National Park Service
Marine Invasive Species
Monitoring Program
5 spines
U.S. Department of the Interior
Glacier Bay National Park and
Preserve
3 Bumps
What is an invasive
species?
Why are they a problem?
As their name suggests, this species is native to
European waters. Over time it has been
introduced to multiple new habitats, including
the Atlantic and Pacific coasts of North America.
Although green crabs have been detected only
as far north as Vancouver Island in British
Columbia thus far, models indicate that the
species will be able to survive in coastal Alaskan
waters. European green crabs are aggressive
predators, eating clams, mussels, marine
worms, and crustaceans that are important
foods for native marine animals. If green crabs
invade Alaskan waters, they could be a serious
threat to native crabs and fisheries.
What should you do if you find one?
If you find a green crab, don’t throw it back in the water! Keep it in a container
with information about where and when you found it. Then put it into a freezer
or preserve it with alcohol. Contact 1-877-INVASIV for more information.
The green crab’s distinguishing features are 5 spines, or teeth, on each side of its fan
shaped shell and 3 rounded lobes between its eyes. The two backmost legs are
flattened. The abdomen (underside) color ranges between green, orange, and red, and
the dorsal (top) side of its shell is a mottled dark green with yellow patches.
Invasive species come from other
parts of the world and can be
harmful to the environment,
natural resources, humans, and
the economy. Invasive species
are transferred between regions
by people intentionally or
accidentally. For marine invasive
species, common forms of transfer
include ship’s ballast water, hull
fouling, and aquaculture.
"Invasive species have large
effects on native biodiversity,
cause hundreds of billions of
dollars in economic damages, and
complicate the management of
natural ecosystems around the
world." (Strayer, 2006)
Invasive tunicates documented in Pacific
waters: Botrylloides violaceus, Botryllus schlosseri,
Styela clava, Didemnum sp., and Ciona intestinalis.
Picture by John Southern
What about
Glacier Bay?
So far, no invasive green crabs
or tunicates have been detected
in Glacier Bay through our
monitoring efforts. For green
crabs, we set out traps once a
month during the summer in the
lower intertidal area of Bartlett
Cove. For tunicates, we
suspend settlement plates from
our three docks quarterly to
detect whether any tunicates
colonize the surfaces. Atlantic
Salmon are the only marine
invasive species detected within
park waters to date. We will
continue collaborating with
partner agencies to detect
marine invasive species.
What is a tunicate?
Tunicates, or sea squirts, are marine invertebrates (lacking
a back bone) that grow attached to surfaces. They might
be confused with a sponge, but they are more resistant to
touch. They can range in color, including orange, red,
yellow, black, translucent, cream, and blue. They can be
solitary (completely independent and generally fairly
large) or colonial (congregations of zooids that aggregate
by budding, like corals). Tunicates filter feed by siphoning
plankton from the water. Tunicates belong to the Phylum
Urochordata, which are more closely related to
vertebrates (including humans) than any other
invertebrate group. There are a number of native species
in Alaskan waters; however, several non-native species
have been detected.
Botrylloides violaceous (orange morph) – an
invasive colonial tunicate. SERC
Why are they a problem?
Tunicates are a fouling organism that can smother other marine
organisms and coat surfaces, such as boats and docks. They filter out the
water’s phytoplankton, thus depriving other species of their nutrition.
Since larval tunicates can be transported in ballast water and adults can
foul boat hulls, tunicates can easily disperse to new waters, where they
can readily establish in the absence of natural predators. In the coastal
Pacific waters of North America, the Smithsonian Environmental
Research Center (SERC) coordinates a monitoring program ranging from
Tijuana Slough, CA to Port Valdez, AK.
Ciona intestinalis – an invasive
solitary tunicate. SERC
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For more information: Whitney Rapp, Invasive Species
Coordinator, Glacier Bay National Park and Preserve,
Gustavus, AK 99826 – whitney_rapp@nps.gov, 907-697-2603