While some species may quickly die off, others thrive in their new surroundings, often to the point of posing a threat to the existing ecological order. Such is the case with Mnemiopsis leidyi, a fist-sized jellyfish that has spent the past decade menacing the waters of the Caspian Sea. The invasion of Mnemiopsis leidyi, or Leidy's Comb Jelly, has caused the Caspian's fish stocks to plunge, affecting the livelihoods of many local fishermen.
Zari Rustamov is from the village of Nardaran on Azerbaijan's Abseron Peninsula. He said his catches of sprats (kilki) have grown more and more meager in the years since the comb jelly first made an appearance. He said the jellyfish "is small [and transparent], like water. We didn't have this thing before. Sometimes you look at the water, you reach out and your hands are full of them. And when it's there, there are no fish. Fish avoid getting close to them."
The watery invader has a voracious appetite, devouring much of the Caspian plankton that provides the sprats' main sustenance. Furthermore, Mnemiopsis reproduces at an alarming rate. It can double its size in a single day, reach maturity within two weeks, and then lay as many as 1,200 eggs a day for as long as several months.
The dropping fish stocks have forced many fishermen off the job. Many owners of fishing vessels have been forced to sell their boats in order to pay off their debts. The spread of the Mnemiopsis is expected to eventually taper off. But that may come too late to save the Caspian's fish stocks.
Tariel Mammadli is chief adviser on Caspian biodiversity at Azerbaijan's Ecology Ministry. "If there is no fight against [Mnemiopsis], all living things may disappear from the [Caspian] Sea," he said. He describes the sea's ecology as like a chain. If the plankton link is broken, "everything disappears."
Mnemiopsis made its Eastern debut two decades ago, in the Black Sea, after being transported from the U.S. Atlantic coast in the hull of a ship carrying ballast water to maintain its stability. When the ship emptied its ballast water, the jellyfish began its feast on Black Sea plankton, causing a more than 80 percent decrease in fish stocks there.
The arrival of a second American jellyfish, Beroe ovata, marked an important change in the late 1990s. The newcomer began dining on Mnemiopsis, causing its almost immediate decline, and allowing a resurge in the Black Sea's valuable anchovy stocks.
But Mnemiopsis once again began to travel, and showed up in the Caspian Sea in 1999. This time the culprit is believed to have been the ballast water of a boat shipping through the Volga-Don canal linking the two seas. A decline in plankton quickly followed. In 2000 alone, scientists estimated that Caspian sprat stocks had decreased by 50 percent.
Could the Beroe ovata once again prove the solution? Hossein Negarestan works for the Iranian Fisheries Research Organization in Tehran. He told RFE/RL that studies have been conducted on the safety of releasing a second jellyfish species into the Caspian. As long as the process is handled carefully, he said, it should not create any new ecological problems.
"We found out that [Beroe] only eats Mnemiopsis leidyi and [that] when there are no more Mnemiopsis leidyi, [the Beroe] dies off. Scientists agreed that Beroe ovata can be the best solution to this problem. [However,] we need to be careful not to carry any other individual [species in] with the water. Scientifically speaking, all aspects have been cleared out," Negarestan said.
All five Caspian states -- Russia, Kazakhstan, Turkmenistan, Azerbaijan, and Iran -- now have to endorse the introduction of the Beroe ovata to the sea. It is an expensive and technically difficult process.
Tariel Mammadli, from Azerbaijan's Ecology Ministry, said the Caspian states are close to an agreement, and that Iran and Russia have already promised to contribute funds. "This year, the Caspian commission on bioresources will find a positive solution to the issue," he said. The five littoral states must reach an agreement and then begin a search for funding.