Toxicant effects on the zoospore stage of the marine macroalga Ecklonia radiata (Phaeophyta: Laminariales)

Marine macroalgae provide both food and habitat for a range of other organisms in nearshore coastal areas. The effect of contaminants upon macroalgae is therefore an important aspect to consider in the regulation of marine effluent discharges. Unfortunately, a lack of standardized bioassay protocols has limited the extent to which macroalgae have been used in routine toxicity testing. In the present study, the effect of selected reference toxicants (hexavalent chromium, copper and zinc) upon germination and growth of zoospores of the marine macroalga Ecklonia radiata (C.Ag.) J.Ag. was investigated in 48 h bioassays. E. radiata is often a dominant member of near-shore subtidal communities in temperate Australia, New Zealand and South Africa, regions in which toxicological data for native species are lacking. Release of zoospores was induced in the laboratory and settled spores were exposed to the metals. Zoospores from 3 different populations in Western Australia and 1 population in Victoria were tested to evaluate geographic variation in response. There were no significant differences in 48 h ECS, values between the populations tested. At 20 degrees C, ECS, values for germination ranged between 54.9 and 65.1 mg l(-1) for chromium, 320 and 470 pg l(-1) for copper and 18.1 and 18.6 mg l(-1) in 2 bioassays conducted with zinc. Germination of control zoospores was greater than 90% in all bioassays. Germination tube growth was the more sensitive of the 2 endpoints examined. EC50 values for growth ranged between 31.8 and 47.5 mg l(-1) for chromium and 180 and 210 mu g l(-1) for copper. Coefficients of variation for EC50 values from tests with chromium or copper were between 24 and 47% for germination and 11 and 54% for germination tube growth. With its wide distribution, ecological significance and simple bioassay methodology, E. radiata is well suited for use in routine marine toxicity testing.