Visible light-dependent degradation of long-chain alkenes in killed cells of Emiliania huxleyi and Nannochloropsis salina

Photosensitized degradation rates of phytoplanktonic n-alkenes under visible light exposure were determined in laboratory experiments. Killed cells of Emiliania huxleyi and Nannochloropsis salina were used as source of biogenic alkenes. In E, huxleyi killed cells, minor C31 and C33 n-alkenes were strongly photodegraded, while the major C37 and C38 n-alkenes appeared particularly recalcitrant towards photochemical processes. This particular photochemical recalcitrance has been attributed to the chemical structure and localization of these hydrocarbons in the cells. Most of the n-alkenes of N. salina were strongly photodegraded in killed cells. The photodegradation of phytoplanktonic alkenes showed apparent second-order kinetics with respect to light exposure, and the half-life doses obtained logically decrease with increasing number of double bonds in these compounds. These results strongly suggest that significant amounts of phytoplanktonic n-alkenes must be photodegraded in the euphotic zone of the oceans during senescence. © 2001 Elsevier Science Ltd.