Gradients of disturbance and environmental conditions shape coral community structure for south‐eastern Indian Ocean reefs

Jens Zinke,Maria Beger,Nicholas A J Graham,Marji Puotinen,Ming Feng,Scott N Evans,Zoe T Richards,Timothy R Mcclanahan,Rebecca Fisher,Shaun K Wilson,George Shedrawi,Michael Stat,Joseph Maina,Jean‐Paul A Hobbs,Stuart N Field ,Cordelia H Moore ,Russ Babcock ,Emily S Darling ,James Gilmour

doi:10.1111/ddi.12714

Abstract

AbstractAimTo describe, model and assess the relative importance of environmental and climatic factors likely influencing the regional distribution of coral cover and assemblages with contrasting life histories and susceptibilities to bleaching.LocationWe compiled the first comprehensive empirical dataset for coral communities in the south‐eastern Indian Ocean (SEIO), incorporating information from 392 sites along the western coast of Australia and offshore atolls/islands across ~19° of latitude.MethodsWe assessed hard coral cover and community composition to genus using point‐intercept transects or point‐count analysis of digital images taken along transects. We explored spatial variation in environmental conditions and in composition of corals with contrasting life histories. After de‐trending the temporal patterns, we assessed the relative importance of environmental metrics to coral cover, life histories and bleaching susceptibility using a full subsets model‐selection approach with generalized additive mixed models, accounting for both temporal and among site variation.ResultsThe distribution of temperature, light, the frequency of temperature anomalies and tropical cyclones appear to be drivers of coral community structure. Functional diversity of low‐ to mid‐latitude coral communities may convey some resilience to thermal stress, while higher latitude communities dominated by Competitive and Bleaching‐Susceptible taxa may lack this functional resilience. These patterns likely reflect varying historical exposure to cyclones and temperature anomalies.Main conclusionsAs evident in recent years, changing background conditions and regimes of disturbance in coming decades will shift the distribution, functional diversity and resilience of coral reefs throughout the SEIO. The rate and magnitude of environmental change will ultimately determine the future of the tropical reefs and whether the higher latitude reefs provide some refuge from climate change. Our study highlights the need to quantify the distributional properties of key environmental metrics to better understand and predict reef condition through coming decades.

Highlights

Cycles of disturbance and recovery are a key feature of coral reef ecosystems (Connell, 1978; Rogers, 1993), where multiple diversity-disturbance relationships exist depending on the interaction between the frequency and intensity of disturbances (Hall et al, 2012)
The background environmental conditions at the SEIO reefs and their exposure to disturbances reflected their geographic setting, with variation being high among regions and comparably low among reefs within regions (Fig. 2; Table 1)
Variation (SD) in SST was highest at Ningaloo Reef, Shark Bay and the Rowley Shoals, indicating that these sites are exposed to a wide range of temperatures (Table 1)

Summary

Introduction

Cycles of disturbance and recovery are a key feature of coral reef ecosystems (Connell, 1978; Rogers, 1993), where multiple diversity-disturbance relationships exist depending on the interaction between the frequency and intensity of disturbances (Hall et al, 2012). Management actions aimed at maintaining the diversity, functional integrity and resilience of coral reef ecosystems are ideally based on understanding how inherent environmental conditions interact with disturbance regimes to shape coral community structure (Iwamura et al, 2010; Klein et al, 2013; Maynard et al, 2015a). This type of information is increasingly important, because many reefs face cumulative threats from a combination of natural and anthropogenic stressors operating at multiple scales (Hughes et al, 2003, 2010, 2017). Areas dominated by relatively benign conditions associated with shallow, clear waters as well as low wave action and nutrient loads are often characterised by the proliferation of corals with ‘Competitive’ life-history traits (e.g, branching Acropora), following the definition of Darling et al (2012, 2013)

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Discussion

Conclusion