1. Mytilus trossulus in Scotland: achievements and perspectives
Joana Dias, Ian Davies, Mike Snow
Oban, 21st October 2009

2. Presentation 1. Background 2. Main questions (2007-2009)
3. Developing tools for the molecular identification of species
4. Understanding species distribution in Scotland
5. Can we exploit differences in spawning times to favour M.edulis settlement?
6. Can we exploit differences in salinity to favour M.edulis settlement?
7. Investigating the origin of M. trossulus in Scotland
8. Main outcomes
9. Future plans

3. 1. Background
Mytilus trossulus, M. edulis and M. galloprovincialis are close species
the 3 species maintain distinct morphological characteristics
hybrids are described as possessing intermediate characteristics
identification based on morphology complicated due to :
hybridization
environmental influence
M. trossulus
M. edulis
M. galloprovincialis

4. 1. Background M. trossulus occurs: In cultivation:
Extensively in the Baltic Sea and West and East coasts of North America
No known impact on natural populations of other species
In cultivation:
It is not farmed in the Baltic due to its appearance and poorer meat contents
In Atlantic Canada the industry favours M. edulis production

5. 1. Background
In Scotland, mussels represent the most important sector of the shellfish aquaculture industry
The sheltered conditions of sea Lochs offer great potential for aquaculture
Production is dependent on the natural availability of spat
Fragile-shelled M. trossulus reported from Loch Etive in 2005
Responsible for losses in production and profitability

6. 2. The project (2007/09) main questions
What is M. trossulus distribution in Scotland?
How can production be managed to favor M. edulis?
Is M. trossulus a native species?

7. 3. Developing tools for molecular identification
The Me 15/16 markers
Target a region of a gene of specific length to each species
Individual identification by PCR and electrophoresis
Fragments of different lengths show different migration patterns in a gel M
(1) M. edulis 180 bp
(2) M. trossulus 168 bp
(3) M. galloprovincialis 126 bp
(4) M. edulis x M. trossulus
(5) M. trossulus x M. galloprovincialis
(6) M. edulis x M. galloprovincialis
Gel showing PCR products from all mussel species and hybrids. (M) 50 bp marker.

8. 3. Developing tools for molecular identification
Development of a real-time PCR method
For the identification of adults and larvae
Based on the Me 15/16 markers
Highly specific and sensitive
Fully automated and able to process a high number of samples

9. 4. Understanding species distribution
Sampling of 30 mussels from 34 beaches, 10 marinas and 46 farms
30 x 90 = 2700 mussels
Gill tissue removed and preserved in 70% ethanol at -20ºC
Bulk tissue of 30 mussels within each sample
Total of 90 bulk samples
Samples screened using real-time PCR
5 mg
of tissue

10. 4. Understanding species distribution
Beaches
Marinas
Farms

11. 4. Understanding species distribution
M. trossulus detection from beaches were very low
No evidence of being an invasive species
M. trossulus was significantly detected at marinas and 4 farm sites
Suggests preferential development in artificial structures
The surveys show M. trossulus presence to be restricted to the Argyll and South Highland areas
What can we do to favor M. edulis production at sites where M. trossulus impact is most felt?

12. 5. Can we exploit differences in spawning?
We sampled 150 adult mussels every month for 1 year
Selected 20 M. edulis, 20 M. trossulus, 20 hybrids
Histological analysis of gonad maturation stages
We took a plankton sample simultaneously every month
DNA extraction
Testing of real-time PCR identification of larvae

13. 5. Can we exploit differences in spawning?
Species maturation
M. edulis matures earlier than M. trossulus
Hybrids follow M. trossulus pattern
M. trossulus spawn during a longer period

14. 5. Can we exploit differences in spawning?
Planktonic larvae
M. edulis and M. trossulus larvae peaks are synchronized
M. trossulus larvae are generally more abundant
M. trossulus oversettlement is likely to occur
larvae/m3
larvae/m3

15. 6. Can we exploit differences in settlement?
An experiment was set to investigate differences in settlement due to salinity and spawning behaviour
Ropes were deployed from Feb to July 2008
Unusual settlement of sea squirts and sea stars!
Proven unpredictability of
physical, biological, environmental factors in the field…

16. 7. The origin of M. trossulus in Scotland
Ongoing investigation...
So far, phylogeographic patterns indicate Scottish M. trossulus is indistinguishable from Canadian stock
The challenge now is to distinguish natural colonization from potential more recent introductions 16

17. 8. Main outcomes A novel real-time PCR assay was developed
cost and time-efficient screening of large number of samples
Identification of adults and larvae
Surveys show distribution to be restricted to SW Scotland
M. trossulus unlikely to threaten native species populations
Preferential development in pontoons and aquaculture ropes
Life strategies are not sufficiently different to allow management strategies aimed at favouring M.edulis settlement
M. trossulus impact restricted largely to aquaculture...

18. 9. Future plans
Is it possible to eradicate/greatly eliminate M.trossulus from sites?
A plan is being established to remove M. trossulus from Loch Etive
Coordination in place to decide on the most environmental and economically sustainable approach
A diving survey of potential natural beds has recently taken place
Methods will be put in place to monitor the elimination of M. trossulus
Response to a SARF project call expected soon
18 months project to support an industry lead approach
Development of a voluntary code of good practices
Will act as a coordinator between all issues/parties/activities ongoing 18

19. Thank you Hellenic Centre for Marine Research, Heraklion, Greece
Stuart Piertney, University of Aberdeen, UK
Colleagues at Marine Scotland Marine Laboratory
Association of Scottish Shellfish Growers (ASSG)
All mussel growers involved in the project
Joana Dias:
Mike Snow:
This project is funded by the ECOSUMMER Marie Curie research network under the EU Sixth Framework Programme in collaboration with the Marine Scotland Marine Laboratory and the University of Aberdeen in Scotland, and the Hellenic Centre for Marine Research in Greece.