The introduction of the North American signal crayfish (Pacifastacus leniusculus) to UK waterways has caused a severe decline in populations of the native white-clawed crayfish (Austropotamobius pallipes), both through competitive exclusion and by transmitting a deadly disease known as crayfish plague, caused by the oomycete Aphanomyces astaciAphanomyces\ astaciAphanomyces astaci.
Which of the following correctly classifies the ecological status of the native white-clawed crayfish, the introduced signal crayfish, and the crayfish plague pathogen Aphanomyces astaci Aphanomyces\ astaci\,Aphanomyces astaci in UK waterways?
White-clawed crayfish: Indigenous species; Signal crayfish: Invasive non-indigenous species; Aphanomyces astaciAphanomyces\ astaciAphanomyces astaci: Pathogenic species
White-clawed crayfish: Non-indigenous species; Signal crayfish: Indigenous species; Aphanomyces astaciAphanomyces\ astaciAphanomyces astaci: Pathogenic species
White-clawed crayfish: Indigenous species; Signal crayfish: Non-invasive species; Aphanomyces astaciAphanomyces\ astaciAphanomyces astaci: Keystone species
White-clawed crayfish: Indigenous species; Signal crayfish: Invasive non-indigenous species; Aphanomyces astaciAphanomyces\ astaciAphanomyces astaci: Mutualistic species
