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

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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