Snow cover affects ice algal pigment composition in the coastal Arctic Ocean during spring

摘要

Specific pigments produced by algae and their degradation products can provide considerable information on the taxonomic composition and photo-physiological state of algal communities. However, no previous study has looked at ice algal pigment composition in the high Arctic. We examined the bottom ice algal pigment composition in the Canadian Beaufort Sea under various snow cover conditions during the spring bloom (March to June 2008). During the early and peak bloom periods, pennate diatoms (pigment Type 2, containing chlorophyll [chl] c_2 and c_3) dominated the chl a biomass. Diatoms containing chl c_1 (pigment Type 1) and chlorophytes were only present under high snow cover. A more diverse community was observed during the post-bloom when only low snow cover sites remained due to snow melt, with higher relative contributions of chlorophytes, prasinophytes and dinoflagellates, associated with the loss of diatoms, along with increased abundance of large empty diatoms (from microscopy) and with signs of a deteriorating physiological condition (increases in chlorophyllide a and the allomer of chl a). The ratio of photoprotective to photosynthetic pigments was generally higher at low snow cover sites, increasing seasonally with the bottom ice irradiance. Low snow cover sites differed also by having more Type 2 diatoms, increased photoprotection and greater chl a biomass during the early bloom. In addition, these sites showed increases in chl a degradation pigments that may be due to the presence of chlorophyllide-rich pennate diatoms, since the increasing biomass suggests healthy physiological conditions at that time. This study highlights the important influence of light and the light-acclimation plasticity in Arctic sea ice algae.