Benthic Food Webs in Antarctica : Would you care for some more (micro)algae?

Abstract

The West Antarctic Peninsula (WAP) is experiencing rapid warming, which will impact ecosystem processes, particularly ice-algae dynamics. As they are a vital food source for local primary consumers, this disruption is likely to cascade throughout the communities via trophic interactions. To study these effects, we sampled shallow-water benthic communities along the WAP in February 2023, focusing on Macroalgae Forests (n=2) and Sedimentary Soft Bottoms (n=3) at Dodman Island (66°S) and Blaiklock Island (67.5°S). Basal resources (sediment-associated POM, water-column POM, macroalgae, microphytobenthos) and benthic invertebrates (n=410, 49 morphospecies) were collected for stable isotope analysis. Using carbon and nitrogen ratios and Bayesian tools, we explored differences in food webs between Macroalgae Forests and Sedimentary Soft Bottoms addressing three key questions: 1) Are ice-algae more crucial as basal resource in one habitat? 2) Is there a difference in trophic diversity between Macroalgae Forests and Sedimentary Soft Bottoms? 3) How does the vertical food web structure differs between the two habitats? In the Sedimentary Soft Bottoms communities, consumers stable isotopes ratios showed a switch towards less negative carbon values, typical of ice-algae in Antarctica. This could suggest a higher vulnerability of Sedimentary Soft Bottoms communities along the WAP to alterations of ice-algae dynamics. What is more, in communities of similar species diversity, Layman metrics highlighted a higher trophic diversity in Macroalgae Forests compared to Sedimentary Soft Bottoms, supported by a wider range of basal resources. Altogether, this increased trophic diversity may indicate greater resilience of Macroalgae Forests communities to future changes. Finally, consumers in Sedimentary Soft Bottoms tended to occupy a higher trophic position than those in Macroalgae Forests, resulting in a higher mean trophic position. This may reflect a diet shift by generalist invertebrates—common in Antarctica—toward more consumption of fresh or degraded animal organic matter in habitats with fewer basal resources.