The salinity tolerance of eggs and hatchlings of selected aquatic macroinvertebrates in south-east Australia and South Africa

The effect of rising salinity levels on freshwater ecosystems is of concern in many parts of the world, including Australia and southern Africa. Most studies on the salinity tolerance of freshwater macroinvertebrates only consider older life-stages, which are suspected of being more tolerant than early life-stages, such as eggs and hatchlings. The salinity tolerances of ten taxa from south-east Australia and two taxa from South Africa, to the artificial seawater, Ocean Nature, were investigated. From the Barwon River in south-west Victoria, the following taxa were tested Amarinus lacustris (Hymenosomatidae), Paratya australiensis (Atyidae) Physa acuta (Physidae), Lymnaeidae, Plectrocnemia sp. (Polycentropodidae), Anisocentropus sp. (Calamoceratidae), Hydrobiosidae, unidentified Polycentropodidae and Dinotoperla thwaitesi (Gripopterygidae). Chironomus tepperi ( Chironomidae) from a laboratory colony stocked from central New South Wales was also investigated. The South African limpets Burnupia stenochorias (Ancylidae) were collected in the Eastern Cape and shrimps Caridina nilotica ( Atyidae) from a colony stocked from Kwazulu-Natal were studied. The salinity tolerances of the eggs and hatchlings ranged from 0.8 to > 47 mS cm(-1) with a mean of 17 mS cm(-1). Where reliable estimates are available, the eggs or hatchlings had a salinity tolerance between 5% and 100% of the 72-hour LC50 of older stages, although for insects this was <50%. This study has thus confirmed that salinity tolerances of young stages can be less than the acute tolerances of older stages.