Elucidating an optimal diet for captive Acropora corals

Abstract

Developing an optimal heterotrophic feeding regime has the potential to improve the growth and overall health of captive corals. This study evaluated the efficacy of seven unique feeding strategies for Acropora loripes, Acropora millepora, and Acropora tenuis nubbins: a novel, micro-bound diet (ATF), a novel, dissolved diet rich in long-chain polyunsaturated fatty acids (LC-PUFA) (LONG), a novel, dissolved diet lacking in LC-PUFA (SHORT), a phytoplankton diet of Isochrysis galbana (ALG), co-feeding of LONG and ALG (COMB), unfiltered seawater (RAW), and an unfed treatment of filtered seawater only (CTL). After 90 days, all species showed the highest growth in the ALG treatment. There was a negative correlation between growth and total lipid concentration, indicating that Acropora corals have a low tolerance for lipid-rich diets. Coral appeared to perform best in the relatively natural treatments, namely the ALG, CTL, and RAW, which recorded higher growth and increased proportions of high-energy lipid compounds such as wax esters, triacylglycerols, and the fatty acids, 16:0 and 22:6n-3. Meanwhile the formulated diets (ATF, LONG, SHORT) promoted greater proportions of structural lipids and indispensable, membrane-bound fatty acids including 20:5n-3 and 20:4n-6. Despite the SHORT diet being low in LC-PUFA, corals fed this diet showed few significant differences in several individual LC-PUFA compared to most other treatments, suggesting that these were obtained via de novo synthesis, or selectively retained from initial reserves. Ultimately, this study showed that phytoplankton represents a promising vehicle of nutrient delivery for captive Acropora corals.