Copper Tolerance of Amphibalanus amphitrite as Observed in Central Florida
Copper tolerance in the invasive barnacle Amphibalanus amphitrite has been observed in Florida by the Center for Corrosion and Biofouling Control since 2012 and by Weiss (1947). To test the theory that this barnacle preferentially settles on copper coated surfaces to avoid settlement competition by other sessile species, a series of two experiments and a literature review of historical copper toxicity tests on larval barnacles was conducted. The barnacle A amphitrite was preferentially used in many previous toxicity studies because it is readily available, has high fecundity, and is more sensitive to some toxicants than other species, including the native barnacle A eburneus. In order to resolve the difference between observed recruitment by A amphitrite on copper coatings, with reported copper sensitivity as larvae in lab experiments, an in situ field experiment was performed. A series of panels coated with paint containing different concentrations of copper was immersed at the Florida Institute of Technology static test site at Cape Marina, located in Port Canaveral, FL during two different seasons: winter with low fouling pressure and summer with high fouling pressure. During the winter, the barnacle A amphitrite and an invasive species of bryozoan Watersipora subtorquata complex recruited on low copper content surfaces, but did not occupy enough space for competition to be a factor. During the summer, the barnacle A amphitrite recruited almost exclusively on the highest copper content panels, while the bryozoan W subtorquata complex recruited on the low copper content panels, similar to the pattern seen in winter. The native barnacle Amphibalanus eburneus settled exclusively in the inert surfaces. Through these results, it can be determined that A amphitrite likely responded to higher competition pressure by recruiting to higher copper treatments, unlike W subtorquata complex and A eburneus. A second set of experiments was designed to look at settlement preferences of A amphitrite. In one experiment, larvae of the barnacle A amphitrite were isolated in mesocosms with the choice of settlement on the high copper-content coated surface, that it readily recruited on in the previous experiment, and an inert surface. In the second experiment larvae of both A amphitrite and A eburneus were placed in the mesocosms with same choice of substrate. A amphitrite settled in significantly higher numbers on the inert surfaces rather than settling evenly on both surfaces, regardless of whether there was competition from a congenitor or not. Given the results of the previous in situ experiment this result was not expected. Copper tolerance in the barnacle A amphitrite has been observed through recruitment studies and observations in several parts of Florida. Though this barnacle is known to be sensitive to copper in the literature, the anomaly of its recruitment to copper coated surfaces is yet to be determined. Settlement studies of A amphitrite revealed a preference for settlement on inert surfaces without competing recruits, which is indicative of the literature sensitivity results but not the observed recruitment of this organism.