Marine aquaculture as a source of propagules of invasive fouling species.

Non-indigenous species tend to colonize aquaculture installations, especially when they are near international ports. In addition to the local environmental hazard that colonizing non-indigenous species pose, they can also take advantage of local transport opportunities to spread elsewhere. In this study, we examined the risk of the spread of eight invasive fouling species that are found in mussel farms in southern Brazil. We used ensemble niche models based on worldwide occurrences of these species, and environmental variables (ocean temperature and salinity) to predict suitable areas for each species with three algorithms (Maxent, Random Forest, and Support Vector Machine). As a proxy for propagule pressure, we used the tonnage transported by container ships from Santa Catarina (the main mariculture region) that travel to other Brazilian ports. We found that ports in the tropical states of Pernambuco, Ceará, and Bahia received the largest tonnage, although far from Santa Catarina and in a different ecoregion. The ascidians Aplidium accarense and Didemnum perlucidum are known from Bahia, with a high risk of invasion in the other states. The bryozoan Watersipora subtorquata also has a high risk of establishment in Pernambuco, while the ascidian Botrylloides giganteus has a medium risk in Bahia. Paraná, a state in the same ecoregion as Santa Catarina is likely to be invaded by all species. A second state in this region, Rio Grande do Sul, is vulnerable to A. accarense, the barnacle Megabalanus coccopoma, and the mussel Mytilus galloprovincialis. Climate change is changing species latitudinal distributions and most species will gain rather than lose area in near future (by 2050). As an ideal habitat for fouling organisms and invasive species, aquaculture farms can increase propagule pressure and thus the probability that species will expand their distributions, especially if they are close to ports. Therefore, an integrated approach of the risks of both aquaculture and nautical transport equipment present in a region is necessary to better inform decision-making procedures aiming at the expansion or establishment of new aquaculture farms. The risk maps provided will allow authorities and regional stakeholders to prioritize areas of concern for mitigating the present and future spread of fouling species.

Invasive species fouling Perna perna (Bivalvia: Mytilidae) mussel farms.

Invasive, fouling species increase management costs and reduce mussel growth, which jeopardizes mariculture. We studied the distribution of eight invasive species in Santa Catarina, the leading mussel producer in Brazil. Our goals were to determine their spatial distribution and prevalence on farm structures (buoys, long lines, and mussel socks), as well as understand the relevance of propagule pressure (recruitment), port distance, and area of the farm in this distribution. Although present in all sites, adult and recruits distribution were spatially restricted, showing that species might have a metapopulation structure. The most prevalent species were the ascidian Styela plicata, the barnacle Megabalanus coccopoma, the bryozoan Schizoporella errata, and the polychaete Branchiomma luctuosum. Recruitment was the main driver of three species distribution while distance to port explained only one species distribution. Based on those results, we discuss policy options, management, and regulation enforcement, that can be used in the mussel aquaculture elsewhere.