Effects of Marine Debris Caused by the Great Tsunami of 2011

The Great Tōhoku Earthquake, or Great East Japan Earthquake, with magnitude 9.0, struck off the coast of Japan on March 11, 2011, and triggered a massive tsunami. This event was a natural disaster of staggering proportions, causing loss of human life, property destruction and environmental damage.

With the tsunami, about 5 million tons of debris swept from the land and coastal systems into the ocean. The Government of Japan estimates that 70% of that debris sank close to shore, leaving 1.5 million tons floating in the North Pacific with the potential to arrive on North American and Hawaiian coastlines.

The first confirmed instances of Japanese tsunami debris washing up on the shores of North America occurred in March 2012. Since then, over 1600 debris sightings have been reported, of which 60 pieces could be confirmed as Japanese-origin tsunami debris. This includes two large concrete docks, originally from Misawa, Japan, that were found on beaches in Oregon and Washington (with a number of non-native species attached) and more than 200 small boats, many of which have been confirmed as lost during the tsunami. The North American coast already endures marine debris from terrestrial and aquatic sources, but there may be additional impacts from the increase in abundance and differing debris types due to the tsunami.

Aside from the impacts of additional marine debris itself, there is the possibility of debris carrying coastal Japanese species to North American coasts. The two docks together had hundreds of Japanese species and tens of thousands of individuals attached, alive, and some reproductively active. Many of the species were not known previously from North America and have the potential to invade coastal ecosystems. For example, species of sea stars, hydroid , mussels and fish collected from tsunami debris have been confirmed as non-native to the Pacific coast of North America.

As a result of generous funding from the Government of Japan, through its Ministry of the Environment (MoE), PICES has initiated a new project to investigate the impact of tsunami-generated marine debris. The goal of Project ADRIFT (Assessing the Debris-Related Impact of Tsunami) is to assess and forecast the effects of this debris, especially those related to non-indigenous species (NIS) and potentially invasive species on ecosystem structure and function, the coastlines, and communities of the west coast of North America and Hawaii, and to suggest research and management actions to mitigate any impacts.

This 3-year effort (April 2014 - March 2017) is directed by a Project Science Team (PST) made up of researchers from Canada, Japan, the United States and the PICES Secretariat, and is co-chaired by Thomas Therriault (Department of Fisheries and Oceans, Canada), Hideaki Maki (National Institute for Environmental Studies, Japan) and Nancy Wallace (NOAA Marine Debris Program, USA).
The project focuses on three main areas of research:
  1. Surveillance and monitoring of tsunami-generated marine debris landfall;
  2. Modeling movement of marine debris in the North Pacific; and
  3. Risk (including potential impacts) from invasive species to coastal ecosystems.

Surveillance and monitoring

The surveillance team continues its surveillance activities for British Columbia, Canada and began surveillance for Hawaii. The Hawaiian Islands receive a large amount of baseline marine debris and the unique flora and fauna of the region makes the potential introduction of invasive species a concern for state authorities. In Year 2, high resolution aerial surveys were conducted for the main Hawaiian Islands and analysis of the resulting images completed. The results highlight some islands for increased mitigation and monitoring efforts and shows which shorelines accumulate large amounts of debris. Re-analysis of the shoreline monitoring data with the additional 2015 data showed a sharp increase in the influx of debris items for 2015. The webcam system installed at a site in Oregon continues to be monitored and the images have been analysed. The temporal dynamics of debris on coastal beaches have found to be strongly related to onshore winds and coastal upwelling.

Modeling Movement of Tsunami Debris

The modeling group refined their models in Year 2 using observations from the monitoring and surveillance teams. The optimized models successfully reproduce the main peaks of JTMD arrivals in 2012-2015 and predict much of the remaining floating debris is entrained in the Pacific gyre and may continue to arrive in the future. The models were then used to estimate the trajectories of individual debris items, such as the large floating docks, and the accompanying environmental conditions that the associated biota would have experienced during the journey

Figure: Probable pathways and probable trajectories of Misawas docks found in a) Oregon, 4 June 2012, b) north of Molokai 18 September 2012 and c) Washington 18 December 2012. d) Probable pathway of Molokai dock after Hawaiian sighting. Image provided by Nikolai Maximenko, University of Hawaii

Risk of Invasive Species

In Year 2, the collection and analysis of biota associated with tsunami debris items continues. To date, over 500 samples of JTMD have been acquired from Alaska, British Columbia, Washington, Oregon, California, and the Hawaiian Islands, and have either been analyzed or are in the process of being studied. This work consists in large part of the identification of the species on the debris, utilizing both morphological and genetic approaches, as well as the screening of mussels for the presence of endoparasites. The majority of items intercepted and analyzed are from Washington, Oregon, and the Hawaiian Islands, and include vessels, post-and-beam lumber, floats (buoys), pallets, baskets, and a wide variety of additional objects.

Identification of species by taxonmic experts continues, with 58 scientists from Japan, China, Russia, Singapore, the United States, Canada, Mexico, Australia, Norway, and Germany engaged in the research. Both morphological and genetic analyses remain in progress. Overall, 352 Japanese species have been identified as surviving transoceanic rafting, including 80 species of algae. 77% of the invertebrate diversity is represented by 4 major phyla (Bryozoa, 69 species; Mollusca, 55; Crustacea, 54; Annelida, 37). In Year 2, JTMD items continued to arrive on North American and Hawaiian shorelines. JTMD objects recovered in March 2016 included new Japanese species such as the sea anemones Anthopleura asiatica and Diadumene lineata, not observed in previous years. The continued recoveries of new objects and new drift species indicate that quantities of JTMD with associated Japanese species remain in the North Pacific Ocean and will continue to arrive.

The risk assessment team has begun to build upon and incorporate the results of the modeling, monitoring and biodiversity research. Two workshops were held in Year 2 to develop a risk assessment framework to evaluate the risk of tsunami debris as a vector of invasive species. The risk of individual species will be evaluated using a database of life history traits, characteristics and invasion histories we compiled for all species associated with tsunami debris. A risk assessment screening tool will be applied to each species in Year 2 and the gathered information made available in an online resource.

Figure: Haplotype distribution and spanning network tree for the JTMD brown algal species Petalonia fascia. Image provided by Hiroshi Kawai, Kobe University

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