Abstract
BackgroundThe endosymbiotic dinoflagellates (genus Symbiodinium) within coral reef invertebrates are critical to the survival of the holobiont. The genetic variability of Symbiodinium may contribute to the tolerance of the symbiotic association to elevated sea surface temperatures (SST). To assess the importance of factors such as the local environment, host identity and biogeography in driving Symbiodinium distributions on reef-wide scales, data from studies on reef invertebrate-Symbiodinium associations from the Great Barrier Reef (GBR) were compiled.Methodology/Principal FindingsThe resulting database consisted of 3717 entries from 26 studies. It was used to explore ecological patterns such as host-specificity and environmental drivers structuring community complexity using a multi-scalar approach. The data was analyzed in several ways: (i) frequently sampled host species were analyzed independently to investigate the influence of the environment on symbiont distributions, thereby excluding the influence of host specificity, (ii) host species distributions across sites were added as an environmental variable to determine the contribution of host identity on symbiont distribution, and (iii) data were pooled based on clade (broad genetic groups dividing the genus Symbiodinium) to investigate factors driving Symbiodinium distributions using lower taxonomic resolution. The results indicated that host species identity plays a dominant role in determining the distribution of Symbiodinium and environmental variables shape distributions on a host species-specific level. SST derived variables (especially SSTstdev) most often contributed to the selection of the best model. Clade level comparisons decreased the power of the predictive model indicating that it fails to incorporate the main drivers behind Symbiodinium distributions.Conclusions/SignificanceIncluding the influence of different host species on Symbiodinium distributional patterns improves our understanding of the drivers behind the complexity of Symbiodinium-invertebrate symbioses. This will increase our ability to generate realistic models estimating the risk reefs are exposed to and their resilience in response to a changing climate.
Highlights
The global decline of coral reefs has generated a broad interest in the widespread symbiosis of reef invertebrates with dinoflagellates of the genus Symbiodinium
The database only includes information obtained with techniques that focus on the dominant Symbiodinium types in the resident symbiont population of the host, excluding information on background Symbiodinium obtained with quantitative PCR (qPCR) (e.g. [36,56])
The Principal Component Analyses (PCA) explained 87% of the variation in the environmental data and a strong spatial distribution of the sea surface temperatures (SST) groups was evident with increasing SSTs and SSTw across the latitudinal gradient (Figure S2A)
Summary
Despite the clear importance of Symbiodinium in the survival of the holobiont (host plus symbionts), Symbiodinium genetic identity has rarely been used to model the risk of reef deterioration or their ability to maintain key functional processes under stress by resisting or adapting to change [2,3]. Symbiont-host specificity as well as biogeography underlie distributional patterns [8,9]. These patterns are mostly studied at the scale of several reefs. To assess the importance of factors such as the local environment, host identity and biogeography in driving Symbiodinium distributions on reef-wide scales, data from studies on reef invertebrate-Symbiodinium associations from the Great Barrier Reef (GBR) were compiled
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