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 () disturbance to barnacle (, ) 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, cyprids are smaller than cyprids, and recruitment is higher than recruitment. Thus, we hypothesized that LDEs on recruitment would be weaker than those on 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 and recruitment and recruit size. As hypothesized, the LDEs on recruitment were weaker than the LDEs on recruitment. Additionally, recruits were smaller than recruits. However, the LDEs on recruit size were as strong as the LDEs on recruit size, indicating that the smaller recruits are not less susceptible to LDEs than recruits. Since recruitment was higher than recruitment, we propose that the higher recruitment compensated for the LDEs on recruitment. Our findings indicate that the detected differences in LDEs on barnacle recruitment are related to barnacle recruitment intensity but not recruit size.