When an animal species suddenly appears in a new environment, the consequences can be grim. 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 last decade menacing the waters of the Caspian Sea. Also known as Leidy’s comb jelly, this organism’s arrival has caused the Caspian’s fish stocks to plummet, affecting the livelihoods of many local fishermen.
Zari Rustamov is from the village of Nardaran on Azerbaijan’s Apsheron peninsula. He said his catches of sprats (kilki) have dwindled 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 declining fish stocks have forced many fishermen off the job. Many owners of fishing vessels have had to sell their boats to pay their debts. The spread of the jellyfish 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 resembling 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 Atlantic coast of the United States in a ship’s ballast water. When the ship emptied the water, the jellyfish began its feast on Black Sea plankton, causing a more than 80% drop in local fish stocks. The arrival of a second American jellyfish, Beroe ovata, heralded a major change in the late 1990s. The newcomer began dining on Mnemiopsis, causing its almost immediate decline, and enabling the Black Sea’s valuable anchovy stocks to recover.
But the comb jelly had not completed its journey, turning 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%.
Could 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 carried out 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 none left, [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 – must now endorse introduction of Beroe ovata, an expensive and technically difficult process. According to Mammadli, the Caspian states are close to an agreement, and Iran and Russia have already promised to contribute funds. “This year, the Caspian commission on bio-resources will find a positive solution to the issue,” he said. The five littoral states must reach an agreement and then begin looking for funding.