Associations of benthic foraminifera (Protozoa: Sarcodina) of inner shelf sediments around the cavalli islands, north‐east new zealand

Abstract

Census data on foraminiferal tests (live plus dead) from 55 dredge samples (0–41 m depth) of surficial sediments around the Cavalli Islands are analysed by non‐hierarchical classification, principal components, and minimum spanning tree techniques. The samples are grouped into 4 associations with 5 subassociations. Characterising species of each association are found by calculating ‘association scores’ for each species, based on its dominance, fidelity, and relative abundance within each group. The 4 associations are: A. Elphidium charlottensis — subassociations Al. Elphidium charlottensis/Elphidium oceanicum/(Virgulopsis tur‐ns), A2. Elphidium charlottensis/'(Elphidium oceanicum/Elphidium simplex) — in sandy beach gravel or fine to very fine sand in shallow bays (intertidal to 6 m depth) on a sheltered coast; B. Pileolina zealandica/Cibicides marlboroughensis — subassociations B1. Discorbis dimidiatus/Elphidium novozealandicum/Pileolina zealandica, B2. Pileolina zealandica/Cibicides marlboroughensis‐/Neoconorbina pacifica, B3. Cibicides marl‐boroughensis/Quinqueloculina seminula/Notorotalia olsoni — widespread in clean, medium to coarse sand or shell gravel in moderately exposed or current‐swept locations (5–10 m depth); C. Planoglabratella opercularis/Pileolina harmed/Neoconorbina pacifica, in shelly, very coarse sand or shell gravel in shallow (6–9 m), strongly current‐swept, wave‐battered channels; D. Cassidulina carinata/Bulimina submarginata/Globocas‐sidulina canalisuturata, in fine to very fine sand in the deeper (29–41 m), northern parts of the Cavalli Passage. Associations A, B, and D, or variants thereof, are recognisable in similar environments elsewhere around northern New Zealand. Associations characterised by abundant plastogammic foraminifera, such as glabratellids and buliminoidids (e.g., C), have not previously been identified around New Zealand and are rare elsewhere. The habit of fusing together in plastogammic pairs during the sexual phase of reproduction appears to be an adaptation to survival in strongly current‐swept environments. Species diversity (Fisher 3 index, Information Function) and Evenness increase regularly with increasing depth. There is also good correlation between these foraminiferal associations and the macrofaunal associations recognised from the same dredge samples. © 1982 Taylor & Francis Group, LLC.