Diatoms by the numbers
Diatoms are a lineage of unicellular photoautotrophs within the heterokont algae(Goertzen and Theriot 2003; Graham and Wilcox 2000). Given sufficient moisture and sunlight, diatoms can thrive in virtually any habitat, though they are principally found in association with submerged surfaces (benthic) or suspended in the water column of lakes and oceans (planktonic). The importance of marine planktonic diatoms in the biogeochemical cycling of many elements, particulary carbon and silica, cannot be overstated. As a whole, marine phytoplankton account for >46% of global net primary production, despite representing only 0.2% of global primary producer biomass (Behrenfeld and Falkowski 1997; Falkowski et al. 1998; Field et al. 1998). Diatoms alone account for ≥40% of marine primary production, thus contributing 20–25% of global net primary production (Nelson et al. 1995; Werner 1977), which is more than all the world’s rainforests (Field et al. 1998). Diatoms play an integral role in the transfer of photosynthetically fixed carbon to consumers. Diatom storage products include chrysolaminaran and a suite of highly unsaturated fatty acids, which are an excellent food source for invertebrate grazers (Anderson and Cummins 1979; Müller-Navarra et al. 2000). Nutrient flux from deep, nutrient-rich waters into the euphotic zones of areas of coastal upwelling or high convective mixing promotes the diatom primary production that sustains the world’s fisheries (Falkowski et al. 1998).
The diatom cell wall is composed of hydrated amorphous silica. Silica comprises ~25% (by weight) of the earth’s crust (Iler 1979). A silica molecule weathered from land into the oceans passes through a diatom ~39 times before being buried in marine sediments (Martin-Jezequel et al. 2000; Treguer et al. 1995). Diatoms control biogeochemical cycling of silica in the sea, where the element is relatively scarce because of their high demand for it (Martin-Jezequel et al. 2000; Nelson et al. 1995; Treguer et al. 1995).
No one can agree on the estimated number of diatom species. Diatomists currently recognize 10,000–12,000 diatom species (Norton et al. 1996)—a small fraction of the estimated 200,000 diatom species worldwide (Mann and Droop 1996). Some have estimated that total diatom diversity might exceed 10,000,000 species (Norton et al. 1996).
References
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Behrenfeld, M. J., and P. G. Falkowski. 1997. Photosynthetic rates derived from satellite-based chlorophyll concentration. Limnology & Oceanography 42:1-20.
Falkowski, P. G., R. T. Barber, and V. Smetacek. 1998. Biogeochemical Controls and Feedbacks on Ocean Primary Production. Science 281:200-206.
Field, C. B., M. J. Behrenfeld, J. T. Randerson, and P. Falkowski. 1998. Primary production of the biosphere: Integrating terrestrial and oceanic components. Science (Washington D C) 281:237-240.
Goertzen, L. R., and E. C. Theriot. 2003. Effect of taxon sampling, character weighting, and combined data on the interpretation of relationships among the heterokont algae. Journal of Phycology 39:1-22.
Graham, L. E., and L. W. Wilcox. 2000. Algae. Prentice Hall, Upper Saddle River.
Iler, R. K. 1979. The Chemistry of Silica: Solubility, Polymerization, Colloid and Surface Properties, and Biochemistry. John Wiley & Sons, New York.
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Martin-Jezequel, V., M. Hildebrand, and M. A. Brzezinski. 2000. Silicon metabolism in diatoms: Implications for growth. Journal of Phycology 36:821-840.
Müller-Navarra, D. C., M. T. Brett, A. M. Liston, and C. R. Goldman. 2000. A highly unsaturated fatty acid predicts carbon transfer between primary producers and consumers. Nature 403:74-77.
Nelson, D. M., P. Treguer, M. A. Brzezinski, A. Leynaert, and B. Queguiner. 1995. Production and Dissolution of Biogenic Silica in the Ocean - Revised Global Estimates, Comparison with Regional Data and Relationship to Biogenic Sedimentation. Global Biogeochemical Cycles 9:359-372.
Norton, T. A., M. Melkonian, and R. A. Andersen. 1996. Algal biodiversity. Phycologia 35:308-326.
Treguer, P., D. M. Nelson, A. J. Vanbennekom, D. J. Demaster, A. Leynaert, and B. Queguiner. 1995. The silica balance in the world ocean: a reestimate. Science 268:375-379.
Werner, D. 1977. Introduction with a note on taxonomy. Pp. 1-17 in D. Werner, ed. The Biology of Diatoms. University of California Press, Berkeley.