Responses of Coral Reef Fish to Changes in Coral Cover: French Polynesia

Working in lagoons on the north shore of Moorea (French Polynesia) throughout 2002-2003, Holbrook et al. (2008) used a combination of reef surveys and field experimentation to (1) estimate the functional forms of the local relationships between variation in coral cover and three attributes of the associated fish assemblage (species richness, total abundance and species composition), and (2) isolate the influence of variation in the cover of living coral tissue from that due to merely the physical presence of the coral, be it living or dead. The latter objective was achieved with the help of 25 experimental patch reefs, which they constructed on a sand plain in the Maharepa lagoon by transplanting different proportions of live and dead colonies of the branching coral Pocillopora eydouxi, while the first objective was achieved by scuba divers who identified and counted all reef-associated fish and mapped the corals in each of nineteen 50- x 10-m survey plots located mid-way between the shore and barrier reef in the Vaipahu and Maharepa lagoons.

Results indicated that "all measured attributes of the fish community were insensitive to changes in live coral cover over a wide range before falling sharply as live coral cover approached zero," and they determined "there was qualitative agreement in the pattern of abundance response of fish with variation in cover of live coral between the experiment and field surveys." More specifically, Holbrook et al. state that "the apparent tipping point for these attributes of the fish community occurred when cover of live coral fell below 5%."

"Taken together," as they describe it, "the results suggest that local fish assemblages could be resistant to variation in abundance of live coral, changing significantly only as coral becomes rare, while recovery may occur with only modest increases in live coral." Stated another way, the three researchers say that after a major disturbance, such as a bleaching episode, "the observed functional relationships in [their] study suggest that biodiversity, trophic structure, and overall abundance of fishes could essentially recover to their pre-disturbance states after only a modest return in the cover of living coral."