Survivorship and vertical distribution of coral embryos and planula larvae in floating rearing ponds

Outdoor floating rearing ponds were used for mass rearing of eggs and embryos of Acroporid corals that were transported from slicks on the sea surface, after simultaneous spawning at Akajima, Okinawa, on May 23, June 13, 2003, and June 1, 2004. The mortality rate of embryos (i.e. until about 70 hrs post-fertilization) was high and varied by slicks, ponds and over time in a single pond. However, the mortality rate lowered among swimming planula larvae. A pond mean of 43% of the stock on Day 3 or 134 inds/l survived until Day 6 when they achieved viability for settlement. The embryos were concentrated on the surface of ponds, but the planulae were distributed more or less evenly throughout the water column. By reducing the density of embryos on the surface and providing shade to avoid direct sunlight, it will be possible to produce in the ponds more planulae able to settle on the substrate.