Colonisation vs. disturbance: the effects of sustained ice-scouring on intertidal communities

Shoreline plant and animal communities close to a retreating tidewater glacier on the sub-Antarctic island of South Georgia displayed a series of physical and biological gradients from the open sea to the glacier terminus. These included increasing scouring intensity caused by floating and/or grounded ice fragments as well as decreasing diversity and abundance of both macroflora and macrofauna. The correlation between gradients suggests that shoreline scouring intensity can be directly quantified from plant diversity and abundance, and that the colonisation of coastlines exposed to sustained ice-scouring is not stochastic like that following single massive ice-scouring events, but directional like recovery from small scale disturbances. However, colonisation following small-scale disturbance events is much more rapid than that associated with continual scouring. Indeed recovery from continual scouring is so protracted that affected shores are held for a prolonged period at a particular phase of the normal spring annual spring colonisation process by local ice-scouring intensity.