The Crayfish Plague Pathogen Aphanomyces astaci in Ireland

Area of Science:

• Aquatic Ecology
• Invasive Species Biology
• Pathogen Ecology

Background:

• Crayfish plague, caused by Aphanomyces astaci (Ap. astaci), devastated European freshwater crayfish post-1860 introduction.
• North American crayfish and contaminated gear facilitate Ap. astaci spread, reducing native populations.
• Ireland was a refuge for Austropotamobius pallipes until Ap. astaci introduction in 1987, with re-emergence in 2015.

Purpose of the Study:

• To review the timeline of Ap. astaci introduction and spread in Ireland.
• To identify Ap. astaci genotypes and their distribution across Irish water catchments.
• To discuss the implications of Ap. astaci presence without its natural host and the role of non-indigenous species.

Main Methods:

• Review of historical records and scientific literature on crayfish plague in Ireland.
• Molecular analysis of Ap. astaci from mass mortality events to determine genotypes.
• Spatial analysis of pathogen detections across Irish water catchments (2015-2023).

Main Results:

• Ap. astaci re-emerged in Ireland in 2015, detected in 18 catchments by 2023.
• Multiple Ap. astaci genotypes were identified, with uneven distribution suggesting human-mediated spread.
• The pathogen is present in Ireland without its primary North American host species.

Conclusions:

• Human-mediated transport of contaminated equipment is the primary driver of Ap. astaci spread in Ireland.
• The presence of diverse Ap. astaci genotypes highlights multiple introduction events or rapid diversification.
• Effective management strategies are crucial to control Ap. astaci and mitigate impacts on native crayfish populations.