Benthic Foraminifera of the Agulhas Bank coastal shelf in the vicinity of Plettenberg Bay, South Africa: a reconnaissance survey

Susanne Hempel,Burg Flemming

doi:10.1007/s00367-021-00691-x

Abstract

The study area is located on the inner Agulhas Bank around Plettenberg Bay, southern Cape Province, South Africa (Fig. 1). The Agulhas Bank is a transitional environment between the cold-temperate Benguela Current regime of the south-eastern South Atlantic and the warm-temperate Agulhas Current regime of the south-western Indian Ocean. Three distinct faunal assemblages (A, B and C) were identified in the study area. These are aligned in three consecutive, coast-parallel belts, assemblage A forming the inshore belt, assemblage C the offshore belt and assemblage B the in-between belt. Assemblage A is composed of Textularia-group individuals and Pararotalia sp., Cibicides lobatulus and Planorbulina mediterranensis. It occupies the nearshore belt up to 50 m water depth in sediments composed of very fine, fine and medium sands, with some coarse and very coarse sands. Assemblage B is composed of Bolivina cf. pseudopunctata, Cassidulina laevigata, Ammonia beccarii, Bolivina tortuosa and Bulimina elongata. It occupies water depths from 50–70 m, but may locally extend down to 90 m and, within the bay itself, upward to 20 m in fine and very fine sands containing some medium sand and mud. Assemblage C is dominated by Cassidulina laevigata, Bolivina cf. pseudopunctata, Bulimina elongata and Ammonia beccarii. In contrast to assemblage B which is dominated by B. cf. pseudopunctata, assemblage C is dominated by C. laevigata. Assemblage C is mainly confined to water depths of 70–100 m in sediments dominated by very fine sand (0.063–0.125 mm) containing some coarser sediment and mud. The distribution of the forams with respect to water depth, sediment composition and other environmental parameters suggests that it is mainly controlled by a combination of environmental parameters. No tangible relationship was found between the open shelf foraminifer communities and those of estuaries and lagoons along the South African coast.

Highlights

The earliest study of benthic Foraminifera from the South African shelf was carried out by Brady (1881), who analysed two samples collected in the course of the famous ‘Challenger Expedition’ (1872–1876)
Germany 2 Wilhelmshaven, Germany conducted in geological contexts (Martin 1974, 1981; McMillan 1974, 1987, 1993; Cooper and McMillan 1987; Wright et al 1990; Franceschini et al 2005) and that with few exceptions (Toefy et al 2003, 2005), studies on extant taxa were largely missing
The study is based on altogether 35 sediment samples (Fig. 1) selected from a larger sample suite (Flemming, unpublished) collected in March 1982 in the course of the Agulhas Bank Studies programme of the former National Research Institute for Oceanology (CSIR), Stellenbosch, South Africa

Summary

Introduction

The earliest study of benthic Foraminifera (forams) from the South African shelf was carried out by Brady (1881), who analysed two samples collected in the course of the famous ‘Challenger Expedition’ (1872–1876). This was followed by the foram study of Heron-Allen and Earland (1915) on the Kerimba Archipelago off the coast of Mozambique. Germany 2 Wilhelmshaven, Germany conducted in geological contexts (Martin 1974, 1981; McMillan 1974, 1987, 1993; Cooper and McMillan 1987; Wright et al 1990; Franceschini et al 2005) and that with few exceptions (Toefy et al 2003, 2005), studies on extant taxa were largely missing. This disparity has not changed very much since the few studies that were conducted mainly focussing on shallow water, salt marsh and mangrove environments (Schmidt-Sinns 2008; Strachan et al 2015, 2016, 2017; Fürstenberg et al 2017)

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