NCEAS Project 10041

Coral reef degradation: Determining the relative role of top-down and bottom-up factors in the global decline of coral reefs

  • Jennifer E. Smith

ActivityDatesFurther Information
Postdoctoral Fellow1st October 2005—30th June 2008Participant List  

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 (Connell 1978, Hughes et al. 2003, Bellwood et al. 2004). Regardless of the cause, reef degradation generally results in an irreversible phase-shift from dominance by reef-building coral to dominance by fleshy macroalgae (Petraitis and Dudgeon 2004). 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 (McCook 1999). 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 (Smith 2003). 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 I propose to develop conceptual models to determine the relative strength of top-down versus bottom-up control on coral reefs. I also propose to conduct a meta-analysis of these data to test several hypotheses regarding the importance of top-down and bottom-up control across several gradients in the tropics including latitude, diversity and disturbance. Lastly, using a pre-existing database I will assess the role of top-down and bottom-up factors on the success of exotic macroalgae on tropical reefs and conduct a risk assessment to identify species that are likely to be more invasive than others. 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.

TypeProducts of NCEAS Research
Journal Article Salomon, Anne; Gaichas, Sarah; Shears, Nick; Smith, Jennifer E.; Madin, Elizabeth M.P.; Gaines, Steven D. 2010. Key features and context-dependence of fishery-induced trophic cascades. Conservation Biology. Vol: 24. Pages 382-394. (Online version)
Journal Article Sandin, Stuart A.; Smith, Jennifer E.; DeMartini, Edward E.; Dinsdale, Elizabeth A.; Donner, Simon D.; Friedlander, Alan M.; Konotchick, Talina; Malay, Machel; Maragos, James E.; Obura, David; Pantos, Olga; Paulay, Gustav; Richie, Morgan; Rohwer, Forest; Schroeder, Robert E.; Walsh, Sheila; Jackson, Jeremy B.C.; Knowlton, Nancy; Sala, Enric. 2008. Baselines and degradation of coral reefs in the Northern Line Islands. PLoS ONE. Vol: 3(2). Pages e1548.
Data Set Smith, Jennifer E. 2006. Coral reef nutrient herbivore database. (Online version)
Journal Article Smith, Jennifer E.; Shaw, Morrigan; Edwards, Rob A.; Obura, David; Pantos, Olga; Sala, Enric; Sandin, Stuart A.; Smriga, Steven; Hatay, Mark; Rohwer, Forest. 2006. Indirect effects of algae on coral: Algae-mediated, microbe-induced coral mortality. Ecology Letters. Vol: 9. Pages 835-845.
Journal Article Smith, Jennifer E.; Conklin, Eric J.; Smith, Celia M.; Hunter, Cynthia L. 2008. Fighting algae in Kaneohe Bay - Response. Science. Vol: 319. Pages 157-158.
Journal Article Williams, Susan L.; Smith, Jennifer E. 2007. A global review of the distribution, taxonomy, and impacts of introduced seaweeds. Annual Review of Ecology Evolution and Systematics. Vol: 38. Pages 327-359.