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Fossil foraminiferal faunas were studied in four, short, late Holocene cores (two localities) from the low tidal, estuarine fringes of the Waitemata Harbour, which is surrounded by New Zealand’s largest city, Auckland. All cores record similar major changes in their fossil content since the arrival of humans (ca. 1300 AD), with faunal changes continuing through to the 1970s. Molluscs have disappeared from all cores, and the foraminiferal faunas have switched from dominantly calcareous (Ammonia association) to dominantly agglutinated (Textularia–Schlerochorella, Miliammina–Haplophragmoides associations). A twostep change is evident, with an intermediate mixed calcareous-agglutinated faunal zone (1950s–1970s), characterised by peak abundances (13–20%) of Elphidium gunteri and Elphidium excavatum s.l. The faunal changes in each core since human colonisation replicate the faunal zonation in a low tidal transect of surface samples going up the Rangitopuni Estuary at the head of the Waitemata Harbour. Canonical correspondence analyses of the foraminiferal and environmental proxy data from the cores and the modern estuary transect indicate that faunal changes can be largely attributed to decreasing salinity, and additionally lowered pH (causing carbonate dissolution) in the more brackish Rangitopuni Estuary core locality. There is a weak correlation with increased nutrients (TOC, N, P), but sediment grain size and increasing heavy metal concentrations played no major part in producing the faunal changes. Intheestuarytransect,completedissolutionofcalcareousforaminiferalshellsvariesbetweenyears,butoccursupstreamwhere |
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