Species invasions into marine coastal habitats continue at an alarming rate. One is a comb jelly associated with dramatic ecosystem impacts. DTU and an international research team have shed new light on the success behind the invasion, findings published in PNAS.
One of the most notorious invasive marine species is a comb jelly, Mnemiopsis leidyi, that feeds on zooplankton. In recent years, biological invasions like this comb jelly have attracted much attention given their major threat to biodiversity and ecosystems worldwide.
But what characterizes a successful invasion event?
This question has occupied senior scientist from DTU Aqua Cornelia Jaspers and her international research team from Denmark, Germany, France, USA, and Bulgaria. They have addressed the question in one of the most successful marine invasive species the comb jelly Mnemiopsis leidyi by sequencing the entire genome of multiple native and invasive populations.
Read the scientific article Invasion genomics uncover contrasting scenarios of genetic diversity in a widespread marine invader in PNAS
The results shed new light on invasion dynamics:
“Contrary to expectations, the study shows that It is not the genetic diversity of a species per se which decides about a species being a potent invader or not. Rather the amount of animals introduced at once and re-current introductions, ie. continued seedings, seem important for invasion success,” says Cornelia Jaspers.
The North Sea Invasion
The international team led by researchers from Denmark used full genome data to shed light on three independent invasion events of this species in western Eurasia, ie. The North Sea, The Mediterranean, The Black Sea. As for The North Sea and Danish waters, Cornelia Jaspers points to the areas outside the large ports of Amsterdam, Rotterdam and the Wadden Sea area:
“As we have shown, animals can drift up to 2.000 km within 3 months during winter, these areas are highly connected also to Denmark”, says Cornelia Jaspers.
Native to the east coast of Americas, Mnemiopsis was first sighted in western Eurasia in the 1980´s and has since invaded large areas of Western Eurasia.
Human aided transport of species has shown devastating impacts on ecosystems and is regarded as a major driver behind the homogenization of the worlds’ biota, especially for marine systems.
Despite international conventions in place to halt species introductions, the scientists’ genome data suggest that animals have been introduced to the North Sea in the recent past. By resolving temporal dynamics of invasion events, the study uncovered hot-spots of ongoing, recurrent species introductions.
“Uncovering this temporal context to detect such ongoing invasions could be used to stop the introduction of non-indigenous species, which is important to halt the negative consequences of non-native species in the long run,” says Cornelia Jaspers.
The ballast water problem
The fact that the authors show all cases of genetic diversity within the same invasive species over different invasion events indicate that genetic diversity alone is not the major contributor to invasion success of a species. Instead, resolving temporal invasion dynamics via whole genome re-sequencing data are important for understanding invasion events.
The scientists mention the human factor in terms of ships emptying ballast water as well as the lack of preditors in the ocean being invaded by non-native species as two drivers for invasions.
So, how do we halt species introductions in the long run?
“Here effective methods could be to enforce stop of unfiltered or untreated ballast water discharge into the ocean in areas which are clearly defined by a high connectivity with large areas,” says Cornelia Jaspers.
Senior scientist Cornelia Jaspers she is centre leder of the Villum funded Centre for Gelatinous Plankton Ecology & Evolution and she is first author of the study from DTU Aqua.
The scientific article "Invasion genomics uncover contrasting scenarios of genetic diversity in a widespread marine invader" was published in PNAS on Wendesday 15th December.