by Piter Kehoma Boll
Don’t be as fool as the Egyptian Pharaoh in the myth of the Plagues of Egypt. If you happen to find a lake with red water, as in the picture below, it is certainly not blood. It’s simply… a toxic alga!
The creature responsible for this coloration is today’s Friday Fellow: Euglena sanguinea, or the red euglene, a microscopic freshwater protist with a worldwide distribution. This unicellular organisms has a red color due to the presence of astaxanthin, a pigment also found in some fish, like salmon, and in crustaceans, like shrimp and crayfish. Some birds may also have this pigment in their feathers. In red euglenes, astaxanthin acts as a protection against ultraviolet radiation, so that the higher the amount of UV radiation, the redder the algae become.
When the conditions are adequate, usually due to high temperatures and high amounts of nutrients, the red euglene may overpopulate and cover the entire surface of water bodies, making it appear red. Water pollution, especially from domestic wastewater, is one of the main causes of nutrient increase in water bodies and thus a direct cause of many algal blooms.
The red euglene is known to produce euglenophycin, a very potent ichthyotoxin, i.e., a compound that is toxic to fish. As a result, red euglene blooms can lead to high fish mortality, making it an organism of major concern to fish breeders.
– – –
Gerber, S.; Häder, D-P. 2006. Effects of enhanced UV-B radiation on the red coloured freshwater flagellate Euglena sanguinea. FEMS Microbiology Ecology, 13(3): 177-184. DOI: 10.1111/j.1574-6941.1994.tb00064.x
Wikipedia. Euglena sanguinea. Available at <https://en.wikipedia.org/wiki/Euglena_sanguinea>. Access on January 07, 2016.
Zimba, P. V.; Rowan, M.; Triemer, R. 2004. Identification of euglenoid algae that produce ichthyotoxin(s). Journal of Fish Diseases, 27: 115-117.