Low light intensity increased survival of coral spat in aquaculture

Abstract

Coral reef ecosystems are declining and may not recover under future climate scenarios without intervention. Seeding reefs with corals bred in aquaculture is a promising restoration intervention; however, early coral recruits (spat) are vulnerable to overgrowth by benthic algae and maximizing their survival is essential for the feasibility of large-scale breeding operations. This study investigated the optimal light quality and intensity for spat survival and growth in the presence of algal communities typically used in coral aquaculture to induce larval settlement, but which might also outcompete spat and reduce survival during the grow-out period. Spat were exposed to two light spectra (blue and a full spectrum) at four light intensities (5–160 µmol m⁻² s⁻¹) over 12-week post-settlement. Survival was reduced under the highest intensity by nearly 40% compared to the lowest intensity. Light spectrum only affected survival at 60 µmol m⁻² s⁻¹—where survival was higher under blue compared to full spectrum light. Light treatments did not affect final spat size but spat were 33% smaller at the highest light intensity in weeks 6 and 8 due to overgrowth by crustose coralline algae (CCA), which was most abundant under these conditions. Low light intensity, on the other hand, favored green and brown algae, potentially due to their respective physiologies or less competition from crustose coralline algae. These results indicate that low light intensity presents several advantages for maintaining spat in coral aquaculture, including maximizing survival without significantly affecting growth, as well as minimizing husbandry and operating expenses.