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  • Parasitism is “an interaction of species populations in which one (typically small) organism (the parasite) lives in or on another (the host), from which it obtains food (when the parasite may be called a biotroph), shelter, or other requirements. Whereas a predator kills its host a parasite does not.” [1])

In other words, in parasitic relationships the host is harmed while the symbiont benefits, compared to a mutualistic relationship where both benefit.


Examples of parasitic relationships with corals

  • The relationship between corals and Symbiodinium depends on the different “clades [2]
    • some symbionts are less beneficial than others, and those that are less beneficial or are less beneficial and flourish under the right conditions are consistent with features of parasitism [2]
      • oldest clade (Clade A) has high tolerance for environmental stress, including higher temperatures and “high solar irradiances” and they don’t produce as much carbon for the corals [2]
        • corals in this clade have lower health and “lower overall fitness” [2]
      • clade D Symbiodinium flourishes in reefs that are exposed to chronically higher ocean temperatures [2]
        • “higher abundances . . . observed just after coral bleaching caused by thermal stress” [2]
        • corals dominated by this clade “show significantly reduced rates of growth and reproduction” but there is a higher thermal tolerance, providing short term benefits [2]
        • less beneficial symbiont that flourishes in the “right” (wrong for most of the alga in the corals) conditions hurts the corals overall [2]
  • Another example is Acropora corals and parasitic Chlorodesmis fastigiata seaweeds. These seaweeds move in on reef ecosystems and consume the resources that corals rely on.
    • This phenomenon is explored in more detail in a report by Danielle L. Dixon and Mark E. Hay, "Corals Chemically Cue Mutualistic Fishes to Remove Competing Seaweeds [3].



  1. Allaby, Michael, ed. "Parasitism." A Dictionary of Zoology. Oxford University Press, n.d. Web. 20 February 2015.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 Lesser, M. P., M. Stat, and R. D. Gates. "The Endosymbiotic Dinoflagellates of Corals Are Parasites and Mutualists." Coral Reefs 32.3 (2013): 603-11. ProQuest. ProQuest. Web. 20 February 2015.
  3. Dixson, Danielle L., and Hay, Mark E. "Corals Chemically Cue Mutualistic Fishes to Remove Competing Seaweeds." Science. 2012 Nov 9.
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