How one tsunami and lots of manmade debris are triggering a mass marine migration


Credit: Carla Schaffer / AAAS

Following the 2011 East Japan tsunami, more than 280 coastal marine species have been recorded crossing the Pacific by hitching a ride on debris, a new study reveals. Furthermore, a majority of the debris was manmade material that tends to be non-biodegradable, highlighting a key way in which humans are contributing to the transoceanic survival and dispersal of coastal species. On March 11, 2011, an undersea megathrust earthquake struck Japan, triggering a tsunami exceeding 38 meters in height. The coastal damage resulted in millions of objects, ranging in size from small plastic fragments to fishing vessels and large docks, being carried into the Pacific Ocean. Here, James T. Carlton and colleagues assessed the diversity of animal communities on more than 600 pieces of debris from the tsunami that crossed the Pacific Ocean, reaching places such as Hawaii and the west coast of the United States. They documented 289 living invertebrate and fish species arriving from Japan, including macroinvertebrates (235 taxa), fish (two taxa), microinvertebrates (33 taxa), and protists (19 taxa). Since many species were just recorded on one piece of debris, however, the authors estimate that the real number of species that hitched a ride across the Pacific is much higher. They note that manmade and natural debris are vastly different, with the latter largely consisting of short-lived, dissolvable, or decomposable materials, such as biodegradable vegetation, that rarely survive a trip across whole oceans. Notably, the last two major earthquakes that struck Japan occurred before much of the material observed in the 2011 tsunami was being fabricated by humans and widely used. Steven L. Chown discusses this "unprecedented" rafting event in a related Perspective, noting that, "The impact of such a large event depends on how many of the organisms establish a population in the new region to which they have been transported, spread in that region, and go on to influence ecosystems."


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