New habitats of a problematic nature: Many marine invertebrates that normally only occur in coastal regions can live and reproduce on floating plastic waste in the open ocean. This is documented by an investigation in the eastern North Pacific. There, the plastic waste on the high seas is home to three times more coastal species than species that naturally colonize flotsam. According to the researchers, it is becoming apparent that the foreign substances are breaking up previous biogeographical boundaries between marine ecosystems in a problematic manner.
Garbage is now floating around everywhere: the ugly signature of civilization is increasingly shaping the seas, because gigantic amounts of waste end up in the waters every year. Studies show that plastic waste in particular threatens the ecosystems there in a complex way. Because the plastic materials break at best, but are not degraded, which means that they accumulate in nature. The marine litter also forms particularly prominent "eyesores": Due to the current systems of the oceans, the floating material sometimes collects in huge eddies of garbage.
It is already known that plastic waste can also play a role as a habitat for problematic microorganisms and other living beings. The scientists working with Linsey Haram from the Smithsonian Environmental Research Center in Edgewater have now devoted themselves to more detailed research into this aspect. For their study, they examined plastic objects that come from the region of the current eddy in the eastern North Pacific. The accumulation of human waste there is also known as the "Great Pacific Garbage Carpet". As part of the study, the marine biologists recorded the species of invertebrates found on the pieces, along with evidence of their evolution and reproduction.
Lots of alien residents
The evaluations showed that species that normally inhabit coastal habitats were found on more than 70 percent of the plastic waste examined. The 37 species are representatives of the mollusks, arthropods and cnidarians from various taxonomic groups. The garbage was home to three times more of these coastal species than ancestral open-ocean creatures that have historically inhabited the natural flotsam. In detail, the researchers found the greatest variety of coastal species in plastic objects that come from fishing.
In addition, the researchers found evidence that the alien organisms are not only found in the rubbish, but also multiply and spread there. As the scientists explain, the effect is probably due to the characteristics of the unnatural flotsam, which are more similar to those of coastal structures: Plastic objects offer a more durable surface than natural objects made of wood or other biological materials, which degrade comparatively quickly. "We were also surprised at how easily offshore species appeared to be able to colonize new floating objects, including our own instruments - an observation we will continue to investigate," says Haram.
Biogeographical borders become permeable
But a process of considerable importance is already emerging, the researchers summarize: "Our results show that coastal organisms are able to reproduce, grow and survive in the open ocean thanks to the garbage. They form a new kind of community that didn't exist before," says senior author Gregory Ruiz of the Smithsonian Environmental Research Center. “This is a paradigm shift in terms of what we have been considering as a barrier to the spread of coastal invertebrates.” Haram adds: “There is evidence that the biogeographical boundaries between marine ecosystems that have existed for millions of years are being blurred by floating debris change quickly".
According to the researchers, their results also illustrate concrete threats: "The Hawaiian Islands border the North Pacific garbage patch in the northeast," says co-author Nikolai Maximenko from the University of Hawaii at Manoa in Honolulu. “Parts that come from there make up the majority of the garbage that arrives on Hawaii's beaches and reefs. In the past, the islands' fragile marine ecosystems were protected by their great distance from the coasts of Asia and North America. The new results now make it clear that the islands are at increased risk of colonization by invasive species," says Maximenko.
Source: University of Hawaii at Manoa, professional article: Nature Ecology & Evolution, doi: 10.1038/s41559-023-01997-y