Abstract
Three hundred and sixty-seven species (91% endemic to New Zealand) of micromollusc (greatest dimension of adult shell <10 mm) are recorded from the intertidal zone of northern New Zealand. Many of these shells have been washed up dead from deeper water and thus the total diversity is more representative of the inner shelf (0-50 m), but at least 154 species have been found living in our intertidal surveys. Eleven of our species’ records are provincial range extensions, two for the Aupourian Province (northeast coast) and nine for the Cookian Province (west coast). More than twice the number of micromolluscs live in the warmer Aupourian Province (361 spp.) than the west coast Cookian Province (157 spp.). Cluster analysis of 162 spring low-tidal survey localities based on presence/absence data (Jaccard coe cient) of 257 micromollusc species allows the recognition of nine associations that reflect increasing diversity from sheltered inner harbour localities (0-10 species per locality) out to partly sheltered-fully exposed localities around the entrance to the Hauraki Gulf (61-140 species per locality). The cluster subdivision also reflects the lower biodiversity on the open west coast shores compared to the east coast, partly a result of the greater range of habitats present on open east coast shores. The two inner and middle harbour associations occur in both the Waitemata and Manukau harbours on each coast. Two other associations that occur around the entrance to the Manukau Harbour also occur on the coast around the middle reaches of the Hauraki Gulf. One association is restricted to the exposed west coast of the Waitakere Ranges and Awhitu Peninsula and the remaining four associations are restricted to the coast of the inner, middle and outer Hauraki Gulf and Whangarei Harbour on the east coast.
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