Photosynthetic and pigment responses of sea-ice microalgae to changes in light intensity and quality

Abstract

Responses of sea-ice microalgae to changes in light intensity and quality were studied from March to May 1983 on the first-year ice of southeastern Hudson Bay (Canadian Arctic). Photosynthetic parameters P B max , α B and β B of the ice algae progressively increased throughout the sampling season. This increase paralleled the under-ice irradiance; it also paralleled the progressive increase of the diatom Nitzschia frigida in the population, from ≈45% of the cells at the end of March to almost 100% in May. The photosynthetic efficiency ( α B ) and several other photosynthetic parameters doubled when the algae were incubated under blue light, as compared with white light. This result stresses the importance of considering the photosynthetically usable radiant energy (PUR) rather than the photosynthetically available radiation (PAR), when measuring photosynthetic responses to light colour. Ice algae generally had high concentrations of chlorophyll c, which could be an adaptive response to their blue-green light environment. When incubated under white illumination, which corresponded to widening the light spectrum, the algae responded by increasing their proportions of carotenoids and chlorophyll c. These changes were in agreement with the theory of complementary chromatic adaptation. The bottom ice environment of Hudson Bay being limited by light intensity and nutrient resources, the ability to chromatically adapt may become a critical factor in species competition.