Jack T. Moyer

Early sex change: A possible mating strategy ofCentropyge angelfishes (Pisces: Pomacanthidae)

Although the presence of socially controlled sex change in pomacanthid fishes of the genusCentropyge has been known since 1978, it has always been assumed that such sex change occurred only after the death or disappearance of the dominant male in single male social groups. Between 1978 and 1983, we observed several incidences of sex change by ranking female angelfishes within their harems and in the presence of the dominant male in each such harem. This phenomenon was observed inCetropyge interruptus andCentropyge tibicen, and occurred frequently enough to suggest the possibility of early sex change as a normal reproductive strategy in these species. Possible advantages of early sex change are discussed.

Quantitative observations of predation during spawning rushes of the labrid fish Thalassoma cupido at Miyake-jima, Japan.

A rapid upward spawning rush is a nearly universal phenomenon among reef fishes that spawn pelagic eggs. Although spawning rushes have long been considered to have evolved as a defense against egg predators and/or attacks on the spawning fishes by piscivores, these hypotheses have never been tested in the field. We analysed piscivore attacks during three motor patterns associated with group spawning of the labrid fishThalassoma cupido at Miyake-jima, Izu Islands, Japan. Egg predation on group spawnings was also quantified. Of 206 piscivore attacks on spawning fishes by seven predator species, 17.1 (83.1%) occurred during 461 spawning rushes (1/2.7 spawning rushes). No attacks were successful during spawning rushes, and only four kills were made in 206 attacks summed from all three motor patterns associated with spawning, amounting to a piscivore success rate of only 1.9 %. In contrast, gametes from 90 of 213 spawnings (42.3 %) were consumed by nine species of planktivorous fishes. Spawning fish seemed not to recognize egg predators and made no attempt to avoid them, often spawning in the midst of waiting aggregations of damselfishes. Our data indicate that the rapidly of the spawning rush ofT. cupido serves as an excellent defense against piscivores, but is ineffective against egg predators. Evidence is presented from observations of seven other species suggesting that spawning ascents provide little protection against water column egg predators in predator-rich environments.

SUBTIDAL EFFECTS OF A LARGE TYPHOON ON MIYAKE-JIMA, JAPAN

On October 19, 1979, a large typhoon passed within 160 km of the Japanese Island of Miyakejima. The typhoon generated surf in excess of 7 m. A well known bay was surveyed after the storm, revealing significant effects in both the substrate and algal coverage. Disruption was most severe in the 5-10 m depth range; a shallower site was less affected. This may be a result of both large waves breaking farther offshore and the acclimation of shallow areas to typhoons as a result of previous storms of lower magnitude. Decreases in the abundance of 18 species of tropical reef fishes did not follow a depth dependent pattern and were thought to result from both mortality and displacement. It is hypothesized that strong differences in the level of reduction between species resulted from differential mortality due to spatial and behavioral differences between species.