Symbiodinium Genotypic and Environmental Controls on Lipids in Reef Building Corals

Timothy F Cooper,Gavin R Flematti,Sandra M Saunders,Michael Lai,Karin E Ulstrup,Ben Radford,Madeleine J H Van Oppen,Dirk Steinke

doi:10.1371/journal.pone.0020434

Timothy F Cooper, Gavin R Flematti + Show 6 more

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https://doi.org/10.1371/journal.pone.0020434

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Abstract

BackgroundLipids in reef building corals can be divided into two classes; non-polar storage lipids, e.g. wax esters and triglycerides, and polar structural lipids, e.g. phospholipids and cholesterol. Differences among algal endosymbiont types are known to have important influences on processes including growth and the photobiology of scleractinian corals yet very little is known about the role of symbiont types on lipid energy reserves.Methodology/Principal FindingsThe ratio of storage lipid and structural lipid fractions of Scott Reef corals were determined by thin layer chromatography. The lipid fraction ratio varied with depth and depended on symbiont type harboured by two corals (Seriatopora hystrix and Pachyseris speciosa). S. hystrix colonies associated with Symbiodinium C1 or C1/C# at deep depths (>23 m) had lower lipid fraction ratios (i.e. approximately equal parts of storage and structural lipids) than those with Symbiodinium D1 in shallow depths (<23 m), which had higher lipid fraction ratios (i.e. approximately double amounts of storage relative to structural lipid). Further, there was a non-linear relationship between the lipid fraction ratio and depth for S. hystrix with a modal peak at ∼23 m coinciding with the same depth as the shift from clade D to C types. In contrast, the proportional relationship between the lipid fraction ratio and depth for P. speciosa, which exhibited high specificity for Symbiodinium C3 like across the depth gradient, was indicative of greater amounts of storage lipids contained in the deep colonies.Conclusions/SignificanceThis study has demonstrated that Symbiodinium exert significant controls over the quality of coral energy reserves over a large-scale depth gradient. We conclude that the competitive advantages and metabolic costs that arise from flexible associations with divergent symbiont types are offset by energetic trade-offs for the coral host.

Highlights

Reef building corals (Scleractinia) associate with photosynthetic microalgal endosymbionts from the diverse genus Symbiodinium and are considered mixotrophic organisms
This study has demonstrated that in addition to changes in other environmental characteristics, Symbiodinium may exert significant controls over the quality of the energy reserves of coral hosts over a large-scale depth gradient
Most comparative physiological studies of the functioning of Symbiodinium have focused on the trade-off between symbiont type and metabolic costs such as effects on growth or photosynthetic performance

Summary

Introduction

Reef building corals (Scleractinia) associate with photosynthetic microalgal endosymbionts from the diverse genus Symbiodinium and are considered mixotrophic organisms. Lipids in reef building corals can be divided into two distinct categories; non-polar storage lipids such as wax esters and triglycerides, and polar structural lipids such as phospholipids and cholesterol [10]. Given that seasonal variability in lipid contents are specific to non-polar lipid types [10], the lipid fraction ratio has been proposed as an alternative and potentially more robust bioindicator of coral condition [15,16]. Lipids in reef building corals can be divided into two classes; non-polar storage lipids, e.g. wax esters and triglycerides, and polar structural lipids, e.g. phospholipids and cholesterol. Differences among algal endosymbiont types are known to have important influences on processes including growth and the photobiology of scleractinian corals yet very little is known about the role of symbiont types on lipid energy reserves

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