Although it's too early to assess the long term impact on abundance and diversity around Fukushima, there are very few butterflies and many birds have declined in the more contaminated areas. If abundance is compressed, biodiversity will follow.
He has spent 16 years looking at the effects on wildlife and the ecosystem of the 1986 Chernobyl nuclear disaster.
He and his colleagues have also spent the last five years studying how non-human biota is faring in the wake of the 2011 Fukushima nuclear meltdowns in Japan.
But none of this work has received anything like the high profile publicity afforded the 'findings' in the 2006 Chernobyl Forum report which claimed the Chernobyl zone "has become a wildlife sanctuary", and a subsequent article published in Current Biology in 2015 that said wildlife was "thriving" around Chernobyl.
"I suppose everyone loves a Cinderella story", speculated Mousseau, an evolutionary biologist based at the University of South Carolina. "They want that happy ending." But Mousseau felt sure the moment he read the Forum report, which, he noted, "contained few scientific citations", that the findings "could not possibly be true."
Ninety articles later, Mousseau and his research partners from around the world are able to demonstrate definitively and scientifically that non-human biota in both the Chernobyl zone and around Fukushima, are very far indeed from flourishing.
Far from flourishing around Chernobyl, birds and animals are fading
What Mousseau found was not unexpected given the levels of radiation in these areas and what is already known about the medical effects of such long-term exposures. Birds and rodents had a high frequency of tumors.
"Cancers are the first thing we think about", Mousseau said. "We looked at birds and mice. In areas of higher radiation, the frequency of tumors is higher." The research team has found mainly liver and bladder tumors in the voles and tumors on the head, body and wings of the birds studied, he said.
But Mousseau wanted to look beyond cancers, which is what everyone expects to find and what researchers had looked for, but only in humans. There were few wildlife studies, a fact Mousseau found surprising, given nature's ability to act as a sentinel for likely impending human health impacts.
Mousseau and his fellow researchers found cataracts in birds and rodents. Male birds had a high rate of sterility. And the brains of birds were smaller. All of these are known outcomes from radiation exposure.
"Cataracts in birds is a problem", Mousseau said. "A death sentence."
Mental retardation has been found among children exposed to radiation in utero. Mousseau and colleagues discovered the same pattern in the birds they studied. "Birds already have small brains, so a smaller brain size is a definite disadvantage", he said.
Almost 40% of male birds examined were sterile
There were also just fewer animals in general. "There were many fewer mammals, birds and insects in areas of higher radiation", Mousseau said. And they had their hunch as to why.
He and his colleagues extracted sperm from the male birds they caught and were shocked to find that "up to 40% of male birds in the radiologically hottest areas were sterile."
The birds' sperm were either deformed or dead. None would be able to reproduce. The discovery, he said, was "not at all surprising. These are the levels of radiation known to influence reproduction. At the same time, there is no safe level of radiation below which there aren't detectable effects."
Fewer birds have already been observed in the contaminated areas around Fukushima, said Mousseau. "Although it's too early to assess the long term impact on abundance and diversity around Fukushima, there are very few butterflies and many birds have declined in the more contaminated areas. If abundance is compressed, biodiversity will follow."
Five years into the still on-going Fukushima disaster, Mousseau's research continues to uncover "a dramatic reduction in the number of birds and numbers of species in areas of high radiation", he said.
At least in that region, Japan could be headed toward a Silent Spring.
No doubt that Fukushima and Chernobyl are causing genetic damage
The consequences of radiation exposure, says Mousseau, "will have a tremendous impact on the quality of life of these animals, and the length of quality of life. It need not necessarily be cancers", that cause these damages he said. "There is no doubt that the levels of radiation in Chernobyl and Fukushima generate genetic damage."
Fungi and other microorganisms are decomposing at half the usual rate. Trees fall but rot unusually slowly. Leaf matter piles up without much decay, creating a tinder-box risk in the event of forest fires, several of which have occurred in the Zone.
"There is an accumulation of highly radioactive organic matter" in these areas, Mousseau said. All of this could be lofted into the air during a forest fire and redistributed as radiological contamination elsewhere, he points out.
Indeed, a map in an April 2006 edition of National Geographic Magazine, shows that this has already happened, expanding the Chernobyl Zone from its original 30km radius. "High-altitude winds swept radioactive smoke and ash across a wider area, which scientists traced from soil levels of cesium 137, a long-lived isotope," read the map's caption. Major forest fires in the Chernobyl Zone in 2010 and 2015 have likely worsened the situation.
While the radiation spread by Chernobyl fell mostly on land, where it is easier to study the medical effects on humans and animals, the initial Fukushima radioactive plume blew mainly out to sea. And since 2011 when the accident began, further dumping of radioactive water into the Pacific has occurred.
A responsibility to protect the environment and wildlife, not just man
This has led to speculation - and some unscientific and alarmist rumors - that sea life in the Pacific is collapsing due to the Fukushima radiation.
"Catastrophic marine events started 40-50 years ago", Mousseau points out. "Bird populations in the Pacific were in decline long before Fukushima."
One important cause, says Mousseau, is "plastics in the environment that are consumed by marine animals which were in downward spirals long before the Fukushima accident." Marine population decline has likely also been "compounded by climate change", he says.
Indeed, Mousseau, who grew up on Vancouver Island in British Columbia, remembers the local harbor encrusted with star fish when he was a child. Recently, when he took his son there, he found none.
Fukushima cannot necessarily be blamed, as some would wish, but the compounding and potentially synergistic effect of radiation in the Pacific could still be taking its toll, Mousseau avowed.
"We don't know how different environmental stresses interact with each other", he said. "They could be synergistic and related. There is almost no research on this even in the Pacific off Fukushima - virtually nothing on the biological consequences in really contaminated areas."
With "little real science" to rely on, Mousseau says, "we will never know" just how much marine damage the Fukushima disaster may do.
He finds the continued lack of other independent animal studies in radioactive zones frustrating. "We have a responsibility to protect the environment and wildlife, not just man", he said. It may be expensive and difficult to conduct these kinds of studies, but, says Mousseau, "that is not an excuse."
Linda Pentz Gunter is the international specialist at Beyond Nuclear, a Takoma Park, MD environmental advocacy group.
The paper: 'Highly reduced mass loss rates and increased litter layer in radioactively contaminated areas' is by Timothy A. Mousseau, Gennadi Milinevsky, Jane Kenney-Hunt & Anders Pape Møller, and is published in Global Change Ecology. Full version as PDF.