Effect of red tide dinoflagellate diet and cannibalism on the bioluminescence of the heterotrophic dinoflagellates Protoperidinium spp.

Abstract

The effects of diet and cannibalism were assessed from changes in the bioluminescence potential of 2 species of the heterotrophic dinoflagellate Protoperidinium fed 4 species of red tide dinoflagellate prey and also maintained without added prey. The use of bioluminescence as a sensitive indicator of nutritional status and feeding was explored. The bioluminescence of Protoperidinium ci. divergens and P. crassipes was significantly affected by dinoflagellate diet. Total mechanically stimulable luminescence (TMSL) of P. cf. divergens fed different dinoflagellate diets was significantly correlated with feeding frequency (the percent of feeding P. cf. divergens cells) rather than with population growth rate. P. cf. divergens displayed high levels of TMSL and feeding frequency on a diet of Scrippsiella trochoidea which did not support population growth. Diet did not affect the total number of flashes produced per cell; therefore, changes in TMSL with dinoflagellate diet were related to the amount of chemical substrate available for luminescence, rather than changes in the excitation/transduction process. Individually isolated cells remained viable for only 3 to 5 d without food and exhibited reduced bioluminescence. However, cells maintained in groups survived at least 16 d without added prey and maintained levels of bioluminescence similar to those during favorable prey conditions. Cannibalism observed during this time may have enabled cells of P. cf. divergens to feed and therefore produce high levels of bioluminescence in the absence of added prey. Changes in swimming speed were less than changes in bioluminescence. The results of the present study suggest that energy utilization may be prioritized in the following order: swimming (for grazing) > bioluminescence (for reducing predation) > reproduction (for increasing the population).