14:30 〜 14:45
[MIS11-04] Seasonal and altitudinal variations in pigment and species composition of snow algae bloom on the Tsurugi-sawa perennial snow valley in Mt. Tateyama, Toyama, Japan.
キーワード：雪氷、色素組成、群集構造、藻類、越年性雪渓
Snow algae, photosynthetic microorganisms, inhabit the snow surfaces in Japanese mountainous regions during the melting seasons. Snow cover in such areas comprises seasonal snowpacks and perennial snow valleys; the former vanishes in summer, while the latter persists throughout the year. While snow algae bloom has been extensively studied in seasonal snowpacks, there is a gap in understanding their dynamics in perennial snow valleys. This study examines the pigment and species composition of colored snow collected from the Tsurugi-sawa snow valley in Mt. Tateyama, Japan, during the melting seasons of 2021 and 2022. The cell volume biomass of snow algae exhibited a distinct pattern, increasing from June to August in the upstream area near the high-elevation ridges and from August to October in the downstream area of the valley floors. Dominant cells in the upstream samples were identified as orange spherical cells, while oval cells with green and orange pigmentation prevailed in the downstream samples. Analysis of the 18S ribosomal RNA (18S rRNA) gene revealed five major amplicon sequence variants (ASVs) of snow algae belonging to the Chloromonas (Chlorophyta−Chlorophyceae) and Hydrurus (Ochrophyta−Chrysophyceae) groups. Algal community structures in June differed significantly from those in August and October. Pigment composition extracted from the colored snow varied across study sites and seasons. In the upstream area, secondary carotenoid pigments increased from June to August, while in the downstream area, secondary carotenoid pigments dominated in June, shifting to an increase in primary carotenoid pigments from August to October. Notably, this study reports that snow algae emerge from August onwards in perennial snow valleys for the first time. These findings suggest a correlation between the timing of snow algae bloom, community structure, and pigment composition with snow density, solar elevation, and/or shorter daylight duration due to the valley topography.