Climate-linked iceberg activity massively reduces spatial competition in Antarctic shallow waters

Life on Antarctica’s coastal seabed rollercoasters between food-rich, open-water, iceberg-scoured summers and food-sparse winters, when the sea surface freezes into ‘fast-ice’, locking up icebergs, reducing their seabed collisions (scouring). In the last half century, there have been massive losses of winter sea ice along the Antarctic Peninsula, as well as retreat of glaciers and disintegration of ice shelves coincident with rapid recent regional warming [1]. More calving from glaciers and ice shelves coupled with less winter ice should increase scouring of the seabed — which is where most Antarctic species live (http//www.SCAR-MarBIN.be). Polar benthos are considered highly sensitive to change, slow growing and all endemic. However, the only published effect of increased scouring on benthos has been increased mortality of the pioneer species Fenstrulina rugula, adjacent to Rothera Research station, West Antarctic Peninsula [2] (Supplemental information; Figure S1). It is likely that the recent increase in mortality in this species reflects the mortality of other species on hard substrata. A 2013 survey dive at a nearby locality (Lagoon Island) revealed large areas where no live mega- or macro-fauna could be found, the first time this has been observed there despite being regularly visited by scientific divers since 1997. Here, we report the first assemblage level changes coincident with increased scouring.