Tenellia adspersa

Invasion History

First Non-native North American Tidal Record: 1953
First Non-native West Coast Tidal Record: 1953
First Non-native East/Gulf Coast Tidal Record:

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General Invasion History:

Tenellia adspersa was described from Odessa, Ukraine and is now widely distributed around the world, most likely spread by shipping (Roginskaya 1970; Thompson and Brown 1984). It is native in the Eastern Atlantic, from Europe (Norway to Portugal and Spain) and the Western Mediterranean (Roginskaya 1970). In the Baltic, it occurs eastward to the Gulf of Finland (Roginskaya 1970; Evertsen et al. 2004). In much of its European range, it is confined to brackish lagoons (Thompson and Brown 1984).

On the East Coast of North America, the range and invasion status of T. adspersa is unclear, owing to frequent confusion with a very similar native species, T. fuscata (Gould 1870), which has an overlapping range (Marcus 1972; Chester 1996). It has been introduced to Brazil, the West Coast of North America, Japan, and the Caspian Sea (Roginskaya 1970; Antsulevich and Starobogatov 1990). It feeds on many species of hydroids and tolerates a wide range of salinity and temperature (Roginskaya 1970). Hydroid prey include a number of global invaders: Cordylophora caspia, Garveia franciscana, and Ectopleura crocea (Roginskaya 1970). The mode of larval development is variable according the adult's nutritional status, between lecithotrophic development, with a short planktonic period, and planktotrophic development, with a longer planktonic phase (Chester 1996), more favorable for ballast water transport.

North American Invasion History:

Invasion History on the West Coast:

Tenellia adspersa was first found on the West Coast at Point Richmond, San Francisco Bay in 1953 (Jones 1954, cited by Carlton 1979). It was subsequently found at many locations within the Bay, including Berkeley Yacht Harbor in 1963 (Steinberg 1963); Lake Merritt Oakland in 1970 (Carlton 1979); San Leandro in 1993 (Cohen and Carlton 1995); Sausalito around 1995 (Cohen and Carlton 1995), and the Napa River in 2004 (Cohen et al. 2005). It was found on hydroids in Monterey Bay (Steinberg 1963), but was not seen there after 1958 (Carlton 1979). However, it was found in Elkhorn Slough in 1977 (Carlton 1979), and was established by 1998 (Wasson et al. 2001). It was also found in Alamitos Bay, in Long Beach in 1968 (Carlton 1979). In 1986, T. adspersa was found in upper Coos Bay, Oregon (Goddard 1990).

Invasion History on the East Coast:

Tenellia adspersa was first reported from the East Coast in 1969, based on collections made in Chesapeake Bay, starting in 1969 (Marcus 1972). However, its status in the Northwest Atlantic is complicated by confusion with the very similar T. fuscata, described from the Charles River estuary, Massachusetts, which overlaps in range and habitat (Marcus 1972; Vogel 1977). Consequently, we regard T. adspersa as cryptogenic in the Northwest Atlantic, until the status and distribution of the two species is resolved. At least one population, initially identified as T. fuscata, in Great Bay, New Hampshire (Gaulin et al. 1986) was later found to be T. aspersa (Chester 1996). Currently, T. adspersa is known from Great Bay, New Hampshire to Beaufort, South Carolina (Marcus 1972; Eyster 1979; Chester 1996; Caine 1998), while T. fuscata is reported from Maine to Chesapeake Bay (Gould 1870; Franz 1968), with one report from the Indian River Lagoon, Florida (Clark 1995). Vogel (1977) reported both species from Chesapeake Bay, with T. adspersa tending to occur at lower salinities (average 12.5 PSU) than T. fuscata (14.5-30 PSU). On Smithsonian Environmental Research Center (SERC) fouling plates in Chesapeake Bay, Terrence Gosliner found only T. adspersa, but only a few animals were examined (Ruiz et al., unpublished data).

Invasion History Elsewhere in the World:

Tenellia adspersa was described from Odessa, Ukraine on the Black Sea in 1845, but was not found in the Sea of Azov until 1963 (Roginskaya 1970). It could have been overlooked, or transported by ships. Increased salinity in the Sea, due to hydroelectric dams, could have favored the invasion. Its introduction to the Caspian Sea in 1990 was clearly due to transport in ballast water, by ships traversing the canal from the Black Sea (Antsulevich and Starobogatov 1990).

Beyond Europe, it was introduced to brackish waters in Brazil before 1953 (Vannucci and Hosoe 1953, cited by Roginskaya 1970). One specimen was found in the Seto Inland Sea, Japan in 1959 (Baba and Hamatani 1963). More recently, it was found in a bypass canal in Vladivostok, Russia, on the Sea of Japan in 1995, but did not become established (Zvyagintsev et al. 2011). One record is known from Botany Bay, Sydney, Australia in 1988 (Australian Museum Malacology C.155082, Atlas of Living Australia 2014), but establishment is unknown.

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Description

Tenellia adspersa has a slender body and a rounded head with lateral lobes, sometimes prolonged into oral tentacles, resulting in a crescent shape. The rhinophores (dorsal head tentacles) are smooth and cylindrical. There are 2 to 6 rows of cerata (dorsal outgrowths containing nematocysts) across the back, each with 1-3 cerata on each side of the body. The penis has an apical stylet. The animal rarely exceeds 8 mm in length. The overall color is yellowish to pale brown in color with black stippling over the body. Description based on Roginskaya (1970), Marcus (1972), Vogel (1977), Thompson and Brown (1984), and Behrens (1991).

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Taxonomy

Ecology

General:

Tenellia adspersa is a small nudibranch associated with hydroids, often in brackish water. Nudibranchs are simultaneous hermaphrodites and copulate reciprocally or unilaterally. Tenellia adspersa lays its eggs in an oval gelatinous mass containing 3-40 eggs, attached to hydroid stalks (Roginskaya 1970). The mode of development of the eggs varies with the nutritional status of the adults. This species can produce direct-developing larvae, lecithotrophic larvae (<1 day in plankton), and planktotrophic larvae (4-5 days in plankton) (Eyster 1979; Thompson and Brown 1984). Chester (1996) found that development time at 20°C was 5-6 days for eggs of continuously fed animals, but decreased to 3 days for starved animals. Both the type of larva produced and the rate of development appear to be variable between and within populations. This non-genetic variation in larval development is unusual in invertebrates, and is known as 'poeciligony'.

Tenellia adspersa has been reported from lagoons, estuaries, and harbors of warm-temperate to tropical regions. Substrates include rocks, pilings, floating docks, and boat hulls (Steinberg 1963; Roginskaya 1970; Chester 1996). This nudibranch tolerates an unusually wide range of salinity, from 3 to 50 PSU (Roginskaya 1970; Harris 1980), although some populations show reduced reproduction below 10-12 PSU (Harris et al. 1980; Blezard 1999). Tenellia adspersa feeds on a very wide range of hydroids, including Cordylophora caspia, Garveia franciscana, Ectopleura crocea, Gonothyraea loveni, Obelia spp., Protohydra leukarti, Eudendrium sp., and Bougainvillea sp. (Roginskaya 1970; Vogel 1977; Eyster 1979; Harris et al. 1980; Thompson and Brown 1984; Goddard 1990; Caine 1998). The feeding rate can be quite high. One T. adspersa can consume 100 Garveia hydranths in a day (Turpaeva 1963, cited by Roginskaya 1970). Chester et al. (2000) reported lower rates, up to seven C. caspia polyps eaten per day. Experiments indicate that T. adspersa can survive long periods of time without feeding, so that they can prevent the regrowth of hydroids after extensive predation (Chester et al. 2000). In many nudibranchs, the cnidocysts (stinging cells) of hydroids are ingested and then incorporated into the cerata, as a defensive mechanism (Barnes 1983). This is probably the case in T. adspersa.

Food:

Hydroids

Trophic Status:

Carnivore

Carn

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Habitats

General Habitat	Grass Bed	None
General Habitat	Coarse Woody Debris	None
General Habitat	Oyster Reef	None
General Habitat	Marinas & Docks	None
Salinity Range	Mesohaline	5-18 PSU
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Vertical Habitat	Epibenthic	None

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	4	Lowest tested (Harris et al. 1980)
Maximum Temperature (ºC)	25	Field (Eyster 1979)
Minimum Salinity (‰)	3	Lab experiments, cited by Roginskaya (1970)
Maximum Salinity (‰)	50	Lab experiments, cited by Roginskaya (1970)
Minimum Reproductive Salinity	10	Experiments cited by Roginskaya (1970)
Maximum Reproductive Salinity	50	Lab experiments, (Harris et al. 1980)
Minimum Duration	0	Development appears to vary with adult feeding and condition; well-fed adults lay eggs which develop directly, hatching out juveniles. Lower levels of feeding yield lecithotrophic or planktotrophic larvae (Chester 1996). All three modes of development can be seen simultaneously in a population (Eyster 1979; )
Maximum Duration	4.9	Planktotrophic larvae hatched from adults fed at lower levels (Chester 1996).
Minimum Length (mm)	5	Roginskaya 1970
Maximum Length (mm)	8	Roginskaya 1970
Broad Temperature Range	None	Cold-Temperate-Warm-Temperate
Broad Salinity Range	None	Oligohaline-Polyhaline

General Impacts

Tenellia adspersa is of ecological and economic interest because of its predation on a wide range of fouling hydroids, and because its ease of culture permits study of predator-prey relations (Roginskaya 1970; Harris et al. 1980; Gaulin et al. 1986; Chester et al. 2000).

Economic Impacts

High abundances of Tenellia sp. have been reported on fouling plates near power plants in Chesapeake Bay (Cory 1967; Abbe 1987) and in the Sea of Azov (Roginskaya 1970). Tenellia adspersa might have some beneficial impact on fouling in cooling systems if its predation reduced biomasses of hydroids such as Garveia franciscana and Cordylophora caspia (Chester et al. 2000).

Ecological Impacts

Predation: Tenellia adspersa is potentially an important predator on a wide range of hydroids, including widely introduced Garveia franciscana (Rope Grass Hydroid) and Cordylophora caspia (Freshwater Hydroid) (Roginskaya 1970; Harris et al. 1980). In experimental cultures, T. adspersa's chemical cues and predation caused an alteration of C. caspia's growth form, resulting in a greater density of hydranths. This could limit later settlement of T. adspersa's larva, due to predation. Tenellia adspersa predation on C. caspia thus seems to have complex effects; small numbers of T. adspersa might actually increase C. caspia biomass (Gaulin et al. 1986). However, modelling predicts that under a wide range of conditions, T. adspersa will eliminate C. caspia colonies, resulting in succession of hydroids by other fouling organisms (Chester et al. 2000).

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Regional Impacts

N130	Great Bay		Ecological Impact	Predation
Predation by Tenellia adspersa on the hydroid Cordylophora caspia stimulated increased growth and budding in the hydroid, resulting in a denser colony, perhaps favoring the persistence of the colonies (Gaulin et al. 1986). However, population modeling, including reproduction and settlement, indicates that T. adspersa is likely to remove colonies of C. caspia, favoring succession in the fouling community (Chester et al. 2000).
S110	Broad River		Ecological Impact	Predation
Tenellia adspersa was observed feeding on the hydroid Bougainvillia rugosa. However, the rate of predation was reduced by interference from the caprellid Paracaprella tenuis, which flicked the nudibranch away (Caine 1998).
CAR-VII	Cape Hatteras to Mid-East Florida		Ecological Impact	Predation
Tenellia adspersa was observed feeding on the hydroid Bougainvillia rugosa. However, the rate of predation was reduced by interference from the caprellid Paracaprella tenuis, which flicked the nudibranch away (Caine 1998).
NA-ET2	Bay of Fundy to Cape Cod		Ecological Impact	Predation
Predation by Tenellia adspersa on the hydroid Cordylophora caspia stimulated increased growth and budding in the hydroid, resulting in a denser colony, perhaps favoring the persistence of the colonies (Gaulin et al. 1986). However, population modeling, including reproduction and settlement, indicates that T. adspersa is likely to remove colonies of C. caspia, favoring succession in the fouling community (Chester et al. 2000).
SC	South Carolina		Ecological Impact	Predation
Tenellia adspersa was observed feeding on the hydroid Bougainvillia rugosa. However, the rate of predation was reduced by interference from the caprellid Paracaprella tenuis, which flicked the nudibranch away (Caine 1998).

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