Impacts of bleaching on the soft coral Lobophytum compactum. I. Fecundity,fertilization and offspring viability

We document long-term effects of a simulated bleaching event on the reprodu ctive output and offspring viability of the soft coral Lobophytum compactum . Corals were subjected to temperature and solar radiation treatments to pr oduce both moderately (48-60%) and heavily (90-95%) bleached colonies. Alth ough bleached colonies recovered their zooxanthellae within 10 to 18eeks, i mpacts on reproductive output were significant for at least two annual spaw ning seasons. In the first year, both polyp fecundity and mean oocyte diame ter were reduced and inversely correlated with the degree of bleaching, wit h complete failure of fertilization in the group of heavily bleached coloni es. For moderately bleached soft corals, survival and growth of sexual offs pring did not differ significantly from those of unbleached colonies. Altho ugh no further reductions in zooxanthellae densities in experimental soft c orals were recorded throughout the subsequent second year, egg size and fec undity of the heavily bleached soft corals were still significantly reduced 20 months later. Severe bleaching clearly has long-term sub-lethal impacts , reducing overall reproductive output for at least two spawning seasons.