fouling remediation through the use of grazers in shellfish aquaculture

FOULING REMEDIATION
THROUGH THE USE OF GRAZERS
IN SHELLFISH AQUACULTURE
Douglas I. Watson*, Simone Dürr, Daniel Beaz, Eivind
Bergtun, Rik Breur, Juan Cebria, John Davenport, Donald
Fowler, Courtney Hough, John Icely, Alistair Lane, Julie
Maguire, Ana Manjua, Manuel Marhuenda, Kjell Maroni, Joe
McElwee, Halvor Mortensen, David Murphy, John Murphy,
James Newman, Ana Pereira, John Power, Sergio Prieto,
Jeremy Thomason, John Watters, Peter Willemsen.
*Aquaculture & Fisheries Development Centre,
University College Cork, Ireland
© D. I. Watson
© M. Marhuenda
Aquaculture
Biofouling:
Mitigating the
Problem
© D. I. Watson
© H. Mortensen
Introduction
CRAB – Collective Research on Aquaculture
Biofouling
Potential use of grazers within an
aquaculture system
Pilot study used Scallop trays on a long-line
system
Two different grazers effectiveness tested
Three different densities per grazer plus
controls
© D. I. Watson
Aims
To identify potential grazers
and grazer densities which will
control biofouling on
aquaculture structures
To identify grazer differences
in relation to biofouling control:
www.akvarij.net
© S. Dürr
Do different grazers control
fouling better?
Do different grazers control
different taxa?
http://fieldtrip.britishecologicalsociety.org
© S. Dürr
Experimental set-up:
3 Replicates each of Control (no grazers), 2, 5 &
10 grazers
Head Rope
‘Lid’ tray
4 ‘spacer’
trays
4 ‘replicate’
trays
‘Base’ tray
Approx. 2m
Weights
Sampling Protocol
Trays allowed to foul for 2
weeks prior to grazer
introduction
Thereafter sampling was
monthly
What sampled?
Tray weights
Animal weights
Animal sizes (test for growth)
Digital picture (photographic
analysis of fouling)
Tray Weights - Trochids
Initial analysis
3000
Tray Weight (g)
2500
Graphs
Tray weights
Trochid Control
Trochid 2
Trochid 5
Trochid 10
2000
1500
1000
500
0
Apr
May
Jun
Jul
Aug
Sep
Oct
Date
Tray Weights - Urchins
Wilcoxon’s signed ranks test results for tray weights.
Tray Weight (g)
3000
Urchin Control
Urchin 2
Urchin 5
Urchin 10
Urchin Comparison
2000
1000
0
Apr
May
Jun
Jul
Aug
Date
Sep
Oct
Nov
p-value
Control vs. 2 Grazers
0.022
Control vs. 5 Grazers
0.035
Control vs. 10 Grazers
0.022
2 Grazers vs. 5 Grazers
0.052
2 Grazers vs. 10 Grazers
0.022
5 Grazers vs. 10 Grazers
0.398
Initial analysis cont’d
Graphs
Grazer size
Wilcoxon’s signed ranks test results
for urchin test size – density
comparison
Urchin Size
42
40
Urchin Comparison
38
Diameter (mm)
p-value
Urchin 2
Urchin 5
Urchin 10
2 Grazers vs. 5 Grazers
0.059
2 Grazers vs. 10 Grazers
0.036
5 Grazers vs. 10 Grazers
0.093
36
34
32
30
28
Apr
May
Jun
Jul
Aug
Date
Sep
Oct
Nov
Image J – Photographic analysis
% ‘Openness’ of trays studied
% obtained using Thresholding & Voxel counter
plug-in
Results
No significant difference between the effectiveness
of the two grazer species
Generally no significant difference between
densities of grazers of the same species
Trochid exception being 2 vs. 10 grazers
Urchin exception being Control vs. 2 grazers
Results: Multivariate analysis
% cover of major foulers (as identified by
farmers) obtained via photographic analysis
Results analysed in the community
interpretation package PRIMER
Grazer and community differences drawn
from analysis
PRIMER Analysis
MDS
ANOSIM
results showed
significant
difference in
community at
p<0.02
PRIMER Analysis cont’d
SIMPER analysis
Within group similarity >87%
for both grazer species
Average dissimilarity between
grazers = 15.47
‘Clean Tray’ & ‘Open Mesh’
more indicative of urchin
grazing
Categories in table represent
>90% of the community
dissimilarity between the two
grazer species
Urchin
Clean Tray
Sponges
Trochid Colonial
Ascidians
Serpulids
Mussels
Open Mesh
Conclusions
Pilot study therefore:
Short in duration
Limited replication
Grazers show potential as their use appears to
assist with fouling reduction
Significant differences (at 95% CI) seen for tray weights
between control and all urchin densities
Grazer species choice shown to be potentially
important at controlling specific taxa
More manipulation required (grazer size etc.)
Grazers may be successful as part of a multistrategy solution to fouling
Future testing
Analyse rest of collected data – to view
any temporal pattern in fouling control
New experiment in 2006 – using 2 urchin
grazers and with stock
Lab tests to look at interaction of grazers
and stock species
Acknowledgements
I would like to thank all of the CRAB partners for their
assistance, particularly James Newman who was
heavily involved in the field work and Dr. Simone Dürr
who assisted greatly with the photographic analysis.
I would also like to thank the EU for funding the project
under the 6th Framework Programme. EC Contract
COLL-CT-2003-500536-CRAB (Collective Research,
FP6). Project information, see www.crabproject.com
Contact: [email protected]
Aquaculture & Fisheries Development Centre,
University College Cork, Ireland