The Effects of Variable Light and Lipids on the Water Column Distribution and Interactions of Phytoplankton

Abstract

The mechanisms and stimuli that control buoyancy and population numbers in planktonic diatoms are poorly understood. Light, lipids, biovolume, size, and ion regulation have been suggested as possible mechanisms controlling water column distribution. In this study, changes in buoyancy of algae grown as combinations of mono and mixed cultures were measured along with the effects of a varying light direction on the water column distribution of the planktonic diatoms Thalassiosira sp. 1, Thalassiosira pseudonana and Staurosira construens var. venter. Clonal populations were grown in monoculture or in factorial combinations under top and bottom light conditions. No difference in water column distribution or growth between samples exposed to light from above or light from bellow was observed. Oil played an insignificant role in buoyancy regulation. The only species that was buoyant throughout the study was Thalassiosira sp. 1. The larger size and surface area-to-volume ratio of this species indicates a relationship between an increase in buoyancy and increased biovolume. Species specific water column distributions were observed between the monoculture study and the mixed culture study, indicating species specific interactions among phytoplankton may play a significant role in influencing their water column distribution and their degree of buoyancy.