Currents propel the spreading of invasive jellyfish

May 25, 2018, Helmholtz Association of German Research Centres
The American com jelly Mnemiopsis leidyi. Credit: Cornelia Jasper/GEOMAR, DTU Aqua

Twelve years ago, the comb jelly Mnemiopsis leidyi, originating from the North American East Coast, appeared in northern European waters. Based on the first comprehensive data collection on the occurrence of this invasive jellyfish in Europe, scientists from 19 countries led by the GEOMAR Helmholtz Centre for Ocean Research Kiel and Technical University of Denmark have now shown that ocean currents play a key role for this successful invasion. The study has been published in the international journal Global Ecology and Biogeography.

When the American comb jelly Mnemiopsis leidyi, also known as sea walnut, conquered the Black Sea as a new habitat 35 years ago, the ecosystem there changed sustainably. The economically important anchovy stocks collapsed since the fish had to compete with the jellyfish for food. Against this background, scientists, fisheries associations and environmental authorities were alarmed when, in 2005, the sea walnut also appeared in northern European waters. Although effects similar to those in the Black Sea have not been observed in the Baltic and in the North Sea yet, scientists are still closely monitoring the development—particularly since many questions on invasion pathways are still largely unclear.

A total of 47 scientists from 19 countries have now published the first comprehensive inventory of Mnemiopsis leidyi in European waters in the international journal Global Ecology and Biogeography. With this data, the interdisciplinary team of authors shows that ocean currents as pathways of invasive jellyfish and other drifting organisms in the seas have been significantly underestimated so far. "To explain the invasion of alien species in marine ecosystems, everybody is focused on transport in or on ships. That is important, but does not explain the whole phenomenon", says lead author Dr. Cornelia Jaspers, Biological Oceanographer at the GEOMAR Helmholtz Centre for Ocean Research Kiel and at the Technical University of Denmark in Lyngby.

As basis for their study, the participants have collected all reliable data on the occurrence of the American comb jelly in European waters since 1990—a total of more than 12,000 geo-referenced data points. "Even this inventory is new, because so far there were only regional studies on the distribution", explains Dr. Jaspers.

In cooperation with oceanographers and modelers, the team linked data on the occurrence of Mnemiopsis leidyi to prevailing currents in European waters. The analysis included not only the flow directions and their strength, but also their stability. The models showed that the steady flow pattern of the southern North Sea closely links the region with much of northwestern Europe, including the Norwegian coast and even the Baltic Sea.

Due to this close connection, not only invasive jellyfish but generally non-native species floating in the sea can be spread over long distances within a very short time. "Using the imported sea walnut as example, we were able to show that these species can travel up to 2000 kilometers within three months," says Hans-Harald Hinrichsen, physical Oceanographer at GEOMAR. Species that arrive in ports in the southwestern North Sea, such as Antwerp or Rotterdam, reach Norway and the Baltic Sea very quickly.

To confirm this connection, the authors used a natural experiment. After a very cold winter season in early 2010, the jellyfish disappeared from the Baltic Sea and large parts of northwestern Europe in 2011 and stayed away until 2013. But after the warm winter of 2013/14, a new population of Mnemiopsis established itself in the Baltic very fast. "This new population was of another genotype than the first invaders. Thus, within a short time, a new immigration took place, driven by the prevailing ," says Dr. Jaspers. Perhaps the new arrivals from the second invasion wave are even better adapted to the local conditions.

Therefore, the authors plead not only to keep an eye on the transport routes across oceans, but also to better investigate the possibilities of spreading within a region. "The study shows that a single gateway, a single port for example, in which ships with invasive species arrive, is enough, to redistribute non-native species across entire regions," she concludes.

Explore further: Wound healing or regeneration—the environment decides?

More information: Cornelia Jaspers et al, Ocean current connectivity propelling the secondary spread of a marine invasive comb jelly across western Eurasia, Global Ecology and Biogeography (2018). DOI: 10.1111/geb.12742

Related Stories

Wound healing or regeneration—the environment decides?

November 30, 2017

An earthworm cut in two parts can survive and regenerate. For humans, the loss of limbs is a severe problem that can only be treated by complex surgery. However, among animals, there are numerous examples of self-healing ...

The Baltic Sea as a time machine

May 9, 2018

Warming, acidification, eutrophication, and the loss of oxygen are examples of major changes being observed or expected for the future in coastal zones around the world. These processes are occurring in the Baltic Sea at ...

Turning jellyfish from a nuisance to useful product

November 8, 2017

Global climate change and the human impact on marine ecosystems have led to dramatic decreases in the number of fish in the ocean. It has also had an unforseen side effect: because overfishing decreases the numbers of jellyfish ...

Voracious comb jellyfish 'invisible' to prey

October 12, 2010

Despite its primitive structure, the North American comb jellyfish can sneak up on its prey like a high-tech stealth submarine, making it a successful predator. Researchers, including one from the University of Gothenburg, ...

Recommended for you

After a reset, Сuriosity is operating normally

February 23, 2019

NASA's Curiosity rover is busy making new discoveries on Mars. The rover has been climbing Mount Sharp since 2014 and recently reached a clay region that may offer new clues about the ancient Martian environment's potential ...

Study: With Twitter, race of the messenger matters

February 23, 2019

When NFL player Colin Kaepernick took a knee during the national anthem to protest police brutality and racial injustice, the ensuing debate took traditional and social media by storm. University of Kansas researchers have ...

Researchers engineer a tougher fiber

February 22, 2019

North Carolina State University researchers have developed a fiber that combines the elasticity of rubber with the strength of a metal, resulting in a tougher material that could be incorporated into soft robotics, packaging ...

A quantum magnet with a topological twist

February 22, 2019

Taking their name from an intricate Japanese basket pattern, kagome magnets are thought to have electronic properties that could be valuable for future quantum devices and applications. Theories predict that some electrons ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.