Species Description: The pleated tunicate, Styela plicata is a solitary benthic tunicate believed non-native to Florida and the western Atlantic, but occurring there in some abundance. The oval, upright body is covered with a tough and leathery cellulose-containing tunic, with numerous rounded warts and pleated grooves. A pair of short siphons are present.
Individuals range in color from light tannish white to gray. Thin red or purple stripes on the insides of the four-lobed siphons are evident as cross-shaped markings at the tips of the closed siphons. Individuals can be found singly or in groups (Carlton and Ruckelshaus 1997, Kaplan 1999, NIMPIS 2002, USGS, ISSG)
Potentially Misidentified Species: In the IRL, Styela plicata may be mistaken for the co-occurring solitary tunicate Molgula occidentalis. This species is smaller and smoother than S. plicata, and side-by-side comparisons should easily differentiate these species. It is somewhat more difficult to distinguish S. plicata from the co-occurring congener (and fellow nonindigenous species) S. canopus (=S. parita). S. canopus is smaller, approximately 20-40 mm, and typically has externally striped siphons.
Regional Occurrence: Various authors list Styela plicata native or cryptogenic on the U.S. east coast (ISSG, NIMPIS 2002), but other authors consider the organism to be non-native in the western Atlantic (Da Rocha and Kremer 2005). The putative native range of the species is the the Indo-Pacific (Carlton and Ruckelshaus 1997, Lambert and Lambert 1998, Lambert 2001). Bingham (1992) and Carlton and Ruckelshaus (1997) list S. plicata as an introduced species in Florida.
IRL Distribution: Styela plicata is a widespread and abundant component of the IRL fouling community, commonly encountered near inlets and also well into the interior of the lagoon (Mook 1983).
Age, Size, Lifespan: NIMPIS (2002) reports Styela plicata individuals commonly range from 40-70 mm in size and that they may reach 90 mm.
Kott (1972) reports a life span of less than 1 year for S. plicata populations examined from Moreton Bay, Australia.
Abundance: In the IRL, Mook (1981, 1983) noted that Styela plicata was an abundant organism that dominated the fouling community, often to the exclusion of barnacles, in areas where large predatory fish were not present.
Reproduction: Styela plicata is a protandric hermaphrodite, with individuals starting out as functional males and then becoming functional females later in life. Sequential hermaphroditism insures fertilization through outcrossing. Sperm and eggs are shed to the water column via excurrent siphons and fertilization is external (Yamaguchi 1975, NIMPIS 2002).
S. plicata have been reported to reach sexual maturity in 2 months during the summer and 5 months in the winter (Yamaguchi 1975).
Embryology: Gamete release and fertilization in Styela plicata reportedly occurs in the late afternoon, with free-swimming, tadpole-like larval hatching out the following morning and typically becoming capable of settling to the benthos the same day (Yamaguchi 1975, NIMPIS 2002). Although larvae begin probing for suitable settlement sites shortly after hatching, they can extend their time in the water column for up to 2 days without negative consequence (Thiyagarajan and Qian 2003).
Sciscioli et al. (1978) note the tendency for larvae to settle onto previously colonized experimental settlement panels, suggesting environmental cues from adult conspecifics may be important. Larval nutrition is in the form of maternally supplied yolk contained in an envelope surrounding the eggs (Pisut and Pawlik, 2002).
Temperature: Temperatures in the range of 11-28°C permit spawning, and optimal spawning temperature occurs around 28°C (West and Lambert 1975, Yamaguchi 1975).
Salinity: Baker et al. (2004) report that Styela plicata in the greater Tampa Bay ecosystem occur in salinities ranging from full seawater down to around 20 ppt.
Trophic Mode: Styela plicata is a sessile, benthic filter-feeder. The incurrent siphon takes water into a sieve-like pharyngeal basket that filters out food of the appropriate size class before water is pumped from the animal via the excurrent siphon.
Associated Species: Styela plicata occurs alongside a number of different animal and algal taxa that comprise hard fouling intertidal and subtidal communities, although none of these associations are likely to be obligate.
Burrowing molluscs are found in the tests of some solitary tunicates including Styela spp., and copepods, amphipods, shrimps, crabs, and other small crustaceans often take up residence within Styela and other ascidians (Kott 1997, Pearse 1947).
Invasion History: Styela plicata is among the most common introduced ascidian species worldwide (Baker et al. 2004). Its present-day distribution is widespread but disjunct (da Rocha and Kremer 2005). The true native range of S. plicata is unknown but believed by several authors to be roughly the Indo-Pacific (Carlton and Ruckelshaus, 1997, Lambert and Lambert 1998, Lambert 2001).
Although ballast water transport has been suggested as a potential invasion pathway, it may be of only minor importance. The short larval duration indicates that S. plicata is unlikely to have been transported across great distances either as free-living water column inhabitants or as larvae in ballast water. Long-distance transport as adult fouling inhabitants on ship hulls is considerably more likely as a recurring means of introduction. S. plicata is a common hull-fouling species in tropical and warm temperate ports throughout much of the world. Accidental transport in shipments of live bivalves is another probable introduction route (Carlton 1979, Lambert 2001). Despite considerable evidence supporting the contention that the organism is not native to U.S. waters, Styela plicata was originally described in 1823 from specimens collected from the hull-fouling community on a ship in Philadelphia, PA. The organism was reported from U.S. coastal waters ranging from North Carolina to Texas in the 1880s, and had been reported from California by 1915. S. plicata had also been reported from Australia by the 1870s and from Brazil by 1883 (Fofonoff et al. 1999, Da Rocha and Kremer 2005). The presence of the organism in Chesapeake Bay was only conclusively documented when it was recovered on experimental fouling plates in 2002 (Fofonoff and Ruiz unpublished data).
Potential to Compete with Natives: Styela plicata appears capable of outcompeting native species. Lambert and Lambert (1995) report that S. plicata appears to have replaced the native solitary tunicates Pyura haustor and Ascidia ceratodes in parts of their California range.
Possible Economic Consequences of Invasion: Styela plicata is a widespread and common fouler of buoys, pilings, nets and other floating or submerged manmade structures. It is also a common fouler of aquaculture cages, bags, and nets. If fouling is severe, costly cleaning of gear is required to avoid still costlier loss of stocks (Da Rocha and Kremer 2005).
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