Alien barnacle Amphibalanus amphitrite epizoic on two native oyster species in the southern Gulf of Mexico: spatio-temporal variability and current status of its epibiosis

The study examines the current invasive status of the barnacle Amphibalanus amphitrite on natural populations of two native oyster species (the eastern oyster Crassostrea virginica and the mangrove oyster C. rhizophorae) in a estuary of the southern Gulf of Mexico. The spatio-temporal variability of the frequency of occurrence, density and coverage of A. amphitrite on shells of each oyster species was examined and compared with those of other native congeners (A. eburneus, A. venustus and A. improvisus) with which it coexists. These three variables were significantly higher in C. rhizophorae than in C. virginica and were within the range recorded for its congeners. The density of this invasive barnacle varied significantly at spatial and temporal scales. Its highest overall mean density occurred in February (at temperatures 26–27°C and salinities 29–32). Multivariate analyses showed a separation of Amphibalanus assemblages into three main groups according to variations in their composition and abundance among sampling sites and dates. It was also determined that salinity and sedimentation rate were the variables that best explain the distribution of the Amphibalanus species within the estuary. The limited presence of A. amphitrite on C. virginica reefs is likely due to (amongst other factors) the relatively higher sedimentation loads (370–5709?g?m^?2?d^?1) and lower salinities (9–23) recorded in these sites. This study can act as a reference point for the subsequent monitoring of this invasive species, since possible increases in its population density and competitive ability could threaten the integrity of oyster populations and other organisms in the southern Gulf of Mexico.