Limpet disturbance effects on barnacle recruitment are related to recruitment intensity but not recruit size

Intertidal limpets are important grazers along rocky coastlines worldwide that not only control algae but also influence invertebrates such as common barnacles. For instance, grazing limpets ingest settling barnacle cyprid larvae (hereafter cyprids) and push cyprids and barnacle recruits off the substrate. Such limpet disturbance effects (LDEs) can limit barnacle recruitment, a key demographic variable affecting barnacle population establishment and persistence. In this study, we examined limpet (Lottia cassis) disturbance to barnacle (Chthamalus dalli, Balanus glandula) recruitment on the Pacific coast of Hokkaido, Japan, as information on limpet-barnacle interactions from this region is missing. We investigated, for the first time, whether barnacle size and recruitment intensity influence LDEs on barnacle recruitment. Small barnacles may be less susceptible to LDEs than larger barnacles, because small size may reduce the propbability of limpet disturbance. Moreover, recruitment intensity can influence LDEs, as high recruitment can compensate for LDEs on barnacle recruitment density. In Hokkaido, C. dalli cyprids are smaller than B. glandula cyprids, and C. dalli recruitment is higher than B. glandula recruitment. Thus, we hypothesized that LDEs on C. dalli recruitment would be weaker than those on B. glandula recruitment. To test our hypothesis, we conducted a field experiment during which we manipulated limpet presence/absence on the interior surfaces of ring-shaped cages. After four weeks, we measured barnacle recruitment and recruit size on the interior surfaces of the cages and found negative LDEs on C. dalli and B. glandula recruitment and recruit size. As hypothesized, the LDEs on C. dalli recruitment were weaker than the LDEs on B. glandula recruitment. Additionally, C. dalli recruits were smaller than B. glandula recruits. However, the LDEs on C. dalli recruit size were as strong as the LDEs on B. glandula recruit size, indicating that the smaller C. dalli recruits are not less susceptible to LDEs than B. glandula recruits. Since C. dalli recruitment was higher than B. glandula recruitment, we propose that the higher C. dalli recruitment compensated for the LDEs on C. dalli recruitment. Our findings indicate that the detected differences in LDEs on barnacle recruitment are related to barnacle recruitment intensity but not recruit size.

Effects of crowding on fecundity in barnacles: Semibalanus (Balanus) balanoides, Balanus glandula, and Chthamalus dalli

Phenotypic plasticity of relative investment in shell, eggs, and somatic tissue was examined with experimental population density manipulations in field populations of the intertidal barnacles Semibalanus (Balanus) balanoides from Massachusetts and Balanus glandula and Chthamalus dalli from Washington State, U.S.A. Individuals of S. balanoides of comparable somatic tissue weights produced larger clutches of eggs when crowded and columnar than when conical and uncrowded. Individuals of C. dalli showed a similar pattern. Individuals of B. glandula showed the opposite pattern: at comparable somatic tissue weights, conical uncrowded individuals made slightly larger clutches of eggs than did crowded, columnar individuals. In all cases the greatest shell investment per unit somatic tissue weight was associated with the greatest clutch investment per unit somatic tissue weight.