UVB cause of rising marine deaths

10 August 2012 Last updated at 09:37 By Matt Bardo Reporter, BBC Nature

Increased ultraviolet radiation has caused a sharp rise in the deaths of marine species, scientists have found.

An international team gathered information from previous studies looking at the effects of ultraviolet B (UVB) radiation on marine life.

Their work shows a close link between UVB levels and death rate, particularly in algae, corals and crustaceans.

The team believe this is the first time the effect of UVB on the health of marine ecosystems has been calculated.

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Reef belief

Corals are particularly sensitive to UVB according to recent research and entire colonies have been wiped out in recent years. But under the right conditions, these remarkable animals can thrive:

"In our study, mortality is the biological response which showed the greatest sensitivity to UVB radiation," said lead author, Dr Moira Llabres from the Mediterranean Institute for Advanced Studies in Spain, who worked on the paper with the Catholic University of Chile and the University of Western Australia.

The article is published in the journal Global Ecology and Biogeography.

"Ultraviolet B radiation has caused a steep increase in deaths among marine animals and plants," said Dr Llabres.

UVB radiation is known to impair photosynthesis, nutrient absorption, growth and reproductive rates in certain species but this is thought to be the first attempt to quantify the damage it does to marine ecosystems.

"The organisms most affected are protists, such as algae, corals, crustaceans and fish larvae and eggs," she said.

"UVB radiation represents a big threat to sea life because it is affecting marine ecosystems from the bottom to the top of the food web."

The attention of many scientists has been focused on the effect of global warming, ocean acidification and eutrophication in recent years but Dr Llabres said that the evidence suggests UVB radiation, which has risen because of damage to the ozone layer, may be an important and overlooked factor behind the decline:

"Krill decreased 60 times in abundance in the Southern Ocean between 1970 and 2003, while UVB radiation increased considerably during this time interval."

"The decline in corals in the tropics and subtropics is consistent with the increased levels of UVB, so the increase of the water temperature may not be the sole cause of this decline," she said.

Algae are also sensitive to UVB, which is significant because they are "primary producers of the ocean", Dr Llabres told BBC Nature.

"I do not think it is difficult to distinguish the effect of UVB radiation from acidification and eutrophication but all these phenomena are closely related and most likely act together through synergies."

The scientists were surprised that the hole in the ozone layer has been pushed down the environmental agenda in recent years following the success of the Montreal Protocol - the 1987 environmental treaty agreement that aimed to phase out substances that damage the ozone layer, such as chlorofluorocarbons (CFCs).

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New research on acidification

Carbon dioxide pollution from burning fossil fuels has changed the chemistry of the world's seas in a process called ocean acidification. A new international study has added to our understanding of the impact this could have on marine life.

• Evidence already exists suggesting that ocean acidification can limit the ability of marine species to develop their skeleton or shells by making it harder for them to access calcium carbonate in the water.
• Results from this new study suggest that animals such as clams and sea snails have evolved to form lighter shells in places where it is harder to access the required chemicals.
• The study demonstrates the potential for marine life to adapt to changing water chemistry but experts do not know whether marine life will adapt quickly enough, as ocean acidification continues.

Source: British Antarctic Survey

"The Montreal Protocol (first signed in 1987) was successful in avoiding further deterioration of the ozone layer and established the foundations for its recovery, but this recovery has not yet occurred," said Dr Llabres.

"This misconception is surprising given the evidence that high levels of UV continue affecting human health, such as skin cancer and ocular damage."

Scientists observed record destruction of ozone over the Arctic in 2011 and the hole over Antarctica only reached its maximum in 2006, according to figures from the National Aeronautics and Space Administration (NASA).

It is not thought that the hole in the ozone layer will recover for decades, partly because CFCs take around half a century to even reach it, meaning damage may not be evident for a long time after the CFCs are released.

"I think that more investigation should be focused on the UVB effects on marine ecosystems because high levels of UV radiation continue reaching the biosphere actually," said Dr Llabres.

"It will be vital to know how UVB radiation affects the predation between the organisms in the marine communities."

Source: http://www.bbc.co.uk/nature/19170802

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