Effect of light and feeding on the fatty acid and sterol composition of zooxanthellae and host tissue isolated from the scleractinian coral Turbinaria reniformis

Abstract

The fatty acid and sterol compositions of zooxanthellae and animal fractions of the scleractinian coral Turbinaria reniformis were investigated under different light and feeding conditions, to study the symbiont-host exchanges. Nubbins were maintained during 6 weeks under two light levels (100 mmol photons m 22 s 21 and 300 mmol photons m 22 s 21 ) and two feeding levels (starved and fed with zooplankton) in a factorial experiment. There were greater proportions of some polyunsaturated fatty acids (PUFA; e.g., C18:4 n-3, C20:5 n-3, C22:6 n-3) in the zooxanthellae than in the host, suggesting that these PUFA were synthesized by the algae and transferred to the animal. Conversely, C20:4 n-6 exhibited a greater proportion in the host and might have been synthesized by the animal. Light affected the chlorophyll content, the rates of photosynthesis, and the lipid production of all coral samples. Corals maintained in high-light conditions had lower relative phytol content but higher concentrations of fatty acids (FA) and sterols than the shaded corals. Feeding also affected coral metabolism, but differently according to the light level and despite the fact that the host did not directly incorporate the zooplankton lipids (PUFA and cholesterol). In low light, feeding resulted in an increase of growth rates and storage lipid concentrations, mainly saturated fatty acids (SAFA) and membrane constituents (PUFA and sterols). In high light, the lipid energy from the food was directed toward an increase in calcification, as well as in chlorophyll content and protein content. This study highlights the importance of feeding in sustaining coral metabolism, especially when light, or stress events, is limiting photosynthesis.

Distribution of lipids and fatty acids in corals by their taxonomic position and presence of zooxanthellae

“…4), but only 4 FA variables (16:0, significantly differed in these groups and had higher average content in zooxanthellate specimens (Table 4). Predominance of 16:0, 18:3n-6, and 18:4n-3 in FA of hexacoral zooxanthellae have been previously reported (Al Moghrabi et al 1995, Papina et al 2003, Zhukova & Titlyanov 2003, Treignier et al 2008. The level of 18:3n-6 and 18:4n-3 was very low in azooxanthellate alcyonarians (Imbs et al 2007b), gorgonians (Imbs et al 2009), and hexacorals Balanophyllia sp., Tubastrea aurea (Table S3), T. coccinea, and T. micrantha (Latyshev et al 1991).…”

“…The composition of lipids depends on the light regimes (Meyers 1979, Saunders et al 2005. Turbinaria reniformis maintained in high-light conditions had higher concentrations of fatty acid (FA) and ST than the shaded corals (Treignier et al 2008). Lipid content in corals varies during the annual cycle.…”

Heterotrophic and autotrophic assimilation of fatty acids by two scleractinian corals, Montastraea faveolata and Porites astreoides

“…This mass balance model assumes that the transfer of the specific fatty acids from the zooxanthellae via translocation to the host, and from external food sources through heterotrophic feeding, both occur with little (, 1% propagated experimental error) or no isotopic fractionation and that there is no endogenous synthesis of these particular fatty acids. For EFAs (including DHA, EPA, and ARA) and C 16:0 SAFA, minimal isotopic fractionations occur during translocation in symbiotic associations (Johnston et al 1995;Treignier et al 2009) and during direct assimilation from external food sources by heterotrophs (Rieley et al 1999;Jim et al 2003). The second assumption is also valid for EFAs, as invertebrates are generally unable to endogenously synthesize EFAs in any appreciable quantity (Bell et al 2007).…”

“…In the case of nonessential fatty acids, including SAFAs, which can be synthesized de novo by the consumer, the d 13 C values will reflect the competing processes of assimilation and de novo synthesis (Villinski et al 2004). The d 13 C values of fatty acids produced by zooxanthellae and zooplankton differ by more than 5% (Treignier et al 2009), adding to the success of this isotopic approach in elucidating dietary preferences in symbiotic relationships within scleractinian corals (Treignier et al 2009) and tridacnid clams (Johnston et al 1995).…”

“…Zooxanthellae can supply up to 100% of the animal host's requirements for energy under ideal conditions (Muscatine et al 1981), whereas during bleaching episodes, the host may acquire all of its metabolic requirements from heterotrophic feeding (Grottoli et al 2006). Corals require fatty acids to live and reproduce; fatty acids can function (1) as energy reserves (Grottoli et al 2004), with saturated (SAFAs) and monounsaturated (MUFAs) fatty acids stored as triglycerides and wax esters (Oku et al 2002;Rodrigues et al 2008); (2) as membrane constituents in the form of phospholipids; and (3) as polyunsaturated fatty acids (PUFAs) (Tchernov et al 2004;Imbs et al 2007;Treignier et al 2008), which include molecules critical for reproduction and membrane fluidity (Ulrich 1994). PUFAs include a specific subset of fatty acids, known as essential fatty acids (EFAs), that coral hosts cannot endogenously manufacture in appreciable quantities and thus presumably must procure from their diet (Latyshev et al 1991;Bell et al 2007).…”