Category Archives: Marine Life

Study Identifies Pathogen Responsible For Sea Star Mass Die Offs Along Pacific Coast

By Jay T. Cullen

Sea star with Sea Star Wasting Disease photographed by the author at Botanical Beach near Port Renfrew BC in July 2014.

This diary summarizes a newly published paper by Hewson and colleagues in Proceedings of the National Academy of Sciences of the USA which investigated the cause of sea star die offs along the west coast of North America. This diary is part of series dedicated to summarizing scientific research on the impact of the triple meltdowns at the Fukushima Dai-ichii nuclear power plant on the North Pacific Ocean and the health of residents of North America. Northeast Pacific sea stars have experienced a mass die off recently and have disappeared from certain coastal ecosystems as a result. The Hewson et al. paper presents evidence that the cause of the wasting disease can be transmitted between affected to healthy individuals. The disease-carrying agent is virus sized and likely sea star-associated densovirus (SSaDV) which is found in greater numbers in diseased versus healthy sea stars. They also detected SSaDV in museum specimens of sea star dating from 1942 indicating that the virus has had a long term presence along the North American west coast.


There have been many speculative news items which have linked the release of radionuclides from Fukushima to the North Pacific Ocean to the most recent outbreak of sea star wasting which is occurring in west coast intertidal habitats. This is despite the fact that, for example, Fukushima derived radionuclides have still yet to be detected in coastal seawater collected up and down the North American Pacific coast.

Beginning in June 2013 massive numbers of sea stars have succumbed to sea-star wasting disease (SSWD) whereby they rapidly deteriorate, losing limbs, and turn into piles of slime. SSWD is an old term used to describe similar outbreaks of wasting that have occurred since at least 1979. The geographic extent and number of species impacted by the current SSWD outbreak is unprecedented. Affected individuals present with behavioural changes, lethargy, deflation, limb curling and loss, lesions and death. Very few individuals with symptoms are observed to recover.

Photographs of SSWD-affected stars (A) asymptomatic P. helianthoides, (B) symptomatic P. helianthoides, and (C) symptomatic P. ochraceus. Disease symptoms are consistent with loss of turgor, loss of rays, formation of lesions, and animal decomposition. (D) Map showing occurrence of SSWD based on first reported observation. (E) Transmission electron micrograph of negatively stained (uranyl acetate) viruses extracted from an affected wild E. troschelii from Vancouver . The sample contained 20–25-nm diameter nonenveloped icosohedral viral particles on a background of cellular debris (primarily ribosomal subunits) and degraded viral particles of similar morphology.

Hewson and colleagues examined affected and asymptomatic sea stars to demonstrate that an infective agent was responsible for SSWD. To do this they took homogenized SSWD affected sea stars and administered an inoculate or a heat killed inoculate of virus size containing filtrate to tanks containing healthy individuals. Results of these experiments indicate that heat killed inoculates did not lead healthy individuals to develop SSWD while inoculates with potentially live viral particles lead to SSWD symptoms in the previously healthy population. Previously healthy sea stars had very low loads of a virus callled Sea Star-Associated Densovirus (SSaDV) while after developing symptoms much higher amounts of SSaDV were found in the sea stars.

(A) Proportion of stars remaining asymptomatic after inoculation with control (heat-killed) or virus-sized fraction (VSF) of asteroid homogenates in first (Expt 1) and second (Expt 2) challenge. (B) Change in SSaDV load between initiation of viral challenge and termination of experiment (i.e., animal expiry in live challenge or euthanasia of control animals). Note difference in scale.
The authors then looked for the virus in asymptomatic and SSWD affected individuals in the wild finding that affected individuals were about 3 times more likely to be virus carrying than asymptomatic individuals. The virus was also found in plankton, sediments and other echinoderms. The presence of the virus in plankton and in filtration media of public aquaria affected by SSWD is consistent with observations that the disease could spread through ocean currents between infected and uninfected areas of the coast.

The authors conclude by pointing out that the spread of SSWD along our coast is most consistent with an infectious agent. Based on their observations and laboratory experiments this agent is most likely SSaDV which has been present along the coast for at least 72 years. Fukushima in not mentioned once in the article as there is no scientific evidence to relate SSWD to the trace concentrations of Fukushima derived radionuclides present offshore.

The authors identify outstanding questions as follows:

How exactly (by what mechanism) does SSaDV kill sea stars?
Are there other microbial agents involved in the wasting/death process?
What triggers outbreaks of SSWD?
How will the absence of important predators like sea stars affect the marine ecosystem along our coast?

The study highlights the increasingly recognized importance of marine viruses in helping to shape community structure and ecosystem dynamics in the ocean.

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Release, Dispersion and Fate of Radioactive Strontium From Fukushima in the Northwest Pacific Ocean

By Jay T. Cullen

The purpose of this diary is to summarize recent models and measurements of the release of strontium-90 (90-Sr, half life 28.8 yr) to the ocean resulting from the triple meltdowns at the Fukushima-Daiichi nuclear power plant in March 2011. This post is part of an ongoing series aimed at understanding the impact of the disaster on the North Pacific Ocean and residents of the west coast of North America. 90-Sr is a beta-emitting element that is a radiological health concern given its relatively long half life and similar chemistry to the nutrient calcium (Ca). Previous peer-reviewed work indicate that releases of 90-Sr were about 30-10,000 fold less than 137-Cs and similar to the release of 90-Sr from the Chernobyl disaster in 1986 and about 600-fold lower than the releases from atmospheric weapons tests that peaked in the mid-1960’s. Given maximal release rates after the disaster, modeled activities of 90-Sr in the marine foodweb and in fish that accounts for bioconcentration and accumulation predict maximal dose rates from Fukushima to human consumers three orders of magnitude less than doses owing to the presence of 137-Cs in marine products and thus well below maximum dose limits thought to be detrimental to public health. Continue reading Release, Dispersion and Fate of Radioactive Strontium From Fukushima in the Northwest Pacific Ocean

Fukushima Radionuclides in Pacific Albacore Tuna Off the US Coast

Tuna and gamma spectra. (Neville et al. 2014)
Tuna and gamma spectra. (Neville et al. 2014)

By Jay T. Cullen

Introduction

As part of an ongoing series documenting the impacts of the Fukushima disaster on the North Pacific and west coast, this post summarizes a recently published study by Delvan Neville and colleagues in the peer-reviewed journal Environmental Science and Technology. The paper reports measurements of Cesium-134 and Cesium-137 in 26 albacore tuna caught off the west coast of North America between 2008 and summer 2012. Because of its relatively short half-life (~2 years) 134-Cs is an unambiguous tracer of radionuclides released from the Fukushima Dai-ichi disaster which began in March 2011. Fish collected in 2011 and 2012 had higher 134-Cs and 137-Cs that was due to Fukushima sourced cesium in the Pacific. Fish collected in 2008-2009 had lower 137-Cs activities that largely reflected historic releases of the isotope from atmospheric nuclear weapons testing in the 20th century. The authors conclude that given the highest levels of Cs isotopes measured in albacore tuna, human consumption of the fish would not not represent a significant increase in annual radiation dose. The corresponding radiological health risk due to Fukushima derived radiocesium in these tuna is, therefore, very small. Continue reading Fukushima Radionuclides in Pacific Albacore Tuna Off the US Coast

Looking For Fukushima Radionuclides in Fish Caught Off the West Coast of Canada

by Jay T. Cullen

The purpose of this post is to report measurements of radioactivity in fish caught off the west coast of Canada based on the work of InFORM team member Dr. Jing Chen.  A collaborative effort between Health Canada, Department of Fisheries and Oceans Canada, and the University of Victoria was published in May 2014 in the peer-reviewed, open-access scientific journal Radiation Protection Dosimetry (link). The authors examined the activities of cesium radioisotopes (134-Cs half-life ~2 years and 137-Cs half-life ~30 years) that were released in large quantities due to the triple reactor meltdowns at Fukushima Dai-ichi Nuclear Power Plant in 2011 as well as a naturally occurring polonium isotope (210-Po) that can pose radiological health concerns for human consumers of marine fish. Samples of chum and coho salmon, halibutsablefish and spiny dogfish were analyzed and none were found to contain detectable levels of Fukushima derived radionuclides. Radiation doses to human consumers were determined by assuming a conservative worst case scenario where Cs isotopes were present at detection limits of the measurement and found to be 18 times lower than doses attributable to the naturally occurring, alpha-emitter 210-Po. The authors conclude that the radiation dose from Fukushima derived isotopes present in fish caught in Canadian waters represent a very small fraction of the annual dose from exposure to natural background radiation. Based on these measurements, at present, Fukushima derived radionuclides in fish do not represent a significant radiological health risk to Canadians. Continue reading Looking For Fukushima Radionuclides in Fish Caught Off the West Coast of Canada