The population dynamics and productivity of Asellus Aquaticus (L) in Loch Leven, Kinross

Abstract

The population dynamics of Asellus aquaticus (L) in the shallow rocky areas of Lock Leven has been studied in the context of the information supplied by the International Biological Programme project on the loch . From the qualitative and quantitative results a picture of the life cycle in this particular loch has been built up, from which it has been concluded that the cycle has no synchrony with day length or other external factor, other than temperature. Once the temperature is high enough to allow successful copulation and rearing of young the animal reproduces as often as possible, under the constraint of temperature regulating durátion of growth to sexual maturity, development time of eggs and the intermoult period between releasing young and readiness for copulation. The timing of breeding activity and the period of reproductive stasis were comparable to other temperate studies and mid-way between studies from colder and warmer climates. Productivity data was calculated and compared with other results in the literature, from which it was suggested that food substrates available in the habitat influenced the production efficiency irrespective of the amount of available cover - which had a greater effect on the standing crop. Laboratory food preference tests and assimilation experiments indicated that Asellus eats the most easily ingested food substrate from the habitat, irrespective of its assimilability. Growth experiments using a variety of food substrates under various conditions indicated that growth was affected by the type of food available. From this it was suggested that the production efficiency values observed in the various studies from the literature varied according to the food substrate available: where a highly assimilable one was present, such as benthic algae, the production efficiency was high; where a poorly assimilable one was present, such as macrophyte remains, the production efficiency was lower. The significance of Asellus to the Loch Leven ecosystem is reappraised in the light of the results, especially as a source of food for trout and perch.