Temporal changes in settlement, lipid content and lipid composition of larvae of the spawning hermatypic coral Acropora tenuis

Stored lipids in marine planktonic larvae play an important role in buoyancy and as an energy source and thus are a key to understanding the dispersal and settlement potential of larvae. However, little is known about lipid content and composition in different coral species or their temporal changes during larval dispersal. We examined the lipid content and composition of eggs and planula larvae of Acropora tenuis, a reef-building coral, and their temporal changes over the course of larval dispersal and settlement. The total content and composition of lipids in newly released planulae of the brooding corals A. brueggemanni, Pocillopora damicornis and Heliopora coerulea were also examined for comparison. A. tenuis eggs were positively buoyant; lipids accounted for 85% of their dry weight, but decreased to 50% of their dry weight within 30 d after spawning. Wax esters were a major component of lipids in the eggs; they decreased appreciably by 5 d after spawning and decreased thereafter. In contrast, the phospholipid content remained almost constant. The period of rapid decrease in wax esters occurred before settlement, suggesting that A. tenuis planulae consume mainly wax ester lipids as an energy source during the planktonic phase. In contrast, the lipid content of H. coerulea planulae, which have a shorter dispersal period, was lower (41% of dry weight) than that found in 5-d-old planulae of A. tenuis and newly released planulae of A. brueggemanni and P. damicornis (>58% of dry weight). Triacylglycerols in lipids were detected in P. damicornis and H. coerulea planulae, which settle quickly after release, but not in A. tenuis or A. brueggemanni, suggesting that triacylglycerols are used for rapid energy. These findings suggest that lipids are used for buoyancy and as an energy source and are related to differences in the dispersal period of planulae among coral species.