PROXY FORAMINIFERAL RECORD OF HUMAN IMPACT ON NEW ZEALAND’S COASTAL MARINE ENVIRONMENT (Invited Presentation)

New Zealand was the last significant land, except for Antarctica, to be colonised by humans. Since then, in the last 800 years, 70% of the forest has been felled, 46% of the native land birds have become extinct and the human population now exceeds 4 million. In the marine realm, fish stocks and natural populations of edible shellfish have been decimated. Studies on foraminiferal faunas in Holocene sediment cores show that the impacts of heavy metals and other pollutants discharged into coastal waters are low, with localised production of anoxic zones around major sewerage outfalls prior to the switch to on-land treatment. In many enclosed harbours and estuaries there has been a dramatic decline in the abundance and specimen size of molluscs the cause of which has puzzled ecologists and been attributed to increased mud accumulation, heavy metal pollution or eutrophication. Our studies in cores from several of these estuarine harbours show rapid changes in the foraminiferal faunas coincident with the decline/loss of molluscs. In each core there is a rapid decline in calcareous foraminifera (mostly Ammonia) and replacement by agglutinated species. These up-core changes in foraminiferal faunas mimic their present day up-estuary zonation, which correlates strongly with decreasing salinity and pH. The foraminiferal record provides strong proxy evidence that it has been increased freshwater runoff that has caused the dieback of shellfish stocks in these estuarine habitats and that well-intentioned efforts to restore them by further reducing the discharge of sediment, nutrients and pollutants are unlikely to succeed. Age models for our cores show that that the declines were not coeval and increased runoff has resulted from forest clearance, urban sprawl and treated water discharges from sewerage plants.