Increasing jellyfish blooms are a symptom of the challenged health of our oceans. Where fish have been fished down or out, jellyfish thrive. Where oxygen levels drop too low for many organisms, jellyfish thrive. Where a community then flips from fish-dominated to jellyfish dominated, recovery is difficult to achieve.
Jellyfish blooms clog fishing nets, intake pipes of desalination and nuclear plants, cause mass mortality of salmon in coastal farms, decimate fisheries already in steep decline, and sting swimmers out of the water at beaches everywhere.
In a new book Stung!: On Jellyfish Blooms and the Future of the Ocean, Lisha-ann Gershwin documents the ravages of jellyfish blooms and the deterioration of marine ecosystems, and her final conclusion is a very cold bath: we have permanently wrecked the oceans, we can’t fix what we have done, and all we can do now is adapt to the inevitable lousy changes that have already begun.
What do we do with that? Ignore it, I think, and continue to try to mitigate the extent of the changes. The new IPCC report clearly illustrates the different outcomes of different levels of atmospheric CO2, and the long-term advantages of stabilizing those levels soon are extraordinarily clear.
But Gershwin also writes about some of the remarkable biology of jellyfish, for they are more than just graceful but dangerous animals. Perhaps the most intriguing is one of a group of small species of the genus Turritopsis, which grow to about half a centimeter in diameter and are now common in most tropical and temperate oceans.
Like most jelly fish, it has a two part life cycle. When jellyfish (medusae) are sexually mature, they shed eggs and sperm into the water, and then die. A fertilized egg develops into a tiny creeping planula larva that settles onto some hard substrate and then grows into a colonial hydroid or polyp that feeds on microplankton in the surrounding water. Eventually other buds on the hydroid develop into very small medusae which then escape and swim off.
All Turritopsis do this, and because they are all small as adult jellyfish, less than 1cm in bell diameter, they are also very small when they first break free of their hydroid source, less than 1mm in diam.
At least one species of Turritopsis though has remarkable further capabilities.
When starved or physically damaged, where other jellyfish would just die, the medusae of this species instead can undergo an amazing transformation. The mouth and tentacles are resorbed, and the bell shrinks into a blob-like cyst that falls to the bottom, attaches to the substrate, and grows into a hydroid or polyp colony once again, reversing the usual life cycle. And there large numbers of new medusae develop, all clones of the original damaged medusa.
This is truly an extraordinary event, about as close to immortality as one can get.
Not surprisingly, as our medical use of stem cells grows ever greater, we are very interested in how cells that had been specialized for one function in the medusa ‘transdifferentiate’ into quite different cells in the hydroid.
Meanwhile, Turritopsis has spread around the world’s oceans, from Spain to Japan to South Africa, probably assisted by the ballast water of transport ships. It is wonderfully adapted to survive in this changing world, and may in turn play a role in the changes.
And it is also a reminder of how extraordinary it is to be a living being on Planet Earth, whether as a jellyfish or as a curious human.