Pseudodiaptomus marinus -

P. marinus originates in the northwest Pacific Ocean ^[2]. It is a marine species found mainly in the coastal water of Japan, Russia, South Korea and China ^{[3, 4]}.

First observation in Belgium

In 2010, this copepod was observed for the first time in Belgium, in the Port of Zeebrugge ^[4].

Spreading in Belgium

After the first observation in 2010, the species was observed in the estuary of the Western Scheldt, around the Port of Ostend and further at sea, on the ‘Vlakte van de Raan’ sandbank ^[4]. In 2015-2016, during a monitoring campaign in the Belgian part of the North Sea, this species was present –  in variable abundances –  in all samples, with peak densities of 560 individuals per m² ^[5].

Spreading in neighbouring countries

Before 1970, P. marinus was already observed as an introduced species in the Indian Ocean (Mauritius, 1964; the Andaman Islands, 1968) and the Atlantic Ocean (Hawaii, 1964) ^[6-8]. The species continued its spread along the west coast of North America. P. marinus has been observed in Mission Bay, California (1986) and Puget Sound, Washington (2001) ^{[9, 10]}.

P. marinus was observed in Europe in 2007, in the north of the Adriatic Sea ^[11]. Later, in 2010, the species was found in the Canal ^[3], along the French Atlantic coast near Calais Harbour (2010) and the coastal waters of Gravelines (2011). Here, the species survives and reproduces, but its abundance remains low ^[3]. The species was also observed at the French Atlantic coast in the Gironde estuary ^[3]. Near the Southern Bight of the North Sea – between the British and Dutch coast – P. marinus was recently (2012) observed in the Continuous Plankton Recorder Survey ^[12]. Also in German waters was P. marinus observed during biological monitoring (2011) ^[12]. Scientists predict that P. marinus might spread to the coastal waters of the Baltic and Eastern North Sea ^[12]

P. marinus was introduced in at least two ways: (1) together with other imported species used for aquaculture, like oysters and mussels originating from Japan, or (2) through the discharge of ballast water ^{[3, 9, 11, 12]}.

Both may have contributed to its introduction to the northern Adriatic Sea ^[10]. Many Asian ships use the Mediterranean Sea to reach Europe ^[3]. But, it is unlikely that the first introduction to the English Channel (Calais, 2010) took place because of aquaculture, as regionally only mussels and fish originating from Europe are used. Therefore, it is suspected that the species was introduced through transoceanic vessels, originating from the Californian coasts ^[3]. Finally, the established population in Calais probably spread northwards via the prevailing sea currents along the French, Belgian, Dutch and German coasts ^{[3, 12]}

The study by Rajakaruna et al. (2012) identified, based upon the water temperature, the regions that P. marinus can potentially colonise. The coastal area of Belgium is within this area ^[13]. P. marinus possesses eurythermal and euryhaline properties, which is confirmed by its occurrence in both tropical and northern (Japanese and Russian) waters as well as in waters with variable salinity ^{[3, 12, 14]}.

The species prefers eutrophic areas, where the food supply is always high ^[15]. P. marinus feeds on both plant material and detritus. The species has an optimal strategy to lower the risk of predation by a combination of living in eutrophic areas with high turbidity and its epibenthic behaviour ^{[14, 16]}

Variations in the population structure of P. marinus in the Belgian part of the North Sea are best explained by the water temperature (optimal range between 20-25 °C ^[17]) and chlorophyll-a concentrations. Variations in the salinity and changes in the concentration of nitrogen do not seem to affect the distribution of P. marinus ^[5]. This non-native species is worldwide considered a potential pest, due to its resistance to adverse conditions and its tolerance to changes in salinity (2.5 to 38 PSU) and temperature (5-28 °C) ^[16].

In addition to dispersal via ballast water and with other aquaculture organisms, the prevailing sea currents also determine the local dispersal of P. marinus: the currents carrying the zooplankton to nearby areas ^{[3, 12, 18]}.

The progressive degradation of coastal zones ^[19] could be advantageous for P. marinus since this species feeds on detritus and lives in zones with high turbidity ^[20]

There are few effects associated with the introduction or establishment of P. marinus. A negative impact was observed in the southern bays of California. Here, the population of a native species, namely Pseudodiaptomus euryhalinus, has declined, presumably due to the introduction of P. marinus. However, further research is required ^[9]. The effect of P. euryhalinus near the Belgian and French coast is currently unknown. So far, no specific measures have been taken to control the species.

P. marinus is a small calanoid copepod (Calanoida), about 1 mm in size. Females grow taller than male individuals. Its body consists of two parts: the anterior prosome and posterior urosome. The urosome is smaller than two-thirds of the prosome. The prosome is long, slender and can be subdivided into two parts: the cephalosome, forming the head, and the metasome, forming the trunk. The cephalosome is rounded and caries two pairs of antennae. The metasome carries five pairs of swimming legs ^[6]. The genus Pseudodiaptomus contains several species distinguished by differences in the male’s fifth pair of legs ^[9].

The females carry the eggs in a brood pouch under the abdomen ^{[9, 21]}. Because the eggs are carried, this increases their chance of survival ^[15]. At lower temperatures, the rate of egg production appears to be much lower. The development time (from egg to adult) is on average 13 days, which is short enough to ensure high numbers under the right conditions ^[22].

During the day, this copepod lives near the bottom (epibenthic way of life). At sunset, it moves higher up the water column, where it is part of the so-called animal plankton or zooplankton ^[23-25]

[1]          World Register of Marine Species (WoRMS) (2020). Pseudodiaptomus marinus Sato, 1913. [http://www.marinespecies.org/aphia.php?p=taxdetails&id=360352] (2020-11-17).

[2]          Walter, T.C. (1987). Review of the taxonomy and distribution of the demersal copepod genus Pseudodiaptomus (Calanoida : Pseudodiaptomidae) from southern Indo-West Pacific waters. Aust. J. mar. Freshw. Res. 38(3): 363-396. [http://www.vliz.be/nl/imis?module=ref&refid=229692]

[3]          Brylinski, J.-M.; Antajan, E.; Raud, T.; Vincent, D. (2012). First record of the Asian copepod Pseudodiaptomus marinus Sato, 1913 (Copepoda: Calanoida: Pseudodiaptomidae) in the Southern Bight of the North Sea along the coast of France. Aquat. Invasions 7(4): 577-584. [http://www.vliz.be/imis/imis.php?module=ref&refid=229638]

[4]          Walter, T.C.; Boxshall, G. (2018). Belgian Register of Marine Species. World of Copepods database. Pseudodiaptomus marinus Sato, 1913. [http://www.marinespecies.org/berms/aphia.php?p=taxdetails&id=360352]

[5]          Deschutter, Y.; Vergara, G.; Mortelmans, J.; Deneudt, K.; Schamphelaere, K.; De Troch, M. (2018). Distribution of the invasive calanoid copepod Pseudodiaptomus marinus (Sato, 1913) in the Belgian part of the North Sea. BioInvasions Records 7(1): 33-41. [http://www.vliz.be/nl/imis?module=ref&refid=292779]

[6]          Grindley, J.R.; Grice, G.D. (1969). A redescription of Pseudodiaptomus Marinus Sato (Copepoda, Calanoida) and its occurrence at the Island of Mauritius. Crustaceana 16(2): 125-134. [http://www.vliz.be/imis/imis.php?module=ref&refid=229641]

[7]          Pillai, P.P. (1976). A review of the calanoid copepod family Pseudodiaptomidae with remarks on the taxonomy and distribution of the species from the Indian Ocean. J. Mar. Biol. Ass. India 18(2): 242-265. [http://www.vliz.be/imis/imis.php?module=ref&refid=229646]

[8]          Jones, E.C. (1966). A new record of Pseudodiatomus marinus Sato (Copepoda, Calanoida) from brackish waters of Hawaii. Crustaceana 10(3): 316-317. [http://www.vliz.be/nl/imis?module=ref&refid=229672]

[9]          Fleminger, A.; Kramer, S.H. (1988). Recent introduction of an Asian estuarine copepod, Pseudodiaptomus marinus (Copepoda: Calanoida), into southern California embayments. Mar Biol. (Berl.) 98(4): 535-541. [http://www.vliz.be/imis/imis.php?module=ref&refid=227306]

[10]        Lawrence, D.L.; Cordell, J.R. (2010). Relative contributions of domestic and foreign sourced ballast water to propagule pressure in Puget Sound, Washington, USA. Biol. Conserv. 143(3): 700-709. [http://www.vliz.be/nl/imis?module=ref&refid=229682]

[11]        Da Olazabal, A.; Tirelli, V. (2011). First record of the egg-carrying calanoid copepod Pseudodiaptomus marinus in the Adriatic Sea. Marine Biodiversity Records 4(e85): 1-4. [http://www.vliz.be/nl/imis?module=ref&refid=229691]

[12]        Jha, U.; Jette, A.; Lindley, J.A.; Poster, L.; Wootton, M. (2013). Extension of distribution of Pseudodiaptomus marinus, an introduced copepod, in the North Sea. Marine Biodiversity Records 67: 53. [http://www.vliz.be/imis/imis.php?module=ref&refid=229644]

[13]        Rajakaruna, H.; Strasser, C.; Lewis, M. (2012). Identifying non-invasible habitats for marine copepods using temperature-dependent R0. Biological Invasions 14(3): 633-647. [http://www.vliz.be/imis/imis.php?module=ref&refid=229650]

[14]        Liang, D.; Uye, S. (1997). Seasonal reproductive biology of the egg-carrying calanoid copepod Pseudodiaptomus marinus in a eutrophic inlet of the Inland Sea of Japan. Mar. Biol. (Berl.) 128(3): 409-414. [http://www.vliz.be/imis/imis.php?module=ref&refid=229645]

[15]        Sabia, L.; Uttieri, M.; Pansera, M.; Souissi, S.; Schmitt, F.G.; Zagami, G.; Zambianchi, E. (2012). First observations on the swimming behaviour of Pseudodiaptomus marinus from Lake Faro = Osservazioni preliminari sul comportamento natatorio di Pseudodiaptomus marinus dal Lago di Faro. Biol. Mar. Medit. 19(1): 240-241. [http://www.vliz.be/nl/imis?module=ref&refid=229681]

[16]        Sabia, L.; Zagami, G.; Mazzocchi, M.; Zambianchi, E.; Uttieri, M. (2015). Spreading factors of a globally invading coastal copepod. Mediterr. Mar. Sci. 16(2): 460-471. [http://www.vliz.be/nl/catalogus?module=ref&refid=288142]

[17]        Uye, S.; Iwai, Y.; Kasahara, S. (1983). Growth and production of the inshore marine copepod Pseudodiaptomus marinus in the central part of the Inland Sea of Japan. Mar. Biol. (Berl.) 73(1): 91-98. [http://www.vliz.be/nl/imis?module=ref&refid=331245]

[18]        Jiménez-Pérez, L.C.; Castro-Longoria, E. (2006). Range extension and establishment of a breeding population of the Asiatic copepod, Pseudodiaptomus marinus Sato, 1913 (Calanoida, Pseudodiaptomidae) in Todos Santos Bay, Baja California, Mexico . Crustaceana 79(2): 227-234. [http://www.vliz.be/imis/imis.php?module=ref&refid=229643]

[19]        Zenetos, A.; Gofas, S.; Morri, C.; Rosso, A.; Violanti, D.; García Raso, J.E.; çinar, M.E.; Almogi-Labin, A.; Ates, A.S.; Azzurro, E.; Ballesteros, E.; Bianchi, C.N.; Bilecenoglu, M.; Gambi, M.C.; Giangrande, A.; Gravili, C.; Hyams-Kaphzan, O.; Karachle, P.K.; Katsanevakis, S.; Lipej, L.; Mastrototaro, F.; Mineur, F.; Pancucci-Papadopoulou, M.A.; Ramos Esplá, A.; Salas, C.; San Martín, G.; Sfriso, A.; Streftaris, N.; Verlaque, M. (2012). Alien species in the Mediterranean Sea by 2012. A contribution to the application of European Union’s Marine Strategy framework Directive (MSFD). Part 2. Introduction trends and pathways. Mediterr. Mar. Sci. 13(2): 328-352. [http://www.vliz.be/en/imis?module=ref&refid=288228]

[20]        Shang, X.; Wang, G.; Li, S. (2008). Resisting flow - laboratory study of rheotaxis of the estuarine copepod Pseudodiaptomus annandalei. Mar. Freshw. Behav. Physiol. 41(2): 109-124. [http://www.vliz.be/nl/catalogus?module=ref&refid=297640]

[21]        Uye, S.-I.; Yuzuru, I.; Kasahara, S. (1982). Reproductive biology of Pseudodiaptomus marinus (Copepoda: Calanoida) in the Inland Sea of Japan. Bull. Plankton Soc. Japan 29(1): 25-35. [http://www.vliz.be/nl/catalogus?module=ref&refid=297645]

[22]        Huang, Y.; Zhu, L.; Liu, G. (2006). The effects of bis(tributiltyn) oxide on the development, reproduction and sex ratio of calanoid copepod Pseudodiaptomus marinus. Est., Coast. and Shelf Sci. 69(1-2): 147-152. [http://www.vliz.be/nl/catalogus?module=ref&refid=297653]

[23]        Uye, S.-I.; Kasahara, S. (1983). Grazing of various developmental stages of Pseudodiaptomus marinus (Copepoda: Calanoida) on natural occurring particles. Bull. Plankton Soc. Japan 30(2): 157-158. [http://www.vliz.be/nl/imis?module=ref&refid=229671]

[24]        Valbonesi, A.; Harada, E. (1980). The vertical distributions of some copepods and a mysid in a near-shore water of Tanabe Bay. Publ. Seto Mar. Biol. Lab. 25(5-6): 445-460. [http://www.vliz.be/imis?module=ref&refid=297619]

[25]        Liang, D.; Uye, S. (1997). Population dynamics and production of the planktonic copepods in a eutrophic inlet of the Inland Sea of Japan. IV. Pseudodiaptomus marinus, the eggcarrying calanoid. Mar. Biol. 128: 415-421. [http://www.vliz.be/nl/catalogus?module=ref&refid=297634]

VLIZ Alien Species Consortium (2020). Pseudodiaptomus marinus. Non-native species of the Belgian part of the North Sea and bordering estuaries anno 2020. Flemish Institute for the Sea (VLIZ). 6 pp.