A toxic bloom of Nodularia spumigena Mertens in Orielton Lagoon, Tasmania

Abstract

A bloom of Nodularia spumigena Mertens occurred in Orielton Lagoon, Tasmania, a shallow, eutrophic coastal embayment, between December 1992 and March 1993. The N. spumigena bloom was preceded by a eustigmatophyte bloom and was followed in March-April 1993 by a bloom of the diatoms Nitzschia closterium (Ehrenb.) Smith and Chaetoceros socialis Lauder. The Nodularia spumigena bloom may have been stimulated by low salinity (15-20 g kg^-1) in the lagoon during December and January. Culture experiments with N. spumigena strains isolated from the lagoon showed best growth at salinities between 0 and 24 g kg^-1 and less optimal growth at a salinity of 35 g kg^-1. Akinete production in culture was positively correlated (P < 0.001) with increasing salinity of growth media. The collapse of the N. spumigena population may have been triggered by decreasing water temperature in March, although this cannot be conclusively proven with the limited physico-chemical data available. High-performance liquid chromatographic (HPLC) analyses of bloom samples showed high concentrations (2000-3500 µg g^-1 dry weight) of the cyclic pentapeptide hepatotoxin nodularin in samples collected during the peak of the N. spumigena bloom in January and February. Nodularin content of the bloom decreased as the population declined, owing to the decrease in abundance of N. spumigena and the release of nodularin by dying cells. A culture of N. spumigena isolated from Orielton Lagoon produced nodularin at concentrations comparable to those observed in field samples. A second HPLC peak, eluting very close to nodularin and with a similar ultraviolet spectrum, was observed in some field samples. This compound may be the ADDA-C8 stereoisomer of nodularin.