Salinity tolerance of the South African endemic amphipod Grandidierella lignorum (Amphipoda: Aoridae)

Abstract

The endemic amphipod Grandidierella lignorum is an organism potentially suited to the toxicity testing of coastal water and sediment in South Africa. The ranges of salinity and temperature at which G. lignorum can be used for toxicity testing were investigated under laboratory conditions, in order to avoid potential confounding effects induced by these non-contaminant factors on test data interpretation. The data are discussed in the context of the known ecology of this amphipod. Amphipods were exposed to salinities of 0–56 for 96 h. Salinities were prepared using natural seawater and synthetic sea salt. Grandidierella lignorum tolerated all salinities, but showed highest survival at salinities of 7–42. Salinity tolerance was modified by temperature, with highest survival occurring between 10 and 25 °C. These represent the range of conditions at which toxicity testing can be performed. Salinity tolerances to natural and synthetic seawater did not differ significantly. Synthetic sea salt can thus be used to manipulate the salinity of media for toxicity testing without it acting as a confounding variable. The tests performed also highlight the importance of resting laboratory-cultured G. lignorum for up to six weeks between the harvesting of individuals for use in experiments.