Environmental controls on benthic foraminiferal and thecamoebian associations in a New Zealand tidal inlet

Abstract

Census data on benthic foraminiferal and thecamoebian tests in 52 surface sediment samples from Purakanui Inlet, Otago, New Zealand, are analyzed by cluster and correspondence analyses. Faunas are grouped into 10 sample associations with the following characterizing species: A) Trochammina inflata - at or above mean high water level in high salt meadow, salt marsh or grass; B) Jadammina macrescens/Trochammina inflata - at or above mean high-water level on the edge of high salt meadow; C) Trochamminita salsa in sandy soil at around mean high-water spring, possibly influenced by fresh groundwater seepage; D) Pontigulasia compressa/Trochamminita salsa/Difflugia capreolata - at high tide level in the bed of the main freshwater stream flowing into the inlet; E) Haplophragmoides wilberti - in salt marsh and grass at mean high-water level on the edge of the inlet; F) Miliammina fusca - in Sarcocornia muddy low salt meadow and sandy mud flats between mid and high tide levels; G) Elphidium excavatum - over a wide area of tidal sand flats in the upper and middle parts of the inlet; H) Ammonia beccarii/Elphidium excavatum - in three areas of tidal sand flat in association with G, but with slightly lower salinity and nutrients; I) Elphidium excavatum/Haynesina depressula - intertidally and subtidally around the inner end of the entrance channel in the vicinity of the flood tide sand delta; J) Zeaflorilus parri - intertidally and subtidally in the shallow, current swept entrance to the inlet. These correlate closely with the 8 species associations produced by cluster analysis. Canonical correspondence analysis indicates that the following factors in decreasing order of importance are most influential in determining the faunal distribution: tidal exposure, salinity, percentage of mud, proximity of the open sea, organic carbon, phosphate and intertidal vegetation type.