Antarctic shallow water benthos under glacier retreat forcing

The West Antarctic Peninsula is one of the fastest warming regions on Earth. Faster 20 glacier retreat and related calving events lead to more frequent iceberg scouring, 21 fresh water input and higher sediment loads, which in turn affect shallow water 22 benthic marine assemblages in coastal regions. In addition, ice retreat creates new 23 benthic substrates for colonization. We investigated three size classes of benthic 24 biota (microbenthos, meiofauna and macrofauna) at three sites in Potter Cove (King 25 George Island, West Antarctic Peninsula) situated at similar water depths but 26 experiencing different disturbance regimes related to glacier retreat. Our results 27 revealed the presence of a patchy distribution of highly divergent benthic assemblages within a relatively small area (about 1 km2). In areas with frequent ice 29 scouring and higher sediment accumulation rates, an assemblage mainly dominated 30 by macrobenthic scavengers (such as the polychaete Barrukia cristata), vagile 31 organisms, and younger individuals of sessile species (such as the bivalve Yoldia 32 eightsi) was found. Macrofauna were low in abundance and very patchily distributed 33 in recently ice-free areas close to the glacier, whereas the pioneer nematode genus 34 Microlaimus reached a higher relative abundance in these newly exposed sites. The 35 most diverse and abundant macrofaunal assemblage was found in areas most 36 remote from recent glacier influence. By contrast the meiofauna showed relatively 37 low densities in these areas. The three benthic size classes appeared to respond in 38 different ways to disturbances likely related to ice retreat, suggesting that the 39 capacity to adapt and colonize habitats is dependent on both body size and specific 40 life traits. We predict that, under continued deglaciation, more diverse, but less 41 patchy, benthic assemblages will become established in areas out of reach of glacier-42 related disturbance