Abstract
The ecological success of shallow water reef-building corals has been linked to the symbiosis between the coral host and its dinoflagellate symbionts (herein ‘symbionts’). As mixotrophs, symbiotic corals depend on nutrients 1) transferred from their photosynthetic symbionts (autotrophy) and 2) acquired by host feeding on particulate organic resources (heterotrophy). However, coral species differ in the extent to which they depend on heterotrophy for nutrition and these differences are typically poorly defined. Here, a multi-tracer fatty acid approach was used to evaluate the trophic strategies of three species of common reef-building coral (Galaxea fascicularis, Pachyseris speciosa, and Pocillopora verrucosa) whose trophic strategies had previously been identified using carbon stable isotopes. The composition and various indices of fatty acids were compared to examine the relative contribution of symbiont autotrophy and host heterotrophy in coral energy acquisition. A linear discriminant analysis (LDA) was used to estimate the contribution of polyunsaturated fatty acids (PUFA) derived from various potential sources to the coral hosts. The total fatty acid composition and fatty acid indices revealed differences between the more heterotrophic (P. verrucosa) and more autotrophic (P. speciosa) coral hosts, with the coral host G. fascicularis showing overlap with the other two species and greater variability overall. For the more heterotrophic P. verrucosa, the fatty acid indices and LDA results both indicated a greater proportion of copepod-derived fatty acids compared to the other coral species. Overall, the LDA estimated that PUFA derived from particulate resources (e.g., copepods and diatoms) comprised a greater proportion of coral host PUFA in contrast to the lower proportion of symbiont-derived PUFA. These estimates provide insight into the importance of heterotrophy in coral nutrition, especially in productive reef systems. The study supports carbon stable isotope results and demonstrates the utility of fatty acid analyses for exploring the trophic strategies of reef-building corals.
Highlights
The evolutionary success of symbiotic reef-building corals within typically nutrient-poor oceans is attributed to their symbiosis with dinoflagellates [1]
We provide a comprehensive evaluation of the trophic strategies of symbiotic corals by 1) examining the composition of multiple tracers, 2) applying three established fatty acid indices in the novel context of coral trophic ecology, and 3) estimating the contribution of various sources of polyunsaturated fatty acids (PUFA) to each coral host species
For the fatty acid composition of host tissue, P. speciosa was significantly different than P. verrucosa (P(perm)
Summary
The evolutionary success of symbiotic reef-building corals within typically nutrient-poor oceans is attributed to their symbiosis with dinoflagellates [1]. Symbiotic reef-building corals have different trophic strategies that support their distribution across a wide range of environmental conditions [2]. Symbiotic corals obtain nutrients from their photosynthetic dinoflagellate endosymbionts ( ‘symbionts’; autotrophy) and from feeding on particulate resources in the water column (heterotrophy), including bacteria, detritus, flagellates, phytoplankton, and zooplankton [5]. The low bioavailability and concentration of dissolved organic matter makes it a minor potential component of coral nutrition in contrast to nutrients being i) transferred from symbionts and ii) assimilated from heterotrophic feeding on particulates [5,7]. The role of heterotrophy greatly varies in relation to environmental factors and species-specific feeding rates, with heterotrophic carbon accounting for a significant, but highly variable, proportion of daily requirements in some coral species [8]. Lipids are important for energy storage and comprise a major constituent of coral carbon content and overall dry weight, with variation in total lipids among species [10]
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