In the video: an invasive crab threatens the northern streams (photo: Nature and Parks Authority)
Concern has arisen in recent days in the northern region following the invasion of river crayfish into streams in the region, and now there is concern that the animal will continue to spread in bodies of water and may also reach the Sea of Galilee.
These crustaceans belong to the class of "super crustaceans" within the "hertanians" and are characterized by large pincers, they are relatives of the lobsters, but live in fresh water.
These are large crabs that may even reach a length of tens of centimeters.
After they were discovered, the Nature and Parks Authority began actions designed to stop their further spread. Dr. Dana Milstein, an aquatic habitat ecologist in the Science and Interface Division at the Nature and Parks Authority, said that "establishment of species "Invaders in Israel is not a new phenomenon, it exists in a terrestrial environment, in the sea and in fresh water bodies. However, recently we have witnessed unusual invasions of river crayfish in natural and artificial water bodies, this phenomenon causes great concern."
As in previous cases, in which invasive species appeared in the Israeli nature, the crayfish also arrived illegally - the crayfish are kept and traded in Israel illegally, among other things in the aquarium and ornamental industry, and a search on the net shows that crayfish can be purchased in Israel.
Their owners are often upset with them, sometimes because they bought them small and after they grew up and started causing damage, or after breeding, when the breeders feel sorry for the offspring.
In these cases, they find alternative habitats for them and release them into the environment.
Sometimes in ornamental ponds or other bodies of water in an urban environment, or worse - in natural aquatic habitats.
The invasive cancer that threatens the rivers of the north (photo: official website, Nature and Parks Authority)
Milstein said that "for the first time we encountered the appearance of crayfish in 2008, when a population was found in a quarry near Givat Olga. In 2015, a population was established in Nahal Yarakon. About a year ago, a population was recorded in the banks of the square, and in the last three months, three new populations of different species of crayfish were located, Among other things, in the Bett and Shih streams."
According to Milstein, "One of the species we find more and more in nature is the red swamp crab. It is a crab that is dark red in color and reaches about 12 cm in size.
It originated in the southeastern United States and northern Mexico, but the species has already expanded its distribution to other regions of the United States and invaded various countries in Asia, Europe and Africa.
When individual individuals of the red swamp crab are released into nature, their ability to establish and establish populations is very large.
The species can exist in a large variety of habitats, including streams, reservoirs, ponds, swamps and even habitats that dry out seasonally.
The species is resistant and highly adaptable to a variety of environmental conditions including water salinity, low concentrations of oxygen, different ranges of water temperature and even pollution."
"The reproductive strategy of the species also makes it an effective invader, as it is characterized by a short life cycle and high reproductive potential. It reaches sexual maturity within a few months, and a 12.5 cm long female can produce up to 500 eggs," Milstein explained. "In every habitat, he will find suitable food for himself, since he is characterized by the fact that he eats everything and knows how to collect both plant food and animal food.
Therefore, the chance that even a small number of individuals released into the wild will establish a population is very high."
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An effective invader thanks to the reproductive strategy (photo: official website, Nature and Parks Authority)
Milstein noted that monitoring the red swamp crab in different parts of the world showed its negative effects.
According to her, "When it invades a habitat, it becomes an important element there that affects not only the plant and animal societies, but the functioning of the entire habitat. Since cancer has a preference for plant food, it causes a change in the plant society and damage to the variety of species. It is known that it causes damage to the societies of the water inhabitants In general, this includes molluscs, other invertebrates, amphibians and fish, as a result of predation and competition for resources such as habitats and food."
Milstein further explained that the crab's behavior also changes the composition of the substances in the water, as it digs holes, and this action releases a nutrient that in many cases encourages the development and bloom of toxic algae.
"In addition to these, it is known that the cancer is a host for various parasites, accumulates toxins in its body, thus causing their accumulation in the food web," Milstein continued.
"The negative effects of cancer on the habitat are so dramatic that the resilience of the habitat is damaged and it becomes more sensitive and vulnerable to the penetration of additional invasive species."
In the past, invasive species have already arrived in the Sea of Galilee and established themselves in the lake - about 13 years ago, an invasive snail became the dominant snail in the lake.
Its name is "Thiara scabra", and since it was identified in the Sea of Galilee, tests and monitoring have revealed that it constitutes over 90 percent of all snails in the Sea of Galilee.
About four years ago, two additional species of snails were identified that invaded the Sea of Galilee.
One of the two relatively new species is known by the name "Tarebia granifera".
It is an invasive species in many parts of the world, with the potential for damage due to the transmission of parasites that harm fish and humans.
It originated in Southeast Asia, but the harmful interference of man managed to spread the snail in Africa and South and North America.
This snail then joined a resident who was a little older than him in the Sea of Galilee - "Pyrgophorus sp", which originates from the Caribbean islands.
In a study published several years ago by Dr. Tamar Zahari, David Cummings and Benny Soleimani from the Kinneret Research Laboratory at the Sea and Lake Research Institute in Israel, it was written that the invasive species are pushing the natural species out of the Kinneret. Five species of snails were known in the lake. One disappeared already in the 1970s The previous one, the other four are considered rare. "The appearance and takeover of invasive species and the disappearance of local species that have lived in the area for a million years are phenomena that indicate the continuation of the trend of reducing the ecological stability of the lake, which harm the biological diversity of the lake and probably also the food web, and therefore they should be a source of concern." wrote the researchers.
"When it invades a habitat, it affects its entire function" (photo: official website, Nature and Parks Authority)
Like the crayfish, the snail invasion was made possible by the irresponsible behavior of humans.
The Tarebia granifera, for example, is recognized as a biological cleaner in the aquarium industry and thus managed to spread around the world and become a nuisance.
It is known to host parasitic worms that cause disease in humans and fish.
The increase in salinity in the Sea of Galilee gives it an advantage over other species and it can also survive for weeks in a humid environment without water, by burrowing in the sand.
The appearance of the Pyrgophorus sp snail also illustrates how harmful human actions can be.
According to speculations, this snail came with a plant called "water lettuce".
This plant is also an invasive species that apparently came to us as a popular plant in ornamental ponds.
Nine years ago the invasive plant reached the mouth of Nahal Zalmon in the Sea of Galilee.
The same plant may invade and spread to streams and quiet water areas such as estuaries or internal lagoons and cause local ecological damage, mosquito hazards and damage to habitats.
Studies show that the invasion of the watercress can cause ecological damage leading to the suppression of habitats of local species and a decrease in the amount of oxygen in the water.
Also, the plant may cause clogging of drainage canals, disruption and damage to water pumping facilities.
The Nature and Parks Authority stated today that "after it has penetrated and established itself in new habitats, the extermination of the crayfish is almost impossible. There are various methods of collection, but extermination through collection alone is usually not effective. The use of poisons is impossible because it is not selective for river crayfish. Therefore, the use of poisons will also cause very serious damage to other water habitats that are not the target of the extermination and further serious damage to the habitat. The conclusion is that the best way to deal with the penetration and invasion of additional river crabs or other species is prevention. It is extremely important that the public cooperates in this aspect and avoids the release of animals and plants into the wild , aliens to Israel's ecosystem. Remember, the damage can be enormous and irreversible."
The Nature and Parks Authority said in view of the new threat that a team was formed which, in addition to the representatives of the Authority, also includes academics from various fields and other experts.
According to Milstein, "We began conducting a comprehensive literature survey to study extermination attempts carried out in the world, where they succeeded or where they failed and why, and from this to develop a suitable protocol for the various invasion sites in Israel. At the same time, we began to test the effectiveness of different methods for collecting adults and young people, in the various habitats On these we are even promoting, in collaboration with researchers from the academy, studies aimed at developing new pest control methods."
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