Synidotea laticauda

Invasion History

First Non-native North American Tidal Record: 1897
First Non-native West Coast Tidal Record: 1897
First Non-native East/Gulf Coast Tidal Record: 1998

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General Invasion History:

Synidotea laticauda was described from San Francisco Bay, California, by Benedict in 1897 and was later found in Willapa Bay, Washington in 1987 (Chapman and Carlton 1991). However, it has not been found in other West Coast estuaries. This isopod's limited West Coast range, its taxonomic affinities with Indo-Pacific species, and its association with fouling communities are indicative of introduced status (Carlton 1979; Chapman and Carlton 1991). Synidotea laticauda was discovered on the East Coast in South Carolina, Chesapeake Bay, Delaware Bay, and Hudson River estuary in 1998-2003, (Bushek and Boyd 2006; Elizabeth Jewett personal communication 2002; Pederson et al. 2003; South Carolina Department of Natural Resources 2007) and in European estuaries in 1975-2009, from the Guadalquivir River, Spain, to the Westerschelde Estuary, Netherlands (Mees and Fockedey 1993; Cuesta et al. 1996; Soors et al. 2010; Faasse 2012). Synidotea laticauda is possibly a junior synonym of the Northwest Pacific species S. laevidorsalis (Miers 1881), together with two species in Atlantic South America (S. marplatensis, S. brunnea) and two in Southeast Australia [(S. grisea, and S. keablei) (Chapman and Carlton 1991; Chapman and Carlton 1994)]. These synonymies have been disputed by Poore (1996), but nonetheless, biogeographical considerations support the status of S. laticauda as an introduced species on the West and East coasts of North America, and within Europe. A recent morphological and genetic identification of S. laticauda from the Yangtze estuary, China, supports the hypothesis that S. laticauda is an estuarine species of Asian origin (Liu et al. 2017).

Molecular analysis is needed to examine the taxonomic and invasion status of this species. Chapman and Carlton (1991) synonymized S. laticauda with the Northwest Pacific S. laevidorsalis. This synonymy has been questioned, and by implication, the introduced status of Synidotea laticauda/laevidorsalis in San Francisco Bay (Poore 1996). Synidotea laevidorsalis was described from 'Jatiyama Bay' (=Tateyama Bay?), Japan (Miers 1881, cited by Benedict 1897; Chapman and Carlton 1991), and ranges from Vladivostok, Russia and Hakodate, Japan to the Yangtze River estuary (Huang 1981, cited by Carlton and Chapman 1991) and Pusan, South Korea (Kang and Yun 1988). Most of the records appear to be shallow marine locations with seagrass and algae (Kang and Yun 1988) but S. laticauda was abundant on pilings and fouling plates, among brackish water fauna in the Yangtze estuary (Huang et al. 1981; Liu et al. 2017).

A consequence of Poore's argument (Poore 1996), is that many authors (e.g, Soors et al. 2010; Faasse 2012) assume that S. laticauda is native to San Francisco Bay and the West Coast, ignoring the biogeographical history of San Francisco Bay, which makes the evolution of an endemic isopod of this species group improbable (Carlton 1979; Chapman and Carlton 1991). The hypothesis of the synonymy with S. laevidorsalis and introduced status for the South American and Australian populations remains unresolved (Schram 2010; James Carlton; John Chapman, personal communications). The careful application of molecular methods, with sufficient sampling of the populations over their various ranges, may be needed to resolve the status of these nominal species (Geller et al. 2010). Synidotea laticauda has been collected and identified by morphological and molecular methods in the Yangtze estuary, China, within a probable native region (Liu et al. 2017). Further morphological and ecological studies of the S. laticauda/laevidorsalis complex are desirable. Cryptic diversity and invasions are likely within this isopod group.

North American Invasion History:

Invasion History on the West Coast:

Synidotea laticauda was described from San Francisco Bay, California, by Benedict in 1897 (Benedict 1897). Many specimens were collected from the Bay in the 'Albatross' US Fish Commission Surveys of 1912 (USNM 53123-53296, U.S. National Museum of Natural History 2015), at 7-29 m depth. It has been found throughout the bay and into the Sacramento-San Joaquin Delta (Menzies and Miller 1979; Carlton 1979). It is generally found in estuarine waters, ranging from salinities of 1 to 30 PSU, and is associated with hydroids, particularly the introduced Garveia franciscana (Menzies and Miller 1972; Carlton 1979; Cohen and Carlton 1995). Gewant and Bollens (2005) found it to be the third most abundant macro-zooplankton species in San Francisco Bay, with its highest densities in the South Bay, during October-January. In 1987, it was collected in Willapa Bay, Washington, and is assumed to be established there (Chapman and Carlton 1991).

Invasion History on the East Coast:

Synidotea laticauda was first collected in the Stono River, just outside Charleston Harbor in South Carolina, in 1998 (USGS Nonindigenous Aquatic Species Program 2007). It was later found further south in the Combahee River and Dawho Rivers (South Carolina Department of Natural Resources 2007). In 1999, it was discovered in Delaware Bay, at the Haskins Shellfish Laboratory, at the mouth of the Maurice River. In 2005, it was found over about 40 km of the bay's length on the New Jersey side, from the Cohansey River to Dennis Creek (Cape May County), at a salinity range of 22-4 PSU. Up to 29,000 animals were collected in the Maurice River in October, 2004 (Bushek and Boyd 2006). In 2002, S. laticauda was collected in Norfolk Harbor, Virginia, in the Chesapeake Bay (Elizabeth Jewett personal communication 2004, identified by Marilyn Schotte, U.S. Museum of Natural History). Later collections were made in the James River estuary, on the hulls of obsolete cargo ships in 2006 (Davidson et al. 2008); at Gloucester Point in the York River (Emmett Duffy, personal communication, 10/4/12); and off Curtis Point, Shady Side, Maryland, on the West River (12/17/14, Robert Aguilar, personal communication). In 2003, S. laticauda was collected at the mouth of the Hudson River, at the South Street Seaport in fouling communities. In 2006-2009, it was found to be common in benthic samples and on piers of the Tappan Zee Bridge (New York State Department of Transportation 2012). While East Coast collections are spotty, they do indicate that S. laticauda is widespread in mesohaline-polyhaline regions of estuaries from South Carolina to the Hudson River, New York, and can be locally abundant.

Invasion History Elsewhere in the World:

Synidotea laticauda was collected in European waters in the Gironde estuary, France, as early as 1975, but was originally misidentified as the native Idotea emarginata. It was found over a range of 1-20 PSU, but was most abundant at 3 PSU (Mees and Fockedey 1993). Later European collections were in the Guadalquivir River estuary, southern Atlantic Spain in 1991-1994 (Cuesta et al. 1996); the Scheldt estuary, Belgium in 2005 (Soors et al. 2010); and the Westerschelde estuary, the Netherlands in 2009 (Faasse 2012), all under estuarine conditions (0.4-24 PSU).

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Description

Synidotea laticauda is an estuarine isopod orignially described from San Frnacisco Bay (Benedict 1897). The recent geological history of the Bay and the absence of similar species on the West Coast suggested origins elsewhere (Carlton 1979). Chapman and Carlton (1991; 1994) suggested a synonymy of S. laticauda with the Indo-Pacific S. laevidorsalis, together with several Australian and South American species, but this was strongly dispuited by Poore et al. (1993). Specimens of Synidotea laticauda have now been identified morphologically and genetically, from the Yangtze River, a likely native site. A specimen of 'S. laevidorsalis' from Korea also was genetically identified as S. laticauda (Liu et al. 2017). More widspread studies of the worldwide S. laticauda/laevidorsalis complex are desirable. However, Liu et al.'s description of the Chinese specimens and their habitat matches that of North American and European specimens, so the name S laticauda is now generally accepted (Nuño et al. 2018; Ruiz-Delgado et al. 2019).

The body outline of Synidotea laticauda is a truncated oval shape, with a strongly concave pleotelon posterior margin, a deep median groove, and a squared-off head with a shallow median indentation. The eyes are dark and bulge outward. The pleotelson is about 1/3 the body length, and only slightly longer than wide. Ovigerous females are broader than males, or non-ovigerous females. The cephalon and peraeon lack scales, tubercles, or ridges. The first 3 peraeonites have evenly rounded edges, while the borders of the other peraeonites are fairly straight. The anterior medial edge of peraeonites 2-4 have a crescent or half-moon pattern, which becomes narrower on posterior peraeonites. Peraeonite 4 is the widest part of the body. In S. laticauda, the 5th segment of Antenna 2 is long and prominent. In males, segments 1-3 bear long setae (Menzies and Miller 1972, illustration). Antenna 2 can be stretched back to pereaonite 5. The pereiopods increase in length posteriorly. Pereiopods 2-7 are longer than the body width. The maxillipedal palp consists of three segments. Pleopods 2 are modified for copulation, with the inner ramus of each modified into a needle-like stylet, the appendix masculina. Adult males reach 25 mm in length, but females are smaller, reaching 16 mm. The background color of live animals is tan, mottled with dark brown, and with a darker mid-dorsal stripe. This description is based on: Benedict 1897, Richardson 1905, Schultz 1969, Menzies and Miller 1972, Chapman and Carlton 1991, Cuesta et al. 1996, Poore 1996, Bushek and Boyd 2006, Brusca et al. 2007, Faasse 2012.

Synidotea spp. is a widely distributed genus, with many species in polar, temperate, and tropical climates, in deep and shallow waters, and in both marine and estuarine habitats (Schultz 1969; Menzies and Miller 1972). Chapman and Carlton (1991) proposed that S. laticauda in San Francisco (California) and Willapa Bays (Washington); and S. marplatensis Giambiagi, 1922 and S. brunnea Pires and Moreira, 1975 from the Atlantic coast of South America were synonyms of the Northwest Pacific S. laevidorsalis Miers 1881, and were introduced by shipping to their various habitats. Chapman and Carlton (1994) added the Australian species S. keableri and S. grisea to the list of probable synonyms of S. laevidorsalis. Most of the biometric characters that had been used to distinguish these species were size-dependent. When these measurements were plotted against body length, these nominal species clustered along a single line (Chapman and Carlton 1991; Chapman and Carlton 1994). Poore (1996) noted differences in body shape, coloration, and setae number and location between the putative species which he considered independent of body size. However, Chapman and Carlton (1991) note that setation can vary with age and time between molts. The status of these various putative species is uncertain. Molecular studies of these isopods are highly desirable to resolve their taxonomy and invasion history.

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Taxonomy

Ecology

General:

Male Synidotea laticauda are larger than females, with pleopods modified into stylets and the presence of an appendix masculina, which is involved in copulation. The young are brooded by the female, and development is direct (Menzies and Miller 1972; Poore 1996). Females in Delaware Bay had broods of 12 to 70 young (Boyd 2008).

Synidotea laticauda is known primarily from shallow (0-10 m) estuarine habitats, at polyhaline to oligohaline salinities. It tolerates wide ranges of temperature, 0-28C in the Delaware Bay (Bushek and Boyd 2006). In San Francisco Bay, California, it ranges from salinities of 1 to 29 PSU (Menzies and Miller 1972), and has been found at salinities within this range in Delaware Bay, Chesapeake Bay, the Guadalquivir estuary (Spain), and the Schelde estuary (Belgium-Netherlands) (Mees and Fockedey 1993; Cuesta et al. 1996; Soors et al. 2010; Faasse et al. 2012; Ruiz et al., unpublished data). However, they appear to be absent from completely fresh waters (Menzies and Miller 1972; Mees and Fockedey 1993; Ruiz-Delgado et al. 2019), and do not survive experimental transfers (Boyd 2008). This species is a weak osmoregulator, and is most abundant at 15-25 PSU, close to its isosmotic point, where metabolic costs of osmoregulation are least (Delgado-Ruiz etal. 2019).

Synidotea laticauda is an active swimmer, but its movements and migrations have not been described (Gewant and Bollens 2005). It is assumed to feed on the hydroid Garveia franciscana in San Francisco Bay (Menzies and Miller 1972). In Delaware Bay, S. laticauda fed on Nereid polychaetes, bryozoans, juvenile S. laticauda, dead oysters, dead S. laticauda, fish flesh, Ulva, and the leaves of Spartina alterniflora (Boyd 2008). Fishes with one or more S. laticauda in their gut contents were White Perch (Morone americana), Oyster Toadfish (Opsanus tau), White Catfish (Ameiurus catus), American Eel (Anguilla rostrata), and Atlantic Croaker (Micropogonias undulatus) (Boyd 2008). In Suisun Marsh, in the San Francisco estuary, isopods (probably mostly S. laticauda) were eaten by Tule Perch (Hysterocarpus traski), Prickly Sculpin (Cottus asper), Staghorn Sculpin (Leptocarpus armatus), Yellowfin Goby (Acanthogobius flavimanus, introduced), and Striped Bass (Morone saxatilis, introduced), but appeared to be prey of only moderate to minor importance (Feyrer et al. 2003).

Most records of the related species synonymized with S. laevidorsalis and South American and Australian species are reported from algae, seagrass, or mangrove habitats, apparently at higher salinities and more marine conditions than those of S. laticauda (Moreira 1972; Pires and Moreira 1975; Kang and Yun 1988; Poore 1996)

Food:

Polychaetes, bryozoans, isopods, algae, carrion

Consumers:

Fishes

Trophic Status:

Omnivore

Omni

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Habitats

General Habitat	Coarse Woody Debris	None
General Habitat	Oyster Reef	None
General Habitat	Marinas & Docks	None
General Habitat	Rocky	None
General Habitat	Unstructured Bottom	None
Salinity Range	Oligohaline	0.5-5 PSU
Salinity Range	Mesohaline	5-18 PSU
Salinity Range	Polyhaline	18-30 PSU
Salinity Range	Euhaline	30-40 PSU
Tidal Range	Subtidal	None
Tidal Range	Low Intertidal	None
Vertical Habitat	Epibenthic	None

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Tolerances and Life History Parameters

Minimum Temperature (ºC)	0	Delaware Bay (Bushek and Boyd 2006)
Maximum Temperature (ºC)	30	Experimental, Delaware Bay (Boyd 2008)
Minimum Salinity (‰)	1	Field data, San Francisco Bay (Menzies and Miller 1972); 2 PSU, Guadalquivir Estuary, Spain (Ruiz-Delgado et al. 2019, lab survival)
Maximum Salinity (‰)	35	Experimental, Adults and juveniles (5, 11, 25 C) The upper value from field data is 29.1 in San Francisco Bay (Menzies and Miller 1972). This was the highest salinity tested in San Francisco Bay (Menzies and Miller 1972) and the Guadalquivir estuary, Spain (Ruiz-Delgado et al. 2019).
Minimum Length (mm)	3.9	Probably immature, Spain (Cuesta et al. 1996)
Maximum Length (mm)	25.3	Spain (Cuesta et al. 1996, probably male); female, 16 mm (Netherlands, Faasse 2011).
Broad Temperature Range	None	Cold temperate-Warm temperate
Broad Salinity Range	None	Oligohaline-Euhaline

General Impacts

No economic or ecological impacts have been reported for Synidotea laticauda in its introduced range. However, it may be a significant benthic predator, or food item for fishes in some locations (Menzies and Miller 1972; Boyd 2008).

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