Invasion History

First Non-native North American Tidal Record: 1986
First Non-native West Coast Tidal Record: 1986
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Pseudodiaptomus marinus has been considered native to the Northwest Pacific, from Peter the Great Bay, Russia and northern Hokkaido, Japan to Hong Kong and the Philippines (Brodskii 1967; Fleminger and Hendrix Kramer 1988; Walter 1989; U.S. National Museum of Natural History 2012). The identity of specimens from the Indian Ocean, Mauritius (Grindley and Grice 1969) and the Andaman Islands (Pillai 1980, cited by Fleminger and Hendrix Kramer 1988) is in doubt (Fleminger and Hendrix Kramer 1988). This copepod has been introduced to Hawaii (Jones 1966), Mexico (Jiménez-Pérez and Castro-Longoria 2006), California (Fleminger and Hendrix Kremer 1988; Orsi and Walter 1991), Italy (de Olazabal and Tirelli 2011; Sabia et al. 2012), and France (Brylinski et al. 2012). A genetic analysis found that the likeliest source of the population in San Francisco Bay was Japan. This analysis also suggested that southern populations, from Xiamen, China, may represent a separate species (Ohtsuka et al. 2018). Specimens from the southern part of the known range, including Hong Kong and the Philippines, should be reexamined.

North American Invasion History:

Invasion History on the West Coast:

In 1986, Pseudodiaptomus marinus was discovered in the San Francisco Bay (Orsi and Walter 1991) and Mission Bay, California (Fleminger and Hendrix Kramer 1988). In the San Francisco estuary, P. marinus was found in western and central Suisun Bay near Port Chicago at salinities of 4-19 PSU (Orsi and Walter 1991). This copepod is abundant in the South, Central, and San Pablo Bays in periods of high (20-30 PSU) salinity (Bollens et al. 2011). In 1988, P. marinus was found in Tomales Bay, just north of San Francisco (Orsi and Walter 1991; Kimmerer 1993). In southern California, P. marinus was found to be abundant in Mission Bay in 1986-1987, and in Agua Hedionda Lagoon in 1987, but was absent in San Diego Bay (Fleminger and Hendrix Kramer 1988). In surveys in 2000-2001, this copepod was collected in San Diego Bay, Mission Bay, and Los Angeles-Long Beach Harbors (Fairey et al. 2002). In southern California and Tomales Bay, this species occurred at high salinities (33-34 PSU, Fleminger and Hendrix Kramer 1988) and 27-35 PSU (Kimmerer 1993). Fleminger and Hendrix Kramer (1988) considered experimental aquaculture programs at the Hubbs Marine Institute to be a possible vector for the introduction of P. marinus in Mission Bay. Ballast water seems a more likely vector overall, but does not explain why Mission Bay and Agua Hedionda Lagoon were invaded before San Diego Bay (Fleminger and Hendrix Kramer 1988).

In 1998, P. marinus was collected further south and north on the West Coast. To the south, it was found in Ensenada, Baja California, Mexico in the Bahia de Todos Santos (Jiménez-Pérez and Castro-Longoria 2002). To the north, a single specimen of P. marinus was collected in Elliott Bay, Washington, but no further specimens were found in Puget Sound (Cordell 1998). In 1998, it was found in ballast water of a ship en route to Vancouver, British Columbia, before and after mid-ocean exchange (Levings et al. 2004), and was found in both West Coast and trans-Pacific ships docking in Puget Sound (Cordell et al. 2008a).

Rajakaruna et al. (2011) used experimental life-history data (Uye et al. 1983) to model the potential worldwide range of P. marinus. High-to-medium probability ranges on the West Coast extended from Baja California to San Francisco Bay- the low probability range extended to Puget Sound and the Strait of Georgia. On the East Coast, this copepod was predicted to be capable of colonizing the region between Cape Cod, Massachusetts and Cape Hatteras, North Carolina (Rajakaruna et al. 2011).

Invasion History in Hawaii:

Pseudodiaptomus marinus was collected in 1966 in the Alai Wai Canal, Oahu (Jones 1966).

Invasion History Elsewhere in the World:

In 2007 and 2009, 15 specimens of Pseudodiaptomus marinus were collected in the Adriatic Sea, Italy, near Rimini and Monfalcone, but this copepod was not considered to be established there at this time (de Olazabal and Tirelli 2011). However, it was collected in 2008 in the Lao di Faro, a small lagoon in Sicily and soon became the third most abundant copepod there (Sabia et al. 2012). In 2010, P. marinus was collected in Calais Harbor, and later in the English Channel off Gravelines, both in France. Small numbers of males, ovigerous females, and copepodites, suggest that this copepod is established off France at a very low density (Brylinski et al. 2012). This copepod was also found further south, in the Gironde estuary (Sautour and Dessier, pers. comm., cited by Brylinski et al. 2012), and in Bilbao, Spain (in 2010, Uriarte et al. 2016). In 2016, P. marinus was collected in the Black Sea, and is now established in Sevastopol Bay, at 18 PSU and 8-25 C (Svetlichney et al. 2019).


The bodies of adult female Pseudodiaptomus marinus have the head separate from the thorax, but the 1st thoracic segment is partially fused with the head. The cepalothorax is widest at midlength, and the anterior end of the body forms a rounded angle. Near the tip, dorsally, is a single eye, which is visible, both in dorsal and lateral views. The 4th and 5th thoracic, swimming-leg bearing, segments are fused. The ends of the last thoracic segment are produced into short acute processes (flanges, points) at the end of cephalothorax. The urosome has four segments, all but the last bearing a row of spinules on the posterior edge, with setules increasing in size with each successive segment. The genital segment (1st urosome segment) is very swollen ventrally, produced into a short, wide protuberance, directed backward. The antennules (1st antenna) are symmetrical, with 21 segments. The 2nd to 4th pairs of swimming legs bear wide spines, serrated on both sides, on the outer sides of their exopodites and on the tips of the legs. The 5th pair of legs is symmetrical, uniramous, with 4 segments, and ends with 3 terminal spines. The distal joint bears 2 apical spines. Total body length is 1.25-1.53 mm. Females carry a single mass of eggs. Description based on Brodskii 1967 and Fleminger and Hendrix Kramer 1988.

The body of adult males is slightly more slender than that of the females. The urosome has 5 segments, with segments 2-4 bearing a row of spinules on the posterior edge. The left antenna has 21 segments and resembles the females'. The right antenna has 20 segments, with segments 12 to 15 enlarged, and a hinge-joint at segments 16-17. The 5th pair of swimming legs is complex and asymmetrical. The distal segment of the endopod of the right leg lacks apical appendages, and is paddle-like with short spines. The terminal segment joint of the left leg bears a spine with multiple points. Male 5th legs are somewhat variable in form and this appears to be random, rather than geographical. Description based on Brodskii 1967 and Fleminger and Hendrix Kramer 1988.

The morphology of copepodite and naupliar stages of this copepod have been described (Uye and Onbe 1975). This copepod is characteristic of marine waters, but is common in polyhaline and mesohaline waters of estuaries.


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Maxillopoda
Subclass:   Copepoda
Order:   Calanoida
Family:   Pseudodiaptomidae
Genus:   Pseudodiaptomus
Species:   marinus


Potentially Misidentified Species



Planktonic calanoid copepods mate in the water column. Males use their modified antenules and 5th pair of swimming legs to grasp the female and transfer spermatophores to the female's genital segment. Female Pseudodiaptomus marinus carry eggs in one symmetrical cluster under the urosome (Barnes 1983; Cordell et al. 1992; Cordell et al. 2007). Eggs hatch into nauplii which go through six stages. The first stage, NI, has 3 pairs of appendages and is unsegmented - each molt has additional appendages and/or more differentiation of segments. The sixth stage (NVI) molts into a first copepodite stage (CI), with the basic form of the adult, and fully differentiated feeding structures, but with only two pairs of swimming legs and only one urosomal segment. The copepod goes through five additonal molts, with increasing numbers of swimming legs, urosomal segments, and sexual differentiation. The sixth (CVI) stage is the male or female adult (Uye and Onbe 1975; Barnes 1983). In the laboratory at 20 C, development from eggs to mature adults took about 20 days (Uye and Onbe 1975). Estimated generation times in the field (Fukuyama Harbor, Japan) were 63 to 17 days at average temperatures of 11.6 to 24. 4 C (Liang and Uye 1997).

Pseudodiaptomus marinus, like many other copepods of its genus, is characteristic of coastal waters and the lower parts of estuaries (Walter 1989; Orsi and Walter 1991; Bollens et al. 2011). Late copepodites and adults of the genus Pseudodiaptomus often have strong epibenthic tendencies, particularly by day, and when carrying eggs. Adults cling to hard surfaces using adhesive hairs on their antennules and filter in place. This tendency is strongest in adult females (Sabia et al. 2012, P. marinus, Italy; P. pelagicus, Narragansett Bay, Fofonoff, personal observations). All life stages feed on phytoplankton, although adults may also capture ciliates, rotifers, and copepod nauplii (Barnes 1983).

Adult Pseudodiaptomus marinus tolerated salinities of 4 or 5 to 44 PSU ((Orsi and Walter 1991; Svetlichny 2019), and temperatures of 8 to 37 C (Liang and Uye 1997; Jiang et et al. 2009; Svetlichny 2019). Females apparently survive periods of low temperature in a state of dormancy, without carrying eggs sacs (Svetlichny 2019).


Phytoplankton, protists, detritus

Trophic Status:

Suspension Feeder



General HabitatUnstructured BottomNone
General HabitatMarinas & DocksNone
General HabitatCoral reefNone
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone
Vertical HabitatPlanktonicNone

Tolerances and Life History Parameters

Minimum Temperature (ºC)88 C, lab, Svetlichny et al. 2019; 8.9 CField, Fukuyama Harbor, Seto Inland Sea, Japan (Liang and Uye 1997)
Maximum Temperature (ºC)36.9Experimental, 48 h Critical Thermal Maximum (Jiang et et al. 2009)
Minimum Salinity (‰)4Field data, bottom salinities in Sacramento-San Joaquin estuary, CA (Orsi and Walter 1991).
Maximum Salinity (‰)44Experimental (Svetlichny et al. 2019)
Minimum Reproductive Temperature15Field Data, appearance of nauplii- Fukuyama Harbor, Japan, Liang and Uye (1997)
Minimum Length (mm)1.2Adult length (Brodskii 1967; Fleminger and Kramer 1986)
Maximum Length (mm)1.5Adult length (Brodskii 1967; Fleminger and Kramer 1986)
Broad Temperature RangeNoneCold temperate-Warm temperate
Broad Salinity RangeNoneMesohaline-Euhaline

General Impacts

There are no reported impacts of Pseudodiaptomus marinus. In Southern California, it may compete with the native P. euryhalinus (Fleminger and Kramer 1988), but this possible interaction has not been studied directly.

Regional Impacts

NEP-VIPt. Conception to Southern Baja CaliforniaEcological ImpactCompetition
In Southern California estuaries (Mission Bay, Agua Hedionda Lagoon) where Pseudodiaptomus marinus had invaded, the native P. euryhalinus was absent (Fleminger and Kramer 1988). However, competition between these species has not been studied.
P030Mission BayEcological ImpactCompetition
In Southern California estuaries (Mission Bay, Agua Hedionda Lagoon) where Pseudodiaptomus marinus had invaded, the native P. euryhalinus was absent (Fleminger and Kramer 1988). However, competition between these species has not been studied.
P023_CDA_P023 (San Louis Rey-Escondido)Ecological ImpactCompetition
In Southern California estuaries (Mission Bay, Agua Hedionda Lagoon) where Pseudodiaptomus marinus had invaded, the native P. euryhalinus was absent (Fleminger and Kramer 1988). However, competition between these species has not been studied.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NWP-4a None 0 Native Estab
NWP-4b None 0 Native Estab
NWP-3b None 0 Native Estab
NWP-3a None 0 Native Estab
NWP-2 None 0 Native Estab
SP-XXI None 1966 Def Estab
NEP-VI Pt. Conception to Southern Baja California 1986 Def Estab
NEP-V Northern California to Mid Channel Islands 1986 Def Estab
NEP-III Alaskan panhandle to N. of Puget Sound 1998 Def Unk
P020 San Diego Bay 1987 Def Estab
P030 Mission Bay 1986 Def Estab
P023 _CDA_P023 (San Louis Rey-Escondido) 1987 Def Estab
P050 San Pedro Bay 2001 Def Estab
P090 San Francisco Bay 1986 Def Estab
P110 Tomales Bay 1988 Def Estab
P290 Puget Sound 1998 Def Unk
P023 _CDA_P023 (San Louis Rey-Escondido) 1987 Def Estab
P050 San Pedro Bay 2001 Def Estab
P093 _CDA_P093 (San Pablo Bay) 1986 Def Estab
MED-VII None 2007 Def Estab
NWP-5 None 0 Native Estab
EAS-III None 0 Native Estab
NEA-II None 2011 Def Estab
NEA-V None 2010 Def Estab
MED-III None 2008 Def Estab
MED-IV None 2015 Def Estab
MED-IX None 2016 Def Estab
MED-II None 2010 Def Estab
MED-V None 2016 Def Estab
P040 Newport Bay 2015 Def Estab
P062 _CDA_P062 (Calleguas) 2015 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
27129 Fairey et al. 2002) 2006 2006-03-14 San Diego Bay Plankton 02 Def 32.7204 -117.2180
27131 Fairey et al. 2002 2002 2002-03-04 San Diego Bay Plankton 02 Def 32.7204 -117.2180
27161 Fairey et al. 2002) 2001 2001-12-19 San Diego Bay Plankton 05 Def 32.6706 -117.1285
27199 Fleminger and Kramer 1988 1987 1987-05-01 Agua Hedionda Lagoon Def 33.1425 -117.3286
27716 Cohen and Carlton, 1995 1986 1986-01-01 Suisun Bay Def 38.0713 -122.0581
30428 Fleminger and Kramer 1988 1986 1986-01-01 Mission Bay Def 32.7791 -117.2288
31399 Fairey et al. 2002 2001 2001-12-19 San Diego Bay Plankton 03 Def 32.7223 -117.1849
31902 Fairey et al. 2002 2001 2001-10-11 LA Harbor Plankton 05 Def 33.7423 -118.2016
32679 Fairey et al. 2002 2002 2002-03-04 LA Harbor Plankton 02 Def 33.7636 -118.2502
32682 Fairey et al. 2002 2006 2006-11-21 LA Harbor Plankton 02 Def 33.7636 -118.2502
32926 Fairey et al. 2002 2006 2006-11-20 San Diego Bay Plankton 06 Def 32.6437 -117.1236
32929 Fairey et al. 2002 2001 2001-12-19 San Diego Bay Plankton 06 Def 32.6437 -117.1236
33529 Fairey et al. 2002 2001 2001-07-11 LA Harbor Plankton 03 Def 33.7694 -118.2259
33708 Orsi and Walter 1991; Kimmerer 1993 1991 1991-01-01 Tomales Bay Def 38.2100 -122.9400


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