October 17 2012

12:00 LSB 2320

Sally Holbrook
Dept of Ecology, Evolution and Marine Biology, UC Santa Barbara

Abrupt State Change and Resilience in Marine Ecosystem - What Coral Reefs are Telling Us


The occurrence and causes of abrupt transitions between ecosystem states are of great concern and the likelihood of such transitions is increasing for many ecological systems. However, identification of state shifts and their underlying mechanisms has proved challenging. Given world-wide trends, it is critical that we better understand processes that facilitate the rapid return of reefs to a coral dominated state following pulse perturbations. Since many perturbed reefs have undergone a persistent state shift to high cover of macroalgae, knowledge of how herbivory operates is of paramount importance. While control of macroalgae is necessary for a return to coral dominance, it is not sufficient - failure of corals to recruit following a disturbance will keep the reef in a degraded state. Coral settlement rates can scale with adult abundance, so widespread decline in coral cover could lead to persistent recruitment failure. Reefs around Moorea, French Polynesia have consistently returned to coral dominance following major disturbances. Following recent perturbations, populations of herbivores - particularly parrotfishes - increased rapidly, which prevented macroalgae from increasing on the fore reef despite the near complete loss of coral. The numerical response of parrotfishes was facilitated by the presence of nursery habitat in the lagoon where they recruit before moving to offshore reefs. Recruitment of corals to denuded forereef habitat has been robust, indicating substantial larval connectivity with source populations. These findings underscore the importance of connectivity and the need to protect functionally critical nurseries that enhance resilience of coral reefs.

WEDNESDAY, October 17, 2012











































































































































































































































































































































































































































































































































































































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