POPULATION-DYNAMICS OF GOBY PARAGOBIODON ECHINOCEPHALUS AND HOST CORAL STYLOPHORA-PISTILLATA

The goby Paragobiodon echinocephalus is an obligate associate of the branching coral Stylophora pistillata. Population fluctuations of both species were observed over 3 yr on the reef flat of Sesoko Island, Okinawa, Japan. Coral growth was negatively correlated with size, because partial death or destruction often occurred in large corals. The number and maximum size of gobies in a coral were positively correlated with coral size. Small corals (< 5 cm diameter) were seldom used, while large corals (> 15 cm) were almost always inhabited by 2 or more fish. The goby spawned from April to November, and juveniles (7 to 15 mm) increased in summer. The number of gobies and the corals occupied by gobies increased with the influx of juveniles. The goby population declined during winter and spring except in a year when corals > 5 cm became abundant. When the number of large corals decreased, large gobies (30 to 40 mm) decreased in number and the occupation rate of smaller corals increased. Mortality of marked fish (> 15 mm) was correlated with that of corals. Thus the population fluctuation of the goby was affected by both the availability of host coral and the goby's seasonal reproductive cycle.