In 2011 an earthquake struck East Japan. The 8.9 magnitude Sendai earthquake generated a huge tsunami, which pulled an enormous amount of man-made debris with it as the waters moved over the coastlines of Japan and back out to the ocean. This created what’s known as a biological rafting event, where marine life gets caught up in the debris and travels with the ocean currents.
The use of non-organic materials such as plastics, fiberglass, and metals has resulted in a lasting durability of these rafts and means that marine species travel farther distances post-tsunami.
A group of researchers inventoried what marine species traveled across the Pacific Ocean between 2012 and 2017. They documented nearly 300 species that traveled from Japan to the western United States via docks, buoys, ships, and other debris.
The dispersal of debris and its associated hitchhikers was influence by the North Pacific Ocean gyre current system. This system of circular ocean currents is influence by global wind patterns and the earth’s rotation, pulling debris with it.
Starting in 2012, plastic debris accompanied by marine life has landed on coastlines from Midway Atoll to Hawai‘i Island and from south central Alaska to central California. This resulted in the researchers documenting the arrival of 289 living invertebrate and fish species that had never previously been reported as arriving from from Japan via rafting event.
Select Summary Findings
Of those species that found their way to the western United States, 85% of the species were comprised of five invertebrate groups: mollusks, annelids, cnidarians, bryozoans, and crustaceans. Of all the documented arrivals, the majority arrived in the Pacific Northwest (Washington and Oregon) between the North latitudes 42°03.27′ and 47°54.19′ and the arrivals peaked between 2012 and 2014.
The researchers discovered that species continued to arrive from Japan after near six years at sea. This was four years longer than had previously been documented.
More Plastic in the Ocean Leads to More Invasive Species
The volume and longevity of rafting species arriving post-Tsunami leads to concern about how the use of plastics and other non-organic materials that end up as ocean debris can be a contributing factor to enabling invasive species (related: Ocean Garbage Patches). The authors note that natural rafting debris such as trees degrade quickly and preventing long-distance rafting events.
The ending paragraph notes:
Most of the world’s megacities are in the coastal zone and will continue to be so, greatly increasing the quantity of nonbiodegradable material available to be swept from watersheds and off of coasts. Large storms also inject debris fields into the ocean; in turn, cyclones (hurricanes and typhoons) and other storm activities are increasing due to global climate change. Human-mediated amplification of marine debris provides new opportunities for species to surmount historic ocean barriers.
Carlton, J. T., Chapman, J. W., Geller, J. B., Miller, J. A., Carlton, D. A., McCuller, M. I., … & Ruiz, G. M. (2017). Tsunami-driven rafting: Transoceanic species dispersal and implications for marine biogeography. Science, 357(6358), 1402-1406.