Biological invasions by alien species are causing widespread environmental changes that threaten biodiversity and ecosystem services. Environmental and economic damage has been caused in many ecosystems and management efforts to counteract bioinvasions are steadily increasing. Identifying the factors promoting or inhibiting establishment and spread of invasive species can underpin strategies to control their expansion and improve capacity to predict further spread. The Pacific oyster (Crassostrea gigas) has been introduced for aquaculture in many parts of the world and invasive populations have developed, causing significant changes to many coastal ecosystems. In Ireland, aquaculture of Pacific oysters started in the early 70?s, however, whether feral populations are established is not known. This study aimed to assess the status of Pacific oysters in Ireland by characterizing their distribution and abundance, testing factors associated with their spread and assessing the genetic relationship between feral and aquaculture oyster populations.

A repeatable, cost-effective sampling programme that combined semi-quantitative and quantitative approaches was designed to assess the current distribution of feral Pacific oysters in Ireland and identify factors associated with their presence. Oysters were found at 18 out of 69 sites, with densities ranging from single individuals to nine individuals per m2. Analysis of size-frequency distributions revealed that several recruitment events have occurred, probably within the last 6-10 years. Logistic regression indicated that feral oysters were positively associated with hard substrata or biogenic reef, long residence times of embayments and large intertidal areas. A tendency for oysters to occur disproportionately in bays with aquaculture, but > 500 m from it was also found. Small-scale analysis within sites showed that oysters were exclusively attached to hard substrata and mussels. The approach taken provides a rigorous repeatable methodology for future monitoring and a detailed basis for the prediction of further spread of Pacific oysters.

Biotic interactions can play a key role in promoting or inhibiting spread of non-indigenous species. The Pacific oyster (Crassostrea gigas Thunberg, 1793) is commonly found on intertidal shores with hard substrata, but is negatively associated with macroalgae and may be influenced by the macroalgae itself or by predators associated with it. The influence of macroalgae and predation on growth, condition and survival of juvenile Pacific oysters was tested in a field experiment at two intertidal boulder shores using hatchery-reared juvenile oysters deployed on ceramic tiles. After 10 months, condition of oysters was not significantly decreased in the presence of macroalgal canopy. At one site growth was reduced by macroalgae and at the other, it tended to be enhanced, but the effect was not significant. An effect of predation could not be detected. Although spatial variation in survival and growth of juvenile oysters was found, the results suggest that pre-settlement processes and/or post-settlement processes acting upon juvenile oysters at sizes not tested in this study might better explain variation in abundance of Pacific oysters in intertidal habitats.

To reconstruct the recent biological history of feral populations of Pacific oysters in Ireland, temporal genetic variability of farmed and feral oysters from the largest enclosed bay in Ireland was assessed using anonymous and EST-linked microsatellites. EST-markers showed no footprints of selection and were jointly used with anonymous markers resulting in 13 different markers for statistical analyses. Relatively high genetic differentiation was found between aquaculture and feral oysters and between different year classes of oysters from aquaculture. A ten-fold higher effective population size (Ne) ? and a high number of private alleles ? in wild oysters suggest an established feral population that is likely to be self-recruiting and demographically independent from the current aquaculture activities in the estuary.

Using a large-scale survey, field experiments and molecular techniques, this is the first study to have quantified the establishment and distribution of Pacific oysters in Ireland. Results can be used to directly inform strategies and be applied in management and conservation. Compared to the situation in other countries where this species forms extensive reefs and already dominates intertidal habitats, control might be still feasible in Ireland, especially if efforts are focused on areas with higher abundances of wild Pacific oysters. A further cooperation between aquaculture operators, scientists and regulatory and development bodies is urgently needed to allow the development of the aquaculture sector without compromising ecosystem stability.

The data uploaded from this project has contributed to the following papers published in peer reviewed international journals:

Kochmann, J., Carlsson, J., Crowe, T.P., & Mariani, S. (2012). Genetic evidence for the uncoupling of local aquaculture activities and a population of an invasive species ? a case study of Pacific oysters (Crassostrea gigas). Journal of Heredity, 103, (5): 661-671.doi: 10.1093/jhered/ess042

Kochmann J, O?Beirn F, Yearsley J, Crowe T (2013). Environmental factors associated with invasion: modelling occurrence data from a coordinated sampling programme for Pacific oysters. Biological Invasions, 15: 2265?2279.

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There are currently 0 data files and/or information objects connected to this resource. You will need to contact the owners of this resource to enquire if data files and/or information objects will be made available to the public in the future. Contact information for the owners of this resource can be found in the Responsible Parties information section of the metadata.

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SAFER-Data Display URL	https://eparesearch.epa.ie/safer/iso19115/display?isoID=3032
Resource Keywords	Environmental variables, Crassostrea gigas, aquaculture, invasive species
EPA/ERTDI/STRIVE Project Code	2007-B-CD-1-S1
EPA/ERTDI/STRIVE Project Theme	Biodiversity
Resource Availability:	Semi-Private
Limitations on the use of this Resource	Time restrictions based on publishing peer reviewed articles from this research are requested. Please contact Dr Judith Kochmann for more details judith.kochmann@ucd.ie
Number of Attached Files (Publicly and Openly Available for Download):	0
Project Start Date	Tuesday 1st April 2008 (01-04-2008)
Earliest Recorded Date within any attached datasets or digital objects	Monday 1st September 2008 (01-09-2008)
Most Recent Recorded Date within any attached datasets or digital objects	Sunday 30th June 2013 (30-06-2013)
Published on SAFER	Thursday 24th October 2013 (24-10-2013)
Date of Last Edit	Thursday 5th December 2013 at 13:14:05 (05-12-2013)
Datasets or Files Updated On	Thursday 24th October 2013 at 15:03:53 (24-10-2013)

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Description of Geographical Characteristics of This Project or Dataset
A sampling programme was undertaken from May until September 2009 at 69 sites around the coast of Ireland. The sites were selected to represent variation in distance from aquaculture, latitude, wave exposure, embayment residence time, intertidal area (shore width) and habitat type. Sites ranged in area between approximately 3,500 m2 (narrow rocky shores) and 40,000 m2 (mussel beds) and salinities recorded ranged between 22.5 and 35 psu.

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