Assessing the chronic toxicity of copper and aluminium to the tropical sea anemone Exaiptasia pallida

•The tropical sea anemone Exaiptasia pallida is sensitive to metal exposure.•Oral disc growth & asexual reproduction of E. pallida can be used to assess health.•There is limited aluminium toxicity data available for tropical marine organisms.•Exposure to 2270 µg/L aluminium caused 50% less asexual reproduction.•Exposure to 35 µg/L copper caused 50% less growth and asexual reproduction.

The world's most productive bauxite mines and alumina refineries are located in tropical or sub-tropical regions. The discharge water from alumina refineries can contain elevated aluminium (Al, <0.45 µm fraction), from 30 to 1000 μg/L. There is a need for additional information on the toxicity of Al to aquatic organisms to improve the environmental regulation and management of alumina refinery operations in tropical coastal regions. A 14-d chronic toxicity test was developed for the tropical sea anemone Exaiptasia pallida. Asexual reproduction and growth rates of E. pallida were assessed using the number of lacerates produced and oral disc diameter. The comparative sensitivity of E. pallida was assessed through exposure to a commonly-used reference toxicant, copper (Cu) at 28 °C, with asexual reproduction toxicity estimates of 10% (EC10) and 50% (EC50) effect concentrations, calculated as 8.8 µg/L (95% confidence limits (CL): 1-18 µg/L) and 35 µg/L Cu (95% CL: 30-39 µg/L), respectively. Growth rate was a suitable additional endpoint (EC50=35 µg/L Cu, 95% CL: 23-49 µg/L). The EC10 and EC50 for Al (total fraction, based on reproduction) at 28 °C were 817 µg/L (95% CL: 440-1480 µg/L) and 2270 µg/L (95% CL: 1600-3900 µg/L), respectively. The toxicity of Cu and Al was also assessed at 24 °C and 31 °C, representing average year-round water temperatures for sub-tropical and tropical Australian coastal environments. Changing the temperature from 28 °C to 24 °C or 31 °C resulted in up to 45% less reproduction of anemones and increased their sensitivity to Cu (EC50s at 24 °C=21 µg/L, 95% CL: 17-26 µg/L and at 31 °C=23 µg/L, 95% CL: 21-25 µg/L). Sensitivity to Al was reduced at 24 °C with an EC50 of 8870 µg/L (95% CL: 6200-NC). An EC50 for Al at 31 °C could not be calculated. This test is a reliable and sensitive addition to the suite of standardised tests currently developed for tropical marine species.