The effects of a mussel farm on benthic macrofaunal communities in Hauraki Gulf, New Zealand

Abstract

Variation in species assemblages, richness, indices of diversity and dominance, and sediment grain-size characteristics beneath and proximal to a mussel farm off eastern Waiheke Island, Hauraki Gulf, New Zealand, are reported. Species richness and density were elevated beneath the farm, probably attributable to structure afforded by dropped mussel shell; the types of taxa that differed in their distributions and abundances within and outside the farm also differed spatially along three surveyed transects, and temporally; no significant difference in sediment grain size was apparent along a transect extending 20m within the farm to 110m outside of it; and the biological footprint of the farm was limited, extending no further than 20m from its northern boundary. The incidence of neither opportunistic nor sensitive taxa was clearly related to the physical location of the mussel farm when the distributions and abundances of taxa throughout the eastern Waiheke Island region were taken into consideration. The farm is recognised to have a statistically significant effect on sea-bed assemblages of species or no effect at all, with any effect being manifested in an increase in species richness, but not of species traditionally considered opportunists. We deem the most efficient tool to assess rapidly the biological footprint of this farm to be measurement of the outer limit of Perna clumping on the sea bed, rather than the distribution or abundance of any indicator taxon.