M. Omori et al., Significant drop of fertilization of Acropora corals in 1999. An after-effect of heavy coral bleaching?, LIMN OCEAN, 46(3), 2001, pp. 704-706
In June 1999, after devastating coral bleaching in 1998, laboratory fertili
zation of Acropora nasuta, one of the most abundant reef-building corals in
Okinawa, Japan, decreased significantly from usual rates (>94%) to an aver
age uf 42% at a sperm concentration of 10(5) ml(-1). Similar decreases were
observed in four other mass-spawning acroporid corals. We also found a dec
rease in sperm motility in the laboratory. A series of experiments to deter
mine the effects of sperm concentration on fertilization rates revealed tha
t sperm of 10(7) ml(-1) was needed to obtain a rate >80%. Sperm concentrati
on in surface seawater during mass spawning was highest within 1.0 h of spa
wning but decreased sharply thereafter These results suggest that gamete di
lution plays an important role in limiting the fertilization of coral eggs
in the yea. As successful fertilization appears to have been much lower in
1999, we suspect that production of new coral recruits was also reduced gre
atly. Current and future sea-temperature increases thus pose a severe poten
tial threat to coral reefs by increasing the frequency of coral bleaching a
nd consequently leading to further declines of coral recruitment and hence,
reef corals.