Brackish Foraminifera in New Zealand: A Taxonomic and Ecologic Review

Abstract

Approximately one third (11 species) of the world obligate brackish foraminiferal taxa occur in New Zealand's estuaries and upper reaches of enclosed harbours, inlets and lagoons. The previously confused local taxonomy of New Zealand's obligate (11 species) and common facultative (9 species) brackish foraminifera is integrated with current overseas usage. Nineteen of the 20 brackish species in New Zealand have a world-wide distribution. All 20 species occur in northern New Zealand (lat 35?S) with a progressive decrease in diversity to 13 species in the south (lat 47?S). Cluster analysis based on the quantitative faunal counts of 68 samples from 5 study areas results in the recognition of nine brackish foraminiferal associations. Within brackish settings, salinity and secondly tidal exposure, are the two environmental factors having the strongest influence on foraminiferal distribution. With increasing salinity, brackish faunas increase in diversity, decrease in abundance of agglutinated taxa and increase in abundance of calcareous taxa. The associations exhibit the following general trend correlated with increasing salinity: a. Trochamminita (least saline); b. Haplophragmoides wilberti, Miliammina; c. Ammonia Miliammina; d. Elphidium excavatum, Ammonia Elphidium, Ammonia; e. Marginal Marine (most saline). Five associations are apparently restricted to the intertidal zone: a. Trochammina inflata (above mean high water); b. Trochamminita, Haplophragmoides wilberti (above mean sea level); c. Elphidium excavatum (predominantly mid-tidal); d. Ammonia Elphidium (between mean low and mean high water). Tidal current transport of foraminiferal tests produces mixed assemblages in the mouths and lower channels of New Zealand estuaries (diurnal microtidal and low mesotidal ranges).