Virus-like particles associated with Lyngbya majuscula (Cyanophyta; Oscillatoriacea) bloom decline in Moreton Bay, Australia

Expansive blooms of the toxic cyanobacterium Lyngbya majuscula were observe d in 2 shallow water regions of Moreton Bay, Australia. The rapid bloom dec line (8 to <1 km(2) in <7 d) prompted an investigation of the role of cyano phage viruses in the ecophysiology of L. majuscula. Virus-like particles pr oduced by decaying L. majuscula were observed using electron microscopy. Th e virus-like particles were similar in morphology to viruses in the genus C yanostyloviridae. The effect of viruses on L. majuscula photosynthesis was investigated by: (1) creating a virus concentrate using tangential-flow ult rafiltration of seawater surrounding L. majuscula; (2) inoculating L. majus cula with the concentrate; and (3) measuring photosynthetic response using a pulse-amplitude modulated fluorometer. Virus concentrate addition resulte d in decreased initial fluorescence, decreased photochemical efficiency and decreased electron transport rate in rapid light curves after 5 d. Viruses present within L. majuscula filaments may play an important role in the bl oom dynamics of this ecologically important cyanobacterium.