Magnificent and terrible jellyfish

I spent time recently gathering material about a fascinating animal. A primitive and to all appearances harmless animal, but one that could very well be responsible for a shift in the marine ecosystem. That nightmare creature is in fact the gracious and delicate jellyfish (more than 1,000 known species).

The jellification of the oceans

Imagine an ocean full of gelatinous creatures. That ocean is brimming with jellyfish, but oddly enough, fish and squid are absent or very rare. No sea turtles, no cetaceans, and no seals or sea lions either. The water is strangely warm and acidic, cluttered with plastic, and has a low oxygen content. And no, we’re not talking about the Dead Sea. But this could well be the ocean of the future, and this is what some authors fear. How could this gelatinous creature, made up of 98 percent water, come to dominate the oceans? Its biological simplicity would seem to lend it an advantage.

Delicate umbrella ballets

In its free and mature form, the jellyfish feeds itself by capturing swimming preys that come in contact with its tentacles. It’s a case of passive hunting. The jellyfish, a primitive animal with modest energy needs, can live a long time waiting to capture prey. On the other hand, when food is abundant, it becomes an avid, even insatiable predator – and that’s when uncontrollable proliferation happens.

Headed for the jellyfish apocalypse?

A number of factors, very real, combine to foster the “jellification” cycle.

First, the jellyfish’s primary predators, sea turtles, tuna and sunfish, have become quite rare.

Next, current overfishing has led to a sharp drop in fish stocks. Jellyfish are natural competitors that also feed on krill and small forage fish. They’re highly opportunistic and take advantage of every good opportunity.

The jellyfish’s offensive takes place on another front as well. Jellyfish consume fry and young commercial fish, preventing their recovery. And this could make for an imbalance in our oceans.

That imbalance risks being intensified by the chemical and thermal changes that oceans are currently experiencing. The fact is that jellyfish are much better at resisting those modifications (higher temperature, acidification, pollution, lower oxygen levels) than are other marine species.

Will we be witness to the jellification of our oceans that some people fear? All of us have a responsibility here.

References

• GERSHWIN, Lisa-ann. Stung! On Jellyfish Blooms and the Future of the Ocean, The University of Chicago Press, 2013.
• TEDx lecture given by author Lisa-Ann Gershwin.
• CALCAGNO, Robert, et Jacqueline GOY et coll.  Méduses : à la conquête des océans, Éditions du Rocher, 2014.