Nutritional consistency of macroalgae across a sea ice cover gradient along the Western Antarctic Peninsula.

Sea ice can profoundly influence photosynthetic organisms by altering subsurface irradiance, but it is susceptible to changes in the climate. The patterns and timing of sea ice cover can vary on a monthly to annual timescale in small sub-regions of the Western Antarctic Peninsula (WAP). During the latter part of the 20th century, sea ice coverage significantly decreased in the WAP, a trend that aligns with warming in this area. Macroalgal biochemical components are impacted by light availability, often showing a close relationship between photosynthesis and biochemical compositions. We used satellite imagery of annual sea ice duration and extent as well as water turbidity during ice-free periods to identify 14 study sites that differed dramatically in sea ice coverage but were similar in terms of turbidity along the central WAP between 68° S and 64° S. The common macroalgal species Desmarestia menziesii, Himantothallus grandifolius, Sarcopeltis antarctica, and Iridaea sp. were collected by scuba divers between 5 m and 35 m depth at each site where they occurred, for later biochemical analyses. Overall percentages of major biochemical components as well as carbon and nitrogen percentages and C:N were determined and correlated with four different sea ice indices. Surprisingly, most of the chemical components were not significantly correlated with sea ice cover. The few significant correlations varied between species and chemical components. This indicates that although patterns of sea ice coverage have major implications for macroalgal abundance, on a per-biomass basis, sea ice coverage does not impact the nutritional contributions of macroalgae to food webs.