Assessing the Down-Fjord Mechanistic Relationships of Biodiversity and Abundance of Antarctic Benthic Macrofauna of Andvord Bay

Abstract

Glaciomarine fjords exhibit substantially different ecosystem forcing than adjacent continental shelves and can be highly sensitive to climate warming. Extensive research indicates that subpolar Arctic fjords are heavily influenced by glacial meltwater and sediment inputs, resulting in high turbidity and seafloor burial rates. These physical disturbances yield macrofaunal communities with low abundance and diversity. In contrast, poorly-studied sub-polar fjords along the Western Antarctic Peninsula (WAP) sustain weak meltwater influences, resulting in low turbidity and seafloor burial rates. Thus, benthic communities in WAP fjords may not currently be limited by turbidity and burial disturbance and may have the potential to harbor abundant and diverse macrobenthic communities. Here we characterize the benthic macrofaunal community of Andvord Bay, a subpolar fjord along the warming WAP. We compare down-fjord changes in macrobenthic abundance, diversity, and functional-group structure (groups of organisms with different ecosystem roles) to a variety of potential ecological drivers. These ecological drivers include sediment burial rate, sediment Chl-a concentration (an indicator of labile detritus availability), and sediment-community respiration (an indicator of seafloor detrital carbon flux). Sediment disturbance likely only limits the abundance of benthic communities of the inner fjord regions, but is too weak in the middle fjord to open shelf to limit the communities. The trend in abundance outside of the disturbed inner fjord sites is likely driven by POM flux to the seafloor. In areas of high abundance, the large food flux to the seafloor promotes richness, but the sedimentation disturbance is not enough to promote evenness. As global sea and air temperatures continue to rise, glacial melt and sedimentation in WAP fjords will increase, resulting in low benthic abundance and diversity, resembling present-day Arctic fjords.