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

The effects of diet and cannibalism were assessed from changes in the bioluminescence potential of 2 speclvb of the heterotrophic dinoflagellate Protoperidinium fed 4 specles 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 cf. divergens and P. crassipes was sign~ficantlg affected by dinoflagellate diet. Total mechanically stimulable luminescence (TMSL) of P. cf diveryens fed d~fferent dinoflagellate diets was s ign~f~cant ly correlated with feeding frequency (the percent of feeding P. cf. divergens cells) rather than with populat~on growth rate. P. cf. divergens displayed high levels of TMSL and feeding frequency on a dlet 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 w ~ t h dinoflagellate diet \yere related to the amount of chemical substrate available for luminescence, rather than changes in the excitatiodtransduction process. Individually isolated cells remained viable for only 3 to 5 d w1thou.t food and exhibited reduced biolun~inescence. However, cells maintained in groups surv~ved at least 16 d w~thou t 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 biolurninescence 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 orderswimming (for grazing) > biolurninescence (for reducing predation) > reproduction (for increasing the population).