FAUNAL CHANGES IN WAITEMATA HARBOR SEDIMENTS, 1930S-1990S

A resurvey of Powell's classic study of subtidal, soft-bottom communit ies in the Waitemata Harbour, Auckland, was undertaken to determine th e nature of faunal changes between the 1930s and 1990s. Samples were d redged and associations were intuitively deduced largely on the basis of molluscs and echinoderms, in a similar fashion to Powell's 1930s st udy. Away from the wharves and marinas the soft-bottom fauna is still remarkably rich and diverse, and retains a similar gross pattern to th e 1930s. Fourteen mollusc species (dominantly carnivorous gastropods) appear to have disappeared or suffered major reductions in abundance w ithin the harbour. This has resulted in the disappearance of two of Po well's associations (Tawera-Tucetona, Amalda) from the outer-harbour. There has also been an apparent reduction in the abundance and range o f the turritellid Maoricolpus roseus and a number of associated specie s of the shelly channel sediments in the centre of the harbour. Since the 1930s at least nine New Zealand mollusc species (mostly deposit- a nd suspension-feeders) and one crab appear to have colonised the harbo ur, and nine others seem to have increased in abundance. The establish ment of extensive horse mussel (Atrina) beds north-east of North Head is the most significant of these changes. Three exotic bivalves (Limar ia 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 c hanges will never be determinable. Some may be natural (e.g., spread o f Atrina), but many are attributable to human activities associated wi th New Zealand's largest city (e.g., TBT poisoning, closure of sewage outfalls, increased sediment, fresh water and pollutants, ballast wate r introductions, dredging).