The biology of the soft-shell clam in Ireland. A future aquaculture species?

M. E. Cross*, R. M. O’Riordan, S. C. Culloty.School of Biological, Earth and Environmental Sciences and Aquaculture and Fisheries Development Centre, University College Cork, Ireland.

* maud.cross@ucc.ie

BackgroundThe soft shell clam, Mya

arenaria, currently occupies a large geographical range in the northern hemisphere.

Soft shell clams are found on the European coast from northern Norway to Portugal.

Mya arenaria, or “steamer clam” is a commercially important bivalve in North America, and has the potential to be an exploited species in European waters in the future.

Mya arenaria in the Irish SeaThis project is part of a larger

funded study (SUSFISH) which is researching shellfish management in the Irish Sea.

Soft shell clams are present in the Irish Sea, but little information is currently available on their biology and distribution.

The SUSFISH study aims to assess the potential threat of climate change to the shellfish industry in the Irish Sea.

Objectives of ResearchInvestigate the biology, including the

reproductive cycle, of M. arenaria in the Irish Sea.

To look at the health status of softshell clams and to identify any pathogens.

To study the population genetics of Irish Sea soft shell clams and to see how they compare with elsewhere in the distributional range.

To integrate the data collected on the biology of M. arenaria into future climate change predictions.

Methodology Thirty soft-shell clams are

collected every month from Bannow Bay, Co. Wexford, Ireland, from March 2010 to June 2011.

Bannow Bay is located in the Irish Sea, on the southeast coast of Ireland (52°13’33 N, 6°47’51 W).

General biology, spawning and gametogenic patterns of Mya samples are being investigated.

Each individual is screened for parasites and disease.

Molecular Ecology MethodsStrasser and Barber (2009) used “universal" DNA primers

to amplify the variable mitochondrial cytochrome oxidase I gene (COI).

Gill samples of Irish Sea M. arenaria are being sequenced and findings compared to past results.

Generic primers are used to amplify Bacterial DNA (Ji et al, 2010) Ostreid Herpes Virus (Renault & Arzul, 2001)

DNA samples are also being sequenced to detect the presence of pathogens.

Results - Sex Ratio 432 Mya arenaria have been

collected over 16 months from March 2010 to June 2011.

199 (46%) were female and 229 (53%) were male.

4 (1%) were immature or the sex could not be determined.

The overall female:male sex ratio of 1:1.15 did not show a significant divergence from a 50:50 ratio ( χ2test – NS).

No hermaphrodites were present in the collected samples, and there was no evidence of protandry.

Results – General BiologyAverage weight of all M.

arenaria collected was 74g (+/-4.9g).

Average length of all individuals was 8.2 cm (+/-0.2cm).

Female individuals were both lighter and shorter than male M. arenaria, though this was not statistically significant.

Results – Gonadal Development Female M. arenaria (20X magnification)

Indeterminate Developing Ripe Spawning Spent

Male M. arenaria (20X magnification)

Results – Reproductive CycleOf the collected samples,

male M. arenaria were developing from March to July 2010, with ripe individuals present from May. Spawning began in August and was completed by November 2010.

The female M. arenaria show a less defined cycle, but most individuals collected were ripe or spawning in August and September 2010.

Results – Reproductive CycleIn 2010, M. arenaria matured over

the summer months, with both sexes either ripe or spawning by August.

Spawning was in a single spawning episode and was completed by November.

Gametogenic development appears to have been affected by an unusually cold winter, so completion of spawning may be slightly late in 2011.

The mean temperature at Bannow Bay was highest in June, at 18°C and lowered to 3°C by December 2010.

Results - Disease

Histological methods have not identified the presence of any pathogens to date.

PCR amplification and subsequent sequencing of M. arenaria gill samples using Ostreid Herpes Virus and generic bacterial DNA primers have shown no presence of pathogens.

Results – Molecular Ecology

~ 100 bp

~ 650 bp

At present, no genetic variation has been evident in Irish Sea samples at the variable CO1 site.

Sequencing of Irish Sea Mya arenaria have revealed the common haplotype described by Strasser & Barber (2009) at this site.

SummaryThis study is the first to assemble information on Mya arenaria

in Ireland.Data gathered indicates the presence of a sustainable, healthy

population.Due to softshell clams ability to survive and reproduce in such a

variety of differing areas, and the lack of disease compared to American stocks, it could be an ideal species to culture in European waters in the future.

The data collected here could inform development of a potential fishery.

By continuing to gather this type of information we can develop a sustainable fishery that could support local communities.

Acknowledgements

This project was funded by the Ireland Wales Programme 2007-2013 INTERREG 4A European

Regional Development Fund (ERDF).