Work being done to rehabilitate the beaches in the Haifa area is one of the reasons for the swift spread of an invasive swimming crab, according to a study published this week. Covering the beach with sand created a convenient environment for reproduction, and from there the crabs moved to other beaches, endangering populations of local creatures.
The new study was published in the Journal of Natural History and was conducted by two researchers from the natural history museum in Florence, along with Dr. Bella Galil of the Steinhardt Museum of Natural History in Tel Aviv University and independent researcher Moti Mendelson.
The researchers kept track of the spread of the swimming crab, matuta victor, in the Indian and Pacific oceans. It arrived in the Mediterranean via the Suez Canal and was first spotted in the Haifa Bay area five years ago.
This discovery led to a more systematic surveillance of the crab and its lifestyle, about which little was known. The surveillance discovered a significant increase in the crab population in two main centers, one near the Kiryat Yam beach and the other near the Nahal Naaman estuary in northwestern Israel, which suffers from high levels of pollution.
The researchers believe that the pollution in Nahal Naaman and the additional sand in Kiryat Yam created the conditions for the increase. The sand covered the living creatures on the beach and removed competitors. The pollution also adversely affected the crab’s competitors and made it easier for it to reproduce.
“We created conditions for them like Club Med and turned it into an export industry to other countries, which aren’t exactly happy about it,” said Galil. “They reproduced rapidly and reached the Lebanese coast.” Now the crabs are on other beaches, including those in Antalya, Turkey, 1,500 kilometers from Haifa Bay.
The swift population increase apparently exacerbated the competition for food. The researchers documented fights over food among the crabs, which included hitting with their legs and pincers and attempts to hold a rival crab and turn it onto its back. This is something that hasn’t been observed among crabs anywhere else.
The increase in the population of these crabs causes the sidelining of local crab species and is considered a threat to the ecological system. In light of what happened in Kiryat Yam, Galil thinks the Enviromental Protection Ministry should consider the effect of the domination of invasive species when approving plans for the artificial supplying of sand on the beaches. There is an inclination to expand the use of this method in the coming years to protect the cliff adjacent to the beach, which is in danger of collapsing due to contact with the waves. The sand is meant to serve as a protective layer for the cliff.
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