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:

Mytilicola orientalis is a parasitic copepod known from oysters (Crassostrea gigas, Pacific Oyster; Ostrea lurida, Olympia Oyster) and mussels (Mytilus crassitesta, M. edulis, M. trossulus, M. californianus) (Grizel 1985; Goater and Weber 1996). It also parasitizes clams (Protothaca staminea, Pacific Littleneck; Venerupis philippinarum, Japanese Littleneck), and the gastropod Crepidula fornicata (Rankin 1943, cited by Carlton 1979; Bower et al. 1992). It was described in 1935 from the Seto Inland Sea, Japan, from the bivalves C. gigas (Pacific Oyster) and M. crassitesta (the Asian Black Mussel) (Mori 1935, cited by Odlaug 1946). It has been introduced to Western North America from Morro Bay, California to British Columbia (Bernard 1969; Quayle 1969; Carlton 1979) and the Northeast Atlantic from France (Grizel 1985) to Ireland (Steele and Mulcahy 2001), the Netherlands (Stock 1993), and the French Mediterranean Coast (Clanzig 1989).

North American Invasion History:

Invasion History on the West Coast:

Mytilicola orientalis was first reported from North American waters in 1938 from Willapa Bay, Washington (WA) in Crassostrea gigas (Wilson 1938; cited by Carlton 1979). By 1943, it was reported from Puget Sound, WA (Rankin 1943, cited by Carlton 1979; Odlaug 1946). Its pattern of spread is difficult to discern and it was probably introduced to many locations with early plantings of Pacific Oysters around 1902, and not recognized until after the species was described. This parasite has been found in cultured oysters in Morro Bay, Elkhorn Slough, Tomales Bay, and Drakes Estero, California; and Yaquina Bay, Oregon (Hedgpeth 1962, cited by Carlton 1979; Chew 1965; Katkansky et al. 1967; Katkansky and Warner 1974, cited by Carlton 1979). In San Francisco and Humboldt Bays, it was found in Olympia Oysters (O. lurida) and mussels (Mytilus spp.) (Chew et al. 1965, Katkansky et al. 1967, Bradley and Siebert 1978, all cited by Carlton 1979). In southern British Columbia waters, M. orientalis is widespread in the Strait of Georgia and in Barkley Sound on the western side of Vancouver Island, in C. gigas, M. trossulus, and V. phillipinarum (Quayle 1969; Carlton 1979; Bower et al. 1992; Goater and Weber 1996).

Invasion History on the East Coast:

Mytilicola orientalis was first collected in European waters in 1977, in the Bay of Arcachon, France, on the Bay of Biscay (Goulletquer et al. 2002). In 1979, it was found in Marennes-Oleron, also on the Bay of Biscay (Goulletquer et al. 2002) and in the Mediterranean, in the Thau Lagoon, Sette, France (Clanzig 1989). All of these areas are extensively used for Pacific Oyster culture.


Description

The larval nauplius and copepodite stages of Mytilicola orientalis are planktonic, but the adults settle inside the intestine of a bivalve, where they metamorphose into greatly modified sedentary wormlike forms, with their appendages greatly reduced (Grizel 1985; Goater and Weber 1996). The adult female is 10 to 12 mm in length, and 1.33 mm wide at the largest section. The head is separate from the thorax. The antennules have four segments; the antennae have two. The antennae are modified into hooks used to cling to the host's tissue. The thorax consists of five segments with triangular lateral extensions. The genital segment is fused with the thoracic segments. The female produces paired egg sacs about 7 mm length, containing approximately 200 eggs. The abdomen is narrower than the genital segment and ends in two triangular outgrowths (Grizel 1985; Fisheries and Oceans Canada 2009).

The development of M. orientalis is unknown, but is probably similar to that of M. intestinalis, which consists of 2 nauplius stages, 5 copepodite stages, and a pre-adult stage, before metamorphosis into the parasitic adult (Gee and Davey 1986).


Taxonomy

Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Maxillopoda
Subclass:   Copepoda
Order:   Cyclopoida
Family:   Mytilicolidae
Genus:   Mytilicola
Species:   orientalis

Synonyms

Mytilicola ostreae (Wilson, 1938)

Potentially Misidentified Species

Mytilicola instestinalis
Mytilicola intestinalis is aprasite primarily of Mytilus sp., native to the Mediterranean and introduced to the North Sea. There are morphological differences, but genetic methods are recommended for identification At least one study has mis-identified M. orientalis as M. intestinalis (Goedknecht et al. 2018).

Mytilicola porrectus
Parasite of Geukensia demissa and Mercenaria mercenaria, described from Louisiana

Ecology

General:

Mytilicola orientalis is a parasitic copepod, capable of infecting a wide range of bivalve molluscs. Its most common host is the Pacific Oyster (Crassostrea gigas), but it is known from Ostrea lurida (Olympic Oyster), O. edulis (European Oyster), Mytilus coruscus (Japanese Black Mussel), M. edulis (Blue Mussel), M. galloprovincialis (Mediterranean Mussel), M. trossulus (Bay Mussel), M. californianus (California Mussel), Protothaca staminea (Pacific Littleneck), Venerupis philippinarum (Japanese Littleneck), and the gastrood Crepidula fornicata (Common Atlantic Slippersnail) (Rankin 1943, cited by Carlton 1979; Grizel 1985; Bower et al. 1992; Goater and Weber 1996). The wormlike adult female and male mate inside the host's intestine. The female produces paired egg sacs which hatch into naupli.

The life cycle of M. orientalis has not been studied, but in the similar M. intestinalis, there are two nauplius stages, and 5 copepodite stages, all non-feeding. The planktonic stages are filtered out by the bivalve, and remain within, developing into parasitic adults (Gee and Davies 1986). Patterns of infection suggest that dispersal distance in mussel beds is usually short, because the intense filtration of the bivalves remove the larvae from the water column. The number of copepods per mussel increases with mussel size, but decreases with tidal height, probably because of less time for infection (Goater and Weber 1996).

Food:

Crassostrea gigas; other bivalves

Trophic Status:

Parasite

Paras

Habitats

General HabitatOyster ReefNone
General HabitatMarinas & DocksNone
General HabitatRockyNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Tidal RangeMid IntertidalNone
Vertical HabitatEpibenthicNone


Tolerances and Life History Parameters

Minimum Reproductive Salinity9.6~50% hatching (Brenner et al. 2019)
Maximum Length (mm)12Female (Grizel 1985)
Broad Temperature RangeNoneCold temperate-Warm temperate
Broad Salinity RangeNoneMesohaline-Euhaline

General Impacts

The parasitic copepod Mytilicola orientalis infects oysters, mussels, and clams, including such commercially important species as the Pacific Oyster (Crassostrea gigas), Olympic Oyster (Ostrea lurida), European Oyster (O. edulis), Blue Mussel (Mytilus edulis). Impacts of parasitism on oysters appear to be mostly nonlethal, including local damage to intestinal tissue, and decreased condition factors (increased water, decreased fat content) (Odlaug 1946; Bernard 1969; Grizel 1985; Steele and Mulcahy 2001; Fisheries and Oceans Canada 2009). The extent of damage to mussels is unclear, but heavy infections can lead to mortality (Fisheries and Oceans Canada 2009). This parasite was included on a list of the '100 Worst Invaders' in the Mediterranean Sea (Streftaris and Zenetos 2006).

Economic Impacts

Fisheries: Parasitism by Mytilicola orientalis rarely kills oysters, but can lower their condition factor (increased water and decreased fat content), affecting the perceived quality of the oysters (Odlaug 1946; Grizel 1985; Fisheries and Oceans Canada 2009).

Ecological Impacts

Parasitism: Infection by Mytilicola orientalis appears to rarely result in mortality of oysters, but tissue damage to intestinal tissue and scar formation can reduce the efficiency of digestion, and contributes to decreased condtion factor (increased water content, decreased fat) (Odlaug 1946; Katkansky et al. 1967; Grizel 1985; Fisheries and Oceans Canada 2009). These impacts were variable with geography and season (Deslou-Paoli 1981, cited by Fisheries and Oceans Canada 2009). In Ireland, infection by M. orientalis did not directly affect health or quality of Crassostrea gigas, but was associated with increased infestations by shell-boring Polydora spp. (Steele and Mulcahy 2001).

Regional Impacts

NEP-IVPuget Sound to Northern CaliforniaEcological ImpactParasitism
Infection with M. orientalis resulted in reduced condition factor in Olympia Oyster (Ostrea lurida) in Willapa Bay (Oldaug 1946). Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in Humboldt, Yaquina, and Willapa Bays. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967).
P270Willapa BayEcological ImpactParasitism
Infection with M. orientalis resulted in reduced condition factor in Olympia Oyster (Ostrea lurida) in Willapa Bay (Oldaug 1946). Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in Humboldt, Yaquina, and Willapa Bays. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967).
NEP-IVPuget Sound to Northern CaliforniaEconomic ImpactFisheries
Infection resulted in reduced condition factor (increased water, reduced fat) in Olympia Oyster (Ostrea lurida) in Willapa Bay (Oldaug 1946). Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in Humboldt, Yaquina, and Willapa Bays. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967).
P270Willapa BayEconomic ImpactFisheries
Infection resulted in reduced condition factor(increased water, reduced fat) in Olympia Oyster (Ostrea lurida) in Willapa Bay (Oldaug 1946). Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in Humboldt, Yaquina, and Willapa Bays. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967).
NEA-IIINoneEcological ImpactParasitism
Parasitism by M. orientalis did not directly affect health or quality of Crassostrea gigas, but was associated with increased infections by Polydora spp (Steele and Mulcahy 2001),
P130Humboldt BayEcological ImpactParasitism
Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in Humboldt, Yaquina, and Willapa Bays. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967).
NEP-IIIAlaskan panhandle to N. of Puget SoundEcological ImpactParasitism
Reduced condition factor was reported in infected Pacific Oysters (Crassostrea gigas) in Hood Canal and Oyster Bay, Puget Sound (Katkansky et al. 1967). Highest infection rates in mussels (Mytilus trossulus) in Barkley Sound, British Columbia, were seen in sheltered, muddy areas near the low-tide mark (Goater and Weber 2009).
P290Puget SoundEcological ImpactParasitism
Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in the Hood Canal and Oyster Bay, Puget Sound. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967).
NEP-IIIAlaskan panhandle to N. of Puget SoundEconomic ImpactFisheries
Impacts of Mytilicola orientalis on cultured Pacific Oysters (Crassostrea gigas were considered insignificant by Bernard (1969). Reduced condition factor was reported in infected Pacific Oysters (Crassostrea gigas) in Hood Canal and Oyster Bay, Puget Sound Chew et al. 1965; Katkansky et al. 1967). Reduced condition factor (smaller body mass, higher water content, less fat) reduces the quality of oysters.
P130Humboldt BayEconomic ImpactFisheries
Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in Humboldt, Yaquina, and Willapa Bays. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967). Reduced condition factor (smaller body mass, higher water content, less fat) reduces the quality of oysters.
P210Yaquina BayEcological ImpactParasitism
Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in Humboldt, Yaquina, and Willapa Bays. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967).
P210Yaquina BayEconomic ImpactFisheries
Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in Humboldt, Yaquina, and Willapa Bays. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967). Reduced condition factor (smaller body mass, higher water content, less fat) reduces the quality of oysters.
P290Puget SoundEconomic ImpactFisheries
Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in the Hood Canal and Oyster Bay, Puget Sound. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967). Reduced condition factor (smaller body mass, higher water content, less fat) reduces the quality of oysters.
NEA-IVNoneEcological ImpactParasitism
Parastism of Crassostrea gigas (Pacific Oyster) by Mytilicola orientalis resulted in reduced condtion factor only in spring and fall, when oysters were stressed by low food availability or spawning (Deslou-Paoli 1981, cited by Fisheries and Oceans Canada 2009).
NEA-IINoneEcological ImpactParasitism
Mytilicola orientalis, on the coast of the Netherlands, infected Pacific Oysters (Crassostrea gigas at 2-43% frequency, but also were found in Blue Mussels (Mytilus edulis, 3-63%), Common Cockles (Cerastoderma edule, 2-13%), and Baltic Tellins (Macoma balthica, 6-7%) (Goedknegt et al. 2017a; Goedknegt et al. 2017b). The intensity of infection in M. edulis was strongly correlated with intensity in C. gigas, indicating transmission of the parasite between Pacific Oysters and native Blue Mussels (Goedknegt et al. 2017b).

Stable isotope studies, in the Netherlands, show that M. orientalis gets much of its nutrition from tissues of its host mussel (Mytilus edulis, as well as from the ingested organic material, so that it is more of a parasite than a commensal (Goedknecht et al. 2018).
NEA-IINoneEcological ImpactCompetition

The parasitic copepod Mytilicola orientalis, introduced into the Wadden Sea (Sylt, Gernany) with Pacific Oysters (Magallana gigas) has infected native Blue Mussels (Mytilus edulis) and displaced its native parasite (Mytilicola intestinalis).  Mytilcola orientalis is less successful  than the native parasite at infecting mussels, but the high density of Pacific Mussels allows a highrate of spllover.  Also, aggergation of M. orientalis may interfere with mating of M. intestinalis , resultin in indirect competition (Feis et al. 2022)/

NEP-VNorthern California to Mid Channel IslandsEconomic ImpactFisheries

Reduced condition factor of oysters

WAWashingtonEcological ImpactParasitism
Infection with M. orientalis resulted in reduced condition factor in Olympia Oyster (Ostrea lurida) in Willapa Bay (Oldaug 1946). Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in Humboldt, Yaquina, and Willapa Bays. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967)., Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in the Hood Canal and Oyster Bay, Puget Sound. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967).
WAWashingtonEconomic ImpactFisheries
Infection resulted in reduced condition factor(increased water, reduced fat) in Olympia Oyster (Ostrea lurida) in Willapa Bay (Oldaug 1946). Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in Humboldt, Yaquina, and Willapa Bays. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967)., Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in the Hood Canal and Oyster Bay, Puget Sound. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967). Reduced condition factor (smaller body mass, higher water content, less fat) reduces the quality of oysters.
OROregonEcological ImpactParasitism
Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in Humboldt, Yaquina, and Willapa Bays. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967).
OROregonEconomic ImpactFisheries
Reduced condition factor was also reported in infected Pacific Oysters (Crassostrea gigas) in Humboldt, Yaquina, and Willapa Bays. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967). Reduced condition factor (smaller body mass, higher water content, less fat) reduces the quality of oysters.
CACaliforniaEcological ImpactParasitism

Reduced condition factor was also reported in infected Pacific Oysters (Magallana gigas) in Humboldt, Yaquina, and Willapa Bays. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967).

CACaliforniaEconomic ImpactFisheries

Reduced condition factor of oysters

Reduced condition factor was also reported in infected Pacific Oysters (Magallana gigas) in Humboldt, Yaquina, and Willapa Bays. However, no relation was seen between infection and mortality (Chew et al. 1965; Katkansky et al. 1967). Reduced condition factor (smaller body mass, higher water content, less fat) reduces the quality of oysters.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEP-IV Puget Sound to Northern California 1938 Def Estab
NEP-III Alaskan panhandle to N. of Puget Sound 1943 Def Estab
NEP-V Northern California to Mid Channel Islands 1962 Def Estab
NWP-4a None 0 Native Estab
NWP-3b None 0 Native Estab
NEA-II None 1992 Def Estab
NEA-V None 1977 Def Estab
NEA-III None 1993 Def Estab
MED-II None 1979 Def Estab
NEA-IV None 1993 Def Estab
P130 Humboldt Bay 1963 Def Estab
P070 Morro Bay 1974 Def Estab
P080 Monterey Bay 1974 Def Estab
P090 San Francisco Bay 1974 Def Estab
P100 Drakes Estero 1967 Def Estab
P110 Tomales Bay 1962 Def Estab
P210 Yaquina Bay 1963 Def Estab
P270 Willapa Bay 1938 Def Estab
P290 Puget Sound 1943 Def Estab
NWP-3a None 0 Native Estab
MED-VII None 2016 Def Estab
B-IV None 2018 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
26570 OSPR - Historic Data 1963 1963-01-01 Humboldt Bay General Location Def 40.7864 -124.1922
31992 (Hedgepeth 1962, cited by Carlton 1979) 1962 1962-01-01 Tomales Bay Def 38.1285 -122.8730

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