Quantificationof Factors controlling the Development of Anabaena Circinalis Blooms

ReportNo WSAA 88

January 1995

SYNOPSIS

TheAlgal Bioassay technique has enabled the quantification of several factors ofmajor importance in the development of Anabaenacircinalis, a potentially toxic cyanobacterial species. A combination ofhigh water temperature (optimum 35°C) and saturatinglight intensity (120 mE/m²/sec),comparable to summer conditions, resulted in optimum growth rate. At lowerwater temperatures, photoinhibition of algae occurred at approximately 10% ofoptimum surface light intensity (approx. 2000 mE/m²/sec),indicating that surface blooms are less likely to persist during winter.Increased growth rate was found to occur at a total nitrogen (N) to phosphorus(P) ratio of about 10:1 at constant P and with increasing P concentration atconstant N, although luxuriant uptake of P was found to be very efficient inmaintaining algal cells. This cyanobacterium is a freshwater species displayinginhibition in growth at approximately 7 ppt salinity. Silica too, was found toinhibit the growth of A. circinalisat concentrations above 5 mg/L. Finally, tripton particles were found toinfluence growth rate by the adsorption of P and essential trace elementsrequired by cyanobacteria for growth.

Inorder to prevent the development of cyanobacterial blooms, total catchment management (TCM) must be applied whereby acombination of factors are manipulated to select against this troublesome groupof algae from flourishing in our waterways. Quantification of Anabaena circinalis growth at theenvironmental parameters selected in this study may aid in enabling the mostefficient TCM applications to be made.

Copiesof the Report are available from WSAA, price $A50. Orders may be placed throughthe Bookshop at www.wsaa.asn.au or by email to info@wsaa.asn.au.