A living fossil diatom discovered in Antarctic waters
Science Centres: Aquatic Biodiversity and Biosecurity
A diver collects samples from under the ice in the Ross Sea.
Left: chains of the diatom D. marginopunctatum attached to the red alga Phyllophora antarctica.
Right: the silicified cell wall of D. marginopunctatum.
NIWA researchers recently discovered a living fossil diatom growing as an epiphyte on the red alga Phyllophora antarctica.
The discovery of the chain-forming diatom Drepanotheca marginopunctatum at Cape Evans, near the southern limit of the Ross Sea, highlights the need for careful taxonomic examination of marine benthic flora from poorly studied sites. There are no published reports of living specimens of D. marginopunctatum. The discovery of living specimens in an extreme environment suggests that the diatom now has a very restricted distribution, although the distribution of its fossils suggests that it did once have a global distribution.
Fossils of D. marginopunctatum (formerly included in the genus Eunotogramma) were first described from sediment cores in the San Joaquin Valley, California, and can be traced back to the Upper Cretaceous period. Locally, the genus Drepanotheca has been found in Eocene sedimentary rocks from Oamaru in the South Island and from Mount Discovery in Antarctica.
In our samples D. marginopunctatum was found living at between 20 and 25 m below the surface of the ice. The diatom was abundant on the older parts of the Phyllophora blades collected from 25 m and common on Phyllophora from 20 m deep. (It was not recorded on Phyllophora from shallower depths.) We will conduct more detailed studies of the depth range and latitudinal distributions of D. marginopunctatum during the 2002–03 Antarctic summer season as part of NIWA’s Antarctic marine benthic biodiversity programme.