Predicting the
distribution of maerl
By
Malcolm Thomson
International Centre for Island Technology
Heriot-Watt University (Orkney Campus)
Old Academy
Stromness
Orkney
Scotland
What is maerl?
•
•
•
•
coralline red seaweed
secrete calcium carbonate (CaCO3)
coastal distribution
long lived
Importance of maerl
• commercial
• scientific
– biodiversity
• sensitivity / fragility
– natural & man-made threats
Maerl habitats
• living & dead maerl beds
• small scale “patchiness”
Video:
Wyre Sound, Orkney
Aug 2000
Large scale distribution
• water depth (light penetration)
• water movement
– tides & waves
• temperature
• water chemistry
• seabed type
Project SUMARE
• develop models using a priori
knowledge to delimit the regions where
we would expect maerl to occur (wp1)
ICIT model
• water depth
• tidal velocity
• wave exposure
Existing datasets
•
•
•
•
Admiralty data
MNCR/JNCC
SUMARE fieldwork
ICIT student research
Combined dataset...
Sample
1
2
3
4
5
6
Maerl
depth
band
tide
category
exposure
category
0
0
1
1
0
1
1
2
2
3
1
3
1
1
3
3
2
3
2
3
6
5
3
6
Set of possible conditions
• 11 depth bands
• 4 tidal categories
• 3 exposure categories
• 132 possible scenarios
• ~1750 samples
» assign a frequency to each derived from the
number of occurrences of maerl under each
different scenario
Frequency data
• e.g. for the 11-15m depth band:
Exposure
Tide
1
2
3
1
0.000
0.111
0.000
2
0.000
0.019
0.018
0.241
0.052
0.070
0.000
0.000
0.000
3
4
11-15 m depth band
0 .2 5 0
Frequency
0 .2 0 0
0 .1 5 0
0 .1 0 0
0 .0 5 0
S3
S2
S1
Exposure
0 .0 0 0
1
2
Tidal category
3
4
5 km
Red: 0-15m, tide = 3. exposure = 1, 0.174
Gold: 0-15m, tide = 3, exposure = 2, 0.073
Blue:0-15m, tide = 3, exposure = 3, 0.071
Green: 16-20m, tide = 3, exposure 1-2 = 0.070
Frequency of maerl
Depth
band
Tide
category
Exposure
1
2
3
0-5
3
0.068
0.015
0.000
6-10
3
0.220
0.041
0.063
11-15
3
0.241
0.052
0.070
16-20
3
0.167
0.011
0.000
21-25
3
0.000
0.032
0.040
Predictions...
• an idea under what conditions maerl is
more likely to occur
• a good idea of the conditions where
maerl is not going to occur
Navigation of AUV