AUSTROPOTAMOBIUS TORRENTIUM AS AN INDICATOR FOR HABITAT QUALITY IN RUNNING WATERS?

Abstract

In the present study we tried to quantify the indication value of A. torrentium referring to habitat quality. This variable is expressed as the availability of appropriate refuge stones on the bottom and banks of running waters. The brooks occupied by the indigenous stone crayfish in Lower Austria show a high variability in the current velocity and substrate heterogeneity. Having some experience in hand searching we assumed that the distribution pattern of the crayfish on the stream bed is strongly correlated with the distribution of cobble and pebbles within a certain grain size. The aim of our study was to quantify the dependence of the shelter requirements for A. torrentium on grain size and water velocity, as well as the seasonal mobility of the crayfish. Shelters where velocity exceeded 25 cm s-1 were not occupied. Pebbles with a bearing surface greater than 300 cm2 were preferred, and the probability of crayfish occupation rose quickly as the stone’s bearing surface increased up to 900 cm2. Most individuals changed their location only a few meters (median 4 m). The distance from the point of first capture increased only little within the length of time passed until re-capture, suggesting a conservative use of space.

Keywords

• Austropotamobius torrentium
• substrate heterogeneity
• shelter requirements
• seasonal mobility
• number of crayfish outside shelters
• sexual ratio