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| Photo is a diver dwarfed by a giant jellyfish. Credit: Yomiuri Shimbun from: http://www.livescience.com/13112-giant-jellyfish-blooms-ria.html |
The acid seas were warm
And filled with slimy jellies
In an endless pulsing swarm
But much carbon was sequestered
And the seas began to cool
And teams of bony fishes
Began to swim and school
Our seas are turning acid
And becoming very warm
And the ancient slimy monsters
Once more begin to swarm
I recently saw a frightening programme on Giant Jellyfish infestations in the Sea of Japan. Billions of giant Nomura Jellyfish weighing up to 200kg are choking the Sea of Japan and have destroyed the fishing industry. Similar events are occurring in the Gulf of Mexico, China's Yellow Sea and in the Black Sea. Overfishing, pollution from fertilisers and global warming have all been implicated but there is no doubt that the ancient jelly-fish which dominated the worlds oceans 300 million years ago are much better at coping with warm, acidic and low oxygen conditions than modern fish. Fisheries are collapsing everywhere and wild ocean fish stocks are now perhaps 10% of what they once were. We are in the process of turning back the clock 300 million years and unless we change our ways quickly we will be truly damned. Scientists are struggling to understand this latest catastrophe but my time as a salt field ecologist has given me an inkling as to what may be going on. I suspect that the balance between benthic and planktonic ecosystems has been disrupted as a consequence of pollution from fertilisers, pH drop from increased dissolution of CO2 and, general ocean warming. Weed-eating fish in the early ponds of a salt-field graze the seaweeds and deposit nutrient in waste onto the floor of the ponds where it is bound up in the mud. The continually grazed seaweeds regrow taking nutrient out of the water column and helping to secure clear water with big populations of fish and carpets of sea-weed. When a catastrophe killed the fish, excess nutrient ended up in the water column where it promoted blooms of phytoplankton and the once clear and fish filled water became a fish-less, soupy mess similar to what has happened in the sea of Japan.
