U. S. Naval Station Invaded

By Bill Frank

   Despite unprecedented security over the past two years that has included troops armed with automatic weapons, the initiation of armed patrols even on the beach, searches, immobile barriers, and intense identification verification, Mayport Naval Station was recently invaded by a foreign foe – a molluscan foe that is.

     The invasive Asian Green Mussel [Perna viridis (Linnaeus, 1758)] has been confirmed living in Duval County waters for the first time at Mayport Naval Station. During a shelling trip to the naval station beach on July 28, 2003, your editor found the species living in numbers on the granite boulders of the south St. Johns River Jetty.  The largest specimen collected measured just over two inches in length (55 mm.). However, it should be noted that under optimal conditions (such as in their native range in the Indian Ocean and Southwest Pacific) Green Mussels might grow to a length of nearly 6 inches (about 150 mm.) The specimens at Mayport were duly photographed, and several dozen were collected as voucher specimens.

Asian Green Mussel [Perna viridis (Linnaeus, 1758)]

Asian Green Mussels from  Mayport Naval Station

   My curiosity aroused, I conducted further trips to the north St. Johns River Jetty in Huguenot Memorial Park (July 31st) and the south St. Mary's River Jetty at Ft. Clinch in Fernandina Beach (August 11th). In both locales a healthy population of Green Mussels was found growing both on the ocean and river sides of the jetty – in each instance in concert with our native species Brachidontes exustus (Linnaeus, 1758) [Scorched Mussel].

    After having so much success in finding this alien invader on local structure, I took additional trips to the rip-rap jetty in the Ft. George River (August 12th), the "Black Rock" structure at Big Talbot Island (August 25th), and various types of structure near Matanzas Inlet in southern St. Johns County (August 27th). No Green Mussels were found at any of these locations nor were any Scorched Mussels suggesting that the two species share a common habitat preference – at least in Northeast Florida. 

    This exotic species was first discovered in Florida during July of 1999, when divers from the Tampa Electric Company (TECO) were performing routine maintenance on the cooling water intake pipes at one of its power generating stations in Tampa Bay and found that the screens on the pipes were partially clogged with the mollusks. It appears likely that the species was transported to Tampa Bay in the ballast water of commercial shipping with the Tampa port being the 11th busiest in the country.

    Since the initial discovery, prevailing currents have spread the mussels southward along the southwest Florida coast to Naples Beach in the Gulf of Mexico (November, 2001). According to the U. S. Geological Survey, this is the first known infestation by this species in the United States although previously the species has been recorded from the waters off Trinidad (1990) and nearby Venezuela (1993) in the Western Hemisphere.

    The presence of the mussels on local jettys is not entirely unexpected. Early this year Dr. W. Henry McCullagh found a moderate number of living adult Perna viridis stranded along with benthic green algae, to which the mytilids were attached at Crescent Beach, St. Johns Co., Florida.  Subsequently during the third week or March, an additional stranding of live specimens was discovered by Ms. Betty DeMarco (Harry Lee’s lab technician) on Atlantic Beach in Duval Co. - some 50 miles north of the initial discovery by Dr. McCullagh. Then on May 12th your editor discovered a recently dead specimen on the beach at Mayport – a location only about 50 meters distant from where the living specimens were ultimately found during July.

    There is no conclusive evidence that the presence of the mussels in northeast Florida is directly related to the initial population in Tampa Bay – especially since the Port Of Jacksonville too gets its share of international shipping traffic. However, it has been theorized that shipping traffic between the west coast of Florida and northeast Florida is in fact responsible for this proliferation.

    The presence of Perna viridis in northeast Florida is only the second known instance of an exotic marine species being found in our waters. The only other instance occurred during the summer of 1986 when Mytella charruana (d'Orbigny, 1846), a species normally found in tropical west America, which we might call the "Charrua Mussel," was found to be clogging the water intake pipes of the Jacksonville Electric Authority’s Northside Generating Station. It too was believed to a result of foreign shipping. Fortunately for us Duval County taxpayers, the species apparently didn’t survive the cold winter temperatures during 1986-1987 and was not observed again.

    Whether the Asian Green Mussel will survive the northeast Florida winter remains to be seen. However, the wife is researching stir-fry recipes for mussels just in case!