Jellyfish replacing fish in over-exploited areas

Jellyfish replacing fish in over-exploited areas
Moon jellyfish, Gijon Aquarium. Courtesy of José Luis Acuña and Julio Arrontes, University of Ontario

( -- Over-fished commercial stocks of plankton-eating fish have been replaced in several locations by jellyfish species. This appears to be something of a paradox because fish move quickly and can see their prey, which suggests their capture of prey should be much more efficient than for jellyfish that move slowly and have to make contact with their prey to know they are present. Now a team of scientists in Spain and the US have discovered he jellyfishes' success is partly based on their large body size and its energy efficiency.

The team studied previously published data on jellyfish species and found that their relatively large body size, long , and their habit of pulsing their bodies to draw plankton-laden water past their tentacles, all increase the chances of capturing nearby , and this body design enables them to compete successfully with the plankton-eating fish such as anchovies and , even though a larger body size is less efficient for swimming.

The study, published in the journal Science, compared mathematical models of factors such as energy efficiency, speed, and size for over 600 species of fish and jellyfish. The researchers, led by José Acuña of the Universidad de Ovied in Spain, found that their size and speed did not give fish as much of an advantage as previously assumed, when features such as the type of body, and a reliance on light were factored in.

The jellyfish swimming style is slow but turns out to be highly efficient in terms of energy expended, and since most jellyfish species are blind, they can continue to feed regardless of the light conditions. These factors enable jellyfish to closely compete with the fish, and when fish numbers are in decline, they can become the dominant species.

The type of body also had an effect on their success. The large, gelatinous jellyfish bodies are composed of around 96% water, and therefore contain disproportionately less carbon than fish bodies, which are made up of compact organic matter. When this was taken into account the researchers found jellyfish could clear the water of to produce energy at a similar rate to the fish. Having a low-carbon body (and stinging cells on the tentacles of some species) also make jellyfish a less appetizing meal for predators than do their competitors.

In some areas where fish stocks are declining, often through over-fishing or pollution, jellyfish are becoming the dominant species. These areas include coastal waters off Japan, Northeastern US, the Black Sea, and the Mediterranean. The increasing numbers could change the nature of marine ecosystems, and in some areas, such as Japanese coastal areas, it is already causing problems for human beach-goers. In Japan, Scotland, and Israel, nuclear power plants drawing water from the sea have also experienced problems and have had to shut down at times through an over-abundance of clogging water intake filters.

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More information: Faking Giants: The Evolution of High Prey Clearance Rates in Jellyfishes, Science 16 September 2011: Vol. 333 no. 6049 pp. 1627-1629. DOI: 10.1126/science.1205134

Jellyfishes have functionally replaced several overexploited commercial stocks of planktivorous fishes. This is paradoxical, because they use a primitive prey capture mechanism requiring direct contact with the prey, whereas fishes use more efficient visual detection. We have compiled published data to show that, in spite of their primitive life-style, jellyfishes exhibit similar instantaneous prey clearance and respiration rates as their fish competitors and similar potential for growth and reproduction. To achieve this production, they have evolved large, water-laden bodies that increase prey contact rates. Although larger bodies are less efficient for swimming, optimization analysis reveals that large collectors are advantageous if they move through the water sufficiently slowly.

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Citation: Jellyfish replacing fish in over-exploited areas (2011, September 16) retrieved 17 October 2019 from
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Sep 16, 2011
Humans are destroying the world's oceans with their disgusting fishing practices and pollution

Sep 16, 2011
I remember taking a rowboat out in Cape Cod in the late 80's. I had to be 16 or 17 years old.

Jellies were everywhere. They were about the size of a golf ball and there was no way to swim. It was a jelly bath.

I was sad to discover that this was a chain-effect caused by fertilizer runoff overfeeding plankton and that it was not going to go away on it's own.

Sep 16, 2011
Humans are destroying the world's oceans with their disgusting fishing practices and pollution

Overpopulation and short-sightedness borne of individualistic greed are to blame. The first can be ameliorated; the second may prove more of a challenge.

Sep 16, 2011
Humans are destroying the world's oceans with their disgusting fishing practices and pollution

Brilliant contribution there.

Those darn humans. Any thoughts beyond that? Any notion of what the core problems are behind the phenomenon you have so brilliantly revealed? Since you obviously care so much, any thought as to how you could change your life and how you could advocate others to do the same to try and see such unsustainable management and habitat degradation reversed? Do you have any conviction to DO something about it other than denounce humans on the internet, which does absolutely nothing? Any thoughts as to what actually needs to happen to improve things?

Just some suggestions on how you might be able to create a worthwhile contribution next time, maybe even in your life.

You are whats wrong. People who see something, but do nothing. It's very easy to point and say "bad", but it can be very hard to actually do something about it. What DO you do about it, bewertow?

Sep 16, 2011
No need to worry one bit.

The Chinese are already have various recipes to turn rapidly spreading jellyfish into delicious Chinese dishes as well as methods to turn the mostly water jellyfish into a meat like product of substance and body.

So by overfishing we are merely helping to create a far more productive biome where wild jellyfish can grow and thrive. LOL

Sep 16, 2011
emsquared - The mass suicides or homicides you are suggesting would likely be frowned upon by the tax collectors and corporate human resources people. We are 80% above sustainable human populations. Not much short of a plague is going to change much now.

Good news though, we don't have do anything. In 2008 scientist studying our global mineable phosphate reserves concluded we had a 300 year supply left. In 2011 a review of these estimates concluded - "Wow! Not really!" (that's probably not a direct quote.) We have less than 30 years to peak phosphate and probably far less because of the simultaneous affects of peak petro/rising fuel prices increasing the rapidity of the economic infeasibility of mining phosphates as their concentrations become lower and lower and scarcer. The new study says all mineable phosphates will be gone in as little as 50 years. Now the killer (literally) - 95% of global food production is mined phosphate dependent and there are no equivalent replacements.

Sep 16, 2011
"Some species of jellyfish contains a lot of protein and are thought to be able to play a large role in ending hunger and malnutrition in poor areas around the world. "

Sep 17, 2011
Time to stop or reduce fishing and start jelling. mmmm jelly fish and chips.

Sep 19, 2011
Dug - Thanks for the write up about phosphate, is it not possible to mine ocean phosphate? Alternatively phosphate is created as a bi product of carbon sequestration. It is inorganic phosphate, is this not a suitable replacement?

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