Abstract
Increasing frequency and severity of disturbances is causing global degradation of coral reef ecosystems. This study examined temporal changes in live coral cover and coral composition in the central Maldives from 1997 to 2016, encompassing two bleaching events, a tsunami, and an outbreak of Acanthaster planci. We also examined the contemporary size structure for five dominant coral taxa (tabular Acropora, Acropora muricata, Acropora humilis, Pocillopora spp, and massive Porites). Total coral cover increased throughout the study period, with marked increases following the 1998 mass-bleaching. The relative abundance of key genera has changed through time, where Acropora and Pocillopora (which are highly susceptible to bleaching) were under-represented following 1998 mass-bleaching but increased until outbreaks of A. planci in 2015. The contemporary size-structure for all coral taxa was dominated by larger colonies with peaked distributions suggesting that recent disturbances had a disproportionate impact on smaller colonies, or that recruitment is currently limited. This may suggest that coral resilience has been compromised by recent disturbances, and further bleaching (expected in 2016) could lead to highly protracted recovery times. We showed that Maldivian reefs recovered following the 1998 mass-bleaching event, but it took up to a decade, and ongoing disturbances may be eroding reef resilience.
Highlights
Increasing frequency and severity of disturbances is causing global degradation of coral reef ecosystems
Rates of recovery are typically measured based on the time it takes for either overall abundance of key groups of organisms or the specific abundance of individual taxa to reach levels apparent immediately prior to the disturbance[5,12], which can be very fast or slow depending upon relative abundance of fast- and slow-growing species[13]
There has been a sustained increase in coral cover at sites surveyed in the Maldives since the 1998 mass bleaching (Fig. 1, Table S1), though recovery has been compromised in very recent years by other acute disturbances (Fig. 1)
Summary
Increasing frequency and severity of disturbances is causing global degradation of coral reef ecosystems. The contemporary size-structure for all coral taxa was dominated by larger colonies with peaked distributions suggesting that recent disturbances had a disproportionate impact on smaller colonies, or that recruitment is currently limited This may suggest that coral resilience has been compromised by recent disturbances, and further bleaching (expected in 2016) could lead to highly protracted recovery times. Rates of recovery are typically measured based on the time it takes for either overall abundance of key groups of organisms (e.g., total coral cover) or the specific abundance of individual taxa to reach levels apparent immediately prior to the disturbance[5,12], which can be very fast or slow depending upon relative abundance of fast- and slow-growing species[13]. Fast-growing tabular and branching corals, for example, are the primary habitat-forming species[14] and are usually very common because they are able to rapidly re-colonise reef habitats following a disturbance[14,15]
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