Community recovery following catastrophic iceberg impacts in a soft-sediment shallow-water site at Signy Island, Antarctica

Abstract

Ice disturbance is possibly the major structuring element of polar nearshore biological communities. Effects range from encapsulation by ice forming on rock substrata to gouging and trampling by bergs. Some 15 to 20% of the world's oceans are affected by this phenomenon, yet measurements of the extent of biological destruction from iceberg impacts and subsequent community recovery are very rare. Communities can be held at early successional stages, or even completely destroyed by scouring, and these effects occur from the intertidal to depths around 500 m in Antarctica. The wide scales of disturbance intensity are thought to add to the overall high levels of Antarctic benthic biological diversity, which has recently been shown to be similar to tropical areas. Data here indicate >99.5% removal of all macrofauna and >90% removal of most meiofauna by iceberg impact on a soft-sediment habitat at Signy Island, Antarctica. Species return was via locomotion, advection or larval recolonisation, and all 3 mechanisms worked on different timescales. Locomotion caused groups to return within 10 d of an impact. Storms with wind speeds around 100 km h-1 induced water movements intense enough to advect meiofauna to the 9 m depth site. However, it was only during the strongest storm which occurred during the study (maximum wind speed 148 km h-1) that water movements were powerful enough to redistribute small macrofauna such as the bivalve Mysella charcoti.