1. D. Roberts Queen’s University, Belfast
Scope for the Restoration of Modiolus modiolus in Strangford Lough, Northern Ireland: Dreams and Realities
D. Roberts
Queen’s University, Belfast

2. Restoration of Modiolus in Strangford Lough
Background
Strangford Lough:listed for designation as a Special Area of Conservation (SAC) under the EC Habitats Directive (92/43/EEC).
A major feature for this candidacy is the sublittoral Modiolus modiolus biogenic reefs which were known to be extensive in Strangford Lough in the 1970s & 80s.
2002: Government Departments and non-government organisations (NGOs) expressed concern about the state of these reefs.
The Strangford Lough Ecological Change Investigation (SLECI), commissioned by EHS, aimed to identify the current conservation status of the Lough and any factors which may have contributed to change.
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Restoration of Modiolus in Strangford Lough

3. Restoration of Modiolus in Strangford Lough
Methods
During summer 2003 over 80 sub-littoral sites were surveyed by divers in Strangford Lough (Figure 1) ; surveys were videoed and also provided material for population and diversity studies.
The presentation is in two parts:
review of the problem
review of options
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Restoration of Modiolus in Strangford Lough

4. Restoration of Modiolus in Strangford Lough
Figure 1: Study site
Strangford Lough N
Ireland
4 km
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Restoration of Modiolus in Strangford Lough

5. Physical characteristics of Strangford Lough
Catchment Area (km2)
771.5
Length (km)
30.0
Maximum Width (km)
8.0
Surface Area LW (km2)
106.2
Surface Area HW (km2)
182.8
Tidal range (m)
3.5
Max. Depth (m) 60
Volume (106 m3)
1 250
Tidal exchange (106 m3)
350
Coastline (km)
240.0
Salinity range
32-34o/oo
Glacial origin
Substrata: bedrock to fine sediments laid out according to tidal water movement
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6. Restoration of Modiolus in Strangford Lough
2003
Modiolus /Chlamys community
Modiolus /hydroid community
Permitted trawl zone
Figure. 2 Distribution of Modiolus biogenic reefs and other communities in Strangford Lough during surveys between 1975 & 1985 and 2003.
CROWN COPYRIGHT
CROWN COPYRIGHT
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Restoration of Modiolus in Strangford Lough

7. Restoration of Modiolus in Strangford Lough
a) Modiolus clump in intact Modiolus/Chlamys biotope. SCR.ModCvar
c) Area of dead Modiolus shell – main channel, north basin.
Figure 3. Stills images from video footage taken in 2003
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8. Restoration of Modiolus in Strangford Lough50
100
150
200
250
300
350
1976
2003
1975
Figure 4. Comparison of Modiolus densities from different locations in 1975/6 and 2003 (bars indicate total range of individuals per m2)
Modiolus Nos m-2
North of long Sheelah
Black Rock
Bird Island Passage
Round Island
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Restoration of Modiolus in Strangford Lough

9. Restoration of Modiolus in Strangford Lough
20.0
a) South Basin (Brown 1974) n = 1006
b) Area A, South Basin
(Present Study 2003)N = 54
18.0
30.0
16.0
14.0
25.0
12.0
20.0
10.0
15.0
8.0
6.0
10.0
4.0
5.0
2.0
0.0
0.0
0 to 5
5 to 10
10 to 15
15 to 20
20 to 25
25 to 30
30 to 35
35 to 40
40 to 45
45 to 50
50 to 55
55 to 60
60 to 65
65 to 70
70 to 75
75 to 80
80 to 85
85 to 90
90 to 95
95 to 100
0-4.9
100 to 105
105 to 110
110 to 115
Size Class (mm)
0.0
5.0
10.0
15.0
20.0
25.0
30.0
0-4.9
Size Category (mm)
c) Area B South Basin
(Present study 2003) n = 136
Size Category (mm)
d) Area C North Basin
(Present study 2003) n = 218
30.0
25.0
20.0
15.0
10.0
5.0
0.0
0-4.9
Size Category (mm)
Figure 5. Comparison of the population profiles of Modiolus modiolus in Strangford Lough for 1974, and 2003 (Areas A, B & C).
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10. Restoration of Modiolus in Strangford Lough
140
BIOTOPES
SCR.ModCvar
120
Phaeophyta
Rhodophyta
Pisces
SCR.ModHAs
MCR.ModT
100
Tunicata
Echinodermata
Total Number of Species per Phylum
Bryozoa 80
Mollusca
Crustacea 60
Chelicerata
Annelida
Sipuncula 40
Nemertea
Platyhelminthes
Cnidaria 20
Porifera
Quadrats
Dives
Total
Quadrats
Dive
Quadrats
Dive
Total
Black Rock Beds 2003
Roberts 1975
W of Round Island 2003
N of Long Sheelah 2003
Brown &
Seed 1977
Figure 6. Comparison of total numbers of species per taxon recorded in quadrat samples and dive videos for each area in 2003 with historical data
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11. Restoration of Modiolus in Strangford Lough
CHANGES IN Modiolus COMMUNITIES
1970s & 80s: Modiolus beds known to be extensive in Strangford Lough (Seed & Brown, 1977; Erwin et al, 1990).
1989: Brown published report suggesting trawling had damaged M modiolus communities in Strangford Lough
fishing returns for scallops (Pecten & Aequipecten), suggested trawling peaked between late ‘80s & early ’90s
Trawling and dredging damage biogenic reefs and seabed communities (Watling & Norse, 1998; Cranfield et al. 2003).
1997 : Service & Magorrian confirmed areas of M. modiolus/ Chlamys varia community, were impacted by mobile gear.
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12. Restoration of Modiolus in Strangford Lough
CHANGES IN Modiolus COMMUNITIES
As a result of this work DARD introduced legislative measures in 1993 to manage fishing activity.
In 1997 Service & Magorrian suggested that reduction in fishing would afford the opportunity to follow recovery
SLECI 2003:
confirmed large-scale reductions in the extent, of Modiolus by both direct observation and broadscale mapping
found no evidence of recovery in extent of Modiolus reefs in impacted areas
found all major habitat types/ biotopes reported by Ulster Museum sub-littoral surveys in the 1970s & 1980s still present
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Restoration of Modiolus in Strangford Lough

13. Restoration of Modiolus in Strangford Lough
Figure 7. Dreams
Strangford Lough N
4 km
CROWN COPYRIGHT
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Restoration of Modiolus in Strangford Lough

14. Restoration of Modiolus in Strangford Lough
Realities
STARTING POINT
Modiolus densites have declined and community structure has changed
However, at intact sites population structure is comparable to earlier studies and recruitment is evident
Modiolus reproduces all year in Strangford Lough
Isolated individuals in impacted areas
ISSUES
Substratum unsuitable for Modiolus spat settlement
Modiolus spat vulnerable to predation
Standing stocks of Modiolus may not produce enough spat for large scale natural re-colonization
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Restoration of Modiolus in Strangford Lough

15. Restoration of Modiolus in Strangford Lough
Options
1. Do nothing
2. Attempt pilot-scale Restoration
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16. Restoration of Modiolus in Strangford Lough
1: Do nothing: Experience Elsewhere
Studies by Cranfield at al & 2003 in the Foveaux Strait, New Zealand, where oyster dredging has occurred over 130 years, contribute to our understanding of interactions between fishing and biogenic reefs :
Before dredging, bryozoan reefs and associated oysters (Ostrea [Tisostrea] chilensis) were tidally oriented in areas of strong current
As well as removing the reefs and oysters, dredging resulted in the release of large volumes of biogenic sediments which were deposited elsewhere and the seafloor reverted to underlying pebble gravel so that the substrates underlying biogenic reefs were exposed
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17. Restoration of Modiolus in Strangford Lough
The Foveaux Strait experiences strong tidal currents which accelerate this process
Surveys in 1998 revealed that some sites which had been unfished for 49 years showed no regeneration of biogenic reefs
Other sites showed the development of biogenic reefs of Modiolus areolatus which were also tidally oriented
Attempts to rebuild a fishery may be more successful if combined with habitat restoration
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18. Restoration of Modiolus in Strangford Lough
2. Pilot-scale Restoration of Modiolus
Bivalve aquaculture needs technology and science:
Technology:
1 Good spat supply
2 Effective intermediate culture
3 Effective growout systems
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19. Restoration of Modiolus in Strangford Lough
2.1 Good spat supply
2.1.1: Collection of wild spat
Deployment of ‘pan-scrub’ spat collectors during and after SLECI produced very low numbers Modiolus (<1% mytilids on collectors)
Spat collectors dominated by Mytilus and other fouling species
Currently trialling other types of spat collectors
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20. Restoration of Modiolus in Strangford Lough
2.1.2: Hatchery production of spat
Preliminary trials equivocal – one or two males spawned under extreme duress
Probable reason – animals in poor condition
Aims – repeat spawning trials with animals in ‘good’ condition
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21. Restoration of Modiolus in Strangford Lough
2.2: Intermediate culture
Sock
Peg
50 cm
Mussel socks (Pergolare)
‘Oyster’ bags
North-west plastic trays
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22. Restoration of Modiolus in Strangford Lough
3 Possible growout systems:
Extension of intermediate culture systems: in bags or north-west plastic trays
Group isolated individuals in bags to form nuclei for restoration at selected sites
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Restoration of Modiolus in Strangford Lough

23. Restoration of Modiolus in Strangford Lough
Restoration also needs:
Science:
Hydrographic information
Estimates of carrying capacity
Identify suitable sites for restoration
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24. Restoration of Modiolus in Strangford Lough
SUMMARY and CONCLUSIONS
Do nothing is not an option because of obligations under the EC Habitats Directive (92/43/EEC).
Best option is to develop appropriate hatchery systems for large scale spat production; intermediate suspended cultivation and transfer to bags for relaying in suitable restoration sites
To support restoration we need scientific backup in the form of more detailed information on the hydrography and carrying capacity of Strangford Lough
Constraints: Climate change
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25. Restoration of Modiolus in Strangford Lough
Acknowledgements
Principal & Co Investigators
Bernard Picton, Ulster Museum; Matthew Service,
DARD;Carys Ann Davies; Annika Mitchell; James
Strong; Heather Moore; Samantha Vize; Alex
Portig; Jane Preston; David Smyth
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Restoration of Modiolus in Strangford Lough