Abstract
The zebra mussel Dreissena polymorpha is a recent introduction to the Irish fauna. Zebra mussels were first documented in Ireland in Lough Derg in 1997 . The first reports of zebra mussels in the Erne system were of mussels attached to boathulls. An initial survey indicated that zebra mussel settlement probably occurred in small numbers in Lower Lough Erne in 1996. The invasion and early population dynamics of the zebra mussel were studied using veliger , juvenile and adult mussel sampling programmes. An investigation into the role of recreational boating as a dispersal vector in Ireland was carried out.
Baseline information on aspects of the Erne system likely to be affected by the zebra mussel invasion was collected. Comprehensive data sets on the limnology of Lough Erne and Anodonta sp were collected. The impacts of zebra mussels on biotic and abiotic aspects of the system were investigated. These aspects included major nutrients, water clarity, total chlorophyll levels and populations of the native unionid Anodonta sp . A series of dredge surveys covering the range of substrata in the Erne system was carried out at over 30 sites throughout Upper and Lower Lough Erne every six months from June 1998 to June 2000 to monitor changes in the zebra mussel and Anodonta populations . A remotely operated vehicle was used to monitor bedrock areas. Water samples were taken every two weeks from January 1999 to December 2000.
All available evidence suggested that zebra mussels became established in Ireland following importation of boats with living attached zebra mussels. The initial distribution of zebra mussels in Lough Erne suggested that zebra mussels first entered Lower Lough Erne as adults attached to boat hulls. Subsequent inoculations within the Erne and Shannon navigation systems, indicated that the likely means of dispersal of zebra mussels to new waterbodies in Ireland were spawning of attached adults on boat hulls and hull scrapings returned to the water.
There was rapid spread of zebra mussels and a significant increase in their density and biomass between June 1998 and June 2000, colonising a wide range of substratum types. The size structure of the zebra mussel population suggested that zebra mussels in Lough Erne can grow up to 15 mm yr- 1 and have a life span of 2.5-3 years or cessation of growth in older mussels . They tend to reach a size of 25-30mm with only a small proportion reaching over 30mm in length. The initial years of the zebra mussel invasion in Lough Erne were characterised by large variations in adult density and biomass among surveys and sites; timing of veliger production and veliger abundance. The presence of overwintering veligers indicated that the conditions in Lough Erne are highly suitable for zebra mussels.
Water quality data showed a significant increase in water clarity and decrease in chlorophyll a levels during 2000 and 2001. A significant increase in silica concentration was documented in 2001, possibly due to decreased uptake by phytoplankton due to zebra mussel filtering impacts. Changes also occurred to long term trends of some nutrient concentrations with a significant decrease in total phosphorus and particulate phosphorus and a significant increase in soluble phosphorus in 2000 and 2001. Zebra mussels may be acting as a phosphorus sink in Lough Erne, although not a permanent sink. There was rapid colonisation of the Anodonta population with a significant decrease in condition of the Anodonta population and an increase in its mortality. It is likely that Anodonta sp will be extirpated in Lough Erne within the next few years.
Further research is needed on the phytoplankton, zooplankton and fish communities to quantify zebra mussel impacts and allow predictions of the likely impacts in other Irish waterbodies invaded by zebra mussels. In addition a management strategy for zebra mussels in Northern Ireland should be developed. This would identify and prioritise vulnerable lakes, predict impacts, assess the effectiveness of control strategies and recommend mitigation measures. Changes in policy such as adopting a policy of cleanlisting with harmonisation of legislation between the two jurisdictions on the island of Ireland would be beneficial in preventing future invaders.
Appendix 1 is a published article and omitted from the scanning. 'First Reported Settlement of Zebra Mussels Dreissena Polymorpha in the Erne System, Co. Fermanagh, Northern Ireland. R. S. Rosell, C.M. Maguire and T. K. McCarthy. Biology and Environment: Proceedings of the Royal Irish Academy, Vol. 98B, No. 3, 191-193 (1999).'
| Date of Award | Dec 2002 |
|---|---|
| Original language | English |
| Awarding Institution |
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