The distribution and ecology of Chirocephalus diaphanus Prévost (Branchiopoda: Anostraca) in Britain

Abstract

The anostracan Chirocephalus diaphanus is at the northwestern limits of its range in Britain. Its distribution, based on records made since first reported nearly three centuries ago, is mapped. Aspects of its ecology and behaviour that have a bearing on its requirements, and therefore on the pattern of its distribution, are noted. It is an almost defenceless, opportunistic species, largely confined to temporary pools where it avoids predators. It occurs in those regions of Britain where a high winter water table is followed by a dry spring and early summer, and is essentially confined to the zone in which there is a deficit between precipitation and evapotranspiration during the six months April to September. Such conditions prevail in the south and southeast. Cooler, wetter, northern and western parts, with their more frequent rain-days and cloud cover, do not favour the formation of suitable temporary pools. The eurythermous nature of C. diaphanus, its ability to remain active at low temperatures, and its tolerance of a wide range of other conditions, enable it to exploit, and to reach maturity in, temporary pools before such predators as can colonize them have had the opportunity to do so. Dispersal and survival during ensuing periods of drought are effected by drought-resistant resting eggs. Possible genetic, reproductive and ecological constraints relevant to events that take place towards the edge of its range are noted.

Keywords :

• Chirocephalus diaphanus
• fairy shrimp
• distribution
• ecology
• Britain