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INVERTEBRATE
INVADERS
Established and Potential Exotics
Gulf of Mexico Region
Funded by the Coastal Impact Assistance Program through the
Mississippi Department of Environmental Quality
For additional copies: [email protected] or 228.818.8890
Writers: Harriet Perry and David Yeager
Editors: Tom Van Devender, Lisa Hendon
and Linda Skupien
Cover photo: David Knott, Southeastern Regional Taxonomic
Center, South Carolina Marine Resources Research Institute
PARTNER INSTITUTIONS AND AGENCIES
The University of Southern Mississippi
Center for Fisheries Research and Development
Mobile Bay National Estuary Program
NOAA National Marine Fisheries Service
Mississippi Department of Environmental Quality
Coastal Impact Assistance Program
Mississippi Department of Marine Resources
Mississippi-Alabama Sea Grant Consortium
703 East Beach Drive • Ocean Springs, MS 39564
228.872.4200 • www.usm.edu/gcrl
AA/EOE/ADAI 12/06
INVERTEBRATE
INVADERS
Established and Potential Exotics
Gulf of Mexico Region
Zebra mussels
Photo:
U. S. Geological Survey Archives
ZEBRA MUSSELS are thought to
have invaded 1/3 of all freshwater aquatic
environments in the United States. These
invasive mussels can produce over one million
eggs in a spawning season, so they multiply
rapidly. Millions of dollars are spent annually to
repair damages and to control their populations.
Initially limited to freshwater, there is recent
evidence that they are becoming salt tolerant
and can invade upper estuarine waters.
Invertebrates
Seven of the top ten ports, by tonnage, are located in
the Gulf of Mexico, increasing the risk of introduction
of invasive invertebrates by ship fouling or ballast water.
Species of jellyfish, sea anemones, starfish, crabs, polychaetes
and mollusks have been introduced through vessel traffic.
Invasive-species expert J.T. Carlton estimates that 7,000 different species of marine life are transported daily around the
world’s oceans and seas. Successful invaders have a short
life span, rapid growth, rapid sexual maturity, high
reproductive capacity, can colonize a variety of
habitat types and are physiologically tolerant.
The zebra mussel is one example of an
extremely successful invader.
Invertebrates
filter-feeding fish must compete with these jellies for the
same food source. Status: First reported in Gulf of Mexico in 1993 when a single specimen was collected from
waters 70 km south of Louisiana by the National Marine
Fisheries Service vessel R/V Oregon II. Populations are
established east and west of the Mississippi River.
Drymonema dalmatinum - No official common name
Spotted jelly
Photo: Alvaro Migotto
Spotted jelly, Phyllorhiza punctata
Vulnerable Locations: Marine waters, Gulf of
Mexico. Native Range: Native to the tropical western
Pacific Ocean, wide distribution in Australian coastal
and lagoonal waters. Suspected Vector: Most likely
arrived via ship ballast or hull fouling to the Caribbean
Sea through the Panama Canal. A small population of
P. punctata has existed in Terrebonne Bay, La., for several
years; vector unknown. Origin of medusae, adult spotted
jellies, that invaded northern Gulf of Mexico in summer
of 2000 is attributed to circulation processes associated
with the Gulf of Mexico Loop Current and spin-off
eddies, although transport from the Terrebonne Bay
population must be considered. Description: Basketballsized jellyfish with a white-spotted, opaque bell; mild
to no sting. Negative Impacts: Direct economic impact
on the trawl fisheries. Jellyfish clog nets, damage boat
intakes and fishing gear, and can cause closure of productive areas to fishing activities. Indirect effects include
predation on the eggs of important forage species and
consumption of bivalve larvae. Fish larvae and mature
Vulnerable Locations: Marine waters, northern Gulf
of Mexico. Native Range: Native to the Pacific and Atlantic oceans. Reported from the Adriatic Sea, Mediterranean Sea, Caribbean Sea and the Atlantic Ocean off
Gibraltar. Also recorded from Argentina, Brazil and Colombia. Suspected Vector: Natural transport via circulation processes associated with the Loop Current and its
spin-off eddies or through vessel fouling. Description:
The umbrella is flatly
Drymonema dalmatinum
rounded and shield
shaped. Color ranges
from reddish-white to
yellow-white; specimens
in the northern Gulf of
Mexico are pink. More
Photo: Jason Steckler
than 150 long stinging
tentacles; dense ribbon-like gonadal and mouth extensions that are shorter than the tentacles also extend
beneath the bell. Can exceed 700 mm in bell diameter
with tentacles in excess of 30 m long. Resembles the
lion’s mane jellyfish, Cyanea capillata. Negative Impacts:
More than 25 million jellyfish were estimated in a
bloom of D. dalmatinum in 1999 off Puerto Rico. If such
a bloom occurred in the northern gulf, there would be a
direct economic impact on the shrimp fishery including
clogged nets, damage to boat intakes and fishing gear,
and closure of areas to fishing activities. Status: Unknown, reported from Alabama and Mississippi.
CRUSTACEANS AND MOLLUSKS ACCOUNT FOR MOST OF THE
INVERTEBRATE INTRODUCTIONS IN THE GULF OF MEXICO.
Brown mussel, Perna perna
Green mussel, Perna viridis
Brown mussel
Vulnerable Locations: High
salinity (27-33 ppt) estuaries
and marine waters, Gulf of
Mexico. Native Range: Green
mussels (Perna viridis) are naturally distributed throughout
the Indo-Pacific. Brown musPhoto: Amy Benson, USGS
sels (Perna perna) are native to
tropical and subtropical regions of the African coastline.
Suspected Vector: Vector for both mussel species is
thought to be international shipping via ballast water
release or hull fouling. Description: The genus can be
distinguished from other North American members of
the family by the absence of one of two muscles used
to close the shell. The two Perna species are difficult to
separate using external characteristics; shells are similar
and can be highly variable. Reliable separation of the
two species requires examination of internal anatomy.
The brown mussel has enlarged sensory papillae along
mantle margins. Color of P. perna varies from reddish
to dark brown to black with marginal areas of yellow
and green. Perna viridis adults are usually various shades
of brown in central portion of shell; juveniles typically
green to blue-green. Occasionally both adults and juveniles are brown, making them difficult to separate from
P. perna. Negative Impacts: Both mussels are biofoulers
that can alter community structure and create fouling
problems in industries that use seawater as coolant.
Brown mussels first appeared in Texas in 1990 on the
Port Aransas jetty and within four years had colonized
1,300 km from Matagorda Bay to Vera Cruz, Mexico.
They are also found on offshore petroleum platforms
in the Gulf of Mexico. Presence of Texas populations
varies; water temperatures at or above 30º C limit
Green
muss
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Photo
Taxon : Southeast
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population growth. Green mussels were first
discovered in 1999 in Tampa Bay, Fla. Current range
extends from Venice, La., to St. Petersburg, Fla. The
green mussel’s greater thermal tolerance will allow it to
disperse throughout the Gulf of Mexico. Status: Green
mussels are currently established only in Florida. The
brown mussel is currently confined to Texas waters with
populations limited by summer temperatures.
Spiny hands swimming crab, Charybdis hellerii
Vulnerable Locations: Lower estuarine, marine
waters of the Gulf of Mexico. Native Range: Japan,
Philippines, New Caledonia, Australia, Hawaii and
throughout the Indian Ocean, including the Red
Sea. Suspected Vector: Both ballast water and drift of
juveniles from
Cuba have
been suggested
as a means of
introduction to
American waters. Description: Fifth
legs flattened;
Spiny hands swimmi
side frontal
ng crab
Photo: David Knott,
So
uth
ea
stern Regional
margin has
Taxonomic Center,
South Carolina Marin
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Resources Research
six sharp,
Institute
Successful Invader
black-tipped teeth; frontal region has six prominent
teeth. Overall color is dark green with dark purple on
walking and swimming legs. Fingers of chelipeds (claws)
are dark purple. Negative Impacts: Unknown. Status:
Reported in Gulf of Mexico from Anna Maria Island,
Fla., (mouth of Tampa Bay). Species has the potential to
successfully colonize marine ecosystems of South Florida
and the Gulf of Mexico.
ing
Bocourt swimm
crab
above and whitish below with a tinge of blue.
Negative Impacts: May compete with the blue crab,
Callinectes sapidus, for food and refuge. Although C.
bocourti is commercially exploited in Central and South
America, it is a smaller crab and less desirable for processing in the United States. Competition among
C. bocourti, C. sapidus and C. similis in northern gulf
estuaries may limit populations of one or more of these
species. Status: Reported from Mississippi and Alabama; extraterritorial occurrences in the northern
Gulf of Mexico are sporadic and suggest that the
species is not currently reproducing.
Green crab, Carcinus maenas
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Bocourt swimming crab, Callinectes bocourti
Vulnerable Locations: Estuarine waters, Gulf of
Mexico. Native Range: Jamaica, Belize to Brazil; center of abundance in coastal waters of northern South
America. Suspected Vector: Ballast water and drift of
juveniles and adults from Caribbean. Description: Flattened fifth legs; frontal margin has six triangular frontal
teeth with tips reaching a nearly common level; color
highly variable, but generally olive green to brown with
reddish markings; chelipeds red to dark reddish brown
Vulnerable Locations: Estuarine and shallow coastal
waters of the Gulf of Mexico. Native Range: Atlantic
coasts of Europe and northern Africa from Norway and
the British Isles south to Mauritania. Suspected Vectors: Dispersed as adults by a variety of anthropogenic
and natural mechanisms including: 1) ballast, 2) ships’
hulls, 3) packing materials (seaweeds) used to ship live
marine organisms, 4) bivalves moved for aquaculture,
5) rafting, 6) migration on surface currents and 7) movement of submerged aquatic vegetation for coastal zone
management initiatives. Once established in an area,
green crabs can spread by planktonic transport of larvae.
Description: Surface of carapace finely granular, about
¾ as long as wide with five yellow-tipped side frontal
teeth; frontal area between eyes has three rounded teeth.
Carapace color is variable, usually mottled, dark brown
to dark green, with granules for the most part yellow.
Females have orange background color and whitish
granules. Walking legs are green, speckled with black;
fourth pair of legs is shorter than the first; last pair is
somewhat flattened and with hairs (setae). Negative
Impacts: Implicated in the destruction of the soft-shell
THE FRESHWATER ZEBRA MUSSEL IS BECOMING SALT TOLERANT.
clam (Mya arenaria) fisheries in New England and the
reduction of populations of other commercially important
bivalves including the scallop, Argopecten irradians, and
the northern quahog, Mercenaria mercenaria. Ability to
outcompete native species for food resources, a high
reproductive capacity and wide environmental tolerances
give green crabs the capacity to fundamentally alter
community structure. They are voracious predators
on other crab species. Status: Dispersed globally, U.S.
reports include Atlantic and Pacific coast estuaries.
It is one of the most successful invaders in coastal
ecosystems. Temperature may limit southward
Green crab
expansion of northeast populations.
Photo:
Kathlyn Sm
it
Zebra mussel, Dreissena polymorpha
Vulnerable Locations: Fresh and estuarine waters of the Gulf of Mexico.
Native Range: Black, Caspian and Azov seas. Suspected Vector: Original
U.S. introduction into the Great Lakes through ballast water; further
dispersal through larval transport and hull fouling. Description:
Small bivalve, usually striped (hence the name zebra). Some specimens dark or light colored with no stripes. Can grow to two inches
long, most under one inch; generally found in clusters. Only freshwater mollusc able to attach to underwater objects and surfaces.
Negative Impacts: Zebra mussels pose a multibillion-dollar threat
to U.S. industrial, agricultural and municipal water supplies
and are a costly nuisance for freshwater shipping, boating and
fishing. Large infestations disrupt aquatic food chains, causing
shifts in native species populations. Status: Established in
the Great Lakes and most of the large navigable rivers in the
eastern U.S. Found in the Gulf of Mexico in coastal Louisiana with a single occurrence in Mississippi Sound.
Photo: U. S. Geological Survey Archives
h
Did You Know?
Whiteleg shrimp, Litopenaeus vannamei
Vulnerable Locations: Estuarine and shallow coastal
waters of the Gulf of Mexico. Native Range: Eastern
Pacific from Sonora, Mexico, to Tumbes in northern
Peru. Suspected
Vector: Aquaculture release.
Description:
The rostrum, the
spinelike projection of the front
Whiteleg shrimp
of the carapace, is
Photo: Robert Adami, Texas Parks &
Wildlife Department
moderately long
and armed with upper and lower teeth; lower teeth number two to four, occasionally five to eight. Closely resembles the common gulf white shrimp, but is a lighter color,
especially the legs, and is sometimes called the “whitelegged” shrimp. Negative Impacts: Exotic shrimp viruses
associated with L. vannamei may pose a risk to Gulf of
Mexico and southeastern U.S. Atlantic wild penaeid
shrimp fisheries. Other crustacean fisheries may also be
at risk from introduced viruses. Status: Aquaculture of
the Pacific white shrimp in the United States began in
Texas and in Florida. Although collected periodically in
commercial shrimp trawls off Texas, there is currently no
evidence that populations have established themselves in
the wild in the northern Gulf of Mexico.
Giant river prawn, Macrobrachium rosenbergii
Vulnerable Locations: Wide range of freshwater and
estuarine ecosystems including swamps, lakes, ponds,
ditches, bays and bayous. Requires brackish water to complete early life stages. Native Range: South and Southeast
Asia, Oceania and the western Pacific. Suspected Vector:
Aquaculture release. In some areas this species is sold in
the aquarium trade. Description: Large shrimp; rostrum
Giant river prawn
Photo: Southeastern Regional Taxonomic Center, South Carolina
Marine Resources Research Institute
long with 11-14 upper teeth and eight to 10 lower
teeth. First and second legs have pincers; pincers in
adult males are blue or orange. Orange spots may be
visible on tail. Negative Impacts: Unknown at present; winter low temperatures in the northern Gulf
of Mexico may prevent establishment of populations
in the wild. Status: Reported from a single bayou in
Mississippi.
FLORIDA HAS THE HIGHEST NUMBER OF INTRODUCED INVERTEBRATES.
MISSISSIPPI HAS THE LOWEST.
Channeled apple snail, Pomacea canaliculata
Vulnerable Locations: Wide range of freshwater ecosystems including swamps, lakes, ponds and
ditches. Native Range: South America. Suspected Vector: Aquarium and aquaculture releases. Description:
Shell is round and, in older snails heavy. Deep sutures
(grooves) separate five to six whorls. Shell opening is
large and round to oval. All apple snails have a tubelike
siphon. There are several species of introduced apple
snails, and an expert may be needed to identify specimens from the wild. Channeled apple snails lay up to
1,000 small pink eggs on hard surfaces such as docks,
plant stems, rocks and seawalls. Negative Impacts: The
channeled apple snail is an agricultural pest that is a
destructive plant eater. This species will eat all types
of aquatic vegetation and has few natural enemies.
Mississippi has banned importation of all members
of the apple snail family. Louisiana has identified the
channeled apple snail as a threat to rice production.
Channeled apple snails are salinity tolerant and can
withstand temperatures found in the northern Gulf
of Mexico. Status: Established in Florida and Texas;
reported from Alabama.
Channeled apple snail
Photo: Florida Department of Environmental Protection
Rapa whelk
Photo:
Juliana Harding
Rapa whelk,
Rapana venosa
Vulnerable
Locations: Estuarine
waters of the Gulf
of Mexico. Native
Range: Marine
and estuarine waters
of the western Pacific, the
Sea of Japan, Yellow and
East China seas, the Bohai Sea.
Suspected Vector: Release of larvae from ballast
water or transport of egg masses from one area
to another. Description: Shell heavy, round and
with a short spire. Body whorl is large and inflated. Shell opening is large, deep orange and ringed
with small teeth. Background color of shell varies
from gray to reddish-brown; most specimens have
black veins that run throughout the shell. Shell
length of specimens from Virginia is four to six
inches. Negative Impacts: Rapa whelks are predatory snails that feed on a variety of bivalves. In the
Chesapeake Bay their preferred prey is the hard
clam, but they will attack other mollusks. Their
occurrence in estuaries in the Gulf of Mexico
may impact oyster populations. Status: Currently
established in Chesapeake Bay in U.S. waters.