Stenothoe gallensis species complex

Invasion History

First Non-native North American Tidal Record: 1957
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 1957

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General Invasion History:

Stenothoe gallensis was described in 1904 from Sri Lanka (Ceylon), and occurs widely in the Indian Ocean. Similar amphipods were found in tropical to warm-temperate waters around the world, sometimes described under different names (e.g. S. cattai Stebbing 1906; S. crenulata Chevreux 1908; S. dentirama Hirayama & Takeuchi 1993), and later treated as synonyms of S. gallensis (Bellan-Santini et al. 1993; LeCroy 2011). Stenothoe gallensis is often assumed to be a widespread invader of Indo-European origin. In the Mediterranean, it was considered a possible 'Lessepsian migrant', through the Suez Canal (Por 1978; Bellan-Santini et al. 1993; Galil et al. 2009). Stenothoe gallensis has been listed as likely introduction in Senegal (Reid 1951), Chesapeake Bay (Fofonoff et al. 2016), Hawaii (Carlton and Eldredge 2009), and New Zealand (Ahyong and Williams 2011). It is an amphipod associated with fouling communities, including algae, hydroids, tubeworms, and tunicates, on pilings, floats, ship bottoms, buoys, mangrove roots, etc., (Shoemaker 1935; Reid 1951; LeCroy 2011).

A recent study of the 'Stenothoe gallensis group' has found that it consists of at least eight species with consistent morphological differences (Krapp-Schickel 2015). The true S. gallensis (Walker 1904) ranges from East Africa to the South China Sea (Kensley 1971; Lowry et al. 2000; Krapp-Schickel 2015). Several of the newly described species have limited known ranges (S. senegalensis- West Africa; S. andamanensis- Andaman Islands; S. clavetta- Bermuda; S. himyara- Red Sea; Krapp-Schickel 2015). Further sampling will probably show that each of these one-location species have larger ranges. At least three species have trans-oceanic or multi-oceanic ranges, and four species occur in the Western Atlantic. We are unsure of the identity of 'S. gallensis' in the Western Atlantic and Hawaii, so we will treat it as a species complex of unknown origin.

Stenothoe crenulata has the largest range of the group. It was described from Mangareva, in French Polynesia and subsequently found in Indonesia (Bali), Hawaii, and the Caribbean (Krapp-Schickel 2015). The first Western Atlantic report of S. crenulata was from St. Thomas, Virgin Islands, in 1905. It was subsequently collected from two locations in Puerto Rico (Shoemaker 1935). In the Caribbean, it is also known from Barbados, Curacao, and Venezuela (Krapp-Schickel 2015). We consider S. crenulata to be, most likely, an Indo-Pacific species introduced to the Western Atlantic. Other species of the S. gallensis complex which have some occurrences in the Western Atlantic are S. cattai (Mediterranean Sea and Bermuda), S. dentirama (Japan and Bonaire), and S. clavetta (so far, known only from the type locality, Bermuda) (Krapp-Schickel 2015).

North American Invasion History:

Invasion History on the East Coast:

Amphipods of the Stenothoe gallensis species complex were first collected in East Coast waters in Beaufort Sound, North Carolina in 1957 (Williams and Bynum 1972). They were reported to be a 'common fouling species, taken occasionally in plankton' (Fox and Bynum 1975). Specimens were collected in lower Chesapeake Bay at Cherrystone and Wachapreague Inlet, Virginia in 1960 (US National Museum of Natural History 2016), and again in 1995 (Ruiz et al. unpublished data). 'Stenothoe gallensis' was found in the Indian River Lagoon, Florida on algal covered rocks (Nelson 1995). The only detailed description of 'S. gallensis' in North American waters (LeCroy 2011) includes a key feature of S. crenulata, the crenulated posterior margin of the merus of gnathopod 2 in males (Krapp-Schickel 2015). However, more examination of East and Gulf Coast specimens is needed to determine their identity.

Invasion History on the Gulf Coast:

In 1978, amphipods of the Stenothoe gallensis species complex were found off the Mississippi Delta in Louisiana (US National Museum of Natural History 2016), and were abundant in the Crystal River estuary, Florida in 1984 (US National Museum of Natural History 2016), and Tampa Bay in 2002 (Grabe et al. 2006). It has also been found near Perdido Key, Alabama (Rakocinski et al. 1996, cited by Le Croy 2011), and on the Texas coast (McKinney, 1977, cited by Le Croy 2011).

Invasion History in Hawaii:

Stenothoe 'gallensis' was first reported from Kaneohe Bay, Oahu in 1935, and in 1944 in Pearl Harbor (Barnard 1955, cited by Carlton and Eldredge 2009). It was also found on Molokai and in Kawahai Harbor, Hawaii in 2002-2003 (Coles et al. 2004). Krapp-Schickel (2015), working from Barnard's (1955) drawings, identified Hawaiian specimens as S. crenulata.

Invasion History Elsewhere in the World:

The nature of Stenothoe 'gallensis' as a group of cryptic species makes it difficult to evaluate its invasion status worldwide. Stenothoe crenulata appears to be widespread in the Caribbean. It was collected in St. Thomas, U.S. Virgin Islands, in 1905, 'from the branchial sac of Microcosmus exasperatus' (a tunicate), and from a 'Cane wharf’ in Guanica Harbor, Puerto Rico in 1915 (Shoemaker 1935). Krapp-Schickel (2015) supported this identification and found it also in Barbados. Additional specimens were collected off Venezuela in 1936 and Curaçao in 1964 (Krapp-Schickel 2015). Another member of the S. 'gallensis' group, S. dentirama, described from Japan, has also been found in Curaçao (Krapp-Schickel 2015). Further sampling, together with morphological analysis is required to determine the native ranges and the extent of invasions in the S. 'gallensis' complex.

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Description

The Stenothoidae family is distinguished by having coxal plates 2-4 greatly enlarged, covering the basal segments of most of the appendages. The abdomen is flexed downward. They are sometimes called 'seed-amphipods', for their laterally-compressed elliptical shape. At least three species have been synonymized with Stenothoe gallensis. Krapp-Schickel (2015) re-split these species and described four others, all roughly resembling the type species, S. gallensis. Some of these species have limited known ranges, while others have been collected in both the Atlantic and Indo-Pacific. At least four of Krapp-Schickel's (2015) species (S. cattai, S. clavetta, S. crenulata, S. dentirama) have been reported from Bermuda or the Caribbean. The specific identity of the 'S. gallensis' in North American waters is unknown, but we will treat the entire complex as introduced. Members of the complex are listed below under 'Potentially Misidentified Species'. We will use a description by LeCroy (2011) of animals from Florida waters. A detailed morphological examination is needed to assign East Coast and Hawaii animals to one of the species in the S. gallensis complex as described by Krapp-Schickel (2015).

In specimens of S. 'gallensis' from Florida, the eye is relatively small. Antenna 1 is less than 1/2 the body length and is equal or slightly longer than Antenna 2. Gnathopod 2 is larger than Gnathopod 1 in both males and females, and is sexually dimorphic. The propodus of gnathopod 1 has a straight to slightly concave posterior margin, roughly equal to the margin of the palm in length. Gnathopod 2 of the male has the posterior margin of the merus scalloped (crenulate) (Lecroy 2011). [This feature matches S. crenulata (Krapp-Schickel 2010)]. The distal palmar tooth is relatively small. On gnathopod 2 in females the propodus has a convex posterior margin, without a distal palmar tooth, and the merus is smoothly curved. Pereiopod 7 has segment 4 (merus) slightly enlarged, with a curved, angular postero-distal tip. Uropod 1 extends beyond Uropod 2. Its peduncle has a distoventral spur. Both Uropods 1 and 2 are biramous. Uropod 3 of the male has the terminal article of the ramus expanded proximally. The telson is oval, with 3-4 pairs of marginal spines. Florida specimens range from 2 to 6 mm, with males generally larger than females (LeCroy 2011). Genetic and molecular studies are needed to determine the identity of East and Gulf Coast specimens of 'S. gallensis', and how they fit into the species described by Krapp-Schickel (2015).

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Taxonomy

Ecology

General:

Amphipods of the Stenothoe gallensis species complex have separate sexes, the young are brooded and development is direct (Bousfield 1973).

Amphipods of the Stenothoe gallensis species complex are known from warm-temperate to tropical climates, and polyhaline to euhaline salinities (Shoemaker 1935; Lecroy 2011; Krapp-Schickel 2015). Among invertebrates, hosts include hydroids (Pennaria sp), bryozoans, polychaete reefs, and the tunicates Didemnum sp., Styela sp., and Microcosmus exasperatus. Stenothoe 'gallensis' is also known from algae, seagrasses, and mangrove roots (Shoemaker 1935; Marsh 1973; Lecroy 2011; Krapp-Schickel 2015). It occasionally occurs in coastal plankton (Fox and Bynum 1975) and has been collected in the mid-Pacific (Krapp-Schickel 2015). Stenothoe 'gallensis' is common in dock, buoy, and ship fouling (Shoemker 1935; Reid 1951; Krapp-Schickel 2015). Its mode of feeding may resemble that of S. valida, which is a suspension feeder - animals sit in place, with uropods pressed against a surface and the body pointed upward at a 30-degree angle, with the antennae and gnathopods in motion, and periodically wiped across the mouthparts (Lewis 1992).

Food:

Phtyoplankton, detritus

Trophic Status:

Omnivore

Omni

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Habitats

General Habitat	Grass Bed	None
General Habitat	Marinas & Docks	None
General Habitat	Rocky	None
Tidal Range	Subtidal	None
Vertical Habitat	Epibenthic	None
Vertical Habitat	Littoral	None

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Tolerances and Life History Parameters

Minimum Salinity (‰)	16	Grabe et al. 2006, Tampa Bay
Maximum Salinity (‰)	37	Approximate Gulf of Mexico salinity
Minimum Length (mm)	2	LeCroy 2011; Krapp-Schickel 2015. Females are generally smaller than males.
Maximum Length (mm)	6	LeCroy 2011; Krapp-Schickel 2015.
Broad Temperature Range	None	Warm temperate-Tropical
Broad Salinity Range	None	Polyhaline-Euhaline

General Impacts

No impacts have been reported for amphipods of the Stenothoe gallensis complex in their native or introduced ranges.

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