Diatoms: By Kevin Miklasz Awards: Miller Writing, Myers DiatomsDiatoms are one of the strangest and most common forms of life in the ocean. Diatoms are a type of phytoplankton, a group of very small plant-like organisms that live by floating in the ocean. They are plant-like because they photosynthesize sunlight, but unlike terrestrial plants their light absorbing pigments are brown, not green. This means that diatoms are distantly related to giant kelp and other brown algae. If you look under a microscope at almost any bit of seawater, youll see plenty of brownish circular or banana-shaped spots- these are most likely diatoms. In fact, diatoms are so common and well-shaped that in the 19th century diatoms were used to test the quality of microscope lenses. The unique and strange feature of diatoms is that they live in a glass house. Diatoms encase themselves in an outer cell wall called a frustrule which is Diatomscomposed of silica, or glass. These glass frustrules provide diatoms with structure and defense, but they are also extremely beautiful. Some high magnification pictures of diatom frustrules are shown to the right. The frustrules are riddled with pores, spikes, spines, and other features that can be less than a micrometer in size. These features are sculptured by the diatoms during their growth and are so consistent, despite being so small, that they can be used as taxonomic features to identity and group diatoms. As floating phytoplankton, diatoms are faced with a classic question- do I sink or do I float? The beautiful frustrules are intimately tied to this question. The frustrule is heavy and therefore constantly pulls the diatom downward, though as photosynthesizers diatoms would rather be near the ocean surface and sunlight. Diatoms can counter their frustule weight by pumping light-weight ions into their cell vacuole (the Diatomsunderwater equivalent of inflating a helium balloon) to make themselves lighter and sink slower. Although a far step from active locomotion, this slight control over sinking rate can give diatoms the edge they need to stay near the sunlit ocean surface and survive in a variable and dynamic ocean. Its their way of weighting the die of survival in a chancy, turbulent ocean. My research centers around understanding how diatoms weight the sinking speed dice. Diatoms have evolved to occupy a range of sizes (over three orders of magnitude in diameter) and shapes (elongate and chainlike to short and squat to spiny spheres). How do the various sizes and shapes of diatoms effect diatom sinking speeds? I have discovered that traditional sinking speed theory fails to predict diatom sinking across size and shape because the heavy density of the frustule has not been incorporated into such analyses. By using a combination of size measurements from SEM photography and sinking speed measurements from a highly controlled water column, I have developed a robust theoretical framework which can predict how sinking speed varies across the different evolutionary sizes and shapes of diatoms. This information can help us understand how the diversity of frustule form has helped diatoms to weight the die of survival.
Posted on: Fri, 08 Aug 2014 23:57:18 +0000
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