i cant believe this thread has died away like it has! so because of its importance i have decided to resurrect it!
here is the previous thread..
www.seabreeze.com.au/forums/topic.asp?TOPIC_ID=48867&SearchTerms=jellyfish

and here is some new info that i find very alarming

from:

www.abc.net.au/news/2009-06-08/jellyfish-threaten-to-dominate-oceans/1707640

Jellyfish threaten to 'dominate' oceans

By Anna Salleh for ABC Science Online

Posted Mon Jun 8, 2009 2:25pm AEST
Updated Mon Jun 8, 2009 2:47pm AEST
Nomura jellyfish are the biggest in the world and can weigh 200kgs.

Nomura jellyfish are the biggest in the world and can weigh 200kgs. (Y.Taniguchi/Niu Fisheries Cooperative)



Giant jellyfish are taking over parts of the world's oceans due to overfishing and other human activities, researchers say.

Nomura jellyfish are the biggest in the world and can grow as big as a sumo wrestler. They weigh up to 200 kilograms and can reach 2 metres in diameter.

Dr Anthony Richardson and his colleagues from CSIRO Marine and Atmospheric Research says jellyfish numbers are increasing, particularly in South East Asia, the Black Sea, the Gulf of Mexico and the North Sea.

"We need to take management action to avert the marine systems of the world flipping over to being jellyfish dominated," says Dr Richardson, who is also a marine biologist at the University of Queensland.

He says the Japanese have a real problem with giant jellyfish that burst through fishing nets.

He says other researchers are experimenting with different ways of controlling jellyfish, including using sound waves to explode jellyfish and using special nets to try and cut them up.

Overfishing

Dr Richardson and his colleagues reviewed literature linking jellyfish blooms with overfishing and eutrophication (high levels of nutrients).

Jellyfish are normally kept in check by fish, which eat small jellyfish and compete for jellyfish food such as zooplankton, he says.

But with overfishing, jellyfish numbers are increasing. Jellyfish feed on fish eggs and larvae, further impacting on fish numbers.

To add insult to injury, nitrogen and phosphorous in run-off cause red phytoplankton blooms, which create low-oxygen dead zones where jellyfish survive, but fish cannot.

"You can think of them like a protected area for jellyfish," Dr Richardson says.

The researchers say climate change may also encourage more jellyfish and they have postulated for the first time that these conditions can lead to what they call a "jellyfish stable state", in which jellyfish rule the oceans.

Taking action

The team recommends a number of actions in its paper, published in the journal Trends in Ecology and Evolution and released to coincide with World Oceans Day.

They say it is important to reduce overfishing, especially of small pelagic fish like sardines, and to reduce run-off.

They also say it is important to control the transport of jellyfish around the world in ballast water and aquariums.

Jellyfish are considered simple jelly-like sea animals, which are related to the microscopic animals that form coral.

They generally start their life as a plant-like polyp on the sea bed before budding off into the well-known bell-shaped medusa.

Jellyfish have tentacles containing pneumatocyst cells, which act like little harpoons that lodge in prey to sting and kill them.

The location and number of pneumatocysts dictate whether jellyfish are processed for human consumption.

While dried jellyfish with soya sauce is a delicacy served in Chinese weddings and banquets, not all kinds of jellyfish can be eaten, Dr Richardson says.

According to Dr Richardson, the species increasing in number are not generally eaten.

and then this

A British kite-surfer was left fighting for life after he became trapped in a two mile slick of poisonous jellyfish off the coast of Costa Rica.

www.telegraph.co.uk/news/newstopics/howaboutthat/5481284/Kite-surfer-stranded-in-poisonous-jellyfish-shoal.html

I hate these things, that photo reminds me of Nedlands Baths where I learnt to swim.
We would have to dive into a mass of jellies like that and swim through them to get our swim certificates.
And don't get me started on the ones around Busselton jetty.
At least the Chinese have developed a taste for them
One thing I don't remember in Zoology was the need for these lifeforms in the Eco system.
And they definitely slow us down at Melville by at least 2 knots per run on bad days.

Rant over

Time to really sharpen the leading edge of your fins.

Select to expand quote

He says the Japanese have a real problem with giant jellyfish that burst through fishing nets.

So with more jellyfish breaking fishing nets this means more fish not being caught which in turn means less jellyfish. Problem solved

Select to expand quote

Gestalt said...

and then this

A British kite-surfer was left fighting for life after he became trapped in a two mile slick of poisonous jellyfish off the coast of Costa Rica.

graceman said...

I hate these things

What about the jellyfish ?

From a New scientist article
"If you remove small fish there is every possibility that other species in the food chain, like jellyfish, will have a good time of it," says Tom Anderson, a marine ecologist at the National Oceanography Centre in Southampton, UK.

This is already happening in one of the world's most productive fisheries, the Benguela current off the coast of Namibia in southern Africa. When Christopher Lynam of the University of St Andrews in the UK and his colleagues surveyed the area in 2003, they found that the ecosystem, which once supported large populations of sardines and anchovies, had been taken over by two species of jellyfish. The study estimated the biomass of jellyfish in the region at 12.2 million tonnes, more than three times that of mackerel, hake, sardine and anchovies combined (Current Biology, vol 16, p R492).

The reasons for these changes are complex. Shifts in climate, currents and sea temperature will have played a part, but a major factor is the collapse of the once abundant sardine and anchovy fisheries. In the late 1970s, the total fish catch was around 17 million tonnes per year. Now it is closer to 1 million tonnes. And since jellyfish eat fish eggs and larvae, as well as compete with young fish for food, the shift to a jellyfish-dominated ecosystem rather than a fish-dominated one may be irreversible, say the team.

Blooms of jellyfish have also appeared in the overfished waters of the Black Sea, Alaska, the Mediterranean and the Gulf of Mexico. In the Sea of Japan, overfishing of sardines and anchovies, plus blooms of phytoplankton caused by nutrient-rich coastal run-off, have led to a jellyfish problem of epic proportions: autumn blooms of the giant jellyfish Nemopilema nomurai, which can grow to more than 2 metres in diameter. In 2003 alone this jellyfish cost the Japanese fishing industry over $100 million, "clogging and bursting nets, causing high mortality of the catch due to venom, increasing the risk of capsizing trawlers and giving fishermen painful stings", says Masato Kawahara, a marine ecologist at Hiroshima University in Japan.

Removing fish from an ecosystem may also have other consequences. In the Benguela current, the crash in phytoplankton-eating fish has also been linked to more frequent phytoplankton blooms (Ecology Letters, vol 7, p 1015). That can spell bad news: when the blooms die off, bacteria gobble them up, along with most of the oxygen in the water.

Even overfishing large predatory fish could encourage these blooms. Zooplankton-eating fish thrive once their predators are gone, leading to a decline in their own prey. With fewer zooplankton to feed on phytoplankton, the latter can bloom unchecked.

The collapse of cod, haddock, hake, pollock, plaice and flounder fisheries off Nova Scotia have all coincided with an increase in phytoplankton. So has a reduction in the number of salmon in the north Pacific. And last year, Michele Casini of the Swedish Board of Fisheries in Lysekil, and colleagues, found a strong link between the collapse of cod stocks in the Baltic Sea in the early 1980s and phytoplankton blooms.

Squid, too, are increasingly thriving throughout the oceans. While changes in water temperatures may play a part, the main reason is the removal of their predators. "Almost everything eats squid in the ocean - tuna, marlin and swordfish hardly eat anything else - so if you remove the squid's predators, how can it not have an impact?" says George Jackson of the University of Tasmania in Hobart, Australia. And as squid grow quickly and live for less than a year, their numbers can rise rapidly if the conditions are right. "They're the weeds of the sea," he says.

The best-documented example is the Gulf of Thailand, which has been heavily overfished in recent decades. Here the Indo-Pacific squid Sepioteuthis lessoniana has moved in to fill the gaps in the ecosystem, forcing the fishing industry to adapt. "You see fishermen walking down the beach in Thailand with baskets of squid," says Jackson.

Off the US coast, the Humboldt squid, Dosidicus gigas, has begun to expand its territory north from the east Pacific equatorial waters to the seas off central California. This has happened before, during El Niño years, when the water warmed enough for them to spread their range. The last time this happened, in 1997-98, predation and competition from tuna and billfish sent most of them back south when the waters cooled. In the past five years, though, they have stayed put despite cooler seas, and seem to be thriving. Now they even threaten the Californian Pacific hake fishery.

Walvis Bay Speed spot is one area affected.

It used to be small and violet now they're white and a bit stingy looking



and now they come in droves not as thick as the other's..somethings wrong with the climate i guess[}:)]

Select to expand quote

sausage said...

Time to really sharpen the leading edge of your fins.

He says the Japanese have a real problem with giant jellyfish that burst through fishing nets.

So with more jellyfish breaking fishing nets this means more fish not being caught which in turn means less jellyfish. Problem solved

i seemed to recall seeing some of our swan river moon jellys continuing to swim even after they had been sliced and diced!
i will have to re check this over the next couple of days and i will report back with my findings i just hope fisheries wont be watching when i begin the test!

if this is the case cutting the jellys in half will be a double edge sword (so to speak)
we will make them smaller but there will be twice as many