Establishment of the green mussel, Perna viridis (Linnaeus 1758), (Mollusca: Mytilidae) on the west coast of Florida

AMY J. BENSON¹, DAN C. MARELLI², MARC E. FRISCHER³, JEAN M. DANFORTH³, and JAMES D. WILLIAMS<sup>1

1</sup>U.S. Geological Survey, Florida Integrated Science Center
7920 NW 71^st Street, Gainesville, FL 32653

²Academic Diving Program, Florida State University
036 Montgomery, Tallahassee, FL 32306-2310

³Skidaway Institute of Oceanography
10 Ocean Science Circle, Savannah, GA 31411

Presented at the Eleventh International Conference on Aquatic Invasive Species
February 25 to March 1, 2002, Hilton Alexandria Mark Center, Alexandria, Virginia

ABSTRACT

In 1999, the green mussel, Perna viridis, was first observed in Tampa Bay, Florida.  This was the first reported occurrence of this Indo-Pacific marine bivalve in North America.  The mussels found in Tampa Bay were confirmed to be P. viridis based on both morphological and genetic characteristics. Since the initial discovery, surveys in Tampa Bay and on the west coast of Florida have documented the growth, recruitment, and range expansion of P. viridis.  From November 1999 to July 2000, the mean shell length of a Tampa Bay population increased from 49.0 mm to 94.1 mm, an increase of 97%. Populations of P. viridis are successfully reproducing in Tampa Bay. Recruitment was observed on sampling plates in May and continued through July 2000. The full extent of mussel colonization is not clear, but mussels were found outside Tampa Bay in St. Petersburg, Florida south to Venice. Based on these studies it is evident that P. viridis has successfully invaded Tampa Bay and the west coast of Florida.  The long-term impact of P. viridis on native communities off the west coast of Florida cannot be predicted at this time.

INTRODUCTION

• Green mussels (Perna viridis) are native to the coastal and tropical marine waters of the Indo-Pacific region.
• In the early to mid-1990s, populations were discovered along the coasts of Venezuela, Trinidad, and Jamaica (Figure 1).
• The species was first discovered in the U.S. in 1999 at a power plant in the Tampa, Florida area.
• The green mussel is a known biofouler in power generating plants and on navigation aids in Asia.

Figure 1. Shaded circles represent Perna viridis population along coastlines.

RESULTS

• Phylogenetic comparisons between known Perna species and species collected from Tampa Bay indicated that the Tampa Bay specimens were most closely related to Perna viridis acquired from Trinidad (Figure 2).
• Sequence similarity between Perna species ranged from 78.2% to 99.5% with the highest similarity between the Tampa Bay specimens and P. viridis from Trinidad (Table 1).
• Our results confirm the identity of the Perna species in Tampa Bay as Perna viridis.
   

Figure 2. Inferred taxonomic relationship between Perna viridis in Tampa Bay and other Perna species. The phylogenetic tree was derived from nucleotide sequence comparison of a 713 bp fragment of the mitochondrial cytochrome c oxidase subunit I gene (mtCOI). The tree was artificially rooted with the mtCOI sequence from the ribbed mussel (Geukensia demissa) retrieved from GenBank (U56844). The scale bar indicates 0.1 fixed nucleotide substitutions per site. Numbers refer to bootstrap values (from 100) for each node.

Table 1. Percent sequence similarity (above diagonal) and the number of nucleotide differences between the Tampa Bay Perna species, other Perna type species, and the ribbed mussel Geukensia demissa mitochondrial cytochrome c oxidase subunit I gene.

• The population of Perna viridis in North America has been documented throughout Tampa Bay, in Old Tampa Bay and in Hillsborough Bay (Figure 3).
• Populations of Perna viridis have also been documented outside the Bay in the Gulf of Mexico from Charlotte Harbor north to Treasure Island in Florida.

Figure 3. Locations of P. viridis collected or observed, August 1999 to August 2000.

Figure 4. Mean shell length of Perna viridis individuals collected from Old Tampa Bay, 1999-2000. Data include means, plus and minus one standard error.

• Mean shell length of a mussels was 49.0 mm in November 1999 (Figure 4).
• Subsequent collections from this selected population demonstrated rapid growth as the mean length of mussels increased nearly 92% to 94.1 mm in July 2000.
• Recruitment in 2000 was first detected in May and continued through the mid-July sampling period (Figure 5).

Figure 5. Mean recruitment of Perna viridis to collector plates in Old Tampa Bay, Florida, 2000.  Data include number of recruits per collector per day, plus and minus one standard error.

DISCUSSION

• Perna viridis is the most recent nonindigenous mollusk to enter Florida, probably as larvae entrained in ship ballast water.
• Data and observations demonstrate that Perna viridis is able to grow, over-winter, and successfully reproduce in Tampa Bay.
• To date, green mussels are colonizing mostly manmade habitats such as bridges, docks, channel markers, and buoys.
• This species is thriving where winter water temperatures have reach as low as 12^oC. Water temperatures in their native range are usually 26-32^oC.
• We expect Perna viridis to continue to spread south along the Gulf Coast of Florida, possibly to include the Florida Keys.  Based on temperature tolerances, it is not expected to survive well north of Florida in the Atlantic Ocean (Figure 6).

Figure 6. Predicted range of Perna viridis in the Gulf of Mexico and western Atlantic waters based on near-surface water temperatures. The lower limit of the sub-optimal range based on LC50 of 10oC with two weeks exposure.

• Concern is for the effects Perna viridis may have on the diversity of native communities in Florida, especially if they begin to inhabit mangroves.
• They may also impact the phytoplankton assemblage and increase water clarity through its active suspension feeding much as the zebra mussels have done in the Great Lakes.
• It is expected that many of the nutrients will be cycled into the benthic community as feces or pseudofeces, possibly causing a shift in benthic community dynamics.
• Impacts are expected to continue to include the fouling of unprotected boats and in-water structures such as bridges, seawalls, docks, aids to navigation, and interference with cooling water intakes in electric power generating stations (Figure 7).

Figure 7. Green mussels on bridge piling in Tampa Bay, November 1999.

For full paper, see:

Benson, A. J., D. C. Marelli, M. E. Frischer, J. M. Danforth, and J. D. Williams. 2001. Establishment of the green mussel, Perna viridis (Linnaeus 1758), (Mollusca: Mytilidae) on the west coast of Florida. J. Shellfish Research 20(1): 21-29.

ACKNOWLEDGEMENTS

We thank Daniel O'Connell of Newcastle University, Newcastle, England and Gary Hill, Robert Lewis, Marc Blouin, and Don Hickey of USGS for collecting samples of green mussels in Florida; Suzanne Dilworth of the Center for Coastal Studies, Corpus Christi, Texas for supplying Perna perna samples; Dr. Peter Smith of the National Institute of Water & Atmospheric Research Ltd (NIWA) Wellington, New Zealand for Perna canaliculus samples; and Paul Gabbadon and Addison Titus of the Institute of Marine Affairs, Trinidad for Perna viridis samples. We also thank Jon Fajans of the University of Florida for identifying the commensal invertebrates.