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Volume 4 - 4
| Contents | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
| 4. Fossil Research Reshapes Conventional Wisdom By Dr Tony Ribbink The African Coelacanth Ecosystem Programme (Acep) is the first multidisciplinary biophysical research programme to be undertaken on the east coast of South Africa and the Western Indian Ocean. Oceanographic and geoscience research elements of Acep are now reshaping accepted wisdom about the Mozambique Channel and the Agulhas current, as well as the origin of South African coelacanths. Two significant shifts in knowledge are that the Mozambique current is not a continuous flow but a series of anticyclonic eddies and that the African coelacanths are unlikely to have been strays from Indonesia or the Comoros Islands. “For the first time, we have hard evidence in sufficient detail to be able to challenge long-standing theories about our part of the Western Indian Ocean and therefore to better manage the resources it offers us,” says Dr Tony Ribbink, Programmes Manager for the South African Institute of Aquatic Biodiversity, under whose aegis Acep is run. Acep's geosciences are aimed at defining the coelacanths' structural habitats, while the oceanography is aimed at defining the aquatic medium in which coelacanths live.   One of the few things known about
coelacanths before Acep began in April 2002, was that they live in
submarine canyons in a given temperature range. Research then began
with a survey of the northern KwaZulu-Natal canyon systems to define
potential coelacanth habitats. That meant undertaking South Africa's
first-ever deepwater multibeam bathymetric survey. Marine GeoSolutions
(Pty) Ltd then developed a series of colour-draped bathymetric maps and
three-dimensional models of the canyons that enabled 'virtual' dives on
computer.The maps also provide information for real-life submersible dives and form the basal layer of a marine GIS (Geographic Information System), currently in development. Marine geologists also collected all other extant information about the Mozambique Channel and the Agulhas Current most of it on charts and some dating back to 1939 - and incorporated it into a relational database that will be linked to the GIS. The GIS will include all on-going Acep research data and integrate all the scientific disciplines, to become the most comprehensive, off-shore information resource for the region. Through the Internet, it will become a global research, management and environmental educational tool. While it is easy to identify steep, rocky profiles from the bathymetric maps, predicting where caves are most likely to occur involves sound knowledge of the marine geology of the area. As Dr Ron Uken of the Marine Geoscience Unit at the University of KwaZulu-Natal points out, geological events dictate the development of life, so understanding the geology of coelacanth habitats will not only tell us how they came to be on our coastline, but also what is likely to endanger their survival.  High-resolution, colour-draped maps
produced by multibeam bathymetry enable very accurate predictions of
where ideal coelacanth habitat may be found. Acep's next step is to conduct a seismic study to establish how the various layers of sediment were laid down on the Maputaland continental shelf and how and when sea level fluctuations eroded the shelf to form caves. This will be accompanied by deep-rock and sediment sampling that will include animal and plant fossils. The seismic study will also enable very precise predictions of the occurrence of other species in the area with enormous positive implications for fisheries and tourism. In addition, it will enable predictions about future geological changes, allowing pro-active adjustment of marine activities and economies. In the past 65 years, coelacanths have been found on the African coastline as far north as Kenya and as far south as East London, South Africa. The only coelacanth population known to exist outside of Africa is in Indonesia, giving rise to the theory that African coelacanths were swept east from Indonesia on the strong South Equatorial Current to the northern end of Madagascar and from there, north on the East African (Zanzibar) Current and then south on the Mozambique and Agulhas currents. Coelacanths do not swim very well and so would have been unable to withstand the speed of a current such as that of the Agulhas, which at surface can exceed 2 m s-1. However, a satellite drifter experiment by Acep and an array of current meter moorings deployed by a Dutch research group over a 12-month period across the northern entrance of the Mozambique Channel showed no such continuous southward flow. Instead, it revealed the existence of a series of anti-cyclonic eddies moving slowly southwards. Also, current velocity diminishes quite rapidly with depth, and is especially weak in the numerous canyons off Sodwana. So, the currents tell us that the African coelacanths are probably indigenous rather than strays. Study-ing them has also afforded us a better understanding of our climate, as well as the distribution of biota in a region that is poor in biomass but extremely rich in biodiversity. Tectonics also offers answers to the puzzle of the origin of the African coelacanths. Fossil records show that coelacanths existed all along the north and east coast of the southern hemisphere mother continent, Gondwana. But about 200 million years ago, eastern Gondwana, consisting of Madagascar, India, Antarctica and Australia, split off from Africa and South America. The coelacanths may then have moved into the newly formed narrow ocean channel between Madagascar and Africa. Dr Uken believes that tectonic movement may also account for the separation between the Indonesian and African coelacanths. As India moved northwards, it collided with Asia, forming the Himalayas. This resulted in a significant change in the Indian Ocean's climate and sediment input. A massive influx of sediment from rivers draining the mountains about 10 million years ago, forming turbid barriers could have separated the Indian Ocean coelacanth population into the present western and eastern species. Measurements of temperature down the water column indicate that the coelacanths' preferred temperature range (15-21ºC, normally found at a depth of between 250 and 300m in the Comoros Islands) is accessible at a much shallower depth at Sodwana - typically between 100 and 140 m. The shallowing is caused by an upward tilting of the ocean thermocline in the Agulhas Current, a characteristic of Western Boundary Currents. Shallower depths allow the study of creatures using techniques other than submersibles, such as trimix scuba diving and remote underwater video cameras. An underwater camera system comprised of four video cameras equipped with environmental sensors that transmit images to shore has been developed by the oceanographic team and will come on stream for Acep once it has been adapted for deepwater canyons. For more information about Acep, go to www.coelacanth.ac.za. |
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