Vertical niche separation between two closely related planktonic flagellate species (Rhodomonas lens and Rhodomonas minuta v. nannoplanctica)

Abstract

R. minuta var. nannoplanctica Skuja and R. lens Pascher et Ruttner perform vertical migrations. From sunrise until afternoon they adjust their vertical position to an optimum light-intensity, which is for R. minuta 2.5 times higher than for R. lens. The spatial separation of both species increases throughout the whole light phase. The species distinction between them has been questioned, but can be maintained not only because of morphological differences but because they occupy different niches within the plankton community.