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An Overlooked Culprit in the Decline of Marine Wildlife

May 12, 2015

Story at-a-glance

  • Other manmade threats to marine life include dead zones, plastic pollution, and overfishing
  • An international team of scientists has revealed that ultraviolet B (UVB) radiation could be a significant driver in the worldwide decline of marine wildlife
  • Scientists have primarily focused on other causes for the deterioration of marine ecosystems, such as global warming and ocean acidification
  • Misconceptions have contributed to lack of research into UVB radiation and sea life, including the notion that the hole in the ozone layer has been “fixed,” and also that UVB radiation can’t penetrate the depths of ocean waters
  • Based on the international research team’s findings, more investigation should be focused on the UVB effects on marine ecosystems

By Dr. Becker

An international team of scientists studying previous research on the effects of ultraviolet B (UVB) radiation on marine life has revealed a close association between UVB levels and the death rates of, in particular, algae, corals, and crustaceans.

Pollution (chlorofluorocarbon compounds) is eroding the ozone layer, which raises UVB radiation to levels that affect animal and plant life. This research team, which included scientists from Chile, Spain, and Australia, is the first to document the role of UVB radiation in the worldwide deterioration of marine ecosystems.1

What Is Causing the Widespread Decline of Marine Wildlife?

UVB radiation interferes with photosynthesis, nutrient absorption, growth, and reproduction in certain species, but until now, no one has attempted to calculate the damage it does to marine wildlife.

According to Dr. Moira Llabres of the Mediterranean Institute for Advanced Studies in Spain, "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."

Damage from UVB radiation may be a significant but overlooked factor in the decline of marine wildlife, as scientists have been primarily focused on the effects of global warming, and ocean acidification and eutrophication (a form of water pollution).

For example, according to Llabres, krill decreased 60 times in abundance in the Southern Ocean between 1970 and 2003. During the same time period, UVB radiation increased considerably.

"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," says Llabres.2

The Hole in the Ozone Layer Has Not Been 'Fixed'

Llabres and her colleagues are concerned that the hole in the ozone layer is no longer a priority on the environmental agenda. The Montreal Protocol, signed in 1987, is an environmental treaty agreement that seeks to phase out substances like chlorofluorocarbons (CFCs) that damage the ozone layer. The agreement was successful in halting further deterioration of the ozone layer and laid down the foundation for its recovery, but the recovery has not yet happened.

The impact of UVB radiation has not been fully addressed to date thanks to two key misconceptions: one, that the Montreal Protocol "fixed" the ozone layer, and two, that UVB radiation doesn't penetrate to significant depths in ocean waters.

Experts do not anticipate that the hole in the ozone layer will recover for decades, in part because CFCs take around 50 years to reach it.

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

Effect of UVB Radiation on Marine Ecosystems Needs Further Investigation

The effects of the radiation discussed in the study mainly affect organisms that live near the ocean's surface, such as eggs and larvae of invertebrates and fish, which are exposed to very high UVB levels.

But the report also indicates that marine wildlife in the southern hemisphere seems more resistant to UVB radiation than organisms in the northern hemisphere. Also, resistance has increased over time, which suggests that high death rates of sensitive marine organisms in the southern hemisphere, where UVB radiation levels have increased the most, have already selected for more resistant organisms.3

The takeaway is that increased UVB radiation over the last 40 years could be an unrecognized driver of the widespread decline of marine wildlife often attributed to other causes such as climate warming and other impacts.

Other Threats to Marine Life

  • Dead zones. Dead zones are large areas in oceans, lakes, and rivers that don’t have enough oxygen to support marine life. “Hypoxic” (lacking oxygen) conditions are usually caused by eutrophication, or an increase in chemical nutrients in the water – primarily nitrogen and phosphorus from agricultural runoff. The nutrients lead to excessive blooms of algae, which in turn deplete underwater oxygen levels.
  • Other contributors to dead zones are sewage, emissions from vehicles and industrial plants, and certain natural factors.

    Dead zones can be found across the globe, but are predominantly near areas of heavy agricultural and industrial activity that dump nutrients into the water. The most recognized dead zone in the US is an area about the size of New Jersey located in the Gulf of Mexico, in proximity to the spot where the nutrient-heavy Mississippi River, which collects runoff from farms throughout the Midwest, lets out. The hypoxic conditions in that area have resulted in reproductive problems in fish, lack of spawning, and low egg counts.

  • Plastic pollution. Plastic pollution is plastic waste that makes its way from the land to the sea. A recent report published in the journal Science estimates that as much as 13 million tons flow into the sea every year, and the annual pile could get 10 times bigger over the next decade.4
  • Plastic waste, which includes everything from grocery bags to soft drink bottles and even the micro-beads in washed-off makeup, is a rapidly growing problem for the environment. Plastics, which accounted for about 1 percent of solid waste in 1960, are at over 10 percent today. Most goes to landfills, but a significant portion ultimately makes its way to the ocean.

    Researchers estimate that over 250,000 tons of plastic is floating on the surface of the ocean in huge “garbage patches.” Much more lies below, including small broken pieces that are ingested by marine wildlife.

  • Overfishing. Overfishing is a situation in which more fish are caught than can be replaced through natural reproduction. Overfishing has serious consequences to the balance of life in the oceans, as well as the well-being of coastal communities that depend on fish for their way of life.
  • According to WWF:

    "More than 85 percent of the world's fisheries have been pushed to or beyond their biological limits and are in need of strict management plans to restore them.

    Several important commercial fish populations (such as Atlantic bluefin tuna) have declined to the point where their survival as a species is threatened.

    Target fishing of top predators, such as tuna and groupers, is changing marine communities, which lead to an abundance of smaller marine species, such as sardines and anchovies."5

    You can help by purchasing only sustainable seafood. By purchasing MSC-certified seafood products, you can help encourage and reward responsible fisheries.

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Sources and References

  • 1 Global Ecology and Biogeography, Vol. 22, Iss. 1, pp 131-144, January 2013
  • 2 BBC August 10, 2012
  • 3 University World News, August 5, 2012
  • 4 Science, February 13, 2015, Vol. 347, No. 6223, pp 768-771
  • 5 WWF
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