Recruitment of Balanus glandula Darwin (Crustacea: Cirripedia) into empty barnacle tests and its ecological consequences

Abstract

Two sympatric barnacle species settled and recruited on different substrata on the rocky intertidal shore of the west side of San Juan Island, WA (USA). Chthamalus dalli Pilsbry settled in open space and most recruitment occurred on bare rock. Balanus glandula Darwin settled preferentially inside empty adult barnacle tests. Recruits inside empty tests had an increased early survival but suffered from greater long-term mortality, compared with recruits outside tests. The importance of recruitment into empty tests varied between B. glandula subpopulations: it was less important on the exposed shores of the Olympic Peninsula and was not found in calmer waters of Puget Sound and the Hood Canal. In the San Juan Archipelago, where B. glandula finds a refuge from predation in the higher intertidal, and at the height at which a maximum of reproductive output is to be expected, much of the subpopulation is derived from recruitment in empty tests. Preferential settlement in scarce empty tests resulted in crowded juveniles on a shore with low overall densities of juveniles. A field experiment testing possible cues guiding cyprids into empty tests revealed that cyprids were less attracted to tests with a fresh conspecific scent than to scentless tests.