UV radiation causing rising deaths in marine life

Ultraviolet radiation has caused a steep increase in deaths among marine animals and plants, according to an international team of marine scientists.

They found that the marine life most affected by ultraviolet B radiation (UVB) were protists such as algae, corals, crustaceans, and fish larvae and eggs, thereby affecting marine ecosystems from the bottom to the top of the food web.

The team from the Spanish National Research Council, the Catholic University of Chile and the University of Western Australia synthesised 1,784 published experiments on marine organisms around the world to evaluate the magnitude of impacts caused by increased UVB radiation.

A report on the study was published in the journal Global Ecology and Biogeography.

Until now, the role of UVB radiation as a possible cause of the global decline in the health of marine ecosystems had not been quantified.

The report says a continuous emission of fluorocarbon compounds (CFCs) since the 1970s has led to a reduction of the stratospheric ozone layer and consequent elevated levels of UVB, particularly in the southern hemisphere.

But the impact of increased UVB radiation has not been fully addressed to date because of two key misconceptions: that the Montreal Protocol first signed in 1987 had ‘fixed’ the ozone layer, and that UVB did not penetrate to significant depths in ocean waters.

Although the protocol was effective in preventing further deterioration of the ozone layer, this had not yet recovered and it was now known that damaging UVB radiation could penetrate to considerable depths in clear ocean waters, the paper states.

The latest study builds on evidence of considerable impacts of UVB radiation on marine plankton and ocean processes. The effects of the radiation detailed in the study mainly affect organisms growing near the ocean surface, such as eggs and larvae of invertebrates and fish, which are exposed to very high UVB levels.

But the report says the results also provide evidence that marine organisms in the southern hemisphere are more resistant to elevated UVB radiation than those in the northern hemisphere, and that resistance of organisms in the southern hemisphere has increased over time.

These observations suggest that high mortality of sensitive marine organisms in the southern hemisphere, where UVB levels has increased the most, have already selected for the more resistant organisms.

The experiments included in the research involved organisms and species that had survived after the erosion of the ozone layer caused by CFCs.

Therefore, the results indicate an increase in UVB radiation could have a heavy impact on marine biota; clear evidence of this impact was the reduction in mortality rates of up to 81% when reducing exposure to UVB present in larvae of commercial fish such as cod, anchovies and other organisms, the scientists say.

Increased UVB radiation over the past four decades could be a hidden driver of the widespread decline of marine life, from corals to fish, often attributed to other pressures such as climate warming, overfishing and other impacts, their report says.