Arctic | Lower Trophic Levels MASTER’S ORAL PRESENTATION
Arctic lagoon benthos: Spatial and temporal variation of infaunal communities Presenter: Danny Fraser , danielfraser@utexas.edu, University of Texas Marine Science Institute Susan Schonberg , susan.schonberg@utexas.edu, University of Texas Marine Science Institute Kenneth Dunton , ken.dunton@utexas.edu, University of Texas at Austin Katrin Iken , kbiken@alaska.edu, University of Alaska - Fairbanks Shallow (<5 m) coastal lagoons of the Alaskan Arctic are highly dynamic environments that sustain benthic invertebrate communities. At water depths < 2 m, congelation sea ice of 1.5 - 1.8 m thickness extends nearly to the bottom, often freezing the seabed or exposing infaunal organisms to extreme temperature (-6 C) and hypersaline (>100) conditions. At water depths >2 m, brine exclusion from overlying fast ice can produce slightly hypersaline waters, but the seabed escapes freezing. Spring breakup and river inputs bring a freshwater surge into these lagoons that often exposes benthic organisms to brackish or freshwater conditions for several days. During the summer open-water period, salinities steadily increase from exchange with offshore waters, but increased fetch and summer storms result in highly turbid conditions. Each distinct season represents different disturbances to the benthos that infauna must adapt to, but the seasonal progression of these communities, which are critical feeding habitats for migrating fish and waterfowl, is largely unknown. From 2018 – 2022, our quantitative benthic sampling with the Beaufort Lagoon Ecosystem Long Term Ecological Research in four coastal lagoons during April, June, and August have revealed depth-dependent spatial and temporal variations in their invertebrate community structure. In all four lagoons, the infaunal communities in shallow (< 2 m) areas are low in Shannon diversity (H`) and Margalef species richness (S) and mostly comprised of the same species, including a freeze-tolerant polychaete. Spatial variability in benthic community structure is mostly relegated to the deeper (> 2 m) areas of every lagoon; all four lagoons possessed a distinct community structure mostly driven by different polychaete species. We noted an overall increase in H` and S from east to west across the Beaufort Sea coast. Distance-based redundancy analysis showed differences in deep benthic community structure were attributed to the static variables of longitude, depth, and sediment grain size. We found seasonality of H`, S, and infaunal density was restricted to the shallow (< 2 m) stations of all lagoons, with a resilient benthic community that must reassemble every year. Little seasonality is seen in the deeper stations of all lagoons, suggesting a more stable habitat that likely serves as the source populations for the annual recolonization of shallow benthic communities exposed to freezing and hypersaline conditions.
Alaska Marine Science Symposium 2023 69
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