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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


    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


    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