Faunal changes in Waitemata Harbour sediments, 1930s‐1990s

Abstract

A resurvey of Powell’s classic study of subtidal, soft‐bottom communities in the Waitemata Harbour, Auckland, was undertaken to determine the nature of faunal changes between the 1930s and 1990s. Samples were dredged and associations were intuitively deduced largely on the basis of molluscs and echinoderms, in a similar fashion to Powell’s 1930s study. Away from the wharves and marinas the soft‐bottom fauna is still remarkably rich and diverse, and retains a similar gross pattern to the 1930s. Fourteen mollusc species (dominantly carnivorous gastropods) appear to have disappeared or suffered major reductions in abundance within the harbour. This has resulted in the disappearance of two of Powell’s associations (Tawera‐Tucetona, Amalda) from the outer harbour. There has also been an apparent reduction in the abundance and range of the turritellid Maoricolpus roseus and a number of associated species of the shelly channel sediments in the centre of the harbour. Since the 1930s at least nine New Zealand mollusc species (mostly deposit‐ and suspension‐feeders) and one crab appear to have colonised the harbour, and nine others seem to have increased in abundance. The establishment of extensive horse mussel (Atrina) beds north‐east of North Head is the most significant of these changes. Three exotic bivalves (Limaria orientalis, Theora lubrica, Musculista senhousia) introduced in the 1960s and 1970s have become so abundant in the harbour that they are now codominant characterising species of six of the eight associations recognised in the 1990s. The exact causes of many of these observed changes will never be determinable. Some may be natural (e.g., spread of Atrina), but many are attributable to human activities associated with New Zealand’s largest city (e.g., TBT poisoning, closure of sewage outfalls, increased sediment, fresh water and pollutants, ballast water introductions, dredging). © 1997 Taylor and Francis Group, LLC.