The activity of signal crayfish (Pacifastacus leniusculus) in relation to thermal and hydraulic dynamics of an alluvial stream, UK

Signal crayfish (Pacifastacus leniusculus) are an invasive species of global significance because of their detrimental impacts on freshwater environments and native organisms. The movement of signal crayfish was continuously monitored for 150-days through a 20-m reach of an alluvial stream in the UK. Passive integrated transponder-tags were attached to crayfish, allowing their location to be monitored relative to 16 antennae which were buried beneath the river bed. The activity of crayfish was related to water depth and temperature, which were continuously monitored within the instrumented reach. Crayfish were highly nocturnal, with less than 6% of movements recorded during daylight hours. Activity declined from September and was minimal in November when water temperature was low and flow depth was high. However, relations between environmental parameters and crayfish activity had poor explanatory power which may partly reflect biological processes not accounted for in this study. Water depth and temperature had a limiting relationship with crayfish activity, quantified using quantile regression. The results extend existing data on signal crayfish nocturnalism and demonstrate that, although signal crayfish can tolerate a range of flows, activity becomes limited as water temperature declines seasonally and when water depth remains high in autumn and winter months

Temporal variability in lotic macroinvertebrate communities associated with invasive signal crayfish (Pacifastacus leniusculus) activity levels and substrate character

This is an Open Access Article. It is published by Springer under the Creative Commons Attribution 4.0 Unported Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/Invasive signal crayfish (Pacifastacus leniusculus) are considered to be the most prevalent non-native crayfish species in Europe. Where large populations become established they have significant and long-term effects on benthic macroinvertebrate communities. However, much less is known about how community effects associated with crayfish invasion change in the short-term as a function of varying activity levels during the summer months. We examined the macroinvertebrate community composition of two lowland UK rivers, one which supported a well-established non-native crayfish population (invaded) and one in which crayfish had not been recorded (control). Colonisation cylinders were deployed which recorded community composition over a 126-day time period. Results indicate that once the activity period commences, invasive crayfish consistently altered macroinvertebrate community structure regardless of substrate character. Invaded communities displayed reduced beta-diversity compared to control sites. However, effects on the macroinvertebrate assemblage varied over the period when crayfish were active probably reflecting the behavioural activity of crayfish (which intensifies with increasing water temperature and during the spawning season) and life histories of other macroinvertebrates. The results indicate that crayfish invasions modify macroinvertebrate community composition, but over shorter timescales, the effects vary associated with their activity levels

Response of crayfish to hyporheic water availability and excess sedimentation

Crayfish in many headwater streams regularly cope with seasonal drought. However, it is unclear how landscape changes affect the long-term persistence of crayfish populations. We designed two laboratory experiments to investigate the acute effects of common landscape stressors on crayfish: water withdrawal and sedimentation. The first experiment tested the interaction among water withdrawals (four 24-h water reductions of 0, 15, 30, or 45 cm) and two substrate treatments (pebble and cobble) on the burrowing depth of crayfish. The second experiment evaluated the effects of excess fine sediment (three treatments of 0, 45, and 90% sediment) and substrate type (cobble and pebble) on crayfish burrowing depth. Crayfish were able to burrow deeper into the simulated hyporheic zone in cobble substrate when compared to pebble. Crayfish subjected to greater water withdrawals in the pebble treatment were not able to reach the simulated hyporheic zone. Excess fine sediment reduced the depth that crayfish burrowed, regardless of substrate type. Results from this study suggest excess fine sediment may reduce crayfish persistence, particularly when seeking refuge during prolonged dry conditions