Epibiosis in sedimentary coastal environments: Effects of an introduced barnacle on a native mussel

Abstract

In the mobile sedimentary environment of San Antonio Bay (northern Patagonia), where hard substrate is scarce, the mussel Brachidontes rodriguezii dominates the intertidal zone, there being covered by the introduced epibiotic barnacle Balanus glandula. The aim of this study was to evaluate the distribution and the recruitment of B. glandula on different non-living substrates (cobbles, biogenic debris) and on live-mussel shells and to assess the effect of the epibiotic interaction on the condition index and the attachment strength of B. rodriguezii. Field samplings revealed that adult barnacles mainly fouled live mussels, with the main differences in biomassbeing between the high and mid-intertidal. These differences in barnacle biomass between heights and substrates were greater in spring and autumn than in winter and summer. To assess the recruitment of barnacles, we performed a field experiment manipulating living and non-living substrates. We found no differences in the density of barnacles recruitment; thus, the barnacle distribution on different substrates throughout the intertidal would vary solely according to the settling substrates available. The relationship between epibiosis and the condition index exhibited no pattern. Furthermore, the experimental manipulation of epibiosis (i.e., removing epibionts or adding epibionts mimics) did not affect the condition of the mussels. Finally, the attachment strength of mussels with epibionts was up to fivefold greater than that of clean mussels. In a system with high tidal hydrodynamic energy, epibiosis is thus seen to stimulate a greater byssal production in mussels for the prevention of detachment.