Lipids influence the precipitation, hardness, and morphology of synthetic aragonite: Insights into coral biomineralisation

Coral biomineralisation underpins reef ecosystems, yet its mechanisms remain poorly understood. Lipid vesicles are involved in coral biomineralisation, and their lipid components are incorporated into coral skeletons. Here we show that key membrane lipids (phospholipids, fatty acids, and sterols) influence the formation and properties of aragonite synthesised in vitro under conditions inferred to occur at the coral calcification site. Lecithin, a phospholipid mixture, inhibits aragonite precipitation, and reduces the Vickers hardness of aragonite synthesised under conditions analogous to those of the coral calcification site (Ω _Ar  = 11.3). C18:0 (stearic) fatty acid and cholesterol also reduce hardness, but cause no significant precipitation inhibition. Lecithin and C18:0 fatty acid influence aragonite morphology, in particular reducing grain size. Previous studies indicate that ocean acidification increases the concentrations of coral skeletal organic materials and decreases calcification site pH. The present study demonstrates that increasing phospholipid concentrations at the calcification site and decreasing site pH or Ω _Ar will slow aragonite precipitation and contribute to decreased coral calcification rates under ocean acidification. Understanding how skeletal lipids influence aragonite formation provides new insights into coral biomineralisation and highlights a pathway by which ocean acidification may compromise future reef development.