Seasonal variation in the lipid profile of Acropora millepora at Halfway Island, Great Barrier Reef

To understand how environmental conditions and reproductive events affect coral energetic status, seasonal variations in lipid and fatty acid profiles of the common scleractinian coral,Acropora millepora, were studied from pre-spawning in November 2009 until post-spawning in November 2010 at Halfway Island (in the Keppel Island Group, Southern Great Barrier Reef, Australia). Seasonal chlorophyll levels, photosynthetically active radiation (PAR), rainfall and water temperature were major drivers of the overall coral lipid profile, and this was particularly pronounced in correlations with the important, high-energy lipid, triacylglycerol. This likely reflected changing food sources and feeding modes (i.e. phototrophy vs heterotrophy), which corresponds to the opportunistic feeding behaviour of corals. Water temperature was also a major influencer of the coral fatty acid profile. In particular, saturated fatty acids correlated positively with water temperature, while polyunsaturated fatty acids correlated negatively, reflecting cell membrane fluidity regulation, which is necessary for coral to tolerate changing temperatures. Spawning and maternal provisioning also proved to be a major driver of change in the coral lipid profile. The mass spawning events in spring for both 2009 and 2010 caused reductions in the important coral egg constituents: wax ester, triacylglycerol, phosphatidylcholine and fatty acid 10:0. Interestingly, lipid accumulation was significantly lower in the 2010 spawn compared to 2009, possibly due to lower PAR and chlorophyll levels, reflecting reduced photosynthetic activity and phytoplankton availability. Regardless, in 2010, resource provisioning to egg production was greater than in 2009, suggesting increased reproductive effort in the face of environmental stress. This study demonstrates the strong influence of opportunistic heterotrophy and autotrophy and maternal provisioning on the coral lipid profile. Such information is fundamental to understanding the environmental and biochemical processes underlying coral health and predicting how anomalous events and climate-driven changes will affect coral reef assemblages.