Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide


Pseudodiaptomus marinus



Pseudodiaptomus marinus


  • Last modified
  • 25 September 2018
  • Datasheet Type(s)
  • Invasive Species
  • Preferred Scientific Name
  • Pseudodiaptomus marinus
  • Taxonomic Tree
  • Domain: Eukaryota
  •   Kingdom: Metazoa
  •     Phylum: Arthropoda
  •       Subphylum: Crustacea
  •         Class: Copepoda
  • Summary of Invasiveness
  • P. marinus is a small egg-carrying copepod (Crustacea) typical for estuarine environment in Northwest Pacific. It is euryhaline and eurythermal, while its reproductive and behaviour strategy secures a high rate...

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Preferred Scientific Name

  • Pseudodiaptomus marinus Sato

Local Common Names

  • Netherlands: pacifisch eenoogkreeftje

Summary of Invasiveness

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P. marinus is a small egg-carrying copepod (Crustacea) typical for estuarine environment in Northwest Pacific. It is euryhaline and eurythermal, while its reproductive and behaviour strategy secures a high rate of survival. Spread of the species is mainly due to human shipping activities. Records of P. marinus outside its native habitat have been reported a number of times, particularly along the west coast of North America. More recent records from Northeast Atlantic and the Mediterranean Sea emphasize the need to better acknowledge the presence of P. marinus along intra-coastal and trans-oceanic shipping routes in the European waters. Spread of the species in the shallow waters of the North Sea and to the Baltic is predicted. The impact of P. marinus in introduced areas is not known however it is likely that this species may compete with native plankton species for food resulting in changes to the ecosystem.

Taxonomic Tree

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  • Domain: Eukaryota
  •     Kingdom: Metazoa
  •         Phylum: Arthropoda
  •             Subphylum: Crustacea
  •                 Class: Copepoda
  •                     Order: Calanoida
  •                         Family: Pseudodiaptomidae
  •                             Genus: Pseudodiaptomus
  •                                 Species: Pseudodiaptomus marinus

Notes on Taxonomy and Nomenclature

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P. marinus is placed in the Pseudodiaptomidae G. O. Sars, 1902 family that comprises mostly bottom-dwelling calanoid (Crustacea) often found in coastal environments in the Indo-Pacific region. The genus Pseudodiaptomus includes more than 80 (Sabia et al., 2015). The species are divided into seven species’ groups, primarily distinguished by the presence or absence of endopods on the right and left fifth legs of males (Walter, 1986a). Asiatic species P. marinusSato (1913) belongs to the Ramosus species group.

P. marinus was first described from samples collected from an embayment near Takashima and Oshoro on the west coast of Hokkaido, Japan (Sato, 1913).


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The original morphological description of P. marinus is given by Sato (1913) in Japanese. Description of the species from the Russian part of the Japan Sea may be found in Brodsky (1950) and detailed description of P. marinus from South California can be found in Fleminger and Kramer (1988). Detailed descriptions of specimens from the North Sea are provided by Brylinski et al. (2012). The following description has been based on these sources.

P. marinus is a small, stocky copepod about 1.5 mm in length. Three major regions may be distinguished: cephalothorax, thoracal segments and abdomen ended with furca. The head and thoracal segments form a cephalothorax that is separated from the rest of the thorax. The front part of the cephalothorax is rounded and the middle part is the widest. The cephalothorax is followed by five segments of thorax carrying five pairs of swimming legs. The last thoracic segment has two sharp terminal corners symmetrically directed backwards and downwards. The fifth pair of the swimming legs (P5) consists of either a single branch (female) or two branches (male) and its morphology is of particular importance for the species systematics. Some geographical variations in the morphology of the P5 were observed. For example, on P5 of male P. marinus the number of points in the original description from Northern Japan is three (Sato, 1913), while other Japanese specimens had four to six points (Tanaka, 1966; Nishida, 1985). P. marinus from Mission Bay had three to six points (Fleminger and Kramer, 1988) and P5 from Hawaii four points, so it appears bifid.

The abdomen consists of four segments and is about 2/3 of the chepalothorax length. All segments, excluding the last one, have small rows of spinules on the dorsal side. Genital double-somite inflated with a curved row of spines. The protuberant ventral face of the genital segment falling into two convergent points directed backwards. Furcal rami are almost four times as long as wide with long fine setae on the inner side. The body is transparent with a blue hue and the eye is dark red and clearly visible.


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P. marinus is believed to be native to the Northwest Pacific. The species is reported as common in coastal waters of Japan (Islam et al., 2006); a few findings are known from the Russian waters of the Sea of Japan (Brodsky, 1950), Korea and China. The southern limit of the native range lies in the waters of the Guangdong province, China or Kaohsiung harbour, Taiwan, at approximately 23°N. The northern limit lies somewhere in northern part of the Sea of Japan.

This species is identified outside its native range along the West coast of America, from Washington Pudget sound to Todos Santos Bay in California. The southernmost finding point in the Eastern Central Pacific is Ala Wai Canal, Oahu, Hawaii (approximately 21°N, 158°W).

For the European waters this species is known from the limited number of records. In the north-eastern Atlantic the most northern record is 53° 40′ 27.6′′ N in the North Sea in German exclusive economic zone and the most eastern point is 2°56′ E also in the North Sea. The Mediterranean record from Messina, Sicily (Sabia et al., 2012) is, by far, the southernmost point among the records outside the native range.

Some geographical records of this species have been questioned. These records are from the Indian Ocean: the Andaman Islands (Pillai, 1976), Mauritius (Grindley and Grice, 1969) and Australia (Greenwood, 1977). Walter (1986b) considered the description of the specimens from the Andaman Islands and from Mauritius to be incomplete and might be another species. Fleminger and Kramer (1988) also agreed that the morphology of the specimens from Indian Ocean do not exactly match the original P. marinus description and their systematics need further clarification.

Distribution Table

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The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.

Continent/Country/RegionDistributionLast ReportedOriginFirst ReportedInvasiveReferenceNotes

Sea Areas

Atlantic, NortheastPresentIntroduced2013Brylinski et al., 2012; Jha et al., 2013North Sea: the Southern Bight: in Calais Harbour and off Gravelines and northwards between the Netherlands and British coasts; the German Bight
Mediterranean and Black SeaPresent, few occurrencesIntroducedOlazabal and Tirelli, 2011; Sabia et al., 2012; Pansera et al., 2014; Lucic et al., 2015North Adriatic Sea; lake Faro, Messina
Pacific, Eastern CentralPresentIntroduced Invasive Fleminger and Kramer, 1988; Ruiz et al., 2000
Pacific, NortheastPresentIntroducedRuiz et al., 2000; Lawrence and Cordell, 2010
Pacific, NorthwestWidespreadNativeWalter et al., 2006


ChinaPresentPresent based on regional distribution.
-FujianPresentNativeChen and Zhang, 1965Off Xiame
-GuangdongPresent, few occurrencesNativeShen and Lee, 1963Leizhou peninsula: mouth of Zaikong river , mouth of Chiekong river
-ZhejiangPresentNative2007 Not invasive Jiang et al., 2008Yeqing Bay
JapanWidespreadNative Not invasive Tanaka, 1966; Islam and Tanaka, 2006
-HokkaidoWidespreadNative Not invasive Sato, 1913West coast: takashima, Oshoro; first description
Korea, Republic ofPresentNative Not invasive Soh et al., 2001; Eyun et al., 2007
TaiwanWidespreadNative Not invasive Chang and Fang, 2004Kaohsiung Harbor

North America

MexicoPresentIntroduced2006 Invasive Jimenez-Perez and Castro-Longoria, 2006Todos Santos Bay, Baja California: established breeding colonies
USAPresentPresent based on regional distribution.
-CaliforniaPresentIntroduced1987 Invasive Fleminger and Kramer, 1988; Orsi and Walter, 1991
-HawaiiPresent, few occurrencesIntroduced1967Jones, 1966Ala Wai Canal, Oahu
-WashingtonWidespreadIntroduced Invasive Lawrence and Cordell, 2010Washington Puget Sound


FrancePresent, few occurrencesIntroduced2011 Invasive Brylinski et al., 2012First record for the Atlantic: the southern bight of the North Sea, in Calais harbour and the coastal waters off Gravelines, Bay of Biscay, Southwest of France, Gironde estuary
GermanyPresent, few occurrencesIntroducedJha et al., 2013German Bight
ItalyPresentIntroduced Invasive Olazabal and Tirelli, 2011; Sabia et al., 2012; Pansera et al., 2014; Lucic et al., 2015North Adriatic Sea; Lake Faro, Sicily
Russian FederationPresentPresent based on regional distribution.
-Russian Far EastWidespreadNative Not invasive Brodsky, 1950Sea of Japan: Peter the Great Gulf, Amur bay, Posyet Bay


AustraliaPresentPresent based on regional distribution.
-QueenslandPresent, few occurrencesGreenwood, 1977Moreton Bay

History of Introduction and Spread

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The earliest record of an invasion of P. marinus is from the Eastern Central Pacific by Jones (1966), who found this species during 1964-65 in plankton samples from brackish waters of Oahu, Hawaii. Transport with ballast or other vessel water tanks from Japan was suggested as a possible cause of the invasion. In 1986-87 Fleminger and Cramer (1988) found breeding populations of P. marinus in samples from the South California embayments. The authors explained the introduction as a direct consequence of aquaculture projects in the area, where stocks were imported from Japan. Further spread southward was recorded by Jimenez-Perez and Castro-Longoria (2006). In 1998 the species was found in Todos Santos bay, Baja California. The authors noted, that by 2002 a breeding colony had established there.

The first record of P. marinus from European waters was in November 2007 where it was found along the Italian coast of the northern Adriatic Sea.In 2008, P. marinus was found in Lake Faro (Messina, Italy). The lake is a small coastal brackish water body situated at the north-eastern limit of Sicily and P. marinus is now abundant in the lake (Pansera et al., 2015). It could be interesting mention that in this case the introduction is almost certainly due to aquaculture, since the lake is non navigable and in the waters of the strait of messina, the sopecies is absent.

In 2009 the species was recorded in two different areas of the North Adriatic Sea (Mediterranean Sea) (Olazabal and Tirelli, 2011). Its introduction was probably due to human activity linked to vessel traffic, or the species was accidentally imported with other organisms used in aquaculture and has subsequently ‘escaped’. The latter hypotheses may be supported by the fact that some crustaceans such as Artemia salina, typically used as food for fish larvae, were often being recorded in zooplankton samples.

In the North Eastern Atlantic the species had not been recorded until 2010 when it was found in the southern bight of the North Sea, in both Calais harbour and the coastal waters off Gravelines, France (Brylinski et al., 2012). Further findings confirmed that the species may reproduce in the area. The authors suggested a passive transport of the species via ship’s ballast waters. Records extended the known distribution of P. marinus northwards and across the Southern Bight between The Netherlands and British coasts and add a location further north and east in the German Bight (Jha et al., 2013). This spread could have originated from a population established off the coast near Calais.


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Introduced toIntroduced fromYearReasonIntroduced byEstablished in wild throughReferencesNotes
Natural reproductionContinuous restocking
France Pacific, Northwest 2009 Yes Brylinski et al. (2012) North sea
Hawaii Japan 1964-1965 Jones (1966) In plankton samples
Mexico USA 1998 Aquaculture (pathway cause) Yes Jimenez-Perez and Castro-Longoria (2006) Local shipping and natural spread. Present in Todos Santos bay
Sicily Pacific, Northwest 2008 Aquaculture (pathway cause) Yes Sabia et al. (2012) Lake Faro, Sicily
Slovenia Pacific, Northwest 2015 Lucic et al. (2015) Found in the Port of Koper
USA Pacific, Northwest 1986 Aquaculture (pathway cause) Yes Fleminger and Kramer (1988) Shipping

Risk of Introduction

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With increasing globalization the likelihood of P. marinus being introduced into new areas is increased. This is likely to occur accidentally via ballast water and aquaculture. However, once present in an area P. marinus can spread through coastal waters. For example, Jha et al. (2013) have predicted the spread of P. marinus further north in the North Sea and into the Baltic through coastal currents, or the Kiel Canal if the population found off the coast near Calais thrives (Brylinski et al., 2012). In addition to this, Rajakaruna et al. (2012) have identified habitats that P. marinus may occupy based on modelling of the net reproductive rate as a function of ambient water temperature. The results match well with the field evidence of the species occurrences and may represent a good reference for future research of P. marinus invasions.


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P. marinus is typically found in tropical and temperate, shallow coastal waters, living in estuarine and protected areas, where they can inhabit as brackish so as saline waters.

Habitat List

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Inland saline areas Principal habitat Harmful (pest or invasive)
Inland saline areas Principal habitat Natural
Estuaries Principal habitat Harmful (pest or invasive)
Estuaries Principal habitat Natural
Lagoons Principal habitat Harmful (pest or invasive)
Lagoons Principal habitat Natural
Inshore marine Principal habitat Harmful (pest or invasive)
Inshore marine Principal habitat Natural

Biology and Ecology

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A 625-bp DNA region of the mitochondrial gene cytochrome oxidase subunit I (mtCOI) of P. marinus was sequenced by Euyn et al. (2007). The authors aimed to clarify the phylogenetic relationship of five copepods species belonging to the Pseudodiaptomus genus from Korean waters. The obtained data proved that P. marinus represents a genetically distinct and valid species. However, the validity of the Ramosus group, where P. marinus belongs, requires further verification being not well supported by bootstrap analyses (Euyan et al., 2007).

Reproductive Biology

P. marinus is an egg sac-carrying copepod with direct development. Two egg sacs contain eggs in clutches of 15(January) – 35(May) eggs (Liang and Uye, 1997) which attach to a female's body until the eggs hatch into nauplius larvae. The nauplius molts six times into copepodid larva. This stage resembles the adult, but has a simple, unsegmented abdomen and only three pairs of thoracic limbs. After a further five molts, the copepod becomes the adult form. A cycle from an egg to breeding stage takes about 23 days at 20°C (Uye and Onbe, 1975). No resting stages have been reported for the whole family Pseudodiaptomidae (Grindley, 1984).

In the native range P. marinus reproduces throughout the year (Uye et al., 1982; Liang and Uye, 1997). When the food supply is adequate, the reproductive rates are largely affected by the seasonal temperature (Uye, 1981). Thus, the daily reproductive rates of the natural population of P. marinus in the Inland Sea of Japan were found to be high from May to October, but much lower from January to March (Uye et al., 1982). A study found that in the native range the peaks of egg production were observed when the water temperature range from 20-25°C (Uye et al., 1982). The specific egg production rate for the breeding females was highly correlated to temperature; increasing nine-fold when temperature have changed from 9°C to 26°C (Liang and Uye, 1997). In Fukuyama harbour (Liang and Uye, 1997), a eutrophic inlet of the Inland Sea of Japan, adults (female stages slightly outnumbered males) showed a large abundance peak in June/July and a small peak in September/October. Egg diameter varied from 98 µm in August to 121 µm in February, with the size correlated to temperature negatively. The pattern of seasonal variation in the brood size was similar to that of the body length of adult females, i.e. the size was largest (ca. 35 eggs per egg sac) in May and smallest in September (ca. 20 eggs). In the invaded range egg sacs carrying females were found in San Diego Bay in December, May and June, with maximum total abundance in May and in January (Fleminger and Kramer, 1988).

Fecundity of P. marinus is usually lower than other copepod species (Hirota, 1962; Hirota, 1964; Liang and Uye, 1997). Kiorboe and Sabatini (1994) commented that the lower fecundity of egg-carrying copepods is an adaptation to the potentially elevated mortality of ovigerous females, while the higher fecundity of free-spawning copepods represents an adaptation to compensate the very high mortality of eggs. Indeed, in average 94% of the eggs P. marinus survived to naupliar stage III as it was noted by Liang and Uye (1997).

Physiology and Phenology

According Islam et al. (2006), P. marinus is a medium abundant species, showing generally higher abundance during the summer months. Production of these species depends on chlorophyll-a and is, therefore, associated with active primary production by phytoplankton, that, in turn, has significant correlation with water temperature.

Activity Patterns

In general, species in the genus Pseudodiaptomus tend to be hyperbenthic demersal copepod species. The adults and late copepodits of P. marinus rise into plankton at dusk (or on cloudy days) and remain near to or attached to bottom substrates during the day (Fancett and Kimmer, 1985; Walter, 1986a). Valbonesi and Harada (1980) found that in Tanabe bay, Japan during the day maximum concentration of P. marinus was found in the 0-5 cm water layer above the sea bottom and from 50 cm to the surface layer at night. One of the hypotheses explaining such behaviour is avoiding visual predators, as suggested by Fancett and Kimmer (1985).

In some parts of the range the migration pattern may be influenced by physical factors. For example, in coastal zone the vertical migration pattern is often affected by local water movement in the tidal zone and ferry traffic that could lead to resuspension of plankton. Additionally, Sabia et al. (2012, 2014), who reported finding P. marinus in Lake Faro (Messina, Italy) revealed specific adaptations of the species to the life in a pelagic system of the small coastal brackish water body. Due to the presence of an anoxic layer in the deepest part of the lake, P. marinus had become truly planktonic, a behavioural adaptation to survive in such hostile environment.

Population Size and Density

In the native range P. marinus is often noted as a significant component of plankton copepod community. Thus, in Chikugo estuary, Japan, this species annually contributed 2.7 % (35270 ind/m3) to abundance and 3.1% (126.42 mg/m3) to biomass of all copepod species (Islam et al., 2006).

Population size and density of P. marinus markedly fluctuate throughout the year, but the pattern is differs for different water bodies. In the Inland Sea of Japan Uye et al. (1982) described three distinct peaks: in June-July, August and October, among which the June-July peak was most prominent (9.79xl02 ind/m3). Uye and Kasahara (1983) in the Central part of the Inland Sea of Japan found that production and biomass increase linearly with temperature with maximums during May - June (more than 400 mkg/m3 per day) and in October (approximately 300 mkg/m3 per day). Total annual production was 20.7 mg/m3 per year (Uye and Kasahara, 1983). The authors noted that the species may be occasionally very abundant in small water inlets such as small lagoons. In Fukuyama harbour, Japan adult P. marinus occurred in the plankton throughout the year (Liang and Uye, 1997). Both females and males consist in numbers of less than 40 ind/ m 3 until early May and then increased dramatically to a peak (680 and 555 ind/m3, respectively) in mid-June. This early summer peak was soon followed by a midsummer recession until a small peak occurred in late September.

In the invaded range abundance numbers are usually lower. In 2010-2011 in France waters numbers ranged from 0.2-4.0 ind/m3 (Brylinski et al., 2012). However, the following year, the density increased to 120 ind/m3. In the North Sea only sixty-seven specimens of P. marinus were caught: 15 males, 10 females and 42 copepodites, representing abundances of 0.05, 0.03 and 0.13 ind/m3 (Jha et al., 2013). Similarly low abundance was described in Adriatic Sea comprising 1.6 - 3.2 ind/m3 (de Olazabal and Tirelli, 2011).


P. marinus is reported as being both a herbivore and detritivore feeding at the bottom of waters during the day and moving along the water column at night (Sabia et al., 2014). A study on the feeding habits of P. marinus revealed that feeding behaviour was similar between both sexes of adult, they are capable of consuming particles 2.8 – 63.3 µm in size, preferring larger particles approximately 50 µm (Uye and Kasahara, 1983). The naupli stage consumes smaller particles (less 30 µm), whereas copepodites consume particles of intermediate size. This differentiation allows effective utilisation of particles by P. marinus populations (Uye and Kasahara, 1983). The ingestion rate of P. marinus increases linearly with the increase in particle concentration. In a laboratory study P. marinus was successfully fed on the phytoplankton Monochrysis lutheri [Diacronema lutheri] and Nitzschia closterium [Cylindrotheca closterium] (Uye and Onbe, 1983).

Environmental Requirements

In the native range, Uye et al. (1982) found P. marinus at temperatures ranging from 8.9-28°C and salinity from 28.6-32.3 ppt. In Chikugo estuary, Japan the species is found in waters with temperature about 8.0°C in January to 31.1°C in August, showing nearly equally abundance at a range of saliniies (9-25 ppt) (Islam et al., 2006).

As for the invaded range, in the Atlantic (Calais and Gravelines waters) Brylinski et al. (2012) found P. marinus in samples collected in waters of 1.9-24 m in depth, where temperatures ranged from 5.6-19.0°C and salinity between 33.1-34.2 ppt. The data of de Olazabal and Tirelli (2011) suggest that the species may withstand even higher salinities of up to 37.5 ppt in the Adriatic Sea. Here the species was found 8-29 m in depth with water temperatures of 16–25°C. In the Pacific (South California embayment) P. marinus was found from December to June (with eggs sacs in May, June and December), in shallow waters (depth 2 m) over beds of Zostera marina. The water temperature was 14–22°C and salinity 33-34 ppt (Fleminger and Kramer, 1988). Further south, in Todos santos bay, California the species lives at surface water with temperatures of 14-23°C and salinity 33-34 ppt (Jimenez-Perez and Castro-Longoria, 2006).

Latitude/Altitude Ranges

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Latitude North (°N)Latitude South (°S)Altitude Lower (m)Altitude Upper (m)
53 21

Water Tolerances

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ParameterMinimum ValueMaximum ValueTypical ValueStatusLife StageNotes
Salinity (part per thousand) 9 37.5 Harmful
Water temperature (ºC temperature) 11 25 Optimum
Water temperature (ºC temperature) 5 31 Harmful

Means of Movement and Dispersal

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Natural Dispersal

It is possible for P. marinus to disperse over short distances with water currents. Short-distance transportation has been suggested to have occurred along the western coast of America (Orsi and Walter, 1991; Jiménez-Pérez and Longoria, 2006). Similarly, in the North Sea (Brylinski et al., 2012) the northward drift of nearshore coastal waters in the area can explain the absence of P. marinus southward and the spreading northward (Antajan, 2012).

Accidental Introduction

Brylinski et al. (2012) suggested that the introduction of P. marinus in the southern North Sea is related to ballast water discharge and results in the long distance dispersal of this species. This hypothesis is congruent with the occurrence of P. marinus in the Mediterranean Sea (de Olazabal and Tirelli, 2011). Specific studies of ballast water contents, however, are needed to confirm this hypothesis. Detailed considerations regarding the dispersal of marine species (especially estuarine-coastal forms) with ballast-water is given by Carlton (1985). It is also possible that P. marinus may be transported with aquaculture. Thus, aquaculture of oyster and mussels from Japanese coastal waters were suggested as a vector of introduction of P. marinus in California embayments (Fleminger and Kramer, 1988).

Pathway Causes

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CauseNotesLong DistanceLocalReferences
AquacultureAccidental Yes Yes Fleminger and Kramer, 1988
Interbasin transfersAccidental, often in ballast waters Yes Yes Brylinski et al., 2012

Pathway Vectors

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Impact Summary

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Economic/livelihood Positive and negative
Environment (generally) Negative

Environmental Impact

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Copepods are among the most important secondary producers in coastal and marine ecosystems, representing an important link between phytoplankton, microzooplankton and higher trophic levels such as fish. There are no records of direct environmental impact of P. marinus. This species, however, may compete with native plankton species for space and food, causing changes in ecosystems. Thus, Fleminger and Cramer (1988) noted on the disappearance of the endemic P. euryhalinus from the South California embayments where P. marinus was present. In addition to this, since the introduction of P. marinus into Lake Faro, Sicily, it has become the fourth most abundant copepod species (Sabia et al., 2014).

P. marinus is also a major food source for fish and may have an impact on native species of fish (Islam and Tanaka, 2006; Islam and Tanaka, 2009).

Risk and Impact Factors

Top of page Invasiveness
  • Proved invasive outside its native range
  • Has a broad native range
  • Abundant in its native range
  • Highly adaptable to different environments
  • Is a habitat generalist
  • Capable of securing and ingesting a wide range of food
  • Has high reproductive potential
  • Gregarious
Impact outcomes
  • Ecosystem change/ habitat alteration
  • Reduced native biodiversity
  • Threat to/ loss of native species
Impact mechanisms
  • Competition - monopolizing resources
  • Competition
Likelihood of entry/control
  • Highly likely to be transported internationally accidentally
  • Difficult to identify/detect in the field


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Economic Value

It has been reported that P. marinus is easy to rear under laboratory conditions when compared with other calanoid species (Uye and Onbe, 1975) and it is therefore listed as one of the copepod species recommended for mass cultivation to be used as fishmeal (Omori, 1973). 

Uses List

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Animal feed, fodder, forage

  • Fishmeal


  • Research model

Similarities to Other Species/Conditions

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P. marinus is a small organism and it is difficult to identify it. A key to the American species of Pseudodiaptomus was produced by Walter (1989). He described that P. marinus is distinct from other species of the region by morphology of the fifth swimming leg (P5). While P. marinus males P5 have left and right endopod, other species lack right endopod; P. marinus females P5 lack spinule row on the anterior surface of exopod, whereas females of other species possess a single row on the endopod of P5. Other keys available include Fleminger and Kramer (1988) for American waters, Soh et al. (2001) for Korean waters, Brodsky (1950) for the Sea of Japan and Brylinski et al. (2012) for Atlantic waters.

In Korean waters Soh et al. (2001) revealed interspecific differences between four species of Pseudodiaptomus (P. inopinus, P. marinus, P. nihonkaiensis and P. poplesia), using scanning electron microscopy for examination the morphology of the female genital systems.

Prevention and Control

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SPS Measures

To prevent introduction of marine species with aquaculture a “Code of Practice” was developed by the ICES Working Group on Introductions and Transfers on Marine Organisms (2013). Adherence to these procedures in hand with training and raising awareness (Reise et al., 1999; Gollasch, 2006) will give more control over invasion process.


Cultural Control and Sanitary Measures

Guidelines to minimize the transport of P. marinus in ballast water were developed by the International Maritime organizations (Gollasch, 2006). The measures include the avoidance of particular areas such shallow, infected waters or places with phytoplankton blooms for ballast water uptake. The amount that the discharged ballast water should be reduced and mid-ocean exchange on board is also recommended. Different methods of treatment of ballast waters such as filtering and heating are also advised. Drake and Lodge (2004) suggested that reducing the per-ship-visit probability of initiating invasion may be the most effective way in controlling the rate of biotic homogenization.

Gaps in Knowledge/Research Needs

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The invasion of P. marinus into Atlantic and Mediterranean waters seems to be a recent event and as such much remains unknown about the causes and patterns of the process. Examples include further studies on the ecology of the introduced species with particular highlight on the study of their impact, genetic analysis and risk assessment. Ruiz et al. (2011) also recommended addressing the current uncertainty and future shifts in vector strength.


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09/12/2013 Original text by:

Ekaterina Shalaeva, Consultant, UK

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