Stromatolites
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Definition
Stromatolites (/stroʊˈmætəˌlaɪts, strə-/ stroh-MAT-ə-lytes, strə-) or stromatoliths (from Ancient Greek στρῶμα (strôma), GEN στρώματος (strṓmatos) 'layer, stratum' and λίθος (líthos) 'rock') are layered sedimentary formations (microbialite) that are created mainly by photosynthetic microorganisms such as cyanobacteria, sulfate-reducing bacteria, and Pseudomonadota (formerly proteobacteria). These microorganisms produce adhesive compounds that cement sand and other rocky materials to form mineral "microbial mats". In turn, these mats build up layer by layer, growing gradually over time.
This process generates the characteristic lamination of stromatolites, a feature that is hard to interpret, in terms of its temporal and environmental significance. Different styles of stromatolite lamination have been described, which can be studied through microscopic and mathematical methods. A stromatolite may grow to a meter or more. Fossilized stromatolites provide important records of some of the most ancient life. As of the Holocene, living forms are rare.
Stromatolites are layered, biochemical, accretionary structures formed in shallow water by the trapping, binding and cementation of sedimentary grains in biofilms (specifically microbial mats), through the action of certain microbial lifeforms, especially cyanobacteria.
Gqeberha Coastline
Gqeberha’s coastline is home to living fossils that are credited with creating the living conditions in which animal life could thrive. The first marine tufa stromalites along the South African coast were first described in the early 2000’s. Ongoing research indicates that the recent discovery of numerous and closely spaced living stromatolites on the coastline south of Port Elizabeth ‘appears to be extraordinary’.
A number of these critical and ancient fossils have been identified along Port Elizabeth’s wild side coastline and are currently being studied by the NMMU Shallow Water Ecosystems Faculty. Basically these ancient one celled bacteria were responsible for the creation of the first reefs. Stromatolite Location These bacteria – Cyanobacteria – were also ultimately responsible for one of the most important “global changes” that the Earth has undergone. Being photosynthetic, cyanobacteria (blue-green algae) produce oxygen as a by-product. Photosynthesis is the only major source of free oxygen gas in the atmosphere. As stromatolites became more common 2.5 billion years ago, they gradually changed the Earth’s atmosphere from a carbon dioxide-rich mixture to the present-day oxygen-rich atmosphere. This major change paved the way for the next evolutionary step, the appearance of life based on the eukaryotic cell (cell with a nucleus).
It has been speculated that bacteria found in these organisms were responsible for increasing the level of oxygen in the atmosphere on Earth from much less than 1% to the present day level of 21%. lt was through the oxygen generating activity of stromatolites that other animal life on Earth was able to develop.
A 2014 paper published by Prof Renzo Perissinotto, the NMMU Faculty of Science Research Chair in Shallow Water Ecosystems*, highlights the occurrence of extensive fields of actively calcifying stromatolites. These stromatolites have been recorded at regular distances along a 200-km stretch of coastline, from Cape Recife in the east to the Storms River mouth in the west, with the highest density found between Schoenmakerskop and the Maitland River mouth.
In the paper Prof Perissinotto says; “All active stromatolites are associated with freshwater seepage streams flowing from the dune cordon, which form rimstone dams and other accretions capable of retaining water in the supratidal platform. Resulting pools can reach a maximum depth of about 1m and constitute a unique ecosystem in which freshwater and marine organisms alternate their dominance in response to vertical mixing and the balance between freshwater versus marine inflow. Although the factors controlling stromatolite growth are yet to be determined, nitrogen appears to be supplied mainly via the dune seeps. The epibenthic algal community within stromatolite pools is generally co-dominated by cyanobacteria and chlorophytes, with minimal diatom contribution.”
Indications are very high of large numbers of these stromatolie formed rimstone dams are found in abundance along the coast to Woody Cape and in the recently formed Sanparks Marine Protected Area. It has been a long known fact that one can walk along the seashore between Woody Cape and Bird Island and find fresh water to drink. The Alexandria dunefield is the largest dunefield in the southern hemisphere stretching over 50km of coastline and over 15 000 hectares.
The dunefield and unspoilt coastline of mainly sandy beaches is flanked by Southern Coastal Forest with species such as coast coral trees, real yellowwoods, white stinkwoods and knobthorns in abundance – no development creates perfect conditions for the seepage of fresh uncontaminated water through the dunes and into the sea. In turn creating ideal conditions for large numbers of stromatolite pools all along the shoreline.
Perissinotto notes; “Most extant tufa stromatolite deposits around the world are already protected. Those occurring on the southwest coast of Western Australia, resembling most closely the South African type, are registered as ‘Threatened Ecological Communities’ with the status of endangered ecosystems. Special ‘Ecological Water Requirements’ have been allocated to them, in order to secure their long-term sustainability. Because of threats of residential encroachment, groundwater extraction, coastal development and invasion by alien species, it would be advisable for South Africa to follow the Australian example and place all tufa stromatolite formations under statutory protection.”
References
- Wikipedia (Stromatolite)
- Fossil Museum
- Stromatolites – Living Representatives of the Most Ancient Organisms
- South African Journal of Science
- Perissinotto R, Bornman TG, Steyn P-P, Miranda NAF, Dorrington RA, Matcher GF, et al. Tufa stromatolite ecosystems on the South African south coast. S Afr J Sci. 2014;110(9/10), Art. #2014-0011, 8 pages. http://dx.doi.org/10.1590/sajs.2014/20140011
