Stimulated bioluminescence as an early indicator of bloom development of the toxic dinoflagellate Alexandrium ostenfeldii

Daily patterns of stimulated bioluminescence were recorded throughout an Alexandrium ostenfeldii bloom at a remote shallow site in the Finnish Archipelago Sea. Transect measurements showed highly localized bioluminescence prior to the bloom peak. High bioluminescence, corresponding to peak dinoflagellate biomass, lasted 15 days in mid-August. Large day-to-day variation of bioluminescence intensity was observed throughout the bloom. Bioluminescence intensified after sunset, peaked around midnight and continued during the early morning. Night-time chlorophyll-a (Chl-a) fluorescence was significantly correlated with bioluminescence intensity during the bloom. The relation between Chl-a fluorescence and bioluminescence was indicative of the presence of A. ostenfeldii, confirmed by infrequent cell counts. Low concentrations of cellular paralytic shellfish poisoning toxins were detected throughout the sampling period while higher toxin concentrations were limited to the period where bioluminescence intensities were high and bioluminescence could be easily detected by eye. These results suggest that, under special conditions as described here, autonomous optical measurements may be useful to predict the onset of toxic dinoflagellate blooms, although the highly localized distribution may require advance knowledge of potential bloom locations.