The biogeography and ecophysiology of snow and glacier algae

Abstract

This thesis employed laboratory incubations, cryosphere wide sampling, amplicon sequencing, and
in-situ ecophysiological studies to explore the diversity, biogeography, and adaptations of snow and
glacier algae to their unique frozen environments. These microalgae are some of the least studied
organisms on our planet, yet some of the most vulnerable to climate change which is rapidly
diminishing snowpack and glacier ice resources. Studies on the growth and ecophysiology of
cultured Arctic and Antarctic snow algal strains under gradients of temperature, light, and nitrate
availability revealed that low temperatures (5 °C) increase carrying capacities despite mimicking
high-light stress, confirming studied strains as psychrophilic. Cultured snow algae approached
optimal Redfield carbon-to-nitrogen (C:N) ratios under nutrient replete conditions, which increased
under nitrate-limited conditions.Chloromonas spp. acclimated better to higher light intensities than
Arctic Microglena sp., with datasets highlighting the presence of both inter- and intra-specific
differences in responses to environmental stressors amongst studied strains, alongside the
capacity for dynamic acclimation to suboptimal in-situ conditions. Metabarcoding of 18S, ITS2, and
rbcL for communities sampled across the cryosphere (European Alps, Svalbard, and Signy Island,
Antarctica) revealed extensive cryptic diversity across snow and glacier algae, with unique glacier
algal phylotypes identified in samples from maritime Antarctica. Snow algal genera Sanguina and
Chlainomonas were also shown to have wider distributions than previously known. Subsequent
ecophysiological characterisation of assemblages across sampling sites revealed a complex
interplay between communities and their environment. Abundant algal blooms showed little sign of
nutrient limitation, despite the apparent oligotrophy, underscoring the oligotrophic-bloom-paradox.
Snow algal assemblages displayed variable photophysiology and cellular stoichiometry, with C:N
ratios in comparatively nutrient rich (but still oligotrophic) conditions approaching optimal Redfield
dynamics, matching laboratory findings. Glacier algae however, exhibited more consistent
photophysiology and stoichiometry across locations, with community composition and abundance
better reflecting habitat diversity.

Date of Award	18 Mar 2025
Original language	English
Awarding Institution	University of Bristol
Supervisor	Christopher J Williamson (Supervisor)