Coral reef community composition in the context of disturbance history on the Great Barrier Reef, Australia.

Nicholas A J Graham,Kirsty L Nash,Cindy Huchery,Fraser A Januchowski-Hartley,Karen M Chong-Seng,Benjamin Ruttenberg

doi:10.1371/journal.pone.0101204

Nicholas A J Graham, Kirsty L Nash + Show 4 more

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https://doi.org/10.1371/journal.pone.0101204

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Abstract

Much research on coral reefs has documented differential declines in coral and associated organisms. In order to contextualise this general degradation, research on community composition is necessary in the context of varied disturbance histories and the biological processes and physical features thought to retard or promote recovery. We conducted a spatial assessment of coral reef communities across five reefs of the central Great Barrier Reef, Australia, with known disturbance histories, and assessed patterns of coral cover and community composition related to a range of other variables thought to be important for reef dynamics. Two of the reefs had not been extensively disturbed for at least 15 years prior to the surveys. Three of the reefs had been severely impacted by crown-of-thorns starfish outbreaks and coral bleaching approximately a decade before the surveys, from which only one of them was showing signs of recovery based on independent surveys. We incorporated wave exposure (sheltered and exposed) and reef zone (slope, crest and flat) into our design, providing a comprehensive assessment of the spatial patterns in community composition on these reefs. Categorising corals into life history groupings, we document major coral community differences in the unrecovered reefs, compared to the composition and covers found on the undisturbed reefs. The recovered reef, despite having similar coral cover, had a different community composition from the undisturbed reefs, which may indicate slow successional processes, or a different natural community dominance pattern due to hydrology and other oceanographic factors. The variables that best correlated with patterns in the coral community among sites included the density of juvenile corals, herbivore fish biomass, fish species richness and the cover of macroalgae. Given increasing impacts to the Great Barrier Reef, efforts to mitigate local stressors will be imperative to encouraging coral communities to persist into the future.

Highlights

The last two decades of coral reef research have seen a proliferation of publications charting the declining condition of coral reefs
One way to better understand these changes is through research on community composition of reefs with differing disturbance history, which should quantify ecological processes and physical features that may be important for reef condition [10]
We found substantial differences among reefs, zones and exposure for coral cover, structural complexity and the richness of coral genera

Summary

Introduction

The last two decades of coral reef research have seen a proliferation of publications charting the declining condition of coral reefs. Coral reef communities are known to vary with exposure to wave energy and the ‘zone’ of the reef on which they occur, such as the flat, crest or slope [11,12,13]. These differences are likely driven by variability in a range of natural factors, such as water movement, light penetration and temperature. The majority of studies assessing coral condition in the context of disturbance and recovery have focussed on only one reef zone or level of exposure and many key variables, such as various ecological processes or physical attributes, are often not quantified [18]

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