The impact of invasive crayfish on aquatic ecosystems

Doctoral thesis English OPEN
James, Joanna (2015)
  • Subject: QL

Crayfish are keystone species and ecosystem engineers that affect the structure and function of \ud aquatic ecosystems. \ud Whilst ecological impacts are caused \ud by crayfish in their native range, non\ud -\ud native crayfish species typically have a greater ef\ud fect on some other aquatic organisms and \ud ecosystem processes \ud (Chapter 2). Crayfish are extremely successful invaders that often cause \ud declines in native cra\ud yfish (Chapter 3). Of the \ud 7\ud non\ud -\ud native crayfish species in the UK, the \ud signal crayfish (\ud Pacifastacus leniusculus\ud ) is currently the most widespread (Chapter 3). Field \ud and laboratory data, however, suggest that in parts of the UK signal crayfish are \ud being \ud outcompeted by more recently introduced virile crayfish (\ud Orconectes \ud cf. \ud virilis\ud ) (Chapter 4). \ud Non\ud -\ud native\ud crayfish also threaten native crayfish through disease, notably crayfish plague \ud (\ud Aphanomyces astaci\ud ), transmission. Whilst \ud non\ud -\ud native\ud North American\ud crayfish are largely \ud resistant to \ud A. astaci\ud , infection in susceptible native European species is usually lethal. Within \ud this study 23 signal crayfish populations were screened for \ud A. astaci\ud and 13 were infected \ud (Chapter 5). Virile crayf\ud ish from the UK were also infected with \ud A. astaci\ud , and therefore should \ud also be considered as a transmission pathway for this pathogen in the UK (Chapter 6). Whilst \ud the majority of studies on crayfish symbionts are focused on \ud A. astaci\ud , crayfish host a wid\ud e \ud range of micro and macro\ud -\ud parasites. One group of particular interest are branchiobdellidans \ud (Annelida: Clitellata). Two species of these ectosymbionts, \ud Xironogiton victoriensis \ud and \ud Cambarincola \ud aff. \ud okadai\ud , were recently discovered on invasive signal cra\ud yfish in the UK \ud (Chapter 7). Owing to their abilities to survive for extended periods off the host and reproduce \ud rapidly\ud both species have a high invasion potential in the UK\ud (Chapter 8). Laboratory \ud experiments show that signal crayfish infested with \ud X. victoriensis \ud were less aggressive and \ud poorer foragers than\ud uninfested c\ud rayfish\ud , therefore these symbionts may influence \ud signal \ud crayfish\ud invasion dynamics\ud (Chapter 9)
  • References (57)
    57 references, page 1 of 6

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    Inferred
    Direct and indirect effects. (2018)
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