Seasonal Patterns of Ascidian Settlement at an Aquaculture Facility in the Damariscotta River, Maine

Abstract

Biofouling ascidians represent a serious and costly problem for aquaculture. Although the subject of intensive study for the past decade, little is still known about the timing, intensity, and duration of ascidian settlement, especially in coastal Maine. To assess ascidian settlement, PVC panels were deployed in the Damariscotta River, Maine, on a weekly basis during the summers of 2007 and 2008. Long-term fouling panels were deployed from June to October 2007 to assess the development of mature fouling communities. Settlement of fouling organisms largely occurred during 2 seasonal phases. Early summer (May to July) was dominated by settlement of hydroids and bivalve molluscs; late summer and early fall (August to September) was dominated by ascidian settlement. Overall, ascidians accounted for ∼50–80% of total settlement. The solitary ascidian Ciona intestinalis dominated mature fouling panels, but had low and intermittent settlement levels. The invasive colonial ascidian Didemnum vexillum settled later in the year (starting at the end of July) than other taxa. Specific knowledge of settling patterns of biofouling organisms may provide growers with a means of determining opportune times for deployment of gear to avoid excess fouling.