Settlement rates of the high intertidal barnacle, Balanus glandula, were monitored at three sites in the rocky intertidal zone in Central California simultaneously with measurements of larval concentrations in the adjacent water column. In both 1983 and 1984, settlement rates onto vacant substrate differed among the sites by nearly two orders of magnitude. For all sampling dates, this spatial variation in settlement mirrored the spatial distribution of Balanus glandula cyprid concentration in the water column. A perfect rank correlation was found between cyprid concentrations near a site and subsequent settlement. A noteworthy observation was that the sites switched rank in their settlement rates from 1983 to 1984. This change in settlement rankings matched a switch in rankings for cyprid concentrations.Settlement itself appears to be an important cause of the spatial pattern of cyprid concentrations. Comparing the rates of settlement to estimates of the number of cyprids available at a site suggests that settlement causes a large drain on the cyprid population as a water mass passes over successive sites. No consistent spatial patterns were found in the distribution of other major plankton groups (calanoid copepods) that are similar in size to Balanus cyprids but do not settle.The large differences in settlement rates among these sites were previously shown to be a leading cause of large differences in the structure of benthic barnacle populations. The close correspondence shown here between these large differences in settlement and differences in larval concentrations suggests that nearshore oceanic processes affecting larval arrival contribute to the control of benthic community structure.

Growth and sexual maturity were compared among Monterey Botryllus schlosseri colonies cultured in the laboratory and in Monterey Marina in two separate studies: Phase I April to July 1984, a time when Botryllus growth is rapid in the field, and Phase II December 1984 to March 1985, a time when growth is minimal in the field. Laboratory colonies were kept in tanks of standing, aerated filtered seawater at 15C, 20C, and 24C; the seawater was changed daily or on alternate days. Food types were two concentrations of an algal mixture and five concentrations of Liquifry, a commercially available food for filter-feeding marine invertebrates. All algae-fed colonies did poorly. During Phase I, the colonies kept in Monterey Marina grew much faster than those in the laboratory, but they took longer to reach sexual maturity than the Liquifry-fed colonies grown at 20C and had a lower survivorship. In Phase II, Botryllus growth rates and survivorships in seven of the eight laboratory treatments were better than those of marina colonies. These laboratory treatments yielded a substantial proportion of sexually mature colonies, whereas none of the marina colonies produced eggs during Phase II.

No abstract

No abstract

No abstract