Computer analysis of benthic foraminiferal associations in a tidal New Zealand inlet

Abstract

Census data on benthic foraminiferal tests in 45 surface sediment samples from Pauatahanui Inlet, Wellington, New Zealand, are analysed by Correspondence Analysis and Non-Hierarchical classification techniques. The faunas are grouped into 7 associations: (A) Trochamminita irregularis/Miliammina fusca - at high tide level in a small tidal creek at the limits of salt water influence; (B) Trochammina inflata/Jadammina macrescens - in an extreme high tidal pool, close to the mouth of a small stream; (C) Miliammina fusca/Haplophragmoides wilberti/Trochammina inflata - intertidal and shallow subtidal (to 0.6 m depth), muddy sand over a large area in the upper reaches of the inlet, where most freshwater runoff enters; (D) Elphidium excavatum/Miliammina fusca - intertidal muddy sand associated with shelly beaches on the fringe of association C; (E) Ammonia beccarii/Haynesina depressula - in a wide variety of intertidal and shallow subtidal (to 3 m depth) sediments that form a belt between the more brackish associations (A–D) and the more normal salinity associations (F–G); (F) Bolivina cf. translucens/Textularia earlandi/Bolivina subexcavata - in mud to muddy, very fine sand in a shallow basin (1–2.5 m deep) in the middle of the inlet and in a small, sheltered backwater; (G) Elphidium charlottensis/Patellinella inconspicua/Quinqueloculina seminula - in sandy mud and muddy fine sand, intertidal to 10 m depth, in the mouth, entrance channel and adjacent outer and middle parts of the inlet, where a flush of normal salinity water enters during each tidal cycle.

Using Canonical Correspondence Analysis, the factors most influential in determining the faunal distribution are, in decreasing importance: freshwater influence (salinity), exposure to the air during tidal cycles, proximity to the open sea, tidal current strength and percentage of mud in the substrate.