92 — Tsunami-driven rafting: Transoceanic species dispersal and implications for marine biogeography

After the 2011 earthquake and tsunami off the coast of Japan, many animals and plants washed to sea aboard quite a bit of flotsam.

This article was not solely an excuse to write “flotsam” in a legitimate context, but I would be remiss if I didn’t admit that it was partially responsible.

Much of the rafting material was wooden or otherwise biodegradable; naturally, these rafts soon sank into the Pacific ocean. Much more of this material washed back up on the shores of Japan — but a large fraction of the flotsam(!) instead remained adrift. This fraction was not biodegradable — it was largely made up of plastics or fiberglass and other man-made materials — and the animals and plants aboard these arks continued to float around until washing up on the shores of Pacific Islands and North America.

The debris that arrived (and continues to arrive!) in California traveled at least 5500 miles, but these rafts still contained many fish, annelid, protist, plant, and mollusc species never before found in North America.

This particular transoceanic rafting event is fascinating for several reasons: First, rafting has never been seen at this scale or length of time before. (Published six years after the tsunami, this paper mentions that marine biologists are still today finding new rafts.) This is likely because the majority of the rafting material was non-biodegradable, unlike conventional rafts made of trees, seeds, or other biomass. Second, the rafts themselves exhibited interesting, self-sustaining characteristics. In order to last the many years at sea, the ‘sailor’ organisms must have adapted new reproductive strategies.

As ocean levels rise and more cities with higher populations are concentrated near coastlines, this type of rafting will become increasingly prominant, and it will become important to understand the ecosystemic implications of these rafting events and — if possible — stop them.