09 December, 2018
A microscopic organism is causing a huge clam of the Mediterranean Sea to disappear and ocean scientists are worried.
The pen shell clam is the largest shellfish in the Mediterranean. The clam can grow to one meter in length. Its shell looks something like a huge feather.
For hundreds of years, the clam has provided food and an unusual material, called sea silk, which can be used to make a kind of cloth. The clam also cleans water by filtering out organic material from it.
The European Union named the pen shell clam a protected species many years ago. The clam has been overfished and has suffered from pollution and destruction of its waters. A ban on hunting the clam also has been poorly enforced. They are harvested for food and for their unusual, large shells.
The pen shells can live for many years, but they take years to reach reproductive age. Now, they are disappearing faster than they can be replaced.
New parasite alarms experts
A new parasite which first appeared in 2016, has alarmed experts. It is unclear exactly how the parasite kills the clams.
Scientists say it appears to attack the pen shell's digestive system. The clam becomes unable to close its shell and can be attacked by its enemies.
Maria del Mar Otero is with the International Union for Conservation of Nature. She said, "In less than a year it wiped out (the pen shell population of) the Spanish coast." Then waters of France, Malta, Tunisia and Italy were affected.
The suspected parasite is known only by its scientific name, haplosporidium pinnae. Researchers say it also may be responsible for killing pen shell clams in some Greek waters and those of Turkey and Cyprus.
Scientists are now racing to understand how the parasite spreads. This information is needed to protect the clam.
Pantelis Katharios is a researcher at the Hellenic Center for Marine Research, or HCMR, in Greece. He said scientists are not sure of anything yet, except that the parasite is spreading quickly.
Yiannis Issaris is with HCMR's Institute of Oceanography. He said tests show that the organism, which appears to be killing the clams in Greece, could be the same as the one affecting clams in Spain.
"This is very fresh for the scientific community," he said, "We're still at the stage of recording where it has spread to."
Scientists are carrying out tests in Mediterranean countries where the clams are dying. Some areas of Greece have healthy populations of the clams, but in other areas they have disappeared.
They have found that only the pen shell clams are affected. A similar species, pinna rudis, has been unharmed. And they still do not know why the parasite is so deadly to the pen shell clams.
The parasites might have come from another species and for some reason jumped to the pen shell clam. It also is possible that other conditions including pollution, climate change or water temperature changes could be causing the problem.
Katharios said, "Normally parasites in nature do not have any benefit from harming the host, because they depend on the host."
He added it is not clear what will happen to the pen shell clams or the microorganism affecting them. The big clams could completely disappear taking the parasites with them.
I'm Mario Ritter Jr..
Mario Ritter Jr. adapted this Associated Press report for VOA Learning English. Hai Do was the editor.
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Words in This Story
shellfish –n. an animal, such as a crab or oyster, that has a hard outer shell and that lives in the water
species –n. a group of animals or plants that are similar and can produce young animals or plants
parasite –n. an animal or plant that lives in or on another animal or plant that gets food and protection from it
digestive –adj. related to the process by which food is changed into a simpler form after it is eaten
stage –n. a particular point or period in the development of something
benefit –n. a good or helpful effect