..Lebanon's coast has seen a marked decrease in the number of jellyfish this year as a result of extensive fishing along the Mediterranean coast, environmental activists warn.

While this may be a welcome change for surf lovers, it has caused great concern to environmental organizations and activists involved in preserving marine life.

The diminishing presence of jellyfish has had a negative impact on biological diversity in the Mediterranean waters, marine experts warn.

...while jellyfish invasions are a nuisance to tourists and a hardship to fishermen, for scientists they are a source of more profound alarm, a signal of the declining health of the world's oceans.

"These jellyfish near shore are a message the sea is sending us saying, 'Look how badly you are treating me,' " said Dr. Josep-María Gili, a leading jellyfish expert, who has studied them at the Institute of Marine Sciences of the Spanish National Research Council in Barcelona for more than 20 years.

The explosion of jellyfish populations, scientists say, reflects a combination of severe overfishing of natural predators, like tuna, sharks and swordfish; rising sea temperatures caused in part by global warming; and pollution that has depleted oxygen levels in coastal shallows.

"Human-caused stresses, including global warming and overfishing, are encouraging jellyfish surpluses in many tourist destinations and productive fisheries," according to the National Science Foundation, which is issuing a report on the phenomenon this fall and lists as problem areas Australia, the Gulf of Mexico, Hawaii, the Black Sea, Namibia, Britain, the Mediterranean...

"This decrease has a negative effect on the aquatic environment in Lebanon where jellyfish complete the aquatic food chain," the activist said, adding that "any setback in this chain will cause major problems in the marine environment."

Global warming has also reduced rainfall in temperate zones, researchers say, allowing the jellyfish to better approach the beaches. Rain runoff from land would normally slightly decrease the salinity of coastal waters, "creating a natural barrier that keeps the jellies from the coast," Dr. Gili said.

Then there is pollution, which reduces oxygen levels and visibility in coastal waters. While other fish die in or avoid waters with low oxygen levels, many jellyfish can thrive in them. And while most fish have to see to catch their food, jellyfish, which filter food passively from the water, can dine in total darkness, according to Dr. Purcell's research.

..no good global database exists on jellyfish populations..jellyfish populations in any one place undergo year-to-year variation.