Ascidian Fouling in North Carolina Shellfish Farms

Abstract

Ascidians are marine sessile animals that are particularly abundant on artificial structures, where they often overgrow native species and compete with other filter feeders. North Carolina’s (NC) coastline supports productive aquaculture operations and ascidians are considered pests there. Five shellfish farms and four nearby marinas were surveyed to compare the structure and composition of their ascidian communities using photo-quadrat surveys and presence–absence and abundance matrices, with “marina” and “shellfish farm” as factors. Twelve species were observed in the marinas, but only six in the farms: three native, two cryptogenic, and one identifiable only to the genus level. The three native species (Clavelina oblonga, Perophora viridis, and Molgula manhattensis) have established populations in many world regions and were observed in at least two of the farms visited. The cryptogenic Styela plicata was found in all farms and marinas and was the most abundant species. All species observed in shellfish farms were also present in marinas, with no significant difference in ascidian composition or abundance. Independently of introduction status, species thriving in a wide range of habitats are more adaptable and better suited to establish populations on artificial substrates, resulting in increased maintenance costs for aquaculture operations.