AGrowingProblem? JudithPederson DouglasW.Christel - - PowerPoint PPT Presentation

Didemnum
vexillum
on
Georges
Bank


A
Growing
Problem?


Judith
Pederson
 Douglas
W.
Christel


MIT
Sea
Grant

 College
Program


Dan
Blackwood,
USGS
 Becky
Toppen,
UNH


Purpose
of
Survey


• 1. Find
out
what
fishermen
know
about
Didemnum

• Where
it
is
found
on
Georges
Bank

• How
it
spreads

• How
it
affects
other
species
and
vessel
operaLons

• 2. IdenLfy
potenLal
ways
to
minimize
impacts

• 3. Improve
public
educaLon
about
this
species


Dan
Blackwood,
USGS
 Dan
Blackwood,
USGS


What
Is
Didemnum?


• A
sea
squirt,
or


tunicate


• Filter‐feeder

• Forms
colonies


with
other
sea
 squirts


• Tan,
pink
or
yellow


in
color


• Non‐naLve
species


It
Is
Not
“Monkey
Dung”


• Monkey
dung
is
a
sponge;
Didemnum
is
a
sea
squirt

• Monkey
dung
is
bright
yellow;
Didemnum
is
more
pink
in
color

• Monkey
dung
has
fewer
siphon
holes
or
cloacal
bumps


• Monkey
dung
sLcks
together
beWer;
Didemnum
will
crumble


Monkey
Dung


hWp://habcam.whoi.edu


Didemnum


Larry
Harris,
UNH


Didemnum
Preferences


Hard
surfaces

 (starts
on
undersides)


• Vessel
hulls

• Rocks/cobble

• Lobster
traps


Moderate
temperatures
 (10‐25°C,
or
50‐77°F)


• Dies
back
in
winter,
but
can


survive
cold
temperatures


Depths
up
to
70m
(230’,
35
fa)
 Cannot
tolerate
fresh
water


J.
Dijkstra

 Gretchen
Lambert


ReproducLon
and
Predators


ReproducNon


• Sexual
reproducLon

• Asexual
budding

• Colony
fragmentaLon


Predators


• Periwinkle
snails

• Sea
urchins

• Some
fish
species


Dan
Blackwood,
USGS


BoWom
Types
on
Georges
Bank


C.
Adams.MITSG


Where
Has
It
Been
Found?


Northern
Edge


Page
ValenLne,
USGS


Causes
of
Movement


Mostly
human‐oriented


• Ballast
water

• Hull
fouling

• Aquaculture

• Breaking
up
colonies



– Anchoring
 – Trawling/dredging
 – Using
lobster
traps
in
mulLple
areas


• Other
sources?


Ashley
CouWs,
USGS
 Gordon
King,
USGS
 Gretchen
Lambert


PotenLal
Problems


Fast‐growing
colonies
blanket
boWom
surfaces


Dan
Blackwood,
USGS


PotenLal
Problems


Overgrows
naNve
species,
including
scallops,
mussels,
worms


• Reduces
food
available
for
groundfish
and
lobsters

• May
reduce
movement
of
scallops


Reduces
larval
recruitment


• Overgrows
habitats
used
as
nurseries/predator
avoidance

• May
prevent
scallops
from
seWling
on
the
boWom



Increased
labor
costs
for
vessel
and
aquaculture
operaNons


• May
increase
Lme
to
shuck
scallops

• May
increase
need
to
clean
gear


Reduced
yield
of
seafood


• May
slow
growth
rates
for
groundfish

• May
reduce
survivability
of
shellfish


Other
issues
we’ve
missed?


Dan
Blackwood,
USGS


Possible
MiLgaLon
Measures


Fish
more
in
areas
where
found
 Close
areas
where
found
 Clean
hulls/gear
more
frequently


• Scrape
hulls
at
least
once
a
year

• Clean
traps
frequently
or
reduce
soak
Lmes

• Treat
traps
in
warm/hot
freshwater
before
sebng


Minimize
use
of
gear
in
other
areas

 Discard
scallop
shells
where
dredging
occurred
 Any
other
ideas?


www.derm.qld.gov.au


Thank
You!


Your
input
is
very
helpful
to
our
research.


• Increases
our
knowledge
of
species
interacLons

• Puts
issues
into
perspecLve

• Helps
refine
research
quesLons

• IdenLfies
pracLcal
soluLons


Contact
informaNon:

Dr.
Judith
Pederson


• Telephone:

617‐252‐1741

• Email:

jpederso@mit.edu

• Website:

hWp://seagrant.mit.edu