Food Preference of Juvenile Siganus rostratus and S. spinus in Guam

Tsuda, Roy; Bryan, Patrick

Schools of juvenile Siganus rostratus and S. spinus (Teuthididae) swarm on the reef flats of Guam each year during the months of April and May, and occasionally during June and October. During the month of May 1972, the largest school thus far recorded over the past ten years invaded the reef flats of Guam and provided an opportunity to examine the food habits of the two species. The Fish and Wildlife Division of the Government of Guam estimated there were more than 13 million juvenile teuthidids on the reefs. Our data indicate that the juveniles of both Siganus rostratus and S. spinus are highly selective in the type of algae they eat. One of the more important findings of this study was to define the effect of selective grazing on the algae of the reef flats during those months when schooling occurred. A drastic change occurred in that certain algae were conspicuously absent. For example, the green alga Enteromorpha disappeared completely from the intertidal zone on several beaches around Guam. In fact, all of the Enteromorpha used in the feeding experiments had to be obtained from our outdoor holding tanks. There was also a conspicuous absence of all species of Caulerpa on the reef flats. Likewise, other green algae such as Boodlea composita and Cladophoropsis membranacea, which were abundant a month prior to the schooling, were absent from Pago Bay.

Food Preference of Juvenile Siganus rostratus and S. spinus in Guam

Series