Environmental Factors Controlling the Distribution of Symbiodinium Harboured by the Coral Acropora millepora on the Great Barrier Reef

Timothy F Cooper,Alison M Jones,Marites Canto,Ray Berkelmans,Scarla Weeks,Ben Radford,Karin E Ulstrup,Madeleine J H Van Oppen,Rebecca A O'Leary,Jason Doyle

doi:10.1371/journal.pone.0025536

Abstract

BackgroundThe Symbiodinium community associated with scleractinian corals is widely considered to be shaped by seawater temperature, as the coral's upper temperature tolerance is largely contingent on the Symbiodinium types harboured. Few studies have challenged this paradigm as knowledge of other environmental drivers on the distribution of Symbiodinium is limited. Here, we examine the influence of a range of environmental variables on the distribution of Symbiodinium associated with Acropora millepora collected from 47 coral reefs spanning 1,400 km on the Great Barrier Reef (GBR), Australia.Methodology/Principal FindingsThe environmental data included Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data at 1 km spatial resolution from which a number of sea surface temperature (SST) and water quality metrics were derived. In addition, the carbonate and mud composition of sediments were incorporated into the analysis along with in situ water quality samples for a subset of locations. Analyses were conducted at three spatio-temporal scales [GBR (regional-scale), Whitsunday Islands (local-scale) and Keppel Islands/Trunk Reef (temporal)] to examine the effects of scale on the distribution patterns. While SST metrics were important drivers of the distribution of Symbiodinium types at regional and temporal scales, our results demonstrate that spatial variability in water quality correlates significantly with Symbiodinium distribution at local scales. Background levels of Symbiodinium types were greatest at turbid inshore locations of the Whitsunday Islands where SST predictors were not as important. This was not the case at regional scales where combinations of mud and carbonate sediment content coupled with SST anomalies and mean summer SST explained 51.3% of the variation in dominant Symbiodinium communities.Conclusions/SignificanceReef corals may respond to global-scale stressors such as climate change through changes in their resident symbiont communities, however, management of local-scale stressors such as altered water quality is also necessary for maintenance of coral-Symbiodinium associations.

Highlights

Unicellular photosynthetic symbionts (Symbiodinium spp.) play a vital role in the energy budget, metabolism and secretion of the calcium carbonate skeleton of scleractinian corals [1,2]
This study reports on the correlation between a range of environmental variables and the distribution of Symbiodinium associated with A. millepora collected at different spatial scales: i) along 13u latitude spanning approximately 1,400 km on the Great Barrier Reef (GBR), ii) along a persistent water quality gradient in the Whitsunday Islands spanning approximately 65 km [29], and iii) on populations sampled repeatedly over a number of years at Davies and Trunk Reefs, and the Keppel Islands
Our results suggest that Symbiodinium distribution in A. millepora is not always primarily driven by temperature, but that it is dependent on the combination of a variety of environmental variables

Summary

Introduction

Unicellular photosynthetic symbionts (Symbiodinium spp.) play a vital role in the energy budget, metabolism and secretion of the calcium carbonate skeleton of scleractinian corals [1,2]. The Symbiodinium community associated with scleractinian corals is widely considered to be influenced by host identity and environmental factors and has been shown to shape the coral’s tolerance to environmental extremes [3,4]. Studies conducted throughout the Caribbean and Indo-Pacific have found that while some clade C types occur abundantly under a variety of thermal and light conditions, clade D is generally found in warmer water or turbid environments [4,15,16]. The affinity of clade D to certain environments is host-specific and several studies have found clade D types to be more abundant in both shallow, high light environments [10,13,17] and low light or turbid environments (Great Barrier Reef, GBR; [18,19,20]). We examine the influence of a range of environmental variables on the distribution of Symbiodinium associated with Acropora millepora collected from 47 coral reefs spanning 1,400 km on the Great Barrier Reef (GBR), Australia

Methods

Results

Conclusion