Distribution and reproduction in the epibiotic barnacle Solidoblanus hesperius and correlations with host crab life histories

The acorn barnacle Solidobalanus hesperius , which has a broad subtidal distribution in the North Pacific, often lives as an epibiont on bivalves and commercially important decapod crustaceans. In comparison to other non-epibiotic barnacle species in the same region, S. hesperius has an abbreviated lifespan averaging 6-7 mo. Although S. hesperius commonly occupies crab carapaces, details of the relationship remain unknown. Using barnacles collected monthly from host crabs, we describe the reproductive seasonality and settlement patterns for S. hesperius in relation to the molting patterns of 2 host crabs, Metacarcinus magister and Cancer productus , off the Pacific coast of Oregon, USA. Brooded embryos and mature gonads were observed throughout the year, although broods had a higher prevalence in the spring and mid-summer. Embryos developed quickly, hatching within 1 wk, and individuals as small as 3.8 mm in diameter were found with mature ovaries. We observed a large larval settlement peak in August. The spatial distribution of epibiotic barnacles was correlated with the microtopography of the host crab carapace, with most barnacles occurring in depressions and grooves. These findings indicate that the abbreviated life cycle of S. hesperius is well adapted to life on ephemeral crab carapaces that are molted frequently, and the spatial distribution of settlers may reduce the likelihood that barnacles are lost to abrasion.