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THEOSPREYNature Journal of Newfoundland andLabrador
Winter 2013 Volume 44 Issue 1
NatureNewfoundland and LabradorISSN 0710-4847
8 The Osprey
The Marine Aquatic Invasion Continues
By Kyle MathesonFisheries and Oceans Canada
Aquatic invasive species (or AIS, commonly alsoreferred to as nuisance species, aliens,unwanted visitors, or non-indigenous) are species
that are not native to coastal Newfoundland (NL)
waters. The transport of these species from foreign
locations to our shores is often attributed to human
traffic including, but not limited to exchange of
ballast water from ships, attachment to boat hulls and
fishing/aquaculture equipment, movement of docks
and barges, and transportation of live seafood and
bait. The prospect of climate change and warming
waters may also allow a species to expand its range
into new territory where conditions may have limited
previous spread (such as colder waters in NL). These
species generally share numerous traits that make
them successful invaders. They often dominate
native species in competition for food or living space
due to aggressiveness, fast growth, or rapid
reproduction and population growth. They tolerate a
wide range of environmental conditions, and easily
adapt to different food sources. Once they become
established in a new area they reproduce and spread,
threatening local biodiversity, functions of coastal
marine ecosystems, and human economic activities.
Aquatic invasive species have been an increasing
concern for coastal NL ecosystems during the last 10
years. Collaboration in research and monitoring
programs between scientists at Fisheries and Oceans
(DFO), Memorial University (MUN), and other non-
government stakeholders has provided information
on the abundance and spread as well as the ecology
of several high interest species. In NL to date, the
European green crab, three tunicate (or sea squirts)
species (Violet, Golden Star, and Vase), the Lacy
Crust Bryozoan, and a large green algae know as
Oyster Thief have been documented as invasive
species. Vase tunicate and Oyster Thief were
discovered in NL for the first time in 2012. While
these species are a relatively new ecological threat to
NL, the fishery and aquaculture industries in the
northeastern United States and Maritime Provinces
have battled against and suffered the ecological and
economic consequences of such invasions. For
example, the voracious appetite of green crab led to
substantial declines in the economically important
soft-shell clam in New England, while the clubbed
and vase tunicates have been the most problematic
invasive species for mussel aquaculture operations in
the Maritime Provinces. Species may respond
Green crab (Photo by Kyle Matheson).
Winter 2013 9
uniquely to the different marine environments in NL
compared to elsewhere, but previous knowledge and
experience enhances our ability to prepare for and
manage threats ofAIS in NL.
High amounts of shipping traffic to and within NL
generate vectors that may transport species into the
province from around the globe and once introduced
spread within NL. A National Risk Assessment
identified locations that receive high amounts of
vessel traffic and ballast exchange,
such as Placentia Bay, which has
been an invasive species hotspot in
NL. Although attention has centred
on the risk of ballast exchange,
movement by recreational and small
crafts can act as secondary vectors
that assist and accelerate the spread
of invasive species. Fisheries and
Oceans have been surveying
recreational boaters to understand common routes
and high activity areas within NL (readers are
encouraged to contact AIS DFO, see website below,
if interested in participating in the boating survey).
Such surveys provide critical information to fine-tune
monitoring and research efforts. It is largely
acknowledged that the complete eradication of an
aquatic invasive species is not realistic, especially
once the species has become established. Prevention
and early detection of introduction and spread may
be the most effective management tools. Currently,
regulations are being developed between Provincial
Governments and DFO to manage and control the
introduction and spread of species.
The European green crab has invaded coastlines of
North America for over a century, including more
recent invasions along both the Pacific and Atlantic
coasts of Canada, but was first discovered in North
Harbour, Placentia Bay in 2007. The range and
populations of green crab in Placentia Bay have
exploded and have expanded to the west coast of the
island, particularly in shallow, protected coastal
locations (such as eelgrass beds).
In locations where few green crab
were captured, it has not been
uncommon to capture several
hundred crab the next year. In fact,
numbers have been so large that
research has been unable to
effectively estimate population size
because not enough crab have been
recaptured during tagging
experiments. The high abundances of green crab in
NL (several times that captured in Atlantic Canada or
British Columbia) have surprised many. The
presence of more native coastal crab species larger
than green crab in British Columbia (5 compared to
only one in NL, the rock crab) may act as predators
and limit the population of green crab. Currently,
green crab is the most prominent and destructive
invasive species in NL, and is one of the most
unwanted species globally.
Green crabs are voracious generalist predators and
aggressive competitors. They prefer shellfish such as
"In locationswhere few greencrab were
captured, it has notbeen uncommon tocapture severalhundred crab thenext year. "
(Left) Green crab (Photo by Kyle Matheson). (Right) Oyster Thief(Photo by Terri Wells) .
1 0 The Osprey
mussels and clams and large green crab populations
are having dramatic impacts on local abundances of
these species, practically leaving areas barren. Recent
research by DFO has provided evidence that green
crab feed on juvenile scallops, particularly when
preferred foods become limited. Green crab can also
alter underwater habitats. Crabs dig to find food and
bury themselves, which destroys roots of eelgrass, an
ecologically significant species in Canada and crucial
habitat for many juvenile fish, including Atlantic cod.
Anecdotal evidence suggests that this important sea
grass has declined throughout Atlantic Canada in
areas with increasing green crab
populations. Research by DFO in
2012 throughout Placentia Bay
has shown dramatic declines in
eelgrass coverage in areas with
the largest and longest
established green crab
populations.
As with other locations in
North America, an established green crab population
is nearly impossible to exterminate. For example,
volunteer harvesters captured approximately 350 000
crab in North Harbour (considered the hotspot for
green crab in NL) in under 3 weeks, but it provided
only a temporary reduction in the
invasive crab. Efforts now
include population control with
the objective that decreasing the
number or prominent size of
green crab increases their
vulnerability to natural predators.
The use of green crab as compost
and fertilizer is another option
being considered to control
populations.
Tunicates are aquatic animals
with sac-like bodies protected by
a coat (or tunic) that can live in
large colonies and feed by
filtering out food from water.
While the violet tunicate (first
discovered in Belleoram in 2007)
has not spread outside of
Belleoram harbour, the golden-
star tunicate (first identified in Placentia Bay in
2006) has spread throughout Placentia Bay and has
recently been confirmed in Conception Bay.
Tunicates are referred to as opportunistic animals.
Tunicate larvae settle on new, clean surfaces (such as
wharves or clean boat hauls) with little competition
from existing animals. Once the larvae settle,
invasive tunicates grow rapidly and cover other
plants and animals and deprive them of resources
such as food or light. These characteristics make
tunicates potentially very disruptive to shellfish
harvesters and aquaculture operations. Fortunately,
no invasive tunicates are present
in NL aquaculture operations.
Tunicates are most commonly
transferred between locations by
hitching a ride on boat hauls,
barges, or fishing equipment.
Boat hulls should be inspected
visually, cleaned, and dried on
land for 24 h as fragmentation of
colonies in water only
perpetuates further spread of the species. Anti-
fouling treatments on boats can also effectively
prevent the transfer of invasive tunicates.
Attempts to eradicate populations of these invasive
"Once the larvaesettle, invasive
tunicates grow rapidlyand cover other plantsand animals anddeprive them of
resources such as foodor light. "
Vase Tunicate (Photo by Bob O'Donnell) .
Winter 2013 11