Ecological distribution of benthic foraminifera, offshore Northeast New Zealand

Northeast of New Zealand, nine benthic foraminiferal associations are recognized and mapped (50-3800 m depth) based on cluster analysis of faunal census data (> 63 mu m, 235 species, 56 samples). Similar associations are identified using cluster analysis based on the presence or absence of species. Canonical correspondence analysis shows that the associations correlate most strongly with factors related to water depth, especially decreasing food supply (organic carbon flux) with increasing depth. The depth-stratified distribution of lower bathyal to abyssal (> 1000 m) associations accords well with the deep water masses, and is attributed in part to lower oxygen concentrations in the bottom waters. The two deepest associations, dominated by Alabaminella weddellensis, Epistominella exigua, Bulimina marginata L aculeata, Globocassidulina subglobosa, and Oridorsalis umbonatus, underlie the oxygen minimum zone of Circumpolar Deep Water. A midlower bathyal association dominated by Cassidulina carinata, Alabaminella weddellensis, Abditodentrix pseudothalmanni, and Trifarina occidentalis, underlies Antarctic Intermediate Water. In addition to their bathymetric stratification, mid shelf to upper bathyal (50-600 m) associations also show latitudinal variation that may reflect differences in terrigenous mud (abundant Eilohedra vitrea), bottom current strength, food supply (more abundant Cassidulina carinata) and nutrient remineralization on the seafloor. At depths of < 1000 m, the benthic foraminiferal assemblages of this study are more similar to those off the west coast than those further south down the east coast. This may reflect lower levels of phytoplankton productivity and consequent benthic food supply, than occurs in the vicinity of the Subtropical Front, east of central New Zealand. Individual foraminiferal faunas off northeast New Zealand are more species rich (Fisher Alpha Index, alpha 14-18) than those further south (alpha 10-13). Total foraminiferal species richness (> 50 m depth) is similar off northeast (235 species) and eastern (246 species) New Zealand and higher than off the west coast (150 species).