either one or the other of these factors independently, has involved large-scale field-based correlations and more recently involved factorial field and laboratory manipulations. However, despite much effort there is not consensus in the scientific community as to how these factors independently and interactively influence phase-shift formation. Further, not all phase-shifts are alike; some result in blooms of a single species of algae while others result in a more diverse mixed species assemblage and still others involve invasive non-indigenous species. Through analysis and synthesis of data from the literature this project will develop conceptual models to determine the relative strength of top-down versus bottom-up control on coral reefs. Ultimately these results will help to identify the importance of overfishing and nutrient pollution on reefs by specifically identifying how these factors influence benthic reef community structure. The information generated by this project will be highly useful in implementing sound science-based management decisions for conservation of coral reef ecosystems across the globe.