THE RELATIONSHIP BETWEEN PHOTOACCLIMATION AND PHAGOTROPHY WITH RESPECT TO CHLOROPHYLL-A, CARBON AND NITROGEN-CONTENT, AND CELL-SIZE OF CHRYSOCHROMULINA-BREVIFILUM (PRYMNESIOPHYCEAE)

The chlorophyll content of photosynthetic algae varies as a response t o changes in photon flux density. Mixotrophic algae that are predomina ntly heterotrophic have also been shown to alter their chlorophyll a c ontent as a response to changes in prey density. The marine flagellate Chrysochromulina brevifilum Parke et Manton (Prymnesiophyceae) was su bjected to a range of photon flux densities, both with and without Mar supiomonas pelliculata Jones (Pedinophyceae) as a prey organism, and t he ingestion of prey, chlorophyll a content, carbon and nitrogen conte nt and cell size were monitored. Results demonstrated that the chlorop hyll a content per cell of C. brevifilum changed with photon flux dens ity, but prey density had no effect. Under a relatively low photon flu x density (25 mu mol photons m(-2) s(-1)) both the ingestion of prey a nd the cellular concentration of chlorophyll a were greater than under a higher photon flux density (100 mu mol photons m(-2) s(-1)). Howeve r, the recent history of cultures of C. brevifilum affected both cellu lar chlorophyll a concentration and the ingestion of prey. Chrysochrom ulina brevifilum was found to have a photosynthetic capacity comparabl e to marine phytoplankton in general, with the ingestion of prey provi ding an alternative source of carbon under light-limiting conditions. This is in contrast to Poterioochromonas malhamensis in which phagotro phy appears to be the predominant nutritional mode, with chlorophyll a content increasing as the availability of prey decreases.