Cross-shelf Heterogeneity of Coral Assemblages in Northwest Australia

Molly Moustaka,Jim Stoddart,Margaret Mohring,Richard Evans,Thomas Holmes,Christopher Nutt,Shaun Wilson,Damian Thomson

doi:10.3390/d11020015

Abstract

Understanding the spatial and temporal distribution of coral assemblages and the processes structuring those patterns is fundamental to managing reef assemblages. Cross-shelf marine systems exhibit pronounced and persistent gradients in environmental conditions; however, these gradients are not always reliable predictors of coral distribution or the degree of stress that corals are experiencing. This study used information from government, industry and scientific datasets spanning 1980–2017, to explore temporal trends in coral cover in the geographically complex system of the Dampier Archipelago, northwest Australia. Coral composition at 15 sites surveyed in 2017 was also modelled against environmental and spatial variables (including turbidity, degree heat weeks, wave exposure, and distance to land/mainland/isobath) to assess their relative importance in structuring coral assemblages. High spatial and temporal heterogeneity was observed in coral cover and recovery trajectories, with reefs located an intermediate distance from the shore maintaining high cover over the past 20 years. The abundance of some prominent genera in 2017 (Acropora, Porites, and Turbinaria spp.) decreased with the distance from the mainland, suggesting that inshore processes play an important role in dictating the distribution of these genera. The atypical distributions of these key reef-building corals and spatial heterogeneity of historical recovery trajectories highlight the risks in making assumptions regarding cross-shelf patterns in geographically complex systems.

Highlights

Scleractinian corals are foundation species, underpinning biodiverse and productive coral reef ecosystems and supporting a multitude of environmental processes [1,2]
This study aims to assess the drivers of coral cover, diversity and assemblage composition throughout the Dampier Archipelago by (i) investigating patterns in historical coral cover; (ii) describing present-day spatial patterns in coral cover, diversity, and assemblage composition; and (iii) modelling the effect a suite of environmental and geographical factors has on coral assemblages
Abundant and diverse coral assemblages were observed in marginal environmental predictor of coral cover)

Summary

Introduction

Scleractinian corals are foundation species, underpinning biodiverse and productive coral reef ecosystems and supporting a multitude of environmental processes (e.g., wave mediation and sediment retention) [1,2]. Assemblage composition is largely determined by individual species tolerance to persistent ambient environmental conditions and resilience to stochastic disturbance events (e.g., tropical storms, predator and disease outbreaks and anomalous heating events) [10,11,12,13,14]. In the face of a rapidly changing climate and range of additive stressors, management should endeavor to protect adequate amounts of different coral assemblages, a concept typically referred to as CAR (comprehensive, adequate, representative) reserve design [25]. Marine reserves should span all major bioregions and be configured to adequately protect the full range of coral communities [25] This concept of reserve design requires a strong understanding of how coral assemblages change across space and persist through time

Objectives

Methods

Results

Conclusion