Along with the Great Pacific Garbage Patch if you are a marine conservationist you have undoubtably heard of the alarming rate with which enormous swarms of jellyfish are threatening to take over a oceans. A consequence of climate change? Evidence that our oceans are becoming wastelands, fit for no other life than that of the gelatinous? Or worse…an urban myth?
A recent article in the Proceedings of the National Academy of Sciences (or PNAS, pronounced PeeNAS) highlighted that this notion is based on a few scattered reports rather than a thorough synthesis of jellyfish population metrics. Using data ranging from 1790 to 2011 Condon et al claim that while a strong 20-year oscillation is apparent, there is yet sufficient proof that a significant upward trend in jellyfish populations has occurred.
The authors freely admit that there are many limitations in the data set available for reanalysis. Old records are rare and more recent data are confined largely to the Mediterranean and North Atlantic. Warming seas, eutrophication (or excess nutrient loading) along our coast lines and overfishing are all implicated in what might drive the magnitude of the observed cycles. However, coverage and imagery such as that shown here portray a far greater problem than is necessarily occurring globally. Oscillating climate states caused by ENSO, in conjunction with the PDO, may indeed be the cause of blooms being seen off the coast of Japan. And the fact that there is still uncertainty surrounding the impact of climate change on natural cycles there may indeed be a time when the problem becomes global. But the evidence is not there yet, so we lack the information to claim that Poseidon has been usurped by the Jelly Monster.
I’m reminded of hearing that on average eight spiders a year crawl into your mouth while you are sleeping. I was horrified due to my arachnophobia and the potential increase in caloric intake (I’d prefer ice cream accidentally crawled in my mouth). Anyway, on repeating this to my much smarter husband he did a bit of research i.e googled it, and it turns out it was AN URBAN MYTH, created by someone trying to prove how easily urban myths can be created and spread on the internet. My point is that the world is undoubtedly changing, and more than ever a measure of healthy skepticism is needed before we start losing sleep over the squadron of Scyphozoa threatening to ruin our summer holiday.
You can view the abstract here but or the full article you will need access to PNAS.