Styela clava

Styela clava is an extremely efficient suspension feeder, preying on phytoplankton, zooplankton and other suspended organic materials (NIMPIS 2002). Large solitary ascidians are capable of a high rate of filtration (Lambert and Lambert 2003). Mature S. clava kept in moving water at 10°C filtered 78-175ml of water/g/dry weight of body (Morris et al. 1980). To feed, S. clava pumps water in through the oral aperture, strains the food particles through the branchial filter and pumps the filtered water out through the atrial aperture (Cohen 2005). The pore size on the ascidian mucus sheet covering the branchial filter is approximately 0.2 μm (Lambert and Lambert 1998), small enough to remove bacteria and organic molecules. Osman et al. (1989) found that S. clava predation removed 96% of oyster larvae in the water column. (Clark and Therriault, 2007)

The competitive superiority of S. clava over mussels and oysters presents a major problem for fisheries and shellfish aquaculture. This species competes for food and space with other filter feeders and benthic species but because it does not produce a shell it can grow faster and reach maturity earlier than competing bivalves. (Clark and Therriault, 2007)

Styela clava has the ability to reduce settlement rates of co-occurring species locally but seems to have little effect on post-settlement community dynamics (Whitlatch et al. 1995). In Japan, Denmark and eastern Canada, S. clava has been reported as a major pest of oyster and mussel farms (Cohen 2005). In many places, this species has replaced local ascidians as the dominant member of shallow, protected habitats worldwide (Whitlatch et al. 1995; Lutzen 1999; Lambert and Lambert 2003). (Clark and Therriault, 2007)