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Invasive species are able to survive in the sea in very surprising and extreme environmental conditions

The increase in global trade allows the marine animals to migrate to distant countries to establish themselves and spread as invasive species - when they cause damage to many marine infrastructures and other animals in their new environment.

A new study by Tel Aviv University has for the first time conducted an experiment that simulates the changing environmental conditions during the journey of marine animals that stick to the bottom of container ships. As part of the maritime journey, the animals hitch a ride with the ship and "sail" with it to distant regions of the globe, for example from Southeast Asia to Northern Europe. The experiment showed that the animal's ability to survive the arduous journey depends, among other things, on the type and size of the vessel, the changing sea temperatures and the salinity of the water. The researchers showed that although the routes taken by cruise ships of various sizes are mainly influenced by technical limitations in the port infrastructure and economic trends in the shipping world, in practice a unique geographic route is created that presents the animals on the side of the ship with a completely different series of challenges and environmental conditions.

The researchers warn: "The phenomenon in which marine animals invade other areas is dangerous for the marine environment and the local animals. In the research we showed that through appropriate regulation it is possible to block the phenomenon and prevent the establishment of the invaders in the new areas." 

The research was conducted by research student Doron Barza under the guidance of Prof. Noa Shankar from the School of Zoology, Faculty of Life Sciences and the Steinhardt Museum of Nature at Tel Aviv University. The research was published in the prestigious journal Science of The Total Environment.

Ballast water and sticking to the sides of the ship

Prof. Shanker: "At any given moment, thousands of marine animals move from one place to another using a vessel and they do so in one of two ways: in the ballast water - seawater used to stabilize the ship - or by clinging to the sides and grooves of the vessel. The problem of species invading through ballast water has a legislative solution, but the issue of hitchhikers on the side of the ship remains behind - and meanwhile, many species are transported from place to place on global trade routes.

Acetalans are marine invertebrates that are common all over the world on hard substrates such as rocks, breakwaters and the bottoms of sailing vessels. There are hundreds of species of acetylenes, when the increase in global trade allows them to migrate and sometimes also to establish themselves and spread as invasive species - when they cause damage to many marine infrastructures and of course to other animals in their new environment. As part of his master's thesis, Doron Barza and Prof. Noa Shankar conducted an experiment aimed at testing the survivability of two species of acetylenes, known as pests, during a voyage that represents a typical route for a sailing vessel: from Southeast Asia to Northern Europe.

"We focused on two species of acetylenes that are common in the Mediterranean, also here in Israel, which are known to grow as 'seaweed' on ships," says Doron Barza. "For several months, I built a comprehensive database that included about 200 container ships, and with it I built a representative route for the giant container ships - ships over 395 meters long - and the 'normal' container ships, which are also very large but there are more ports with suitable infrastructure for them I characterized the changes in water temperature, water salinity and chlorophyll concentration as a measure of food availability during sailing and during docking in ports along the route for each type of ship."

In the second step, the researchers reproduced these conditions in the laboratory, and in real time, with the two types of acetylenes. "We found that the environmental conditions, the type of vessel and also the characteristics of the animal itself have a clear effect on the ability to survive in our experiment. When it comes to extreme conditions, for example the combination of high temperature and low salinity that exists in some of the eastern ports, we saw complete mortality in one of the species, while in the other species that was examined, no mortality was observed at all. In practice, ships of different sizes will not necessarily visit the same ports during the journey, even if the journey is broadly similar. Therefore, as the ship will be exposed to a wider range of ports with extreme environmental conditions, the chance of a specific species surviving this entire range of conditions will decrease significantly. Effective regulation to prevent the transition of species should be based on additional similar experiments on groups of animals that pose a risk," adds researcher Barza.

"We were very surprised to find out that a tropical species of acetlan survived the entire journey to Rotterdam, through the Mediterranean Sea to the North Sea," adds Prof. Shanker. "It doesn't mean anything was particularly pleasant for him, but it is a fact that he survived - and you don't need more than a few individuals to establish a population in a new territory. Moreover, due to global warming, we expect that additional species of tropical origin will succeed in thriving in the future in bodies of water that are too cold for them today. The fact that there were ants along the way where almost all individuals died due to the combination of unique environmental conditions, indicates that it will be possible to use these places as environmental barriers for the spread of species."

לThe scientific article

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