Abstract

Crayfish live in such diverse habitats as gravel streams, brooks, ponds and lakes. While some species (e.g. Austropotamobius torrentium) have a clear preference for a special habitat type (gravel streams and brooks) others (e.g. Astacus astacus) are more opportunistic in their habitat choice. In a comparative approach we are investigating the ability of nocturnal crayfish to find odour sources under different flow conditions. Chemical attractants from food or mates are transported by advection and turbulent diffusion of the flowing water. Blindfolded crayfish can find an odour source in an artificial flow tank from a distance of 1.5 m even when upstream obstacles generate strong turbulence and disperse the odour plume into patches and filaments. They may use a combination of rheotactic and chemotactic orientation strategies to navigate through such plumes. In 'no-flow' situations (V < 1 cm/s) typical for many ponds and lakes odour plumes are confined to smaller areas and may be encountered less frequently unless they are stirred up and dispersed by organisms. Crayfish can generate their own flow fields using specialized fan-like appendages, the exopodites of the maxillipeds. Fanning draws odour from distances of several body lengths – depending on the background flow created by other sources – to their chemoreceptors. In the five crayfish species investigated the relative sizes of the fan organs increase with increasing preference for lentic habitats suggesting that flow generation is more important in habitats with no-flow conditions than in lotic flow environments.

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