Rapid decline and decadal-scale recovery of corals and Chaetodon butterflyfish on Philippine coral reefs

Abstract

Environmental disturbances to benthic habitat on coral reefs can affect fish assemblages, with dietary specialists like corallivorous Chaetodon butterflyfishes particularly sensitive to declines in hard coral cover. However, declines in density of corallivorous Chaetodon due to declines in hard coral cover are usually documented for individual environmental disturbances, often with limited quantification of post-disturbance recovery. Here, we documented effects of hard coral loss and recovery on the Chaetodon assemblage for 31 years at four sites in the Philippines. In this long-term “natural experiment”, we documented five environmental disturbance events (two typhoons, two mass coral bleaching events, and one period of destructive fishing) that reduced live branching hard coral cover on average by 61% and density of corallivorous butterflyfish by 47%, with an average duration of decline of 2 years. On average, these disturbance events resulted in an 8% annual decrease in absolute coral cover. We also monitored five periods of hard coral and butterflyfish recovery, with an average 202% increase in branching hard coral cover over 11 years, and a 196% increase in density of corallivorous butterflyfish over 12 years. On average, these recovery periods had a 2.4% annual rate of increase in absolute coral cover. The density of butterflyfish was not significantly affected by marine reserve protection, and thus, changes in butterflyfish density were most likely driven by change in benthic habitat. Assemblage structure of Chaetodon at each site was distinct and remained remarkably consistent for 31 years, despite substantial declines and recovery of coral cover. The difference in the rates of decline and recovery of butterflyfish raises concerns for the persistence of this iconic taxon in the face of increasing frequency and intensity of environmental disturbances to coral reefs.