Influence of Light on Prymnesium Parvum Growth, Toxicity and Mixotrophy

Abstract

The haptophyte Prymnesium parvum has a worldwide distribution, with dramatic increase in blooms in the last years. P. parvum blooms are often associated with massive fish kills and great ecological impacts and economic losses as a consequence. P. parvum is a mixotrophic organism, utilizing organic dissolved substances and particles to support its photosynthetic growth. The ability of P. parvum to produce toxic compounds, and being a mixotroph, makes it capable to outcompete other algal species for essential substances. These mechanisms are mostly enhanced when environmental conditions are not optimal for P. parvum growth. Here we report results on the growth, toxicity and mixotrophy, from experiments where P. parvum cells were grown as monocultures or together with Rhodomonas salina and exposed to different light conditions (dark, 100, 700, 2000 μmol photons m^-2 s^-1). The results showed that P. parvum growth is affected at light intensity of 700 μmol photons m^-2 s^-1 and the cells were photo-lysed when exposed to irradiances above this value. An inverse relationship between cellular toxicity and light intensity was observed, i.e. lower light irradiation induced higher cell toxicity. Phagotrophy was observed in all the conditions. P. parvum reached significantly higher cell densities when growing together with R. salina than in monocultures, while cellular toxicity was significantly reduced in the mixed cultures. Furthermore the presence of prey attenuated the negative effect of the higher irradiations on P. parvum growth.