What is the optimal density of larval seeding in Acropora corals?

Abstract

In situ larval seeding is a low-cost technique that is currently under development for the large-scale restoration of coral populations. One problem that still needs to be solved is the preparation of coral larvae for seeding, i.e., how many larvae are required to restore a certain area? In this study, we focused on the relationship between the numbers of larvae, settlers, and survivors for three months post-settlement to determine the optimal larval seeding density. A comparison of three different larval densities (low, middle, and high) indicated that the number of settlers was proportional to the larval density, suggesting that settler density is determined by the number of larvae supplied. However, the survival rate of settlers on high-density plates was much lower than the corresponding rates on low- or middle-density plates during the first month after settlement. Moreover, most of the seeded corals had not survived on the low-density plates at three months after settlement. Therefore, the middle larval density (i.e., 5000 larvae m−2) appears to be optimal for seeding on grid plates.