Posts Tagged ‘jellyfish blooms’

Jellyfished

Monday, September 30th, 2013
Moon jellyfish (Aurelia aurita) form huge blooms in many of our oceans (guardian.co_.uk).

Moon jellyfish (Aurelia aurita) form huge blooms in many of our oceans (guardian.co_.uk).

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.

Nomura's Jellyfish are giants, up to 200 kg and 2 meters in diameter, and do much damage to fishermen's nets in the Sea of Japan (fastcompany.com).

Nomura’s Jellyfish are giants, up to 200 kg and 2 meters in diameter, and do much damage to fishermen’s nets in the Sea of Japan (fastcompany.com).

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.

Box jellyfish (Cubomedusae) have powerful stings, and drive swimmers out of the water, as they did in the northern Mediterranean this past summer (Selby, flickr.com)

Box jellyfish (Cubomedusae) have powerful stings, and drive swimmers out of the water, as they did in the northern Mediterranean this past summer (Selby, flickr.com)

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.

Turritopsis dohrnii medusa, about 1/2 cm in diameter, with a bright red stomach and a ring of tentacles (turritins.com)

Turritopsis dohrnii medusa, about 1/2 cm in diameter, with a bright red stomach and a ring of tentacles (turritins.com)

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.

Typical life cycle of a hydrozoan jellyfish (devbiol.com)

Typical life cycle of a hydrozoan jellyfish (devbiol.com)

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.

Reversing the usual life cycle, Turritopsis medusa 'transdifferentiates' back into a hydroid (newtimes.pl)

Reversing the usual life cycle, Turritopsis medusa ‘transdifferentiates’ back into a hydroid (newtimes.pl)

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.

Crossota alba is another small hydrozoan medusa, one that lives in deep water and drifts around in the dark, tentacles extended, preying on the plankton that it drifts into (whoi.edu)

Crossota alba is another small hydrozoan medusa, one that lives in deep water and drifts around in the dark, tentacles extended, preying on the plankton that it drifts into (whoi.edu)

Still Eating Jellyfish

Tuesday, February 28th, 2012

I reserved Eating Jellyfish as a domain name about 6 years ago, when the prospect of eating jellyfish seemed an absurd outcome of overfishing, coastal development and pollution now clearly associated with the occurrence of schools or blooms of jellyfish. Jellyfish as the top predators in coastal ecosystems are now even more common. As we are forced to adapt, the idea of eating jellyfish is no longer as absurd as it was. And yes, of course, some cultures have a long history of eating certain species of jellyfish: it is just a very alien idea to the rest of us.

Nomura's jellyfish, Nemopilema nomurai, in the Sea of Japan. Like all jellyfish, it grows to full size in a single season. (natruresmightypics)

Recent reports of unexpected and large jellyfish blooms have come from most parts of the world – from the seas of Japan, China and Europe especially, but also from West Florida and the Gulf of Maine. What actually causes the blooms is not certain, for until recently nobody was really interested enough to try to find out.

But what we know is this: jellyfish blooms are associated with coasts of dense human populations where overfishing, eutrophication, habitat modification, invasive species, and a warming climate may all be involved. One of the most famous and clearest cases occurred in the Black Sea, where overfishing, warmer water, and nutrient enrichment from the Danube made for perfect conditions for a succession of jellyfish to explode in number.

Probably the other most famous blooms involve the giant Nomura’s Jellyfish in the Sea of Japan, each a monster, hard to harvest even if you wanted to, and immensely damaging to fisheries and fishing nets.

Nomura's Jellyfish in the Sea of Japan, is a huge challenge to harvest without sinking the boat.(naturesmightypics)

The most prolific and widespread is Aurelia aurita, the moon jellyfish, for it is globally distributed, and capable of explosive growth into very large populations. I have fond memories from when I was kid on the coast of Maine heaving dead washed up moon jellyfish at my sisters.

The moon jelly, Aurelia aurita, beautiful, graceful, and in every ocean (fins.activin.com)

Why are jellyfish so successful in degraded conditions? In a health ecosystem they compete with fish for access to food – mainly zooplankton. Where overfishing has removed the competing fish, they have few limits to growth. In eutrophic conditions, for instance around the mouths of major rivers carrying high loads of P and N, they also tolerating the lower levels of dissolved oxygen that fish avoid: where coastal nutrients increase, so to do jellyfish. The result is a trophic cascade, a regime change, an ecosystem that is free of fish predators, dominated by jellyfish, and of very little value or interest to humans.

Dan Pauly's famous illustration of the impact of fishing down the food chain, a trophic cascade that ends up with jellyfish as the top predator (ecomarres.com)

What’s ahead, then? All of the stresses – overfishing, eutrophication, warming waters, habitat modification, human population densities are all likely to keep increasing along our coastlines.

We can do a couple of things about this. Of course trying to recover such stressed ecosystems, restoring fish as top predators, is the best, but not most likely outcome. Instead, we can also learn which species of jellyfish are actually possible to harvest and eat (some taste horrible). There are also likely to be some yet-to-be discovered medical uses of some species. And perhaps jellyfish have some potential as supplements to animal feeds.

We also need biologists who can help integrate knowledge of jellyfish ecology with that of the whole ecosystem, making jellyfish part of what fisheries scientists must consider in their attempts to manage both fisheries and ecosystems.

Jellyfish as components of fisheries, and jellyfish as components of our own diets, are facts of life in this critical century.

We just have to suck it up. They’re mostly water anyway.