Effects of glacial discharge on thallus condition of northern rockweed (Fucus distichus) in the Gulf of Alaska

Abstract

Glacial melt due to climate warming is expected to accelerate in high-latitude ecosystems, necessitating an understanding of how this may influence foundation species in coastal systems. The goal of this study was to use a gradient of glaciation along five watersheds in a south-central Alaskan fjord to investigate the relationship between downstream effects of glacial cover and the thallus condition of the habitat-building rockweed, Fucus distichus. We used compositional and biochemical data from F. distichus thallus samples collected across six months from all five watershed sites and related them to nearshore environmental data taken at each month and site. Most thallus condition metrics changed more related to sampling month than watershed glacial cover, with most metrics decreasing over the sampling period. This was possibly related to the build-up of more structural materials such as cell wall and other chemical structural elements during later-season growth. Lipid content was the only metric that differed systematically by watershed glacial cover, with lower lipid content at the sites with higher glacial cover and assumed higher glacial discharge of the watershed. Most thallus condition metrics were related to water temperature, with the increase during the sampling period reflecting a seasonal warming rather than an influence of increased glacial discharge in the summer. Less effects were seen from lower salinity and higher turbidity in the summer related to seasonally increased glacial discharge. These results indicate that F. distichus is tolerant to the currently experienced range of environmental conditions in glacial watersheds, at least during the sampling years. Possible effects of increasing glacial discharge conditions on other F. distichus life stages (e.g., zygotes) that are vital to maintain genetically diverse populations, or the ability of this species to maintain high primary production and provide habitat and high-quality food for coastal consumers under increasing melt or warming conditions, remain uncertain.