Density of coral larvae can influence settlement, post-settlement colony abundance and coral cover in larval restoration

Successful recruitment of new individuals is essential for recovery of degraded coral reefs. Enhancing supply of coral larvae increases initial settlement, however post-settlement survival can be influenced by density-dependent processes. We investigated the influence of larval density on settlement, colony abundance and growth to 24 months for Acropora tenuis in the north-western Philippines, to determine whether larval supply can be optimised to maximise successful recruitment. Thirty different densities of coral larvae were enclosed for five days around settlement tiles and highest total settlement occurred on tiles with highest larval densities. After 12 months, however, colony abundance and coral cover was lower on high density tiles (supplied with similar to 2,500-5,000 larvae) than tiles supplied with similar to 1,000-2,000 larvae. Coral cover at 24 months remained highest on tiles supplied with similar to 1,000-2,500 larvae. Larval density influenced larval substratum selection, with proportionally fewer larvae settling in typically preferred locations as density increased. We conclude that larval density can influence post-settlement colony abundance and coral cover to 12 months, with coral cover trends persisting to 24 months. We show that optimising larval densities can maximise coral recruitment and growth, however oversupply of larvae at very high densities can have negative outcomes for larval restoration.