Invasion History

First Non-native North American Tidal Record: 1938
First Non-native West Coast Tidal Record: 1938
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Melita nitida has a wide native range in the Northwest Atlantic, from the southern Gulf of St. Lawrence to the Gulf of Mexico (Bousfield 1973) and the Caribbean coast of Colombia (Ortiz et al. 2007). This amphipod was first collected on the West Coast in San Francisco Bay, California in 1938 (Carlton 1979; Chapman 1988) and now occurs in estuaries from Howe Sound, British Columbia to the San Gabriel River, near Los Angeles (Carlton 1979; Graening et al. 2012; Murray et al. 2014). In 2000, it was first collected in European waters, in the Scheldt estuary, in the Netherlands (Faasse and van Moorsel 2003) and later (2010) in the Kiel Canal, Germany (Reichert and Beermann 2011).

There is some uncertainty about the identity of the amphipods usually identified as the Northwest Atlantic M. nitida. The Northwest Pacific M. setiflagellata Yamato 1987b is very similar, and has sometimes been considered synonymous, raising the possibility that Asian populations might have been introduced from the Atlantic (Doi et al. 2011) or that West Coast and European populations might have been introduced from Asia (Chapman 2007; Reichert and Beermann 2011; Graening et al. 2012). Currently, most authors use the name M. nitida for the introduced populations on the West Coast and Europe.

North American Invasion History:

Invasion History on the West Coast:

Melita nitida was first collected in the Northeast Pacific at Point Richmond and Lake Merritt (Oakland) in San Francisco Bay, California (CA) in 1938-41 (Carlton 1979). It is now widespread and abundant through the Bay, occurring as far upstream as Collinsville on the Sacramento River during droughts (Cohen and Carlton 1995; Peterson and Vayssieres 2010). It is abundant among tubes of the introduced polychaete Ficopomatus enigmaticus in San Francisco Bay (Carlton 1979; Chapman 1988). Melita nitida is commonly associated with Eastern Oysters (Crassostrea virginica) in its native range, and could have been transported with oyster transplants, but it also occurs in ship fouling communities (Woods Hole Oceanographic Institute 1952) and is a likely candidate for ballast water transport (Cohen and Carlton 1995).

Melita nitida has spread southward on the West Coast in a scattered fashion, to Elkhorn Slough, CA where it was first collected in 1975 (Carlton 1979; Chapman 1988; Wasson et al. 2001), the San Gabriel River estuary, and non-tidal freshwater portions of the Malibu Creek drainage, Los Angeles County in 2002 (M. Born and M. Abramson, Cadien 2007, cited by Graening et al. 2012). However, it has been introduced to many estuaries to the north, including: Coos Bay, Oregon (OR) in 1954 (Carlton 1979); Howe Sound, British Columbia in 1976 (Carlton 1979); Yaquina Bay, OR in 1986 (Chapman 1988); Alsea Bay, OR in 1987 (Chapman 1988); Willapa Bay, Washington (WA) in 1994 (Cohen et al. 2001); Puget Sound, WA in 1998 (Cohen et al. 2001); Humboldt Bay, CA in 2000 (Boyd et al. 2002); and the Columbia River, OR/WA in 2004 (2 specimens, Chapman in Sytsma et al. 2004). The times of first collection, listed above, do not suggest progressive dispersal by coastal currents, but may reflect frequency of collections in different estuaries. Beyond natural dispersal, this amphipod may have spread to West Coast estuaries by human mediated vectors including coastal shipping, bait packed in seaweed, or oyster transplants (Chapman 1988).

Invasion History Elsewhere in the World:

Melita nitida was first collected in the Northeast Atlantic in 1998, in the western Scheldt estuary, Netherlands, where it was found under boulders, often around oysters, near the low-tide mark in polyhaline waters (Faase and van Moorsel 2003). In 2010, 27 specimens were collected in the Kiel Canal, Germany, connecting the North and Baltic Seas, near the Baltic Sea entrance in Kiel (Reichert and Beermann 2011). Future establishment and spread of this amphipod in the North Sea and Baltic seems likely. In 2013-2016, M. nitida was collected at 3 sites on the French coast of the Bay of Biscay: the Gironde estuary, Arcachon Bay (an important oyster-culture site), and Hossegar Lake, near the Spanish border. Shipping is a possible vector in the Gironde estuary and recreational boating is popular on the whole coast (Gouillieux et al. 2016).


Melita nitida has a slender and laterally compressed body with small and oval eyes. Coxal plates 1-4 are large and rounded below. Antenna 1 is long and robust, ~2/3 body length, with a large flagellum of many segments, whorls of stiff setae, and a small accessory flagellum of three segments. On Antenna 2, peduncle segment 5 and the flagellum are densely covered with whorls of stiff setae.

In the male, Gnathopod 1 has a short dactyl, arising on the anterior margin, with the tip curled inward, closing on the inner face of the propodus (segment 6). Gnathopod 2 is larger than Gnathopod 1 in both sexes, but the male has segments 4, 5, and 6 more enlarged, with a smooth, convex palm, and with the dactyl tip closing on the inner side of the palmar angle. The female Gnathopod 2 is similar, but smaller. The basal segments of pereiopods 5-7 are greatly expanded, especially on the posterior-distal corner. The female's Coxa 5 is ventrally extended. The pleon and urosome segments lack dorsal teeth or mucrons (spines or points in the posterior corners). However, Urosome segment 2 has two small clusters of dorsolateral spines. Uropods 1 and 2 are long, extending rearward, beyond the peduncle of Uropod 3. The telson is deeply bilobed, with each lobe having apical and subapical spines. Males reach 12 mm and females reach 9 mm. The color is grayish, with darker bands and a red spot on the head. Description based on: Holmes 1905, Mills 1964, Bousfield 1973, and Chapman 2007.

Parts of the species' range are uncertain, with records which may refer to very similar species. Sheridan (1979, cited by Chapman 1988) described three very similar species (M. elongata, M. intermedia, and M. longisetosa) from the Gulf of Mexico, but Chapman (1988) considered their status uncertain, until comparisons could be made with the lectotypes of M. nitida. Records of M. nitida from the Pacific coast of Mexico (Shoemaker 1935, cited by Chapman 1988; Hendrickx, in Low-Pfeng and Recagno 2012) may refer to an undescribed species of Melita. Melita nitida is nearly indistinguishable from the NW Pacific M. setiflagellata (Yamato 1987b). Some or all West Coast populations could be the latter (Chapman, in Carlton 2007; Graening et al. 2012). Molecular studies of the genus are desirable, but until these are performed we will treat the US West Coast populations as M. nititda.


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Malacostraca
Subclass:   Eumalacostraca
Superorder:   Peracarida
Order:   Amphipoda
Suborder:   Gammaridea
Family:   Melitidae
Genus:   Melita
Species:   nitida


Potentially Misidentified Species

Melita oregonensis
Melita oregonensis Barnard 1954 is a West Coast native of rocky shores (Chapman 2007).

Melita rylovae
Melita rylovae Bulycheva 1955 is a Northwestern Pacific species, introduced to the California coast (Chapman 20007).

Melita setiflagellata
Melita setiflagellata Yamato 1987 is a very similar species described from Japan. Some authors have treated this amphipod as conspecific with M. nitida and an introduction in Japan, but most regard it as native in Japan (Doi et al. 2011). Given the similarity, some populations of 'M. nitida' on the West Coast could actually be M. setiflagellata (Chapman 2007; Graening et al. 2012). Molecular studies of this amphipod are desirable.

Melita sulca
Melita sulca Barnard 1954 is a West Coast native of harbors, cobble bottoms, and kelp beds (Chapman 2007).



Melita nitida is a free-living gammarid amphipod found in shallow, muddy estuaries, salt marshes, mudflats, oyster beds, and fouling communities (Bousfield 1973; Borowsky 1980). In gammarid amphipods, sexes are separate, the young are brooded, and development is direct (Bousfield 1973). Females in Jamaica Bay, New York, had broods of 5-51 embryos, with a mean of 30. Embryos took 10 days to develop at 17C, and 5 days at 21C, and then were brooded as juveniles for less than 2 days before release (Borowsky 1980). Colonization of new patches of habitat is done by adults (Mungia et al. 2007).

Melita nitida is known from temperatures of 0-32C and salinities of 0-35 PSU (Bousfield 1973; Sheridan 1979; Chapman 1988). It is known from a wide range of habitats, including: intertidal mudflats and algal masses, intertidal rocks and debris, clumps of hydroids and bryozoans, floats and pilings, buoys, and crevices under oysters and other bivalve shells (Bousfield 1973; Sheridan 1979; Chapman 1988; Mungia et al. 2007). It was also found in the fouling of a retired cargo ship moored in Suisun Bay, California (Llansó et al. 2011). Melita nitida in the Indian River Lagoon, Florida, fed mostly on seagrass epiphytes, and to a lesser degree on seagrass debris (Zimmerman et al. 1979). Opportunistic predation and scavenging is common in gammarid amphipods, but has not been reported for M. nitida. Likely predators include crabs, shrimps, fishes, and shorebirds.


Epiphytic algae, seagrass debris



Trophic Status:




General HabitatCoarse Woody DebrisNone
General HabitatTidal Fresh MarshNone
General HabitatOyster ReefNone
General HabitatMarinas & DocksNone
General HabitatSalt-brackish marshNone
General HabitatGrass BedNone
Salinity RangeLimnetic0-0.5 PSU
Salinity RangeOligohaline0.5-5 PSU
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Tidal RangeMid IntertidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Temperature (ºC)0Based on geographical range
Maximum Temperature (ºC)32Field data, Florida, (Sheridan 1979, cited by Faasse and van Moorsel 2003)
Minimum Salinity (‰)0Field data, San Francisco Bay (Cohen and Carlton 1995)
Maximum Salinity (‰)35Field data, New England (Bousfield 1973); California (Chapman 1988).
Minimum Length (mm)5Minimum size of females (Borowsky 1980)
Maximum Length (mm)12Adult females, males 9 mm (Bousfield 1973)
Broad Temperature RangeNoneCold temperate-Tropical
Broad Salinity RangeNoneTidal Limnetic-Euhaline

General Impacts

Melita nitida is common in many West Coast estuaries. It is probably a prey item for fishes and shorebirds; however, no specific impacts have been reported.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NA-S3 None 0 Native Estab
NA-ET2 Bay of Fundy to Cape Cod 0 Native Estab
NA-ET3 Cape Cod to Cape Hatteras 0 Native Estab
CAR-VII Cape Hatteras to Mid-East Florida 0 Native Estab
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 0 Native Estab
NEP-V Northern California to Mid Channel Islands 1938 Def Estab
NEP-IV Puget Sound to Northern California 1954 Def Estab
NEP-III Alaskan panhandle to N. of Puget Sound 1976 Def Estab
NEA-II None 2000 Def Estab
CAR-III None 0 Native Estab
P270 Willapa Bay 1994 Def Estab
P130 Humboldt Bay 2000 Def Estab
P170 Coos Bay 1954 Def Estab
P080 Monterey Bay 1975 Def Estab
P090 San Francisco Bay 1938 Def Estab
P200 Alsea River 1987 Def Estab
P210 Yaquina Bay 1986 Def Estab
P260 Columbia River 2004 Def Unk
P290 Puget Sound 1966 Def Estab
P093 _CDA_P093 (San Pablo Bay) 1938 Def Estab
B-III None 2010 Def Estab
NEP-VI Pt. Conception to Southern Baja California 2007 Def Estab
P045 _CDA_P045 (Santa Ana) 2007 Def Estab
CAR-II None 0 Native Estab
NEA-V None 2013 Def Estab
B-IV None 2014 Def Estab
B-VII None 2014 Def Estab
B-I None 2018 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
768140 Ruiz et al., 2015 2012 2012-09-06 Loch Lomond Marina, San Francisco Bay, CA, California, USA Def 37.9736 -122.4802


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