Karlodinium veneficum aka Gymnodinium galatheanum aka Karlodinium micrum; Courtesy of Prof. Allen Place |
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There’s a predator in Maryland waters. In 1996, 1997, and 1999, thousands of fish were killed at the HyRock Fish Farm on the Eastern Shore of the Chesapeake Bay. Water samples revealed the presence of two potential culprits, and after an initial case of mistaken identity, Karlodinium veneficum (then called Gymnodinium galatheanum) was found to be the cause. K. veneficum, a free-swimming phytoplankton or dinoflagellate, was first identified in Walvis Bay, Namibia in 1950 during the second Danish “Galathea” Deep Sea expedition. In South Africa, it caused periodic massive fish deaths, leaving the beaches covered with rotting fish and turning the water red with its thick algal blooms (colloquially known as red tide). In 2008, five fish kills in Chesapeake Bay and the Potomac occurred due to the presence of K. veneficum. This algae species is now considered a long term resident of Chesapeake Bay, and blooms (sometimes resulting in a “mahogany tide”) are monitored by the Maryland Department of Natural Resources.
Map of algal cell counts in the Bay on 6/29/09, K. veneficum marked by green triangles; Maryland DNR |
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Like many dinoflagellates, K. veneficum produces toxins, known as karlotoxins. Karlotoxins causes cells to rupture by increasing the ionic permeability of biological membranes (making them leaky until they explode). Fish are killed by damage to the gill epithelia. K. veneficum can gain energy both by photosynthesis and by the consumption of single-celled organisms. The production of toxins was hypothesized to be a self-defense system against other organisms in the phytoplankton grazing territory with local fish as the unlucky bystanders. Karlotoxins were identified and characterized in the lab of Allen Place of the Institute of Marine and Environmental Technology at the University of Maryland Center for Environmental Science.
In the February 2nd issue of the Proceedings of the National Academy of Sciences, Place and colleagues from the University of Minnesota, The Johns Hopkins University and the University of Hawaii show that karlotoxins are not just used by K. veneficum in self-defense. The toxic predatory strains use karlotoxins as a means of stunning their cryptophyte prey (Storeatula major) before ingesting it. Thus, the presence of prey leads to the presence of toxin. Therefore, by reducing the amount of K. veneficum prey in the Chesapeake and other infected waterways, K. veneficum may produce less toxin, leaving the fish to swim in peace.
Prey reduction (in conjunction with the input of native feeders) may help in developing effective management strategies against other predatory dinoflagellates in Maryland waters. According to the Maryland Department of the Environment, another dinoflagellate, Gyrodinium uncatenum, caused the largest fish kills in the state in 2008, resulting in 142,365 fish deaths. Unlike K. veneficum, G. uncatenum is non-toxic, and fish kills are thought to be caused by low dissolved oxygen produced from the large algal blooms. Like K. veneficum, G. uncatenum could gain energy from photosynthesis alone, but a reduction in prey may reduce the size of algal blooms and fish deaths.
How dinoflagellate prey reduction will be implemented without damaging the Bay ecology or industry is another scientific challenge that I hope I will have the pleasure of blogging about someday.
Did someone actually count 142,365 dead fish? I won’t complain about my job.
I agree, the fish counter job is not my ideal job. An interesting explanation of something we have been hearing about for years.
Hong Kong even has a red tide reporting network!
http://www.hkredtide.org/eng/red.html