Friday 18 January 2019

Mercury and Selenium levels in Jellyfish and Pyrosomes from the Monterey Bay National Marine Sanctuary, California.

Elevated levels of inorganic pollutants in marine wildlife has become an issue of great concern in recent years, with a range of studies showing raised levels of Mercury and Selenium in a variety of organisms. Mercury is a potent toxin to most animals, and has no known metabolic use to any organism, while Selenium is an essential element to most organisms at low levels (and can help organisms to withstand mercury poisoning to some extent), but at higher levels becomes toxic itself. One group in which the presence of these elements has not been studied to any extent is gelatinous macro-plankton, such as Jellyfish (Medusozoans), Comb Jellies (Ctenaphores), Pyrosomes and Salps, (colonial planktonic Tunicates), despite these being a vital source of food to many organisms known to be prone to Mercury and Selenium poisoning, including Sharks, Skates, Turtles, Seabirds, and some Human populations.

In a paper published in the journal Marine Pollution Bulletin on 28 November 2018, Justin Perrault of the Department of Biological Sciences at Florida Atlantic University presents the results of a study on mercury and selenium levels in gelatinous macro-plankton from the Monterey Bay National Marine Sanctuary, off the coast of California.

Perrault analysed eighteen organisms, including five Moon Jellyfish, Aurelia sp., three Purple-striped Jellyfish, Chrysaora colorata, five Pacific Sea Bettles, Chrysaora fuscescens, three Fried Egg Jellyfish, Phacellophora camtschatica, and two Thaliaceans, Pyrosoma sp..

A Purple-striped Jellyfish, Chrysaora colorata. David Wrobel/Scripps Institution of Oceanography.

All of the Jellyfish were found to have extremely low levels of both Mercury and Selenium, significantly lower than those found in Minimata Bay, Japan, in 1969, following a notorious mercury pollution event, but also lower than found in Jellyfish taken from the stomachs of stranded Turtles in Florida, suggesting that animals feeding on Jellyfish in the Monterey Bay area are not at risk from Mercury and Selenium poisoning.

A Fried Egg Jellyfish, Phacellophora camtschatica. Monterey Bay Aquarium.

The Thaliaceans, Pyrosoma sp., did retain significantly higher levels of Selenium than the Jellyfish, a pattern also seen in material from Turtle stomach contents in Florida, suggesting that Thaliaceans are more efficient at sequestering this element in their tissues, but even this was at levels likely to present only a mild risk to animals which eat nothing but Thaliaceans, of which there are none known.

 A Thaliacean, Pyrosoma atlanticum, in a tidal pool at Point Pinos in California. Ryan McGrady/Wikipedia.

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