MEPS prepress abstract  -  DOI: https://doi.org/10.3354/meps12363

Glacial dropstones: islands enhancing seafloor species richness in West Antarctic peninsula fjords

A. F. Ziegler*, C. R. Smith, K. F. Edwards, M. Vernet

*Email: ziegler8@hawaii.edu

ABSTRACT: The West Antarctic Peninsula (WAP) margin is dominated by glaciomarine fjords and has experienced rapid climate warming in recent decades. Glacial calving along the peninsula delivers ice-rafted debris (e.g., dropstones) to heavily-sedimented fjord basins and the open continental shelf. Dropstones provide hard substrate, increase habitat heterogeneity, and may function as island habitats surrounded by mud. We used seafloor photographic transects to evaluate the distribution and community structure of Antarctic hard-substrate megafauna and the role of dropstones as island habitats in three WAP fjords and at three nearby shelf stations. Several lines of evidence indicate that dropstones function as island habitats; their communities adhere to principles of Island Biogeography Theory with (1) a positive correlation between dropstone size and species richness, (2) an increase in the proportion of colonized dropstones with increasing dropstone size and (3) a species-area scaling exponent consistent with island habitats measured globally. Previous work on the soft-sediment megafauna of this region found strong differences in community composition between fjord and shelf sites, whereas we found that dropstone communities differed within sites at small scales (1 km and smaller). We identified 73 megafaunal morphotypes associated with dropstones, 29 of which were not previously documented in the soft-sediment megafauna. While dropstones constituted <1% of the total seafloor area surveyed, they contributed 20% of the overall species richness of WAP megabenthos at depths of 437-724 m. WAP dropstone communities adhere to key principles of Island Biogeography Theory, contribute environmental heterogeneity, and increase biodiversity in the WAP region.