study of dietary calcium and other nutrients and the risk of symptomatickidney stones. N. Engl. J. Med. 328, 833–838.

15. Raghavan K.G. and Tarachand U. (1986). Degradation of oxalate in ratsimplanted with immobilized oxalate oxidase. FEBS Lett. 195, 101–105.

16. Bais R., Rofe A.M. and Conyers R.A. (1991). The inhibition of metabolic oxalateproduction by sulfhydryl compounds. J. Urol. 145, 1302–1305.

17. Bringmann G., Feineis D., Hesselmann C., Schneider S., Koob M. andHenschler D. (1992). A ‘chemical’ concept for the therapy of glyoxylate-induced oxalurias. Life Sci. 50, 1597–1605.

18. Poldelski V., Johnson A., Wright S., Dela Rosa V. and Zager R.A. (2001). Ethyleneglycol-mediated tubular injury: identification of critical metabolites and injurypathways. Am. J. Kidney Dis. 38, 39–348.

19. Morgunov I.G., Kondrashova M.N., Kamzolova S.V., Sokolov A.P., FedochevaN.I. and Finogenova T.V. (2005). Evidence of the glyoxylate cycle in liver of new-born rats. Med. Sci. Monit. 11, 57–60.

20. Popov V.N., Igamberdiev A.U., Schnarrenberger C. and Volvenkin S.V. (1996).Induction of glyoxylate cycle enzymes in rat liver upon food starvation. FEBSLett. 390, 258–260.

21. Davis W.L., Jones R.G., Farmer G.R., Cortinas E., Matthews J.L. and Goodman

D.B. (1989). The glyoxylate cycle in rat epiphyseal cartilage: the effect of vita-min-D3 on the activity of the enzymes isocitrate lyase and malate synthase.Bone 10, 201–206.

22. Freedman B.I., Wuerth J-P., Cartwright K., Bain R.P., Dippe S., Hershon K.,Mooradian A.D. and Spinowitz B.S. (1999). Design and baseline characteristicsfor the aminoguanidine clinical trial in overt type 2 diabetic nephropathy.Control Clin. Trials 20, 493–510.

23. Duncan R.J. (1980). The disproportionation of glyoxylate by lactate dehydro-genase. Arch. Biochem. Biophys. 201, 128–136.

24. Burcham P.C., Kaminskas, L.M., Fontaine F.R., Petersen D.R. and Pyke S.M.(2002). Aldehyde-sequestering drugs: tools for studying protein damage bylipid peroxidation products. Toxicology 181, 229–236.

25. Wandzilak T.R., d’Andre S.D., Davis P.A. and Williams H.E. (1994). Effect of highdose vitamin C on urinary oxalate levels. J. Urol. 151, 834–837.

26. Curhan G.C., Willett W.C., Rimm E.B. and Stampfer M.J. (1996). A prospectivestudy of the intake of vitamins C and B6, and the risk of kidney stones in men.J Urol. 155, 1847–1851.

27. Green M.A. and Fry S.C. (2005). Vitamin C degradation in plant cells via enzy-matic hydrolysis of 4-O-oxalyl-L-threonate. Nature 433, 83–87.

Research Letters South African Journal of Science 101, May/June 2005 255

The bathymetry of theAliwal Shoal, Scottburgh,South Africa

C. Bosmana*, R. Ukena and A.M. Smithb

IntroductionThe Aliwal Shoal (Fig. 1) is one of the best-preserved examples

of the many submerged reefs, parallel to the coast, documentedon the southeastern continental shelf.1–6 These reefs consistprimarily of aeolianite with subordinate beachrock and arethought to represent Late Pleistocene palaeocoastlines.3,4 In1884, the SS Nebo sank after striking the reef; in 1974, the MVProduce similarly sank, coming to rest on the seafloor northeastof the Aliwal Shoal.7 In 1963, the Aimée Lykes grounded on thereef but made it to Durban harbour. Rock samples removed fromthe damaged hull confirmed an aeolianite origin8 and foramini-fera provided a Pliocene–Recent age,9 revised later as Late Pleis-tocene.10 Several researchers have included the Aliwal area inregional studies2,11–13 but none has dealt specifically with this reefand it has remained for the most part unmapped (Fig. 2). In thispaper we present the first detailed geo-referenced map of the

Aliwal Shoal and illustrate its usefulness as a scientific and envi-ronmental management tool.

Bathymetric modellingEcho-sounding data were collected on two separate sea

cruises, in March and June 2001. The survey grid comprisednorthwest–southeast and northeast–southwest tracklines, set120 m apart (Fig. 3). In all, 266 line-kilometres were surveyed.Depth measurements for the bathymetry map were recordedusing an Odom EchoTrac Model 3100 single-beam digital hydro-graphic echo-sounder and a 200-kHz narrow-beam (10°) Odomtransducer. The accuracy of the echo-sounder was 0.01% of totalwater depth, dependent on the accuracy of the value of thevelocity of sound. Navigation and position fixes were providedby a Fugro OmniStar 12-channel differential Global Positioning

aJoint Council for Geoscience/University of KwaZulu-Natal Marine Geoscience Unit,School of Geological Sciences, Howard College Campus, Durban 4041, South Africa.bASC Research, Durban. E-mail: asconsulting@telkomsa.net

*Author for correspondence. E-mail: bosman@ukzn.ac.za

Fig. 1. Locality map of the study area which falls within the ‘Controlled Zone’ of thenewly proclaimed Aliwal Shoal Marine Protected Area (MPA). The RestrictedZones within the Controlled Zone are also shown.

Fig. 2. Maps of the Aliwal Shoal. (a) Bathymetry (10-m intervals) and (b) geologicalmap showing unconsolidated sediment thickness (isopachs in 10-m intervals) andaeolianite (black area). After Martin and Flemming.12

This paper presents the first accurate geo-referenced bathymetricmap of the Aliwal Shoal and illustrates its value as an essential toolfor a wide range of applications useful to the broader scientificcommunity. The dense coverage of echo-sounding data in thesurvey area permitted the construction of a detailed bathymetriccontour map and 3-D model. It showed that the Aliwal Shoal formspart of a much larger offshore reef complex than was previouslyrealized. Morphologically, the Aliwal Shoal is dominated by threedistinct features, namely, the Crown, Spur and Ridge. The high-resolution bathymetric map presented here enabled the accuratepositioning of the boundaries of the Restricted Zones of thenewly proclaimed Aliwal Shoal Marine Protected Area. This geo-referenced GIS-compatible map will form the base map for futurestudies, ranging from the mapping of biological seafloor habitats toocean current modelling, thereby also performing the function of anenvironmental planning and management tool.

System (dGPS) capable of single-second update rate andsub-metre accuracy. Using an average survey speed of 2.5 knots,this translated into a bathymetric data point every 1.29 m alongeach trackline.

In total, 101 433 data points were used to create the bathymetricmodel. All depth values were tidally corrected to the meansea-level (MSL) datum (local tidal range is 2 m). Data weregridded in Surfer version 7 software using point kriging toproduce seafloor contours as used in earlier reef surveys on thesoutheastern continental shelf.14 Grid sizes and search patternswere optimized to represent the reef most accurately using a20 m × 20 m grid with an octant search pattern and a searchradius of 180 m. Digital terrain models were generated usingER Mapper 6.4 and Surfer 8 software to provide three-dimen-sional (3-D) models of the continental shelf (Fig. 4b) in additionto a 2-D contour plot (Fig. 4a), providing visualization of the reefmorphology from any orientation.

Aliwal Shoal morphologyThe Aliwal Shoal forms part of a much larger offshore reef

complex than was previously realized. The seaward expressionof the reef is a narrow ridge with a curvilinear sinusoidal north-east–southwest (coast-parallel) trend (Fig. 4) that has an abruptnorthern edge called the Crown. The landward expression has alinear margin from which a narrow ridge, just over 1 km long(the Spur), projects shoreward. The shallowest part (6 m belowMSL) is located in the northern extremity of the Crown, with agradual increase in depth with distance southwards. The steep-est gradient recorded, on the northern edge of the Crown, is 18°.Other gradients vary from 6.4° on the seaward side to 8° on thelandward side.

The Aliwal Shoal averages 380 m in width in the north, narrowsslightly in the central region but widens to more than 2 km in thesouth, where it bends shorewards (Fig. 2). This southern plateauregion is called the Ridge.8 Northwest of the shoal is a large

bedform, interpreted as submerged spit-bar12 and reinterpretedas a sandridge15 (Fig. 2). The landward side of the shoal, betweenthe Sandridge and the Ridge, is a sand-filled depression, roughlydivided into two basins by the Spur. The depression slopestowards the Sandridge (Fig. 4). The Spur consists in part of anorthwards-migrating, 2–3-m-high subaqueous dune.

The average depth of the Crown is 12.5 m and it contains almostall of the SCUBA-diving locations used by recreational divers,the best known being the Main Pinnacle Ridge and North-EasternPinnacles (Fig. 4). The southern Ridge is deeper with an averagedepth of 19.5 m. This portion and the southern continuation ofthe Crown ridge are characterized by several other isolatedpinnacles. The total area covered by the Aliwal Shoal is in excessof 5.56 km2 and extends westwards to the coast beyond the Ridge.

Data applicationThis dataset provides the first detailed and useful information

on the nature of the seafloor in the Aliwal Shoal area and enabledthe accurate positioning of the newly proclaimed Restricted

256 South African Journal of Science 101, May/June 2005 Research Letters

Fig. 3. dGPS tracklines showing data coverage in the survey area. Also shown arethe Produce and Crown Restricted Zones of the MPA and the 25-m isobath, whichwas used to delineated the Crown Area Restricted Zone.

Fig. 4. (a) Bathymetric contour map of the study area showing the main morpholog-ical features and the boundaries of the Restricted Zones of the MPA. Contourinterval is 2 m. (b) 3-D bathymetric model of the study area; view is from the south,sunshading from 150° with a 75° azimuth.

Research Letters South African Journal of Science 101, May/June 2005 257

Zone of the Aliwal Shoal Marine Protected Area (MPA).16 Basicbiological inventory studies to determine the status of the reefare required for conservation and management planning of theMPA. This relies on reliable knowledge of the location and distri-bution of reef habitats. The bathymetry map of the Aliwal Shoalserves as a spatially accurate base map that is easily importedinto a GIS database, where it can be used as a multi-surfaceattribute model for spatially referenced data. The dataset forms abase map for biological surveys to chart changes to habitatsand biological zones and provides a means to model effluentdischarge and environmental impacts from marine outfall pipe-lines situated north of the study area.

The new bathymetric map also indicates the presence of othershallow, isolated pinnacles that can be used as alternative divesites, alleviating pressure on the more popular dive sites situatedon the Crown. Recreational divers will benefit from the highaccuracy of the map by planning the exact location of their divesand minimizing user conflict within the MPA. Furthermore, itis envisaged that these data will form part of an MPA websiteproviding tourists and divers with geological, biological, andoceanographic information and 3-D ‘fly-through’ visualization.

The bathymetric dataset not only serves as the first accurateand detailed map of the Aliwal Shoal but also serves as a useful‘environmental tool’ which will form the baseline for futurestudies ranging from the mapping of biological seafloor habitatsto ocean current modelling. Integration of all the data types willfacilitate the development of a comprehensive multidisciplinaryenvironmental management plan, which is vital for the futuredevelopment, management and conservation of the AliwalShoal.This paper is published with permission of the director of the Council forGeoscience, and benefited from the comments of two anonymous reviewers.

Received 12 September 2004. Accepted 14 May 2005.

1. Belderson R.H. (1961). The size distribution characteristics of the Recent shallowmarine sediments off Durban, South Africa. M.Sc. thesis, University of Natal,Durban.

2. Flemming B.W. (1978). Underwater sand dunes along the southeast Africancontinental margin — observations and implications. Mar. Geol. 26, 177–198.

3. Martin A.K. and Flemming B.W. (1988). Physiography, structure, andgeological evolution of the Natal continental shelf. In Coastal Ocean Studies offNatal, South Africa. Lecture Notes on Coastal and Estuarine Studies, vol. 26, ed. E.H.Schumann, pp. 11–46. Springer-Verlag, New York.

4. Ramsay P.J. (1991). Sedimentology, coral reef zonation, and Late Pleistocene coastlinemodels of the Sodwana Bay continental shelf, northern Zululand. Ph.D. thesis,University of Natal, Durban.

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8. McCarthy M.J. (1967). Stratigraphical and sedimentological evidence from theDurban region of major sea-level movements since the late Tertiary. Trans. Geol.Soc. S. Afr. 70, 135–165.

9. Carter A.N. (1966). Age of the Aliwal Shoal, South Africa. Nature 211, 507–508.10. McLachlan I.R. and McMillan I.K. (1979). Microfaunal biostratigraphy,

chronostratigraphy and history of Mesozoic and Cenozoic deposits of thecoastal margin of South Africa. Geol. Soc. S. Afr. Spec. Publ. 6, 161–181.

11. Hay E.R. (1984). Sediment dynamics on the continental shelf between Durbanand Port St. Johns (south-east African continental margin). Bulletin of the JointGeological Survey/University of Cape Town Marine Geoscience Unit, 13, 238 pp.

12. Martin A.K. and Flemming B.W. (1986). The Holocene shelf sediment wedge offthe south and east coast of South Africa. In Shelf Sands and Sandstones, edsR.J. Knight and J.R. McLean. Can. Soc. Pet. Geol. Mem. 2, 27–44.

13. Birch G.F. (1996). Quaternary sedimentation off the East Coast of SouthernAfrica (Cape Padrone to Cape Vidal). Bull. Geol. Surv. S. Afr., 118, 55 pp. Councilfor Geoscience, Pretoria.

14. Ramsay P.J. (1990). The use of computer graphics software to produce athree-dimensional morphological and bathymetric model of a Zululand coralreef. S. Afr. J. Sci. 86, 130–131.

15. Ramsay P.J., Smith A.M. and Mason T.R. (1996). Geostrophic sand ridge, dunefields and associated bedforms from the northern Kwazulu-Natal shelf,South-east Africa. Sedimentology 43, 403–419.

16. Republic of South Africa (2004). Marine Living Resources Act, 1998 (Act No. 18of 1998), Government Gazette 468, no. 26433, 3–10.

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Overview of the South African research and

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The registration cost of R1900 for the three-day course includes a work-shop folder, reading pack and all meals. SARIMA members who have paidtheir subscriptions for 2005 are eligible for a 15% rebate (R1615). Accom-modation costs are not included in the registration fee.

The registration form may be downloaded from the SARIMA website(www.sarima.co.za) and the completed form should be e-mailed to

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The course is aimed at professionals who work in research administra-tion and management offices in higher education institutions in SouthAfrica and in organizations that deal with managers and administrators inthese offices. Participants will typically not have received any formaltraining in research management or related fields. It is an introductorycourse but deals comprehensively with all aspects of research administra-tion.

The registration cost of R1900 for the three-day course includes a work-shop folder, reading pack and all meals. SARIMA members who have paidtheir subscriptions for 2005 are eligible for a 15% rebate (R1615).

The registration form and programme may be downloaded from theSARIMA website (www.sarima.co.za) and the completed form should bee-mailed to sarima@sarima.co.za. On receipt of the registration form, aninvoice will be sent for payment, prior to or at the event. The closing date forregistration is 29 September. The events co-ordinator, Margaret Ward, canbe contacted about both workshops on 084 583 6769 between 2 & 4 pm.