Styela plicata (sea squirt) is an ovular, greyish to tannish white benthic tunicate. This solitary sessile invertebrate is cloaked in an unstalked tunic that is large, tough, (Fuller, 2007), warty and ridged (Howey, 1998). Perry & Larson (2004) report that the lumpy surface of the tunic gives it the appearance of cobblestone pavement. Internal structures are protected by this tunic, which is composed largely of cellulose compounds and contains a circulatory system of \"blood\" transport vesicles. Dividing the tunic is a membrane which allows fluid to flow up one side and down the other. S. plicata has an incurrent siphon that intakes water into the pharyngeal basket where food particles are filtered out; the waste is then excreted through the excurrent siphon (Howey, 1998). The two short siphons have red or purple stripes on the inside of the siphons and four lobes (Fuller, 2007). When physically disturbed, S. plicata expels water, which explains why it is called a sea squirt. S. plicata is a very eurythermal tunicate; able to tolerate changes in seawater between 10°-30°C and salinites between 22%-34% (Thiyagarajan & Qian, 2003). NIMPIS (2002) reports that S. plicata can tolerate some pollution and brackish waters. Adults can reach sizes between 40-70mm, even up to 90mm in some cases (NIMPIS, 2002). As a protandric hermaphrodite, S. plicata has \"testes - small and attached along most of the length of each ovary,\" with two gonads on the left side of the body and five on the right (Lambertet al. 2005).
As a defence mechanism, Styela plicata (sea squirt) concentrates deterrant chemical compounds in its gonads so that they may be passed on to larvae, thus protecting them from predation (Pisut & Pawlik, 2002). Alcohol from the body of S. plicata exhibits anti-Hepatitis B properties (STRI, undated). S. plicata harbours the amphiped Leucothoe spinicarpa and an ascidicolous copepod (Thiel, 1998). Cold winters kill S. plicata, limiting its northern distribution to Cape Hatteras, North Carolina. One way this is thought to happen is by dislodgement from substrates during cold (growth inhibiting) periods (Fisher, 1976). Populations of S. plicata fluctuate; they may be abundant one year and absent the next (Lambert & Lambert, 1998).
The eggs of Styela plicata (sea squirt) are surrounded by a complex ovular envelope (Mansuetoet al. 2003) that supplies the larvae with its nutritional requirements (Pisut & Pawlik, 2002). Once hatched, the larvae attempt to find a suitable substrate. S. plicata can have an extended swimming period of over 2 days prior to settlement without a cost to metamorphosis (Thiyagarajan & Qian, 2003). Larval settlement is most successful in the spring and fall (Fisher, 1977). S. plicata has a life span of less than one year that is characterised by rapid growth. Some sea squirts can live between 2-3 years (Lambert & Lambert, 1998). Yamaguchi (1975) reported that S. plicata reached sexual maturity in 2 months during the summer and 5 months during the winter. S. plicata has an extended breeding season, reproducing all year except during winter (NIMPIS, 2002).
Styela plicata (sea squirt) is a host to several different kinds of organisms, including brittle stars, mussels, chitons, sponges, polychaete worms, diatoms, eggs, etc., that live on its tunic (Howey, 1998).
The different life cycle stages of Styela plicata (sea squirt) have different habitat requirements for survival. The larval and juvenile stages of S. plicata live on marinas and docks, oyster reefs, rocks and coarse woody debris, while the adults prefer marinas, docks and hard rocky substrates (NEMESIS, 2006). S. plicata also live in coral reef habitats (STIR, undated). S. plicata is found from the low intertidal zone to depths of 30m (NIMPIS, 2002).
Styela plicata (sea squirt) is a protandric hermaphrodite. Initially, S. plicata is a male, then later it changes to a female. Fertilisation is external; eggs and sperm are released into the water column in the late afternoon and the larvae, 1.3mm in total length (Yamaguchi, 1975), hatch the next morning and settle that day (NIMPIS, 2002). S. plicata undergoes reproductive cycles yearly in conjunction with annual temperature changes. According to West & Lambert (1975), S. plicata must experience a period of darkness; approximately 8.5 hours long, prior to the release of gametes. Spawning can occur between 11°-28° C (West & Lambert, 1975), with 20°C being optimal (Yamaguchi, 1975). Water filtration is not optimal during the release of gametes (Fiala-Medlioni, 1978).
Styela plicata (sea squirt) is a suspension filter feeds that preys primarily on phytoplankton, zooplankton and organic materials. Snails, crustaceans, sea stars and fish have been known to prey on S. plicata (NIMPIS, 2002). Specifically, the species Linatella caudata preys upon S. plicata (Morton, 1989).
Hayes et al (2005) report that Styela plicata was introduced to Australia accidently with the translocation of fish or shellfish.Styela plicata can be introduced to new locations in ship ballast water (Fuller 2007).Styela plicata can be introduced to new locations by hull/ship fouling (Fuller 2007).
Compiler: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Review: Expert review underway: Dr. Richard Osman, Senior Scientist Smithsonian Environmental Research Center., Edgewater, Maryland, USA
Publication date: 2007-05-08
Recommended citation: Global Invasive Species Database (2017) Species profile: Styela plicata. Downloaded from http://www.iucngisd.org/gisd/species.php?sc=952 on 21-09-2017.