Small but laterally extensive buildups, composed of intergrown Bryozoa and serpulids, are ubiquitous along the eastern margin of the Coorong lagoon, SA. The anascan cheilostome bryozoan isMembranipora aciculata(MacGilli vray 1891). Neither the presence ofM. aciculatawithin South Australia nor the buildups within the Coorong lagoon have been reported previously. Dating by14C indicates that the main buildup phase, dominated by Bryozoa, took place some 700 years bp. Salinity increase and water level decrease has led to productivity reduction and subsequent diminished size of the active buildups, along with a reversal of the dominant organisms. Today only sparsely distributed colonies ofM. aciculataremain in this stressed marginal marine setting, indicating that the rate of natural environmental changes can be accelerated by man over a geologically meaningful length of time. Given the present interest in climatic change, this study provides documented evidence for a warmer global climate 700 years bp.