Recruitment of barnacles into empty adult tests

Abstract

In the intertidal zone on a rocky shore in the San Juan Islands, densities of cyprids and juveniles of Balanus glandula Darwin were greater in empty tests of three species of adult barnacles; densities of new recruits were lower on bare rock and rock shaded by Fucus spp. In contrast, densities of new recruits of Semibalanus cariosus (Pallas) were often higher outside of adult barnacle tests than inside except in the high intertidal zone. Both the species of empty tests and intertidal heights significantly affected density of those B. glandula recruiting into tests, but neither B. glandula nor S. cariosus showed a striking preferential recruitment to any one species of empty barnacle test. Densities of B. glandula recruits were usually lower in S. cariosus shells than in shells of B. glandula or Chthamalus dalli Pilsbry, whereas densities of S. cariosus recruits were not especially low in shells of S. cariosus. Density of recruits of B. glandula was less in empty tests inhabited by littorines and limpets. A peculiarity of disproportionate recruitment into empty tests is that recent deaths of adults, not reproductive adults or total empty space, can determine local density of new recruits, as was the case for B. glandula in the high intertidal zone during this study. Because few survive to reproduce at mid and low intertidal heights, enhanced recruitment inside tests could affect overall local recruitment. Physical processes, chemical stimuli, and differential mortality in the cyprid stage could all contribute to this pattern of recruitment.