Invasion History

First Non-native North American Tidal Record: 1960
First Non-native West Coast Tidal Record: 1960
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

Okenia plana was described from the Seto Inland Sea, Japan (Baba 1960), and later found to have wide distribution in the Western Pacific, including the Yellow Sea (Huang 2001), Hong Kong, and the Philippines (Gosliner 2004). It has been found in Australia, from Queensland to Port Philip Bay, New Zealand (Cranfield et al. 1998; Rudman 2004), and on Palmyra Atoll, in the remote mid-Pacific (California Academy of Sciences 2014). The more remote Pacific occurrences probably represent introductions. Okenia plana feeds on widely distributed bryozoans, including Membranipora sp. and Cryptosula pallasiana, which can be transported in hull fouling and on drifting seaweed (Baba 1960; Rudman 2004). In 1960, this nudibranch was discovered in San Francisco Bay, California (CA) where it is widely distributed (Carlton 1979; Cohen and Carlton 1995). It has also been found in Elkhorn Slough and San Onofre, CA (Behrens 1991; Wasson et al. 2001).

North American Invasion History:

Invasion History on the West Coast:

In California, Okenia plana was first reported (as Okenia sp.) from Berkeley Yacht Harbor, San Francisco Bay in 1960 (Steinberg 1960). Subsequently, it was found in the South Bay at Palo Alto Yacht Harbor and San Pablo Bay (China Camp) (Steinberg 1963). It appears to be widespread in the Bay (Carlton 1979; Cohen et al. 2005), and has been found as far inland as Martinez (Cohen and Chapman 2005), and on the hull of an unused cargo ship moored in Suisun Bay (Llansó et al. 2011). This nudibranch was also found in Elkhorn Slough in 1998 (Wasson et al. 2001) and in San Onofre (Behrens 1991).

Invasion History Elsewhere in the World:

Okenia plana was first reported in Australia in 1977 from Melbourne (Keough and Ross 1999) and/or New South Wales (Furlani 1996). It has been found in several port areas in New South Wales, including Sydney Harbour, Jervis Bay, and Botany Bay, and at Woolgoolga, further north (Rudman 2004). It also occurs in southern Queensland (Furlani 1996; Ellis 2000, cited in NIMPIS 2014). This nudibranch was first reported from the northeastern coast of the North Island of New Zealand in 1984 (Cranfield et al. 1998). A record of O. plana on remote, isolated Palmyra Atoll, south of Hawaii, appears to be an introduction, probably by ship fouling (6/2008, CAS-IZ 178437, California Academy of Sciences 2014).


Okenia eolida is a flattened, oval nudibranch, with a weakly differentiated semicircular head, which lacks paired oral tentacles. The foot is expanded. There are five long, finger-like papillae on each side, and a single, long median papilla in the center of the back of the animal. The rhinophores, located behind the first pair of papilla, have many short, blunt filaments (lamellae). There are 8-11 short feather-like gills, arranged in a semicircle on the posterior region. The animal reaches 10-15 mm in size. The body is whitish and is heavily sprinkled with brown spots. The tips of the rhinophores are yellow. Description based on Baba (1960), Behrens (1991), Gosliner (2004), and Rudman (2004).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Gastropoda
Subclass:   Opisthobranchia
Order:   Nudibranchia
Family:   Goniodorididae
Genus:   Okenia
Species:   plana


Hopkinsia plana (Baba, 1960)
Doris eolida (Quoy and Gaimard, 1832)
Okenia plana (Quoy and Gaimard, None)

Potentially Misidentified Species

Okenia vancouverensis
NE Pacfic native, from British Columbia (Behrens 1991).



Okenia plana is a nudibranch which inhabits estuaries, harbors, and open coasts. Nudibranchs are simultaneous hermaphrodites, and copulate reciprocally or unilaterally. We have not found information on the egg masses or larval development of O. plana. Most Northeast Pacific nudibranchs hatch out as planktotrophic larvae, but some have lecithotrophic larvae (Barnes 1983; Behrens 1984; Goddard 2007).

Okenia plana inhabits rocky areas, coral reefs, marinas, and harbors of warm-temperate to tropical regions, including piers, jetties, and floating structures. In San Francisco Bay, it occurs in the Central and South Bays, where salinities are highest, but also in the more variable San Pablo Bay and Carquinez Straits (Steinberg 1960; Steinberg 1963; Cohen and Carlton 1995; Cohen and Chapman 2005). It feeds on bryozoan colonies attached to hard surfaces, but also those growing on seaweeds and seagrass (Zostera). Among the bryozoan prey are Membranipora sp., Cryptosula pallasiana, and Jellyella tuberculata (Rudman 2004; Australian Museum 2014).



Trophic Status:




General HabitatMarinas & DocksNone
General HabitatRockyNone
General HabitatCoral reefNone
General HabitatVessel HullNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Salinity (‰)18.5Field, Carquinez Strait, San Francisco Bay (Carlton and Chapman 2005)
Maximum Length (mm)15Gosliner 2004
Broad Temperature RangeNoneWarm Temperate-Tropical
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

No ecological or economic impacts have been reported for Okenia plana.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEP-V Northern California to Mid Channel Islands 1960 Def Estab
NEP-VI Pt. Conception to Southern Baja California 1995 Def Estab
AUS-X None 1977 Def Estab
AUS-XI None 1983 Def Estab
AUS-VIII None 1977 Def Estab
NZ-IV None 1984 Def Estab
NWP-3b None 0 Native Estab
NWP-2 None 0 Native Estab
NWP-4a None 0 Native Estab
EAS-III None 0 Native Estab
AUS-XII None 1996 Def Estab
P027 _CDA_P027 (Aliso-San Onofre) 1995 Def Estab
P080 Monterey Bay 1998 Def Estab
P090 San Francisco Bay 1960 Def Estab
P093 _CDA_P093 (San Pablo Bay) 1963 Def Estab
SP-XVI None 2008 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
26656 Wasson et al, 2001 (Elkhorn Slough Survey) 1998 1998-03-01 Elkhorn Slough Station 9 Def 36.8398 -121.7435
26722 Foss 2009 2005 2005-10-19 Mare Island Strait - Navy Def 38.1015 -122.2695
26827 Foss 2009 2005 2005-11-14 Cal Maritime Academy/Vallejo Def 38.0661 -122.2299
27108 Foss 2009 2005 2005-10-07 Benicia Waterfront Def 38.0401 -122.1385
27206 Foss 2011 2010 2010-07-13 Port Sonoma/Petaluma R. Def 38.1157 -122.5026
27479 Steinberg 1963, cited by Carlton 1979) 1960 1960-01-01 Berkeley Yacht Harbor,- Berkeley Marina Def 37.8664 -122.3150
27513 Steinberg 1963, cited by Carlton 1979) 1960 1960-01-01 San Francisco Bay - Palo Alto Def 37.4584 -122.1052
27771 Cohen, et al. 2005 (SF Bay Area RAS) 2004 2004-05-23 Pier 39, San Francisco Bay Def 37.8114 -122.4098
28707 Foss 2011 2010 2010-06-03 Treasure Island Def 37.8149 -122.3702
28797 Foss 2011 2010 2010-07-15 San Pablo Bay Pumphouse Def 38.0446 -122.4326
29341 Cohen and Carlton, 1995 1960 1960-01-01 Point Richmond Def 37.9230 -122.3940
32196 Cohen and Carlton, 1995 1960 1960-01-01 San Pablo Bay - China Camp Def 38.0092 -122.4742
32361 Cohen and Carlton 1995 1970 1970-01-01 San Francisco Marina Def 37.8061 -122.4462
33329 Cohen and Carlton 1995 1995 1995-01-01 San Onofre Def 33.3770 -117.5704
767844 Ruiz et al., 2015 2011 2011-09-16 Loch Lomond Marina, San Francisco Bay, CA, California, USA Def 37.9724 -122.4796
767897 Ruiz et al., 2015 2011 2011-09-27 Vallejo Marina, San Francisco Bay, CA, California, USA Def 38.1086 -122.2694


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