Phytoplankton and light during the northern high-latitude winter

• Published in: Journal of plankton research 2010-06, Vol.32 (6), p.899-912
• Main Authors: Eilertsen, Hans Chr, Degerlund, Maria
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Brackish; Fundamental and applied biological sciences. Psychology; General aspects; light; Marine; north; phytoplankton; Skeletonema costatum; Synecology; winter
• ISSN: 0142-7873; 1464-3774
• DOI: 10.1093/plankt/fbq017

Investigations performed on the phytoplankton winter stocks in five of the largest northern Norwegian fjords (Porsangerfjord, Altafjord, Ullsfjord, Balsfjord, Malangen) revealed that phytoplankton biomass was extremely low both in December and February. Concentrations of Chlorophyll a typically were 0.05–0.10 µg L−1. Abundances of vegetative cells were low, and species relevant to the spring bloom were hard to find. The only species that probably can survive the low irradiances that prevails during the winter is Skeletonema costatum sensu lato. From this, but also from the fact that the spring blooms in the area in question are highly reproducible both in terms of timing and species succession, we conclude that the inoculum from the spring bloom is not made up of pelagic vegetative cells that survive the winter. Despite the fact that darkness prevails for almost 2 months during winter, backscattered light (from sky and clouds) may influence the water column. This radiation may, during mid-day, reach phytoplankton photosynthesis compensation (Ic) levels. This is, in our opinion, a rather overlooked and undescribed phenomenon that may prove important for the understanding of photoperiod regulated ecological processes and visual feeding.