Thursday 10 October 2019

Millions of Moon Jellyfish seen in Puget Sound.

The National Oceanic and Atmospheric Administration has reported a vast swarm of Moon Jellyfish, Aurelia sp., in Washington State's Puget Sound. The Jellyfish have been growing in numbers since mid September, in a population boom fuelled by unseasonably warm waters, combined with a high nutrient level in the Sound, which can in turn be traced to high rainfall levels on land, caused by higher evaporation from the warm water. Although the number of Jellyfish in the Sound is startling, there is little cause for concern, as, while Moon Jellyfish can sting, their venom is not generally strong enough to cause a serious health risk to Humans.

Thousands of Moon Jellyfish, Aurelia sp., in the water near the dock of the Orcas Island Yacht Club in Eastsound. Rachel Jitabebe Robert/KomoNews.

Members of the genus Aurelia are inshore Jellyfish found in coastal waters in tropical, subtropical and temperate seas around the world. They are large Jellyfish, reaching a maximum size of about 40 cm in diameter, a slight purplish tinge and four large, horseshoe-shaped gonads. Moon Jellyfish often undergo major blooms in the summer months, due to their tolerance for low oxygen conditions, which are harmful to most of their competitors and predators (Fish and large invertebrates), enabling them to dominate environments where these animals are excluded. This tends to lead to summer blooms in enclosed areas (heat and lack of exchange with the open ocean can rapidly deplete oxygen levels), which can be worse in areas where pollution from agriculture or other Human activities leads to eutrophication (excess nutrients which can lead to eutrophication and the rapid growth of blooms of Algae, Bacteria or other micro-organisms, which absorb oxygen from the water leading Fish and other aquatic organisms to asphyxiate). 

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