Reduced survival of Antarctic benthos linked to climate-induced iceberg scouring

The West Antarctic Peninsula (WAP) is a hotspot of recent rapid regional warming and ice loss(1). The WAP sea surface freezes each winter to form a 'fast-ice' skin that can reduce iceberg drift and collisions between their keels and the sea bed, in what is termed scouring. Scouring disturbance is thus inversely correlated with fast-ice duration(2). We examined long-term records of fast ice, ice scour and mortality of benthos around Rothera research station (WAP) to determine whether there is a biological response from the sea bed coincident with fast-ice changes. Here we show that the duration of fast ice at Rothera has significantly decreased by >5 d yr(-1) over 25 years and that this is strongly correlated with increased ice scour and mortality of benthos in the shallows. The number of experimental markers at Rothera crushed by iceberg scouring increased over the past decade. We found that survival of one of the most common shallow species(3), the bryozoan Fenestrulina rugula, is linked to ice-scour frequency and has markedly decreased over the past 12 years. The chance of colonies reaching two years old, the age at which they typically begin to sexually reproduce, has halved since 1997. These findings suggest that increased scouring of the sea bed has led to higher benthic mortality, with implications for the region's biodiversity.