the distribution of maerl around the orkney islands malcolm thomson
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International Centre for Island TechnologyHeriot-Watt University (Orkney Campus)
Old AcademyStromness
OrkneyScotland
The distribution of maerl around the Orkney Islands
Malcolm Thomson
~SUMARE~
Orkney Islands
20 km
ICIT
Scapa Flow
Wyre Sound
Map of Orkney showing the location of ICIT and Wyre Sound, where the first sea trials of the PHANTOM vehicle are to be held.
what is maerl?
environmental requirements
importance
European distribution
maerl in Orkney
What is maerl?
• coralline red seaweed
• secrete calcium carbonate (CaCO3)
• coastal distribution• long lived• living & dead deposits• “patchiness”
Environmental requirements
• water depth/light penetration • water movement
– tides & waves
• temperature• water chemistry• seabed type
Importance of maerl
• commercial• scientific
– biodiversity
• sensitivity / fragility– natural & man-made threats
Commercial value of maerl
• soil conditioner• water purification• cosmetic ingredient• dietary additive• bone surgery• agricultural - feed, bedding material
European distribution
Maerl in Orkney
• ICIT student research– modelling the distribution of maerl
• SUMARE
Personal accounts
RoxAnn acoustic data
Admiralty navigation
charts
Marine Nature
Conservation Review (MNCR)
Combined data set on maerl distribution
Existing data on maerl
Occurrence of maerl according to
environmental parameters
Figure 1: The distribution of maerl as a function of depth (Admiralty and MNCR data combined)
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0-5 6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-50
Depth category (m)
% o
cc
urr
en
ce
Figure 2: Distribution of maerl as a function of tidal velocity
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
N (0) W (0.1-0.8) M (0.9-3) S (>3)
Tidal stream (knots)
% o
ccu
rren
ce
chart
mncr
Figure 3: Distribution of maerl as a function of wave exposure
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
1 2 3 4 5 6 7 8 9Exposure scale
% o
ccu
rren
ce
chart
mncr
Figure 4: Predicted distribution of maerl in Orkney. ( ) indicates where the presence of maerl has since been confirmed.
General trends:
• < 20m depth• moderate tidal velocity
(0.9-3.0 knots ~ 0.45 - 1.5 ms-1)
• low - moderate wave exposure
Effectiveness of model
• Sound of Arisaig– less accurate
• large scale application• living vs dead??• probability data
Figure 4: The probability of finding maerl at a specific point as a function of depth - Admiralty chart data
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0-5 6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-50 51-55
Depth category (m)
De
pth
dis
trib
uti
on
0
0.005
0.01
0.015
0.02
0.025
0.03
0.035
Pro
ba
bil
ity
of
ma
erl
depth distribution
Probability of maerl
Figure 4: The probability of finding maerl at a specific point as a function of depth - MNCR data
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0-5 6-10 11-15 16-20 21-25 26-30 31-35 36-40 41-45 46-50 51-55 56-60
Depth category (m)
Dep
th d
istr
ibu
tio
n (
%)
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
Pro
bab
ility
Depth distribution
Probability of maerl
Figure 5: The probability of finding maerl at a specific point as a function of tidal velocity
0
10
20
30
40
50
60
70
80
Neg (0) weak (0.1-0.8) mod (0.9-3.0) strong (>3)
Tidal velocity
Tid
al v
elo
city
dis
trib
uti
on
(%
)
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
Pro
bab
ility
of
mae
rl
Tidal velocity distribution
Probability of maerl
Goals of SUMARE re. maerl
“to show the advantages of using autonomous technology” in developing a sustainable extraction policy for maerl
discrimination of living & dead areas
area estimates (patchiness)
navigation
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