Increased algal fouling on mussels with barnacle epibionts: a fouling cascade.

If the external surfaces of epibionts are more suitable to other fouling species than those of their basibionts, a ‘fouling cascade’ might occur where epibionts facilitate secondary colonization by other epibionts. Here we evaluate whether the presence of epibiotic barnalces ( Balanus glandula ) influences the probability of mussel ( Brachidontes rodriguezii ) fouling by ephemeral red algae ( Porphyra sp.) in a Southwestern Atlantic rocky shore. Mussels with barnacle epibionts showed a higher prevalence of Porphyra sp. fouling (32–40% depending on sampling date) than mussels without them (3–7%). Two lines of evidence indicate that barnacles facilitate Porphyra sp. fouling. First, most Porphyra sp. thalli in mussels with barnacle epibionts were attached to barnacle shells (75–92% of cases). Secondly, Porphyra sp. associated with mussels with barnacle epibionts in a proportion that significantly exceeded that expected under random co-occurrence. These results suggest the occurrence of a fouling cascade where barnacle epibiosis on mussels facilitates subsequent algal fouling. Recognizing the occurrence of such fouling cascades is important because they might explain the non-random aggregation of multiple epibiotic species onto a proportionally few individuals of the host species. [ABSTRACT FROM AUTHOR]