Animal life in the area contaminated by radiation after the Chernobyl nuclear reactor explosion two decades ago is still declining, researchers say.
In findings published in the journal Biology Letters last week (Wed, March 18), Professor Timothy Mousseau of the University of South Carolina, USA, and Dr Anders Moller of the University of Paris-Sud, France conclude: "Abundance of invertebrates decreased with increasing radiation, even after controlling for factors such as soil type, habitat and height of vegetation.
"These effects were stronger when comparing plots differing in radiation within rather than among sites, implying that the ecological effects of radiation from Chernobyl on animals are greater than previously assumed."
The findings counter previous research suggesting rebounding animal populations at the site in Ukraine of the 1986 nuclear power plant explosion - the world's worst.
The research team worked in the exclusion zone around the site conducting invertebrate population counts at 731 points over three years from 2006-2008.
They described it as the "most extensive dataset on the abundance of animals" there. Dr Moller said: "We wanted to ask the question: Are there more or fewer animals in the contaminated areas? Clearly there were fewer."
Previously, the two researchers found low-level radiation in the area had a negative effect on bird numbers.
Their methodology included plotting "line transects" through multiple sites and counting insects and spiders found along those lines, while monitoring the corresponding radiation levels.
They discovered "the abundance of invertebrates decreased with increasing radiation", including numbers of bumblebees, butterflies, grasshoppers, dragonflies and spiders.
They also found animals living near the reactor had more deformities than normal.
"Most radiation around Chernobyl is currently in the topmost soil (Shestopalov 1996), where most invertebrates live," they said in the report. "This could negatively affect survival and fecundity, and hence abundance."
The results have implications for "overall ecosystem functioning", they say.
Fewer pollinating insects could affect plant fertility and seeding while fewer spiders - an important predator - could have consequences for other invertebrate populations.
They conclude: "Pollination and predation are considered important ecosystem services (Costanza et al. 1997) and disruption may affect the overall ecosystem functioning, suggesting that the Chernobyl region and its surroundings is a perturbed ecosystem."
But some researchers have challenged the study, claiming an absence of human activity in the exclusion zone has benefitted wildlife.
Dr Sergii Gashchak, a researcher at the Chernobyl Center in Ukraine, told the BBC he drew drew "opposite conclusions" from the data the team collected on birds.
"Wildlife really thrives in Chernobyl area - due to the low level of [human] influence," Dr Gashchak told BBC News.
"All life appeared and developed under the influence of radiation, so mechanisms of resistance and recovery evolved to survive in those conditions."
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