The following represents a modified version of a poster presented
at The Salton Sea Symposium, January 13-14, 2000,
Desert Hot Springs, California,
sponsored by the Salton Sea Authority.
The Diatom Flora of the Salton Sea, California
Mary Ann Tiffany
Center for Inland Waters and Department of Biology
San Diego State University, San Diego, CA 92182
Carina B. Lange
Scripps Institution of Oceanography,
9500 Gilman Drive, La Jolla, CA 92093-0244
Diatoms are unicellular, eukaryotic (cells in which the nucleus is separated from the cytoplasm by a nuclear membrane; i.e. structurally more complex than prokaryotic bacteria), photosynthetic (i.e. they require light for the process of photosynthesis) microorganisms ranging from ca. 2 µm to ca. 2 mm in size. They are found just about anywhere there is light and moisture. They are far more diverse and abundant in freshwaters, where they are the commonest organism found and make up the base of many freshwater food pyramids. In the oceans, diatoms are most abundant in areas of upwelling (coastal and open ocean), where oceanic currents bring up the nutrients from deeper waters to the photic zone, and in polar latitudes. In these regions, they are the most important organisms at the base of the food chain.
Diatoms have a highly differentiated cell wall, which is impregnated with opaline silica, so that their growth is subject to the availability of silicon in the water. The diatom skeleton (frustule) is composed of two valves that fit together in a nested, overlapping fashion like a Petri dish. Diatom classification is based on the features of the skeleton.
Diatoms are important ecological indicators because they are sensitive to such factors as salinity, temperature, pH and pollution. In limnology, freshwater diatoms are the primary tool for reconstructing lake conditions, especially changes in pH and fertility. They play a key role in monitoring acid rain and the pollution of the world's freshwater. With the objective of documenting the diversity of diatoms in the Salton Sea and thus expanding the limited knowledge about these single-celled algae from this extreme environment we set out to identify and photograph all diatom species encountered in the phytoplankton and the phytobenthos of the Salton Sea (see poster). A catalogue of the diatom assemblages is being prepared which will serve as a guideline to the diatom flora of the Sea for use by future students and researchers.
In the Salton Sea there are four general categories of diatoms. Those that live in the plankton float freely about with the water currents. Some diatoms live on the bottom mud or in the algal mats, these are the benthic diatoms. Others, the epiphytic diatoms, attach to the macroscopic green algae which grow on the rocks and other hard surfaces near the shore. Also present in the Sea are diatoms that get washed in by the rivers and other inflows. Many of these probably don't live long in the high salinity but their valves are found infrequently in the water or sediments.
We have found a great diversity of diatoms; 92 taxa were distinguished on their basis of their morphological features at the light- and electron microscope level. These were found after examining samples collected at 19 different sites (including shore and open water samples). Whenever possible, taxa were identified to the level of species using published literature. Some of these are new to science. In addition, a few taxa showed peculiar morphological features, probably as a response to adaptation to the extreme environment of the Salton Sea, and are documented as "morphotypes" in need of further taxonomic work. The most abundant diatoms are marine planktonic species which is not surprising given the salinity and history of the lake. They dominate the phytoplankton assemblage in the summer and fall with densities of about 106 cells per liter. Other common species are mostly found in salt lakes or are usually found in fresh or brackish water.
It is clear that diatoms are a major component of the microorganisms in the Salton Sea. Preliminary studies on the sediments reveal a rich flora preserved in the sediments which holds clues to the past history of the Salton Sea.
General Categories of Diatoms
Muddy Area with Sick Grebe Benthic Flora
The Alamo River
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