Study Finds Invasive Marine Species Hitching Rides Around the World

By Hamodia Staff

Two container ships of the Maersk Line. Kees Torn 

YERUSHALAYIM — A new study from Tel Aviv University included a first-of-its-kind experiment simulating the changing environmental conditions encountered en route by marine animals clinging to the bottom of container ships. Such animals ‘hitch a ride,’ traveling with the ship to distant regions around the globe – for example from Southeast Asia to Northern Europe.

The experiment demonstrated that the animals’ ability to survive the arduous journey depends on factors like the type of vessel and the route it navigates as well as the changing temperature and salinity of seawater. According to the researchers, the routes of vessels of different sizes are determined mainly by technical limitations of infrastructures at different ports, as well as economic trends in the shipping industry. This results in unique geographic routes that create completely different sets of environmental and other challenges for creatures attaching themselves to these vessels. 

The noted that “the phenomenon of marine animals invading distant regions endangers local marine environments and their resident species. In this study we demonstrate that suitable regulation can decrease this phenomenon and prevent potential invaders from reaching new habitats.”

Prof. Noa Shenkar of the Faculty of Life Sciences at Tel Aviv University: “At any given moment, thousands of marine creatures travel from one location to another by marine vessels. They do this in two different ways: in the ballast water – seawater taken on by the vessel for stabilizing, or by clinging to the ship’s hull. The problem of invasive species transferred by ballast is addressed by legislation, but the ‘hitchhikers’ clinging to the ships are not – and thus numerous species are transferred from place to place along international trade routes.”

Ascidians are marine invertebrates that attach to hard surfaces such as rocks, breakwaters, and ship hulls. There are hundreds of species of ascidians, and the rise in global trade enables some opportunistic species to disperse over great distances, sometimes establishing themselves as invasive species and harming both marine infrastructures and local species in their new habitats.

An experiment conducted by research student Doron Bereza, together with Prof. Shenkar, examined the survivability of two species of ascidians, known to be harmful, on a journey that follows a typical trade route – from Southeast Asia to Northern Europe.

Doron Bereza: “We focused on two species of ascidians that are common in the Mediterranean, including Israel, and are known to be transferred by ships. I created a comprehensive database, comprising info from about 200 container ships, and used it to build a route representing the trade routes of two different types of container…In addition, I collected data about changes in seawater temperatures and salinity at different ports along the way.”

Then they exposed both species of ascidians to similar conditions in the lab. Bereza: “We discovered that survivability was significantly impacted by several factors: environmental conditions, the type of vessel, and traits of the animal itself. Under extreme conditions, found in some eastern ports, such as a combination of high temperatures and low salinity, one species died out completely, while no mortality was observed in the other species.

“Additional experiments of this kind, specifically addressing groups of marine animals that pose a threat, can lead to effective regulatory measures for preventing the conveyance of species,” he said.

Prof. Shenkar adds: “We were surprised to discover that one tropical ascidian species survived the entire journey to Rotterdam. This does not mean that the creatures enjoyed their trip, but the fact is that they did survive, and just a few individuals are sufficient for launching an invasive population in the new territory.”

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