Comprehensive Description

Description of Chrysophyceae

The chrysomonads include mainly single-celled and colonial flagellates, but amoeboid (rhizopodial), plasmodial, palmelloid (capsoid), coccoid, filamentous and parenchymatous forms also occur. Chrysomonads are mainly freshwater organisms, with only a few species reported from marine environments and a few from soil and snow habitats. They live in a wide range of freshwater environments from polar regions to the tropics, but most commonly occur in cold temperate lakes, ponds and bogs.
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General Ecology

DMS in the odor landscape of the sea

Dimethyl Sulfide or DMS is present throughout the ocean(1). It’s an important odor component of many fish and shellfish, including clams, mussels, oysters, scallops, crabs and shrimp(2-9). Where does it come from? Usually from the marine plants they feed on.

Many species of plants and algae produce DMS, but not all species produce significant amounts of it. Nearly all of these are marine, and they tend to be in closely related groups with other DMS-producers, including Chlorophyte (green) seaweeds, the Dinophyceae in the dinoflagellates, and some members of the Chrysophyceae and the Bacillariophyceae (two classes of diatoms). Other large groups, like cyanobacteria and freshwater algae, tend not to produce DMS. (10,11)

Why do these groups produce DMS? In algae, most researchers believe a related chemical, DMSP, is used by the algae for osmoregulation- by ensuring the ion concentration inside their cells stays fairly close to the salinity in the seawater outside, they prevent osmotic shock. Otherwise, after a sudden exposure to fresh water (rain at the sea surface, for instance) cells could swell up and explode. In vascular plants, like marsh grasses and sugar cane, it’s not clear what DMS is used for. (12,13)

Freshly harvested shellfish can smell like DMS because DMSP has accumulated in their tissue from the algae in their diet. Some animals, including giant Tridacna clams and the intertidal flatworm Convoluta roscoffensis, harbor symbiotic algae in their tissues, which produce DMSP; this may not be important to their symbioses, but for Tridacna, the high DMS levels can be a problem for marketing the clams to human consumers. After death, DMSP begins to break down into DMS. A little DMS creates a pleasant flavor, but high concentrations offend the human palate.(2,14)

Not all grazers retain DMS in their tissues, though. At sea, DMS is released when zooplankton feed on algae. It’s been shown in the marine copepods Labidocera aestiva and Centropages hamatus feeding on the dinoflagellate Gymnodinium nelson that nearly all the DMS in the consumed algae is quickly released during feeding and digestion.(15) This has a disadvantage for the grazing zooplankton. Marine predators, like procellariiform seabirds, harbor seals, penguins, whale sharks, cod, and coral reef fishes like brown chromis, Creole wrasse and boga, can use the smell of DMS to locate zooplankton to feed on. (8,16,17)

It’s not easy to measure how much DMS is released from the Ocean into the air every year. Recent estimates suggest 13-37 Teragrams, or 1.3-3.7 billion kilograms. This accounts for about half the natural transport of Sulfur into the atmosphere, is the conveyor belt by which Sulfur cycles from the ocean back to land. In the atmosphere, DMS is oxidized into several compounds that serve as Cloud Condensation Nuclei (CCN). The presence of CCN in the air determines when and where clouds form, which affects not only the Water cycle, but the reflection of sunlight away from the Earth. This is why climate scientists believe DMS plays an important role in regulating the Earth’s climate. (12,18)

  • 1) BATES, T. S., J. D. Cline, R. H. Gammon, and S. R. Kelly-Hansen. 1987. Regional and seasonal variations in the flux of oceanic dimethylsulfide to the atmosphere. J. Geophys. Res.92: 2930- 2938
  • 10) Malin, G., Kirst, G.O. 1997. Algal Production of Dimethyl Sulfide and its Atmospheric Role. J. Phycol., 33:889-896
  • 11) Keller, M.D., Bellows, W.K., Guillard, R.L. 1989. Dimethyl Sulfide Production in Marine Phytoplankton. Biogenic Sulfur in the Environment. Chapter 11, pp 167–182. ACS Symposium Series, Vol. 393. ISBN13: 9780841216129eISBN: 9780841212442.
  • 12) Yoch, D.C. 2002. Dimethylsulfoniopropionate: Its Sources, Role in the Marine Food Web, and Biological Degradation to Dimethylsulfide. Appl Environ Microbiol., 68(12):5804–5815.
  • 13) Otte ML, Wilson G, Morris JT, Moran BM. 2004. Dimethylsulphoniopropionate (DMSP) and related compounds in higher plants. J Exp Bot., 55(404):1919-25
  • 14) Van Bergeijk, S.A., Stal, L.J. 2001. Dimethylsulfonopropionate and dimethylsulfide in the marine flatworm Convoluta roscoffensis and its algal symbiont. Marine Biology, 138:209-216
  • 15) Dacey , J.W.H. and Stuart G. Wakeham. 1986. Oceanic Dimethylsulfide: Production during Zooplankton Grazing on Phytoplankton. Science, 233( 4770):1314-1316
  • 16) Nevitt, G. A., Veit, R. R. & Kareiva, P. (1995) Dimethyl Sulphide as a Foraging Cue for Antarctic Procellariiform Seabirds. Nature 376, 680-682.
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  • 2) Hill, RW, Dacey, JW and A Edward. 2000. Dimethylsulfoniopropionate in giant clams (Tridacnidae). The Biological Bulletin, 199(2):108-115
  • 3) Brooke, R.O., Mendelsohn, J.M., King, F.J. 1968. Significance of Dimethyl Sulfide to the Odor of Soft-Shell Clams. Journal of the Fisheries Research Board of Canada, 25:(11) 2453-2460
  • 4) Linder, M., Ackman, R.G. 2002. Volatile Compounds Recovered by Solid-Phase Microextraction from Fresh Adductor Muscle and Total Lipids of Sea Scallop (Placopecten magellanicus) from Georges Bank (Nova Scotia). Journal of Food Science, 67(6): 2032–2037
  • 5) Le Guen, S., Prost, C., Demaimay, M. 2000. Critical Comparison of Three Olfactometric Methods for the Identification of the Most Potent Odorants in Cooked Mussels (Mytilus edulis). J. Agric. Food Chem., 48(4): 1307–1314
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  • 7) Tanchotikul, U., Hsieh, T.C.Y. 2006. Analysis of Volatile Flavor Components in Steamed Rangia Clam by Dynamic Headspace Sampling and Simultaneous Distillation and Extraction. Journal of Food Science, 56(2): 327–331
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  • 9) Sarnoski, P.J., O’Keefe, S.F., Jahncke, M.L., Mallikarjunan, P., Flick, G. 2010. Analysis of crab meat volatiles as possible spoilage indicators for blue crab (Callinectes sapidus) meat by gas chromatography–mass spectrometry. Food Chemistry, 122(3):930–935
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