Toxicity associated with commonly occurring cyanobacteria in surface waters of the Murray-Darling Basin, Australia

Abstract

Surveys of cyanobacterial blooms were made over four consecutive summer seasons (1990-93) in surface waters of the Murray-Darling Basin in south-eastern Australia to determine the incidence and geographic distribution of toxicity associated with a range of recognized taxa.<P.

In all, 231 field samples and 143 cultured isolates, representing 13 genera, were tested for toxicity by intra-peritoneal mouse bioassay. Toxicity was recorded in 42% of all field samples and was expressed quantitatively on the basis of both dry weight and cell number. Anabaena was the most abundant genus in blooms occurring in riverine and wetland habitats, and Anabaena circinalis was prominent in all field samples that were neurotoxic. Neurotoxicity was not demonstrated in any other species of Anabaena, or in any other genus, in both field and cultured material. Assays for anatoxin-a were negative, and symptoms of neurotoxicity in mice were not consistent with those reported elsewhere for anatoxin-a(s).

Hepatotoxic blooms occurred predominantly in standing waters and were invariably caused by Microcystis aeruginosa f. aeruginosa throughout the greater part of the Basin. Toxic blooms of Nodularia spumigena were recorded only in Lake Aiexandrina and Lake Albert at the mouth of the River Murray. Hepatotoxicity was also demonstrated in strains of Cylindrospermopsis raciborskii, which was previously recognized in Australia only as a subtropical cyanobacterium.