First occurrence of the nonindigenous green mussel, Perna viridis (Linnaeus, 1758) in coastal Georgia, United States.

ABSTRACT Since being accidentally introduced into Tampa Bay in the Gulf of Mexico in 1999, the green mussel (Perna viriclis), a native to the Indo-Pacific region, has proliferated and dispersed southwards along peninsular Florida. During 2002 another introduction of P. viridis occurred on the northeast coast of Florida and larval dispersal has also carried the species northward in Atlantic coastal waters. In anticipation of their arrival in Georgia, a campaign was initiated to alert recreational and commercial water users to report all sightings. Observations of living and dead mussels trickled in during 2003 from all over coastal Georgia, confirming the presence of the mussel here for the first time and representing the expansion of the range of this invasive species to its most northerly location in the United States.

KEY WORDS: green mussel, Perna viridis, Georgia, invasive

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The green mussel, Perna viridis (Linnaeus, 1758) is a commonly found mussel of the family Mytilidae in its native tropical waters of the Indo-Pacific region of Asia (Siddall 1980). There the species form the basis for an important aquaculture industry (Qasim et al. 1977, Sivalingam 1977, Sreenivasan et al. 1989, Zhang et al. 1997, Chalermwat et al. 2003). The species is dioecious, sexually matures at 2 to 3 mo of age, lives for about 3 y, and it typically attaches itself to hard structures with byssal threads in densities of up to 35,200 individuals/[m.sub.2] (Huang et al. 1985, Lee 1985, Lee 1988, http://www.fcsc.usgs.gov). Green mussels occur in coastal waters (<10 m), in salinities between 16 and 33 ppt, at temperatures between 10[degrees]C and 35[degrees]C (optimal: 27 to 33 ppt, 26[degrees]C to 32[degrees]C), and exhibit a wide tolerance for turbidity concentrations and pollution (Sivalingam 1977, Sundaram & Shafee 1989, Lee 1986, Tan 1997, Masilamoni et al. 1997, Benson et al. 2001). In parts of their native range, they exhibit rapid growth rates of between 6 and 10 mm/month (Lee 1985, 1986, Walter 1982). These biologic attributes facilitate opportunistic colonization of new areas.

In 1990, the mussel appeared off Trinidad in the Caribbean for the first time, then in 1993 off Venezuela, later in Jamaica, and subsequently in Tampa Bay, Florida in 1999 (Agard et al. 1992, Rylander et al. 1996, Ingrao et al. 2001, Benson et al. 2001). Ballast water releases are believed to have been the most likely route for introductions. In Tampa Bay, this species has fouled bridges, piers, and buoys, and it has even displaced oyster (Crassostrea virginica) reefs (Baker & Benson 2002). In Tampa Bay, juveniles have been recorded at densities of 9,000 to 12,000/[m.sub.2], and adults at 1,000 to 4,000/me; growth rates are rapid, reaching 4-5 mm/wk; and individuals are reproductively capable at between 1 and 2 mo of age (Jonathan Fajans, University of Florida, Department of Fisheries & Aquatic Sciences, pers. comm.). From Tampa, currents have dispersed larvae south along the Gulf Coast to Boca Grande outside of Charlotte Harbor (Benson et al. 2001).

In 2002, reports of the green mussel surfaced on the northeast coast of Florida in the St. Augustine area (Dr. Richard Gleeson, Guana Tolomato Matanzas National Estuarine Research Reserve).

Because the mussel has not yet arrived in the Florida Keys, it is unlikely that the occurrence of the green mussel in Georgia resulted from larval dispersal around the peninsula. This may represent an entirely new introduction, however it is more likely to have resulted from boats and equipment being transferred between coasts without adequate cleaning of attached organisms and draining of bilge water. During early 2003, currents carried the mussel as far north as Jacksonville Beach, Florida and fears arose that it would soon appear in Georgia.

The University of Georgia Marine Extension Service (UGA MAREX) in collaboration with the University of North Carolina at Wilmington are currently conducting a Sea-Grant-funded biologic survey of the major shipping ports in the southeastern United States (Jacksonville, Florida; Savannah, Georgia; Charleston, South Carolina; and Wilmington, North Carolina) for invasive species. The Sapelo Island National Estuarine Research Reserve (SINERR) is also investigating invasives in the Sapelo Island area of coastal Georgia as part of a national monitoring program. In anticipation of the green mussels' arrival, UGA MAREX and SINERR prepared an informative flyer, which was distributed to commercial fishermen, and posted it at marinas and public boat ramps throughout coastal Georgia. The species appearance and biology was described, a photo was included, and anyone finding one of these mussels was urged to collect the specimen and file a report.

The first report in Georgia came in early 2003, from biologists in the Department of Natural Resources (DNR), who observed many green mussels inhabiting artificial reef G, approximately 30 miles offshore from Brunswick (Fig. 1). Green mussels were again observed there during the summer months. Later in the fall, we began to receive reports from throughout the coastal area of Georgia between Savannah and Brunswick (Plantation Creek, Mackay River, Fredrica River, Savannah River, Skidaway River, and Tybee Beach: see Fig. 1). Mussels were collected from the surface to approximately 4.5 m in depth. Mussels were found subtidally on old abandoned crab traps, crab trap floats, rope, boat fenders, and also in the lower intertidal zone on beach jetties. With the exception of the jetties, all other reports were single specimens. The largest living specimen recorded was 70 mm in length, 35 mm in height, and 23 mm in width. The average shell length of all mussels found during the fall (N = 18) was 34.44 mm ([+ or -] 2.98 S.E.).

[FIGURE 1 OMITTED]

During winter 2004, all intertidal individuals on the jetties died. A greater tidal range exists here than in Tampa, and possibly the longer periods of exposure to low air temperatures will limit the mussels' survival in the intertidal zone. This is beneficial to Georgia's oyster reefs, which are primarily intertidal (Harris 1980). Green mussel shells were washed ashore coastwide over the winter (Sea Island, Tybee Island, Jekyll Island, St. Simons Island, and Cumberland Island: see Fig. 1). The largest shell washed ashore measured 95 mm in length.

Only one resident live mussel has been found in inshore waters in 2004; it was pulled from an abandoned crab trap in Sapelo Sound during January (see Fig. 1). It is likely that others have survived the winter in the subtidal zone. On June 8, 2004 a single specimen was found in Dean Creek near Sapelo Island, attached to a floating piece of wood (see Fig. 1). Six live mussels were also collected by the DNR on June 22, 2004 from buoy markings at Georgia Artificial Reef "A", which are 7 nautical miles east of Little Cumberland Island (see Fig. 1). These individuals ranged in shell length from 28.8 to 73.4 mm (mean [+ or -] SE = 50.0 [+ or -] 7.9). We may see newly recruited mussels occurring in inshore waters during the warm summer and fall months, because the lower temperature threshold for gametogenesis of 24[degrees]C (Lee 1988) is typically attained during the month of May in Georgia.

These observations represent the current most northerly reported occurrence of the species in the United States. None have yet been recorded from South Carolina (David Knott, South Carolina Department of Natural Resources, Southeastern Regional Taxonomic Center, pers. comm.). However, established breeding populations in Georgia in combination with mild winters would make this expansion a likely scenario. In Japan, where the species has also been introduced, populations have managed to survive the severest winters in certain areas due to warm water discharges from several factories (Umemori & Horikoshi 1991).

An interesting side observation of the present survey was the rare documentation of 2 Mytilus edulis (L.) individuals in October 2003, one from the Brunswick area and another from Sapelo (identified by Dr. Paula Mikkelsen, American Museum of Natural History). This common bivalve of the northeastern United States region typically does not occur as far south as Georgia.

The zebra mussel, Dreissena polymorpha (Pallas 1771), a native of Eastern Europe, is an infamous freshwater ballast invader that occurs in over 40% of America's inland waterways. Close to $1 billion has been spent on controlling the species in this country over the last 15 years. A marine counterpart to the zebra mussel in the southeastern United States could be the green mussel. Witnessing the economic and environmental problems experienced in the Tampa Bay region on the Gulf Coast of Florida since the introduction of the green mussel there a few years ago, has led to considerable concern in the coastal community of Georgia. UGA and SINERR have recently initiated a specific green mussel monitoring survey in which devices that offer a variety of settling surfaces (Hester Dendy fouling plates, rope, artificial seaweed, and pvc sheets) have been deployed subtidally in various salinities throughout coastal Georgia. Quarterly sampling will provide an assessment of the distribution and abundance of the species here in Georgia and will provide information about its ecological and environmental tolerances for eventual prediction of the geographic and ecological impacts that could occur due to this organism.

ACKNOWLEDGMENTS

The University of Georgia Marine Extension Service, Sapelo Island National Estuarine Research Reserve and NOAA's National Sea Grant Aquatic Nuisance Species Program provided funding for this work. Thanks to Dr. Amy Benson (United States Geological Survey), Mr. Jonathan Fajans (University of Florida), Dr. Harry Lee (Jacksonville Shell Club), and Dr. Richard Gleeson (GTMNERR) for providing information on the Florida green mussel invasion. Thanks to Dr. Marc Frisher (Skidaway Institute of Oceanography) and Dr. Paula Mikkelsen (American Museum of Natural History) for assisting with the positive identification of specimens. Finally, thanks to all those who have participated in these surveys; Mr. Dwight Vernado, Mr. Henry Ansley, Mr. Dominic Guadagnoli, Mr. Brooks Good, Mr. Gabe Gaddis (Georgia Department of Natural Resources), Ms. Ellie Covington, Ms. Marcy Mitchell, Ms. Mary Sweeney-Reeves, Mr. James Nichols, and Dr. Mare Timmons (University of Georgia Marine Extension Service), Dr. Dale Bishop (University of Georgia School of Marine Programs), the Jekyll and Tybee Island 4-H Centers, the Tybee Island Marine Science Center, and members of the public.

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ALAN J. POWER, * (1) RANDAL L. WALKER, (1) KAREN PAYNE (2) AND DORSET HURLEY (3)

* Corresponding author. E-mail: [e-mail]

(1) Shellfish Research Laboratory, University of Georgia Marine Extension Service, 20 Ocean Science Circle, Savannah, Georgia 31411; (2) School of Marine Programs, University of Georgia Marine Extension Service, 220 Marine Sciences Building, Athens, Georgia 30602; (3) Sapelo Island National Estuarine Research Reserve, GA Department of Natural Resources, P.O. Box 15, Sapelo Island, Georgia 31327