Effects of epiphytic Ulva spp. on the marine snail Tegula patagonica (D'Orbigny, 1840) in a coastal Patagonian bay

Epibiosis is a common phenomenon in the marine environment having different effects on the taxa involved. In relative low-energy environments, small algae like the foliose Ulva spp. can attach securely to the shell of molluscs and develop a holdfast. The snail Tegula patagonica is commonly found with crustose algae on its back, though in this study we observed the presence of Ulva spp. This algal genus is typical of seasonal blooms in highly eutrophicated sites. The main objectives of this study were therefore to describe the epiphytic association between Ulva spp. and T. patagonica and to evaluate the potential influence of this interaction on the snail population along a rocky Patagonian shore. To do so, we sampled both the snails and Ulva spp. bimonthly in the low intertidal-shallow subtidal of San Antonio Bay from February 2016 through January 2017. Our results demonstrated that Ulva spp. was mainly attached to the larger snails. This epibiosis influenced the body condition of the females, but did not affect the gonadosomatic index or the dislodgment force. The population of T. patagonica was stable in terms of density and size-frequency distributions of individuals throughout the study period. These findings suggested that no impairment in the fitness of fouled snails occur, indicating that Ulva spp. epibiosis has little effect on the population dynamics of T. patagonica. •Epibiosis prevalence was not correlated with the abundance of Ulva spp.•Ulva spp. was attached mainly to larger individuals.•Epibiosis had little effect on Tegula patagonica fitness.•Population structure did not change during the Ulva spp. seasonal bloom.