The relationship between water quality and indigenous and alien crayfish distribution in the Czech Republic: patterns and conservation implications

* Although the noble crayfish (Astacus astacus L.) and stone crayfish (Austropotamobius torrentium Schr.) are critically endangered European species, their water quality requirements are not sufficiently known. * This study aimed to investigate the physico-chemical tolerance range of the noble and stone crayfish in the Czech Republic compared with those of the invasive spiny-cheek crayfish (Orconectes limosus Raf.). At 1008 sites with crayfish either absent or present, the following 18 physico-chemical variables were investigated: dissolved oxygen, pH, BOD5, CODCr, ammonia, ammonium ions, nitrite, nitrate ions, zinc, copper, iron, aluminium, calcium, sulphates, chlorides, total phosphorus, suspended solids, and conductivity. * For the noble and stone crayfish, only minor differences in water quality were found. This indicates that the water quality requirements of these indigenous crayfish are likely to be very similar. However, significant differences in water quality were observed between locations inhabited by indigenous crayfish and those inhabited by the invasive spiny-cheek crayfish. * Based on these findings, we hypothesize that the invasive species is able to survive in locations with lower water quality. Simple logistic regression models were then used to examine relationships between the presence or absence of noble crayfish and each evaluated water quality variable. The presence of this species was related significantly with those variables that indicate nutrient enrichment (particularly ammonium, BOD5, and nitrite) and to iron. * Overall, although the indigenous crayfish species were found at several sampling sites that had impaired water quality, the statistical analyses indicate that the indigenous species require water of high quality. Improvement in water quality is therefore an important step in sustaining indigenous crayfish populations. Copyright © 2012 John Wiley & Sons, Ltd.