Twenty-three species of planktonic Foraminifera have been identified from surface sediments on the Thukela Shelf (KwaZulu-Natal Bight, South Africa). The assemblage is dominated by Orbulina universa, Globigerinoides ruber and Neogloboquadrina dutertrei, and is referred to the tropical-subtropical zone. Surface-water species (Globigerinoides ruber, G. trilobus, G. sacculifer, and G. conglobatus) dominate over deep-water species (Globorotalia inflata, G. tumida, G. menardii, and Sphaeroidinella dehiscens). Identification keys to species of Globorotalia, Globigerina, and Globigerinoides from the KwaZulu-Natal Bight are provided.
Planktonic Foraminifera are an important source of palaeoceanographic information (Schiebel & Hemleben 2005). Their long palaeontological record, good preservation in sediments and easy collection make them perfect indicators for studies on changes in sea-surface temperature, salinity, and nutrient content (e.g., Spezzaferri & Spiegler 2005; Fraile et al. 2009).
South African foraminifers have been studied for more than 150 years, but most studies, especially recent ones, have been of a geological nature, without any investigation of their distribution pattern (e.g., McMillan 2003; Toefy et al. 2005; and references therein). The diversity and distribution pattern of recent foraminifers, and their application to environmental analyses, have so far been largely ignored. Noteworthy studies on southern African planktonic foraminifers include those of Giraudeau (1993) on the south-western African continental margin and Rau et al. (2002) on the southern margin. Bé and Hutson (1977) provided a regional distribution of planktonic foraminifers in the Indian Ocean, but no systematic research has been undertaken on the eastern continental shelf of South Africa.
Recent interest was initiated by the proposed development of a dam on the Thukela River and the associated impacts on a unique marine ecosystem, the Thukela Shelf, comprising an uncharacteristically wide muddy continental shelf and an associated economically important prawn industry. This system depends on the interaction of fresh water and sediment from the Thukela River, the strong Agulhas Current, and a semi-permanent anti-cyclonic spinning gyre within the KwaZulu-Natal Bight (Bosman et al. 2007).
In this paper we provide results of the taxonomic study of planktonic foraminiferal assemblages from sediments across the KwaZulu-Natal Bight.
General information from samples collected at the Thukela River and Thukela Shelf (TB).
MATERIAL AND METHODS
The study area, approx. 18×25 km in extent, is located immediately offshore of the Thukela River on the Thukela Shelf and forms part of the KwaZulu-Natal Bight (Fig. 1). Surface sediment samples were collected by Shipek grab sampler in 2006 aboard the Marine and Coastal Management research vessel the FRS Algoa (Hunter 2007), and during the Oceanographic Research Institute (ORI) survey in 2008.
In total, 21 samples were analyzed for the foraminiferal fauna (Fig. 2). Samples were washed through 500, 125 and 63 µm sieves, were dried and the two fractions (>500, 500–125 µm) were analyzed. Due to the relative proximity of the sampling sites to the shore, foraminifers were found to be scarce and the required number of 300 specimens per sample could not be obtained for most samples. Thus this study presents results of a semi-quantitative approach.
The relative abundance of individual foraminiferal taxa is expressed as follows: R-rare (1–5 specimens/sample), C — common (6–10 specimens/sample), F — frequent (11–25 specimens/sample), A — abundant (>25 specimens/sample). The sample numbers, depth, location of each sample and sediment character are given in Table 1.
Photographs were taken using a Nikon AZ-100 stereomicroscope and 3-D Nikon imaging software. The classification of foraminifers in this study follows Loeblich and Tappan ( 1987, 1994), Saito et al. (1981) and The Taxonomicon & Systema Naturae (2000).
All examined material has been deposited in the palaeontological collection of the Department of Natural Sciences, Natal Museum, Pietermaritzburg, South Africa.
Order Globigerinida Lankester, 1885
Superfamily Globorotaliacea Cushman, 1927
Family Globorotaliidae Cushman, 1927
Genus Globorotalia Cushman, 1927
Globorotalia cultrata (d'Orbigny, 1839)
Figs 3A, 3D
Globorotalia cultrata (d'Orbigny): Parker 1962: 235–236, pl. 5, figs 3–5; Pflaumann & Krasheninnikov 1978: 891, pl. 5, figs 2–4; Loeblich & Tappan 1994: 100, pl. 184, figs 8–10; Bylinskaya et al. 2002: 132, pl. VIII, figs 7–9.
Globorotalia menardii cultrata (d'Orbigny): Bolli & Saunders 1985: 226, figs 32.3, 34.8–10.
Remarks: G. cultrata is very similar to G. menardii, but differs in having a thinner, more delicate test wall and a narrower peripheral keel. Saito et al. (1981) considered G. cultrata a synonym of G. menardii, whereas Bolli and Saunders (1985) recognized it as a subspecies, G. menardii cultrata.
Distribution: A tropical species, abundant in warm-water regions, but isolated specimens could appear up to 56°N in the Atlantic. Quite rare in our material.
Globorotalia inflata (d'Orbigny, 1839)
Test size variable, usually medium-sized, low trochospiral with 4 subglobular chambers in the final whorl. On umbilical side chambers more inflated than on spiral side, increasing moderately in size as added. Aperture interiomarginal, a high, wide arch.
Remarks: G. inflata differs from other Globorotalia species encountered in having subglobular chambers and in lacking a keel.
Distribution: This species characterizes cool-temperate waters. It is uncommon in the tropical region (Bylinskaya et al. 2002) and very rare in our material.
Globorotalia menardii (Parker, Jones & Brady, 1865)
Figs 3B, 3E
Rotalia menardii: Parker et al. 1865: 20, pl. 3, fig. 81.
Globorotalia menardii: Cushman 1927b: 175; 1931: 91, pl. 17, fig. 1; Bé et al. 1966: 885–896, pls 1–17; Saito et al. 1981: 147, pl. 50, figs 1a—d; Loeblich & Tappan 1987:475, pl. 516, figs 4–11; 1994: 101, pl. 183, figs 1–6; Basov & Krasheninnikov 1995: pl. I, figs 3, 4.
Globorotalia menardii menardii (Parker et al.): Bolli & Saunders 1985: 226, figs 32.4, 34.5–7.
Medium to large biconvex trochospiral test with 5–6 wedge-shaped chambers in the final whorl. On spiral side chambers semi-circular, nearly flat, with curved sutures; on umbilical side triangular, slightly inflated, with radial sutures. Peripheral keel wide. Aperture interiomarginal, umbilical, a low arch with a large plate-like umbilical tooth.
Remarks: G. menardii differs from G. cultrata in being generally larger and in having a robust, thicker test wall with a wider peripheral keel. It differs from G. tumida in having a more circular equatorial outline and a larger diameter, and in being narrower.
Distribution: Equatorial to tropical waters. Only four specimens were found in our material.
Globorotalia tumida (Brady, 1877)
Figs 3G, 3H
Globorotalia tumida (Brady): Cushman 1927a: 91, pl. 19, fig. 12; Bolli et al. 1957: 41–42, pl. 10, figs 2a–c; Parker 1962: 239–240, pl. 6, figs 8–10; Todd 1965: 71–72, pl. 28, fig. 1; Saito et al. 1981: 148, pl. 50, figs 2a–d; Loeblich & Tappan 1987: 475, pl. 515, figs 4–6; 1994: 101, pl. 183, figs 7–12; Bylinskaya et al. 2002: 137, pl. IX, figs 13, 14.
Medium to large; biconvex trochospiral test with 5–6 wedge-shaped chambers in the final whorl. On the spiral side chambers reniform, slightly inflated, sutures curving, thickened; on the umbilical side chambers subtriangular, more inflated, with radial sutures. Peripheral keel distinct, thick. Aperture interiomarginal, extraumbilical, a low arch with a large, plate-like lip.
Remarks: G. tumida has a more elongate and thick test than G. menardii, with a less lobulate periphery and an angular final chamber.
Distribution: An equatorial/tropical species, appearing in warm-water regions only. A single specimen was found in our material.
Globorotalia ungulata Bermúdez, 1961
Figs 3C, 3F, 3I
Globorotalia ungulata: Bermúdez 1961: 1304, pl. 15, figs 6a–b; Blow, 1969: 371, pl. 8, figs 13–15; Pflaumann & Krasheninnikov 1978: 892, pl. 5,figs 5–7; Saito et al. 1981: 155–156, pl. 53, figs 2a–b, 3a–b; Bolli & Saunders 1985: 230, figs 32.2; Loeblich & Tappan 1994: 101, pl. 182, figs 1–12.
Small to medium biconvex trochospiral test with about 5 wedge-shaped chambers in the final whorl. On the spiral side chambers slightly reniform, nearly flat; on the ventral side, subtriangular, inflated. The final chamber has a high umbilical shoulder. Peripheral keel thin. Aperture interiomarginal, a very low slit-like opening at the base of umbilical shoulder with a large plate-like umbilical lip.
Remarks: This species can be easily recognized by its high umbilical face and its thin, shiny, elliptical test. Because of its elongate, somewhat inflated test G. ungulata was occasionally considered to be related to G. tumida; however, we believe it to be closer to the G. menardii—G. cultrata complex.
Distribution: Equatorial and tropical waters. Quite rare in our material.
Key to the species of Globorotalia from the Thukela Shelf
1 Test low trochospiral with subglobular chambers in final whorl inflata
— Test biconvex trochospiral with wedge-shaped chambers in final whorl 2
2 Test wall thin with delicate, thin peripheral keel 3
— Test wall thick with thick peripheral keel 4
3 Test rounded in outline cultrata
— Test more elliptical in outline ungulata
4 Test rounded in outline menardii
— Test elliptical in outline tumida
Genus Neogloboquadrina Bandy, Frerichs & Vincent, 1967
Neogloboquadrina dutertrei (d'Orbigny, 1839)
Figs 4E, 4F, 4H, 4I
Test variable in size, usually medium, a medium-height trochospire with 4–6 subspherical to radially slightly flattened chambers in the final whorl. Chambers increase slowly in size as added, sutures depressed. Aperture a wide and deep opening directly into umbilicus.
Remarks: A few individuals with a lower trochospire and more umbilical aperture were found (Figs 4F, 4I) in our material. These forms may be identified as N. eggeri (Rhumbler, 1901). Saito et al. (1981) separate these species on the basis of a higher spire in N. dutertrei, but Kennett and Srinivasan (1983) suppose that N. eggeri is a junior synonym of N. dutertrei. We tend to agree with the latter opinion at this stage.
N. dutertrei differs from N. incompta in having a bigger and less compact test, and in having more chambers in the final whorl.
Distribution: Equatorial and tropical waters. A common species in our material.
Neogloboquadrina incompta (Cifelli, 1961)
Figs 4D, 4G
Test small with partly embracing chambers, 4 or 4.5 globular chambers in the final whorl. Aperture umbilical, interiomarginal but extending almost to the periphery, a low arch with a thin projecting rim. Wall thin, finely porous, granular.
Remarks: Differs from N. dutertrei in being smaller and in having a more compact test.
Distribution: North Atlantic (surface plankton), latest Pliocene and Pleistocene sediments from northern Japan. Only two specimens were recorded in our material.
Family Pulleniatinidae Cushman, 1927
Genus Pulleniatina Cushman, 1927
Pulleniatina obliquiloculata (Parker & Jones, 1865)
Figs 5A, 5D
Pullenia obliquiloculata: Parker & Jones 1865: 183.
Pulleniatina obliquiloculata (Parker & Jones): Parker 1962: 234, pl. 4, figs 13–16, 19, 22; Todd 1965: 67, pl. 27, figs 2–4; Saito et al. 1981: 96, 98, pl. 30, figs 1a–d, 2a–d; pl. 31, figs 3a–d; Bolli & Saunders 1985: 247, figs 40.4, 41.9–12; Loeblich & Tappan 1987: 480, pl. 524, figs 4–12; 1994: 103, pl. 187, figs 8–13; pl. 188, figs 1–6; Basov & Krasheninnikov 1995: pl. III, figs 7, 8.
Test size variable, rounded in outline, initially a low trochospiral becoming a streptospiral. Spherical chambers becoming radially flattened, very embracing with sutures weak. Aperture a very low, ventrally interiomarginal arch.
Remarks: This species can easily be identified by its rounded polished (glossy) test, being very compact, with embracing chambers.
Distribution: Equatorial and tropical waters. Rare in our material.
Family Candeinidae Cushman, 1927
Subfamily Globigerinitinae Bermúdez, 1961
Genus Globigerinita Brönnimann, 1951
Globigerinita glutinata (Egger, 1893)
Figs 5B, 5E
Globigerina glutinata: Egger 1893: 371, pl. 13, figs 19–21.
Globigerinita glutinata (Egger): Parker 1962: 246–249, pl. 9, figs 1–16; 1967: 146, pl. 17, figs 3–5; Pflaumann & Krasheninnikov 1978: 890, pl. 2, figs 4–6; Saito et al. 1981: 77, pl. 22, figs 1–7; Bylinskaya et al. 2002: 125, pl. I, figs 4–6.
Small to medium trochospiral test with 4 globular chambers in the final whorl; chambers spherical to slightly flattened radially. Primary aperture umbilical, a low arch with a thin lip. Bulla of variable configuration may cover sutures on umbilical side.
Distribution: Cosmopolitan, equatorial to subpolar latitudes. This species is most abundant in subtropical and temperate sediments (Bylinskaya et al. 2002), but is quite rare in our material.
Superfamily Globigerinaceae Carpenter, Parker & Jones, 1862
Family Globigerinidae Carpenter, Parker & Jones, 1862
Subfamily Globigerininae Carpenter, Parker & Jones, 1862
Genus Globigerina d'Orbigny, 1826
Globigerina bulloides d'Orbigny, 1826
Globigerina bulloides: d'Orbigny 1826: 277, list no. 1; Parker et al. 1865: 21, 31, pl. II, figs 55, 56; Brady 1879: 285; Banner & Blow 1960: 3–4, pl. 1, figs 1a–c, 4; Parker 1962: 221, pl. 1, figs 1–8; Loeblich & Tappan 1987: 489, pl. 535, figs 1–7; Saito et al. 1981: 40, pl. 7, figs 1a–d; Loeblich & Tappan 1994: 105–106, pl. 197, figs 1–9; Basov & Krasheninnikov 1995: pl. IV, figs 5, 6; Bylinskaya et al. 2002: 126, pl. I, figs 9–11.
Test size variable, trochospiral, well lobulated, with 4 chambers in the final whorl slowly increasing in size. Chambers spherical or slightly ovoid. Aperture umbilical, interiomarginal, a high arch. Wall smoothly perforated.
Remarks: The species differs from G. falconensis in having a high aperture without a lip. G. bulloides has a more hispid and thicker wall than does Globigerinella calida.
Distribution: A cosmopolitan species, equatorial to subpolar waters. Most abundant in the temperate Atlantic. It is also known for its association with upwelling zones (Bylinskaya et al. 2002). This species is very rare in our material.
Globigerina falconensis Blow, 1959
Small to medium trochospiral test, with 4 spherical chambers in the final whorl. The last chamber is typically smaller than the previous one and ovoid in shape. Aperture umbilical, interiomarginal, a low arch with a thick lip.
Remarks: The species is characterized by a very large variation, and does not always have a reduced last chamber. It can easily be separated from G. bulloides by the smaller aperture with a lip on the last chamber.
Distribution: Subtropical to temperate waters. Very rare in our material.
Globigerina quinqueloba Natland, 1938
Figs 5C, 5F
Globigerina quinqueloba: Natland 1938: 149, pl. 6, fig. 7; Parker 1962: 225–226, pl. 2, figs 7–16; Pflaumann & Krasheninnikov 1978: 888, pl. 2, figs 10–12; Saito et al. 1981: 48, pl. 10, figs 1, 2; Bylinskaya et al. 2002: 127, pl. II, figs 9–11.
Small, low trochospiral test, with 5 subglobular chambers, slightly flattened radially, in the final whorl. The last chamber is elongated and can partially cover the umbilicus like a bulla. Aperture umbilical, interiomarginal with rim-like basal lip.
Remarks: G. quinqueloba differs from other Globigerina species encountered in having five subglobular chambers, slightly flattened radially, in the final whorl.
Globigerina rubescens Hofker, 1956
Globigerina rubescens: Hofker 1956: 234, pl. 32, figs 18–21; Parker 1962: 226, pl. 2, figs 17–18; Pflaumann & Krasheninnikov 1978: 889, pl. 1, figs 11–13; Saito et al. 1981: 50, pl. 11, figs 1a–d; Bylinskaya et al. 2002: 127, pl. II, figs 6–8.
Small trochospiral test with 4 globular chambers in final whorl. Subspherical chambers closely packed, sutures distinct. Aperture umbilical, a high open arch with an imperforate thin rim-like lip. Wall coarsely perforated.
Remarks: This species occasionally has a distinctive pink to red pigmentation in the Late Pleistocene and younger sediments of the Atlantic (Saito et al. 1981; Bylinskaya et al. 2002). Red-coloured forms have not yet been found in surface sediments of the Indian Ocean. The species differs from Globigerinoides tenellus and Globigerinoides ruber in having a more lobulate periphery and in the absence of supplementary apertures; and from other Globigerina species in having a coarsely perforate wall.
Distribution: Temperate to equatorial waters. Very rare in our material.
Key to the species of Globigerina from Thukela Shelf
1 Test with 5 subglobular, slightly flattened radially, chambers in final whorl quinqueloba
— Test with 4 globular or spherical chambers in final whorl 2
2 Aperture a low arch with thick lip falconensis
— Aperture a high open arch without lip or with an imperforate thin rim-like lip 3
3 Aperture without lip, test wall smoothly perforated bulloides
— Aperture with an imperforate thin rim-like lip, test wall coarsely perforated rubescens
Genus Globigerinella Cushman, 1927
Globigerinella calida (Parker, 1962)
Globigerina calida calida Parker: Blow 1969: 317, pl. 13, figs 9, 10; Bolli & Saunders 1985: 256, fig. 5.13; Basov & Krasheninnikov 1995: pl. IV, figs 7–9; Bylinskaya et al. 2002: 126, pl. II, figs 1–3.
Size variable. Low trochospiral test with about 4 initially spherical to slightly radially elongate chambers. Embracing loose so that the final chamber is almost completely detached from the previous whorl and the aperture is visible from the lateral and even spiral side (appears as slit); sutures deep. The aperture is developed as a large umbilical arch.
Remarks: Differs from Globigerina bulloides in loose embracing, radial elongation of the final chambers, visible aperture (slit) on the spiral side, and in having a thinner and less hispid wall. It also differs from juvenile trochoid Globigerinella siphonifera in having less involute chambers and a less hispid surface of the wall.
Distribution: G. calida appears in most of the climatic areas from equatorial to temperate, but is never abundant in assemblages (Bylinskaya et al. 2002). This species is rare in our material.
Globigerinella siphonifera (d'Orbigny, 1839)
Figs 7A, 7B, 7D, 7E
Globigerina siphonifera: d'Orbigny 1839a: 83, pl. 4, figs 15–18.
Globigerinella aequilateralis (Brady): Cushman 1927a: 87; Todd 1965: 64–65, pl. 25, figs 4, 5; Saito et al. 1976: 281–282, pl. 3. figs 1, 2; pl. 6, fig. 7; pl. 8, figs 3, 8; 1981: 26, pl. 2, figs 2a–d; Bolli & Saunders 1985: 253, figs 42.6; 43.5–7, 9, 10; Loeblich & Tappan 1987: 489, pl. 535, figs 8–12; Cimerman & Langer 1991: 57, pl. 60, figs 4, 5.
Hastigerina siphonifera (d'Orbigny): Bolli & Saunders 1985: 251, figs 42.1, 4; 43.1, 2, 8.
This species is very variable, with the test varying from very low trochospiral to planispiral. The test is medium to large. Chambers are spherical to ovate, rapidly enlarging in the adult whorl. Sutures distinct and depressed. The aperture appears as a low, wide symmetrical equatorial arch in the interiomarginal position.
Remarks: G. siphonifera is more hispid than Hastigerina pelagica, and more tightly coiled and planispiral than Globigerinella calida.
Distribution: Tropical — subtropical waters. It appears in practically all our samples, in low abundance.
Genus Globigerinoides Cushman, 1927
Globigerinoides bulloideus Crescenti, 1966
Figs 7C, 7F
Test medium trochospiral, well lobulated, with 4 spherical chambers in the final whorl slowly increasing in size. Primary aperture umbilical, interiomarginal, a wide arch with very thin lip; only one small supplementary aperture.
Remarks: The test of this species is very similar to that of Globigerina bulloides, and it is normally characterized by a wide primary aperture (Bolli & Saunders 1985). Our specimen has an atypically small primary aperture with a thin lip, similar to that of Globigerina falconensis. However, it differs from both G. bulloides and G. falconensis in having a supplementary aperture. G. bulloideus differs from Globigerinoides tenellus in being larger and in having slowly increasing non-embracing chambers.
Distribution: Known from the Middle Miocene of Italy (Bolli & Saunders 1985). Temperate waters, found in Atlantic Quaternary cores (Bylinskaya, unpubl. data). Very rare, two specimens in our material.
Globigerinoides conglobatus (Brady, 1879)
Globigerinoides conglobatus (Brady): Drooger 1953: 142; Parker 1962: 229, pl. 3, figs 1–5; Todd 1965: 62, pl. 25, fig. 3; Pflaumann & Krasheninnikov 1978: 889, pl. 4, figs 4–6; Saito et al. 1981: 56, pl. 14, figs 1a–d; Cimerman & Langer 1991: 57, pl. 60, figs 6, 7; Bylinskaya et al. 2002: 127, pl. III, figs 4, 5.
Test large, medium to high trochospire, subglobular or subquadrate in outline. In the final whorl there are about 3.5 subspherical chambers, rapidly increasing as added but greatly embracing. Primary aperture umbilical, interiomarginal, a long, low asymmetrical arch; secondary supplementary apertures smaller, arch-shaped openings on spiral side.
Remarks: G. conglobatus has a larger and more compact test in adults, and more embracing chambers in juveniles, than does G. ruber.
Distribution: Equatorial to temperate waters. It appears in practically half of our samples, in low abundance.
Globigerinoides ruber (d'Orbigny, 1839)
Globigerinoides ruber (d'Orbigny): Parker 1962: 230, 232, pl. 3, figs 11–14, pl. 4, figs 1–10; Todd 1965: 63, pl. 25, fig. 6; Pflaumann & Krasheninnikov 1978: 889, pl. 3, figs 1–6; Saito et al. 1981: 59, pl. 15, figs 1a–d; Bolli & Saunders 1985: 196, figs 20.1, 2, 6; Cimerman & Langer 1991: 58, pl. 60, fig. 9; Loeblich & Tappan 1994: 107, pl. 203, figs 1–9; pl. 206, figs 10–12; Basov & Krasheninnikov 1995: pl. V, figs 3, 4; Bylinskaya et al. 2002: 128, pl. III, figs 6, 7.
Test small to medium, variable, low or high trochospiral, with 3 characteristic globular chambers in the final whorl and a drop-shaped primary aperture situated symmetrically above suture between two previous chambers. Secondary supplementary apertures are smaller openings on the spiral side. Test may have pink to red pigmentation.
Remarks: The pink-colored forms have not been found in surface sediments of the Indo-Pacific area (Bé & Hutson, 1977; Saito et al. 1981), where they have disappeared at about 120 ka (Thompson et al. 1979). Many specimens in the Indo-Pacific area which could be considered pink varieties have an early whorl or two of light pink chambers and gradually become white in later chambers (Saito et al. 1981).
In our material we also found seven individuals that show aberrant features (Figs 9D, 9E; Table 2). Their tests are medium to large, medium—high trochospiral, very loosely embracing, with 4–5 subglobular slightly flattened chambers in the final whorl. The last chamber is completely detached from the previous whorl and is connected with the penultimate chamber only. The test wall is spinose, strongly perforated. The primary aperture is umbilical, in the form of a broad and deep arch. Secondary apertures are smaller, semicircular or drop-shaped. This form was mentioned as G. ruber forma helicina (Saito et al. 1981: 165, pl. 56, fig. 7), but coiling in our material is markedly looser than illustrated in the aforementioned work.
Distribution: Equatorial to temperate waters, most abundant in the tropical and subtropical areas; it is indicative of warm-water conditions. The species is abundant in our material.
Globigerinoides sacculifer (Brady, 1877)
Globigerinoides sacculifer (Brady): Todd 1965: 63–64, pl. 26, fig. 4; Parker 1967: 156–158, pl. 21, figs 1, 2, 4, text-fig. 5; Saito et al. 1981: 65–66, pl. 17, fig. 2; Basov & Krasheninnikov 1995: pl. V, figs 8, 9; Bylinskaya et al. 2002: 128, pl. IV, figs 1, 2.
Globigerinoides trilobus sacculifer (Brady): Bolli & Saunders 1985: 196, figs 20.13.
Medium to large, low trochospiral test with 3 to 4 globular chambers in the final whorl. Chambers spherical to slightly flattened radially, very rapidly increasing, partly embracing. Final chamber usually incompletely inflated, having a sac-like appearance. Primary aperture interiomarginal, umbilical, a low but quite wide symmetrical arch; supplementary apertures elliptical or subtriangular.
Remarks: The species differs from G. trilobus in the characteristic sac-like shape of the last chamber and in being generally larger.
Distribution: A tropical species, it is an indicator of warm-water conditions. It appears in practically all our samples, in small numbers.
Globigerinoides tenellus Parker, 1958
Globigerinoides tenellus: Parker 1962: 232, pl. 4, figs 11, 12; Pflaumann & Krasheninnikov 1978: 890, pl. 4, figs 1–3; Saito et al. 1981: 50, pl. 11, figs 2a–d; Bolli & Saunders, 1985: 196, fig. 20.7.
Small trochospiral test with strongly lobate equatorial outline, with 4 globular chambers in final whorl. Subspherical chambers greatly embracing without distinct sutures, rapidly enlarging. Primary aperture umbilical, an open and high arch (almost circular in outline) with a thin lip, secondary aperture(s) small and narrow, but visible on even the smallest specimens.
Remarks: The species differs from G. rubescens in having supplementary aperture(s) and a smoother wall, and from G. ruber by its more lobulate periphery and low trochospire.
Distribution: Equatorial to temperate waters. The species is never numerous in assemblages, and very rare in our material.
Globigerinoides trilobus (Reuss, 1850)
Figs 8E, 8F
Globigerina triloba: Reuss 1850: 374, pl. 47, figs 11a–c.
Globigerinoides trilobus trilobus (Reuss): Bolli & Saunders 1985: 196, fig. 20.15.
Globigerinoides trilobus immaturus LeRoy: Bolli & Saunders 1985: 196, fig. 20.14.
Test medium in size, with 3–3.5 globular chambers in the final whorl. The primary aperture is in the form of a low, quite wide symmetrical arch.
Remarks: Differs from G. sacculifer by its globular last chamber, and from G. ruber in the general chamber arrangement and the form of the primary aperture.
Distribution: A tropical species, indicative of warm-water conditions. It appears in practically all our samples, in low abundance.
Key to the species of Globigerinoides from the Thukela Shelf
1 Test very loosely embracing, with 4–5 subglobular slightly flattened chambers in final whorl; last chamber completely detached from previous whorl (Figs 9D, 9E) aberrant form of ruber
— Test not so loosely embracing or sometimes closely embracing , with at most 4 globular chambers in final whorl; last chamber at least partly attached to previous whorl 2
2 Chambers in final whorl greatly embracing 3
— Chambers in final whorl partly embracing or non-embracing 4
3 Test small with 4 globular chambers in final whorl tenellus
— Test large or medium with 3.5 subspherical chambers in final whorl conglobatus
4 One small secondary aperture bulloideus
— More than one secondary aperture 5
5 Primary aperture characteristically drop-shaped, situated symmetrically above suture between 2 previous chambers ruber
— Primary aperture as low, quite wide symmetrical interiomarginal arch 6
6 Final chamber globular trilobus
— Final chamber subglobular, sac-like sacculifer
Genus Sphaeroidinella Cushman, 1927
Sphaeroidinella dehiscens (Parker & Jones, 1865)
Figs 9F, 9G
Sphaeroidinella dehiscens (Parker & Jones): Cushman 1927a, 90, pl. 19, fig. 2; Parker 1962: 234, pl. 5, figs 1, 2; Todd 1965: 67–68, pl. 26, figs 5, 6; Saito et al. 1981: 72, 74, pl. 20, figs 2a–d; Bolli & Saunders 1985: 244, figs 39.1–8; Basov & Krasheninnikov 1995: pl. V, figs 11, 12; Bylinskaya et al. 2002: 137, pl. IV, fig. 10.
Remarks: This species demonstrates a very wide variation in the size and shape of the test, and in the development of apertures.
Distribution: Equatorial to tropical waters, warm-water species. We found three specimens in our material.
Subfamily Orbulininae Schultze, 1854
Genus Orbulina d'Orbigny, 1839
Orbulina universa (d'Orbigny, 1839)
Orbulina universa: d–Orbigny 1839a: 3, pl. 1, fig. 1; Brady 1879: 289; Saito et al. 1981: 70, pl. 19, figs 1a–d, 2a–b, 3a–b, 4–6; Loeblich & Tappan 1987: 494, pl. 541, figs 1–6, 8–11 (not fig. 7); Cimerman & Langer 1991: 58, pl. 60, fig. 8; Loeblich & Tappan 1994: 109, pl. 211, figs 4–7; Basov & Krasheninnikov 1995: pl. V., fig. 10.
Test large, spherical. Wall very thin, coarsely perforated with pores of two distinct sizes.
Remarks: This species is very distinctive in having two life stages, viz. a multichambered trochospiral stage followed by a single-chambered spherical stage (Bé et al. 1973). However, the trochospiral form was not found in our material.
Distribution: Equatorial to temperate waters. Exceptionally abundant in our material.
With a total of 23 species identified in this study from a small area of the subtropic/tropic fauna (Bé & Hutson 1977) (Table 2), the assemblage of planktonic foraminifers in surface sediments on the Thukela Shelf is as rich as assemblages from the south-western continental margin of the whole of southern Africa. Giraudeau (1993) reported 23 species off South Africa and Namibia, a region which includes two different biogeographic zones, i.e. transitional and subtropical (Bé & Hutson 1977).
In the identified assemblage, warm-water species are dominant (Orbulina universa, Globigerinoides ruber and Neogloboquadrina dutertrei) or subdominant (Globigerinoides trilobus and Globigerinella siphonifera). This is characteristic of tropical—subtropical areas (Bé & Tolderlund 1971). G. ruber prevails over Globigerinoides sacculifer in subtropical waters and along continental margins (Bé & Hutson 1977).
Although all our samples represent shallow-water sediments, species with very different depth preferences have been found. The studied assemblage is characterized by a high proportion of Globigerinoides ruber (>20%), with G. trilobus, G. sacculifer and G. conglobatus being less abundant. These species prefer the upper part of the euphoric zone (Venéc-Peyré et al. 1995; Schiebel et al. 2004). Although Globigerina quinqueloba and G. rubescens are known as surface species as well, they are very rare in our material. Deep-water species (Globorotalia menardii, G. tumida, G. inflata, and Sphaeroidinella dehiscens) are generally exceptionally scarce, with the exception of Neogloboquadrina dutertrei that reaches over 11% in the assemblage. Orbulina universa, Globigerinella siphonifera, Globigerina bulloides, Globigerinita glutinata, and Pulleniatina obliquiloculata do not show a strong preference for particular depths within 300 m of water column (Bé & Tolderlund 1971).
The taxonomic diversity of the planktonic foraminifers generally increases toward the outer shelf across the Thukela Shelf. This is hardly surprising, as these unicellular organisms prefer normal marine conditions.
In general, the planktonic foraminiferal assemblage of the Thukela Shelf agrees with the distributional pattern of species drawn by Bé and Hutson (1977), with several insignificant exceptions. Thus, the proportion of Globigerinella siphonifera is approximately the same as expected, whereas the proportions of Globigerinita glutinata, Globigerinoides sacculifer and Globorotalia inflata are slightly lower than those shown by Bé and Hutson (1977), although these authors analysed a different size fraction. These variations are most probably of little value, since the distribution of planktonic forams often demonstrates patchiness (Boltovskoy 1971).
The most striking oddity is a proportion of O. universa, which constitutes over 32% of the total Thukela Shelf assemblage. Earlier researchers (Bé et al. 1973; Bé & Hutson 1977) reported much lower occurrences of this species east of South Africa, with its share not exceeding 5 % in sediment (“fossil”) assemblages. O. universa is considerably more abundant (up to 10%) in live plankton assemblages east of Kenya and south of Madagascar, and is believed to be associated with water temperatures between 18 and 24°C, surface salinities 35.5–36.0‰, dissolved oxygen 4.8–5.1 ml/1, and low phosphate concentration (ca 0.3 µg/l) (Bé et al. 1973; Bé & Hutson 1977).
Our results may reflect changes in ocean conditions since the previous study (Bé & Hutson 1977), or may show the influence of the Agulhas Current, which brings pools of O. universa to the KwaZulu-Natal waters. On a smaller scale, O. universa is substantially more abundant at sampling sites on the outer Thukela Shelf (e.g., samples 15, 19, 22, 23, 25, 26, 30, and C; Fig. 2), away from fresh water influx. This agrees well with the ecological requirements of the species, which prefers cooler temperatures and normal/ elevated salinities, and again, may reflect the direct influence of the Agulhas Current.
Quantitative distribution of planktonic foraminifer species from the Thukela Shelf.
The Agulhas Current may also be responsible for the appearance of Globorotalia menardii (Figs 3B, 3E) in sediments on the Thukela Shelf, although as isolated specimens. This species occurs predominantly in the equatorial region, the Arabian Sea, the Gulf of Aden, and the Bay of Bengal (Bé & Hutson 1977), but may be transported by currents over large distances (Schiebel & Hemleben 2005).
Ms C.L. Hunter (University of KwaZulu-Natal, Durban) and Dr F. MacKay (Oceanographic Research Institute, Durban) are thanked for making their samples available for our study. The staff of the Microscopy Unit of the University of KwaZulu-Natal (Westville Campus) are acknowledged for facilitating access to their sophisticated equipment and for their generous help, and Dr M. Mostovski (Natal Museum, Pietermaritzburg) is thanked for useful discussions during the course of the project. The library of the Natal Museum is acknowledged for providing access to rare publications. Rio Leuci is thanked for providing details on some samples, and Paul Young for skillfully generated Fig. 2. The senior author's research was funded through the NRF (via The Sea and the Coast Programme, The African Coelacanth Ecosystem Project and Incentive Funding for Rated Researchers) and University of KwaZulu-Natal post-doctoral bursaries. We thank an anonymous reviewer for useful comments that helped to improve the manuscript. The senior author is particularly grateful to Prof. Ralf Schiebel (University of Angers, France) for his most thorough review of the first and the revised versions of the manuscript, and for his numerous comments and fruitful discussions.
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