The fine cell morphology of diatom Skeletonema costatum and its ecological significance
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Abstract
The appearance of thin threads attached to cells of the Skeletonema spp. is a relatively uncommon and poorly understood phenomenon. Skeletonema costatum (Greville) Cleve, 1873 forming silicified threads less than 0.2 µm in diameter and up to 50 in length, has been studied for the first time in the Black Sea. The effect of various concentrations of silicic acid (DSi) on fine morphology was investigated, and an assumption about the ecological significance of this phenomenon was put forward. It was shown that the formation of highly silicified threads requires a concentration of DSi above 2 µM. One of ecological meanings of the treads may be the creation of a protective barrier that decreases the grazing of S. costatum cells by tintinids. Another possible ecological significance of threads is that they may promote the formation of dying cell aggregates which drastically increases the cell sinking rate. This process is essential for operating a biological carbon pump in marine ecosystems.