This document discusses a study on the ecological role of seaweed on beaches in the Outer Hebrides islands off western Scotland. The study found that beach-cast seaweed supports a large abundance of macrofauna and is an important feeding ground for migratory shorebirds. While seaweed has potential as a source of biofuel, more study is needed to understand the trophic interactions and potential impacts of harvesting before recommendations can be made. The document provides background on macroalgae as an alternative fuel source and outlines the study areas and key findings on the relationships between seaweed, invertebrates, and shorebirds.

1. Seaweed on the sandy beaches
of the Outer Hebrides: An
important food source for
coastal fauna
Kyla Orr (PhD student)
Supervisors: Sheila Heymans, Tom Wilding and David Hughes
Scottish Association for Marine ScienceCoordination Centre:
Scottish Association for Marine
Science, Oban, Scotland
T: +44 (0)1631 559000
F: +44 (0)1631 559001
E: biomara@sams.ac.uk
W: www.biomara.org
Project supported by the INTERREG IVA
Programme Managed by SEUPB

2. Introduction: Macroalgae for Biofuel
• Marine biomass suggested as alternative energy source to terrestrial
biomass due to its greater productivity and large surface area available for
growth
• Wild macroalgae productivity is ~2.8 times higher than that for sugarcane;
cultured macroalgae ~ 6.5 times more productive than sugarcane (Gao and
McKinley, 1994).
(1) Harvesting of attached macroalgae
Laminaria spp. Vs Ascophyllum nodosum
(2) Growth of macroalgae
on long-lines
(3) Collection of
storm-cast kelp
Three possible sources of macroalgae for Biofuel:
Ecological role
and impacts of
removal ?

3. Study Area
North Uist
Benbecula
South Uist
Uists, Outer Hebrides -
west coast dominated by
soft shores and shallow
offshore reefs populated
with kelp
Large casts of seaweed
after gales
Long history of seaweed
collection from shores

4. Macroalgae subsidies and coastal
communities Detached
seaweed
Birds
Epifauna
(seeking shelter)
BacteriaPOC
Suspension &
deposit feeders
Fishes
Crabs
Carnivorous
invertebrates
Invertebrate
detritivores
Kelp
Beach-cast
seaweed
Floating seaweed

6. Shorebirds and beach-cast
seaweed
y = 0.0055x + 0.0058
R
2
= 0.9107
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 50 100 150
Total Number shorebirds
meanseaweedcover(m2/m2beach)
Normality Test: Kolmogorov-Smirnov test passed (P = 0.8558)
Constant Variance Test: Passed (P = 0.0931)
Slope significantly different from zero (p<0.0001)
Dunlin
Sanderling
Turnstone
Ringed plover
Gull, Larus sp.
Pied wagtail
Starling Oystercatcher

7. 76%
20%
4%
0%
On seaweed
On sand
On Rocks
Atwater line
99%
0%1%0%
Low Tide High Tide
Habitat use by birds on sandy
beaches with seaweed

8. Invertebrates and seaweed
• Majority of fauna found in old seaweed at High Water
Springs (HWS), and in sediment at Low Water (LW)
• Abundance of fauna appears to increase with decay
stage of seaweed
• HWS: average 59,617 individuals/m2
seaweed -
dominated by oligochaete worms and fly larvae
(Oligochaete abundance can reach 1, 000 000 individuals/m2
)
• LW: average 27,747 individuals/m2
-dominated by the
polychaete families Capitellidae and Spionidae.
Capitellid worms

9. Conclusions
• Beach-cast seaweed in Outer Hebrides
supports an abundance of macrofauna
• Seaweed is very important feeding ground
for migratory shorebirds, as well as
breeders relative to other coastal habitats
• Trophic interactions still need to be
investigated before questions can be
answered about harvesting

10. Project supported by the INTERREG IVA Programme
Managed by SEUPB
Funders
Coordination Centre:
Scottish Association for Marine
Science, Oban, Scotland
T: +44 (0)1631 559000
F: +44 (0)1631 559001
E: biomara@sams.ac.uk
W: www.biomara.org
Thank-you