Mytella charruana is a mussel with a shell mostly dark
brown to black exhibiting a wavy dark pattern on a lighter
background. A growth pattern of concentric semicircular rings is
evident on the shell surface. The interior of the shell is
iridescent purple and the exterior of the shell lacks radial ribs (TNC 2006).
Potentially Misidentified Species
M. charruana can potentially be mistaken for the more common IRL
native mussel species Geukensia demissa (ribbed mussel) and
Brachedontes exustis (scorched mussel). Both of these species
exhibit distinct radial ribs on their shell surfaces that the
charru mussel lacks. (TNC 2006).
HABITAT AND DISTRIBUTION
The charru mussel is a tropical bivalve whose native distribution
extends from South and Central America northward through Mexico.
Within the United States populations of this species have
reportedly become established in Florida and Georgia (TNC/UCF
A population of charru mussels now appears to be established
within the Mosquito Lagoon portion of the Indian River Lagoon
system (TNC 2006)
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
Like other mussel species, M. charruana attaches to a variety of
natural submerged and intertidal hard substrates such as oyster
shells as well as man-made structures like water intake pipes,
wood pilings, and driftwood.
Most individuals are less than 2 cm in length, but they can grow
to twice that size.
As of April 2007, charru mussels were still uncommon where they
occurred in the upper Indian River Lagoon region.
Focused efforts to locate and collect specimens had yielded only
about 600 animals since the species was rediscovered in the region
(Linda Walters, personal communication).
Reproduction is sexual with males and females occurring as separate individuals. Fertilization is external, taking place in the water column.
A free-living planktonic larval stage precedes recruitment of
settlement-age animals onto appropriate hard benthic substrata.
M. charruana is a tropical species whose northern distribution
limits are likely dictated by cold intolerance. The die-off of
the Jacksonville power plant founder population in the winter of
1987 is attributed to thermal stress (Boudreaux and Walters
2006). Similarly, the failure of monthly surveys to locate
charru mussels between February 2005 and August 2005 in the
Mosquito Lagoon (Boudreaux and Walters 2006) is likely the result
of significant seasonal die-back associated with colder winter
M. charruana is listed as a euryhaline species by McCann et al. (1996).
Like other mussels, M. charruana is a cilliary-mucus suspension
feeder. Firmly attached to a substrate, immobile mussels use their
incurrent siphon to draw in food-laden water that is then carried
by ciliary action to the branchial chamber. Water is discharged
through the excurrent siphon while food particles of the
appropriate size range are funneled by the labial palps into the
mouth for ingestion and digestion.
The likely nature of the association between charru mussels and co-occurring fouling organisms will be as spatial and/or food resource competitors.
Lee (1987) notes that the first report of M. charruana on the east
coast of Florida occurred in 1986 when large numbers were found in the
seawater intake pipes of a power plant near Jacksonville's
Blount Island on the St. Johns River. Venezuelan tankers that
frequent a nearby port have been indicated as the putative source
of this founder population (McCann et al. 1996), brought in either
as hull fouling organisms or as larvae in ballast water. Despite early
concerns about potential impacts, this exotic mussel failed to
become established; the animals that were present in 1986
experienced a die-off in the winter of 1987 (Boudreaux and Walters
2006, TNC 2006). Carlton (1992) noted that no subsequent
observations of this species in the area were made.
The charru mussel was again found in Florida in the Summer of 2004,
this time within the Mosquito Lagoon basin of the IRL system
(Boudreaux and Walters 2006, TNC/UCF 2006). Since this initial
sighting report, many more charru mussels have been found and their
numbers appear to be increasing. As of Spring 2006, nearly 600
individuals have been collected from the Mosquito Lagoon portion of
the IRL system (TNC/UCF 2006).
Potential to Compete With Natives
The potential exists for a growing population of charru mussels to
compete with native mussels, oysters and other organisms for food
as well as for colonizable substrate to use as living space (TNC
Boudreaux and Walters (2006) suggest that in areas where
populations become established, this species has the potential to
reproduce rapidly and outcompete native mussel populations as well
as populations of oysters already in decline.
Possible Economic Consequences of Invasion
Among the species the charru musel may compete with is the
commercially important native oyster Crassostrea virginica. As
with other hard fouling organisms, negative economic
impacts may also occur if large numbers of charru mussels settle
into and clog municipal seawater intake pipes at power plants and
other coastal utilities (Carlton and Rosenfield 1994).
Boudreaux and Walters (2006) suggest that a rapid response to
this invader in Florida could prevent the sorts of ecological and
economic impacts caused when other non-native mussels like the
zebra mussel (Dreissena polymorpha) and green mussel (Perna
viridis) have become established in new locations.
Boudreaux M.L., and L.J. Walters. 2006. Mytella charuanna along the
Atlantic coast of Florida: A successful invasion? Poster. Society for
Integrative and Comparative Biology 2006 Meeting. Orlando FL - January 4-8,
Carlton J.T. 1992. Introduced marine and estuarine mollusks of North
America: An end-of-20th-century perspective. Journal of Shellfish Research
Carlton J.T. and A. Rosenfield (eds.) 1994. Molluscan introductions and
transfers: risk considerations and implications. Maryland Sea Grant,
College Park, MD. 73 pp.
Lee H.G. 1987. Immigrant mussel settles in Northside generator. The
Shell-O-Gram (Jacksonville Shell Club, Jacksonville, FL) 28:7-9.
McCann J.A., Arkin L.N., and J.D. Williams. 1996. Nonindigenous Aquatic and
Selected Terrestrial Species of Florida: Status, Pathway and Time of
Introduction, Present Distribution, and Significant Ecological and Economic
Effects. Published on the Internet by the University of Florida, Center for
The Nature Conservancy Florida Chapter. 2006. Invasive Mussel Alert: Mytella
charruana found in Florida waters.
The Nature Conservancy and University of Central Florida Invasive Species Alert:
Recurrence of Mytella charruana in Florida waters. September, 2006.