Comparing test systems to measure the salinity tolerance of freshwater invertebrates
AbstractThere have recently been several studies into acute salinity tolerance of freshwater invertebrates using different methods, making comparisons between studies difficult. The alternatives focus on experimental flow regimes and ionic proportions. In this study non-rheophilic riverine taxa collected in South Africa and south-east Australia were variously exposed to solutions of sodium chloride (NaCl) and the artificial sea salt, Ocean Nature, in flowing and still water. South African species: Euthraulus elegans (Ephemeroptera: Leptophlebiidae), Micronecta piccanina (Hemiptera: Corixidae), Burnupia stenochorias (Gastropoda: Ancylidae) and Caridina nilotica (Decapoda: Atyidae); Australian collected species: Daphnia carinata (Cladocera: Daphniidae), Micronecta annae and Physa acuta (Gastropoda: Physidae). The main findings were:
· The salinity tolerances of a range of taxa were not affected by flow regimes
· Taxa were less sensitive to the artificial sea salt than NaCl
· There was, however, a direct relationship between the LC50 values from both salts. This relationship was used to compare the LC50 values from studies testing (artificial or natural) sea-water or NaCl.
· The comparison indicated variation in the mean LC50 between studies that is probably, at least in part, due to the range of taxonomic groups and rarities of species tested.
When comparing the acute salinity tolerance of non-rheophilic invertebrates, the salt source and criteria for choosing species affect the results, but the flow environment probably does not.
Keywords: Stream invertebrates, Acute salinity tolerance, Test system
WaterSA Vol.30(4) 2004:499-506