Branchipodopsis species — specialists of ephemeral rock pools

Abstract

The anostracan Branchipodopsis genus is widespread throughout southern Africa and is the second most speciose anostracan taxon in this sub-continent. Branchipodopsis species are particularly dominant in small short-lived and clear rock pools, to the vagaries of which they are extremely well adapted. Such rock pools were studied in the Drakensberg region, in the eastern Free State and in south-eastern Botswana. Common features of Branchipodopsis-inhabited rock pools are the transparency of the water and the very low conductivity values (generally below 50µScm^-1, often less than 10µScm^-1). These shallow (usually less than 50cm) water bodies with limited buffering capacity show major fluctuations in pH values (often between about pH 4 and 11), depending on the time of the day and the stage in the hydrocycle. Rock pools also closely follow ambient air temperatures with resulting fluctuations of values between 10 and 40ºC. Depending on local climatic conditions, small rock pools are usually short-lived and have several wet/dry cycles during one rainy season. Branchipodopsis species are the record-holders in this race against time with maturation usually being reached within the first week after inundation. Broods of resting eggs are generally small (less than 80 eggs) but are produced almost daily. Often (in 30% of cases in south-eastern Botswana), erratic rainfall does not allow sufficient time for successful maturation and reproduction. As a safe-guarding mechanism in B. wolfi in south-eastern Botswana, only some of the eggs hatch on each occasion, depending on environmental conditions, thus extending the chances for successful recruitment. While short-range dispersal of floating eggs by overflows is common, long-range dispersal (e.g. by wind) seems to be rare and to be restricted to shallow pools with little vegetation. Limited effective dispersal may explain the high number of endemic species (e.g. four in the Drakensberg region) and the large morphological variation in some widespread species such as B. wolfi.


Keywords: anostraca; temporary rock pools; resting eggs; life history strategies; dispersal


(Afr J Aqua Sci: 2000 25: 98-104)