Invasion History

First Non-native North American Tidal Record: 2003
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 2003

General Invasion History:

Hyotissa hyotis has a very wide native range, in the Indian and Pacific oceans from the Red Sea and southern South Africa, to northern Australia, Hawaii, and the eastern Pacific from Mexico to Ecuador (Bieler et al. 2004; Duprat-Bertazzi and Garcia-Dominguez 2005; Academy of Natural Sciences of Philadelphia 2010; Stella et al. 2010; Tan et al. 2010; US National Museum of Natural History 2010). It had been reported in earlier literature from the Atlantic, but the Atlantic form was recognized as a distinct species (H. mcgintyi) in 1985 (Harry 1985, cited by Bieler et al. 2004), although some authors continued to list H. hyotis from the Atlantic. In 2003, genuine specimens of H. hyotis were identified by molecular methods from the Florida Keys (Bieler et al. 2004).

North American Invasion History:

Invasion History on the East Coast:

In 2001, a shell, later identified as H. hyotis, was found off West Palm Beach, Florida in the Atlantic Ocean. In 2003, in an investigation of fouling communities on shipwrecks, divers found some exceptionally large attached oysters on the wreck of the RV 'Thunderbolt', near Marathon Key, on the Gulf side of the Florida Keys. The largest specimens were later identified as H. hyotis, using molecular comparisons with specimens from Guam. The native oyster (H. mcgintyi, McGinty oyster) was also found on the wreck (Bieler et al. 2004). Subsequent collections of H. hyotis were made on the wreck of the USGC Cutter 'Duane,' off Key Largo, and on the wreck of the freighter Eagle in the Florida Keys National Marine Sanctuary, both in 2005, on the Atlantic side of the keys. This oyster is considered established in the Florida Keys (USGS Nonindigenous Aquatic Species Program 2011).

Invasion History Elsewhere in the World:

Hyotissa hyotis was reported from New Zealand, on the hull of a wrecked fishing vessel 10 nautical miles off Cape Brett on the North Island. This and other fouling organisms on the ship were not considered to be likely to become established (Williams et al. 2008). This oyster was also reported from a shipwreck off Pernambuco, Brazil (Lira et al. 2011). However, it is not clear whether H. hyotis was distinguished from the native H. mcgintyi.


Hyotissa hyotis is a very large oyster, with the two unequal valves. The shape is irregular, according to the substrate and conditions of growth. The animal is cemented to the substrate by the left valve. Both valves are solid and thick. The shell is very deeply ridged, with ridges extending to the shell margin, making it strongly saw-toothed. The arches of the valves interlock. The area of attachment of the ligament has a shallow median groove. The hinge is without teeth. The external coloration of the shell is purplish black, while the interior is bluish-white in the center, and bluish-black towards the margin. There is a single purplish adductor muscle scar, located towards the hinge (Bieler et al. 2004; Stella et al. 2010). Living animals are frequently heavily overgrown with fouling organisms. Hyotissa hyotis has been reported to reach 300 mm in size (Thomson 1954, cited by Duprat-Bertazzi and Garcia-Dominguez 2005), although other authors give maxima of 102 (Stella et al. 2010) and 180 mm (Bieler et al. 2004).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Bivalvia
Subclass:   Pteriomorphia
Order:   Ostreoida
Family:   Gryphaeidae
Genus:   Hyotissa
Species:   hyotis


<em>Pycnodonte&nbsp;hyotis</em> (Linnaeus, 1758)

Potentially Misidentified Species

Hyotissa mcgintyi
This Western Atlantic native oyster (McGinty Oyster) was frequently confused in older literature with its Indo-Pacific relative H. hyotis, but was identified as a distinct species. Recently, in a molecular study of that species, specimens of H. hyoti were discovered in Florida (Bieler et al. 2004).



Hyotissa hyotis has separate sexes; males and females can be distinguished by the color of the gonads (Sevilla et al. 1998, cited by Duprat-Bertazzi and García-Domínguez 2005). The mode of larval development is unknown, but spawning in the Gulf of California continued year-round, peaking in the warmest months (Duprat-Bertazzi and Garcia-Dominguez 2005).

This oyster is widespread on tropical rocky shores, coral reefs and shipwrecks. It appears to be limited to warm, high-salinity environments (Bieler et al. 2004; Duprat-Bertazzi and García-Domínguez 2005; Academy of Natural Sciences of Philadelphia 2010; Stella et al. 2010; Tan et al. 2010; US National Museum of Natural History 2010). It is frequently encrusted with fouling organisms, including other oysters (Bieler et al. 2004).



Trophic Status:

Suspension Feeder



General HabitatRockyNone
General HabitatCoral reefNone
General HabitatVessel HullNone
General HabitatOyster ReefNone
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Vertical HabitatEpibenthicNone

Tolerances and Life History Parameters

Minimum Reproductive Temperature20Field observations, Gulf of California
Maximum Reproductive Temperature28.5Field observations, Gulf of California
Maximum Length (mm)300Maximum sizes variously given as 102 (Stella et al. 2010) and 300 mm (Thomson 1954, cited by Duprat-Bertazzi and Garcia-Dominguez 2005).
Broad Temperature RangeNoneWarm temperate-Tropical
Broad Salinity RangeNoneEuhaline

General Impacts

Hyotissa hyotis is an important local fisheries species in its native range, because of its large size and good flavor. However, it does not appear to be cultured or deliberately introduced in other locations (Duprat-Bertazzi et al. 2010). This species has no reported impacts in North American waters.

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
SP-I None 0 Native Estab
NWP-3a None 0 Native Estab
RS-3 None 0 Native Estab
RS-2 None 0 Native Estab
RS-1 None 0 Native Estab
AUS-XIV None 0 Native Estab
AUS-XII None 0 Native Estab
AUS-XIII None 0 Native Estab
EAS-I None 0 Native Estab
EA-III None 0 Native Estab
SP-XXI None 1995 Crypto Estab
GAden Gulf of Aden 0 Native Estab
CIO-I None 0 Native Estab
CIO-II None 0 Native Estab
WA-V None 0 Native Estab
EAS-III None 0 Native Estab
AG-5 None 0 Native Estab
SP-XII None 0 Native Estab
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 2003 Def Estab
SP-VII None 0 Native Estab
S206 _CDA_S206 (Vero Beach) 2003 Def Estab
NEP-VII None 0 Native Estab
NEP-VIII None 0 Native Estab
NEP-IX None 0 Native Estab
SEP-H None 0 Native Estab
SEP-I None 0 Native Estab
SEP-Z None 0 Native Estab
S196 _CDA_S196 (Cape Canaveral) 2003 Def Unk
NWP-2 None 0 Native Estab
EAS-VI None 0 Native Estab
NZ-IV None 0 Def Unk
CAR-IV None 2012 Def Estab
NWP-3b None 0 Native Estab
EAS-IV None 0 Native Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Academy of Natural Sciences of Philadelphia 2002-2024a Malacology Collection Search. <missing URL>

Academy of Natural Sciences of Philadelphia 2006-2014b OBIS Indo-Pacific Molluscan Database. <missing URL>

Bieler, Rudiger; Mikkelsen, Paula; Lee, Taehwan; O"Foighil, Diarmid. (2004) Discovery of the Indo-Pacific oyster Hyotissa hyotis (Linnaeus , 1758) in the Florida Keys (Bivalvia: Gyphaeidae), Molluscan Research Molluscan Research 24: 149-159

Duprat-Bertazzi, Gabriela; Garcia-Dominguez, Federico (2005) Reproductive cycle of the rock oyster Hyotissa hyotis (linne´, 1758) (Griphaeidae) at the La Ballena Island, Gulf of California, Mexico., Journal of Shellfish Research 24(4): 987-993

Lira, Simone Maria de Albuquerque; Farrapeira, Cristiane Maria Rocha; Amaral, Fernanda Maria Duarte; Ramos, Carla Alecrim Colaço (2011) Sessile and sedentary macrofauna from the Pirapama Shipwreck, Pernambuco, Brazil, Biota Neotropica 10(4): 155-165

Paulay, Gustav (1995) New records and synonymies of Hawaiian bivalves (mollusca), Bishop Museum Occasional Papers 45: 18-29

Ruiz, Gregory M.; Geller, Jonathan (2018) Spatial and temporal analysis of marine invasions in California, Part II: Humboldt Bay, Marina del Re, Port Hueneme, and San Francisco Bay, Smithsonian Environmental Research Center & Moss Landing Laboratories, Edgewater MD, Moss Landing CA. Pp. <missing location>

Stella, C.; Murugan, A.; Vijayalakshmi, S. (2010) New distributional records of Hyotissa hyotis (Linnaeus, 1758) family: Gryphaeidae from Mandapam area-south east coast of India, World Journal of Fish and Marine Sciences 2(1): 42-43

Tan, Siong Kiat; Woo, Henrietta P. M. (2010) <missing title>, Raffles Museum of Biodiversity Research, Singapore. Pp. <missing location>

U.S. National Museum of Natural History 2002-2021 Invertebrate Zoology Collections Database.

USGS Nonindigenous Aquatic Species Program 2003-2024 Nonindigenous Aquatic Species Database.

Williams, Rissa; Gould, Brendan; Christian, Sheree (2008) Shipwrecks: an international biosecurity risk?, Surveillance 35(1): 1-6