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Climate Change Shattering Marine Food Chain
Apr 11, 2006
Published on Tuesday, April 11, 2006 by Inter Press Service
 
Climate Change Shattering Marine Food Chain
 
BROOKLIN, Canada -

The loss of reefs will have a catastrophic impact on all marine life.

One-third of the coral at official monitoring sites in the area of Puerto Rico and the U.S. Virgin Islands have recently perished in what scientists call an "unprecedented" die-off.

Extremely high sea temperatures in the summer and fall of 2005 that spawned a record hurricane season have also caused extensive coral bleaching extending from the Florida Keys to Tobago and Barbados in the south and Panama and Costa Rica, according to the U.S. National Oceanic and Atmospheric Administration's Coral Reef Watch.

High sea temperatures are also killing parts of Australia's 2,000-kilometre-long Great Barrier Reef, the world's largest living reef formation. As summer ends in the Southern Hemisphere, researchers are now investigating the extent of the coral bleaching. Up to 98 percent of the coral in one area has been affected, reported the Australian Institute of Marine Science last week.

"The Great Barrier Reef has been living on this planet for 18 million years and we've undermined its existence within our lifetimes," says Brian Huse, executive director of the Coral Reef Alliance, a U.S.-based NGO dedicated to protecting the health of coral reefs.

"Twenty percent of Earth's reefs have been lost and 50 percent face moderate to severe threats," Huse told IPS.

The economic value of reefs globally is estimated at 375 billion dollars, he says.

Coral reefs are uncommon, found in less than one percent of the world's oceans. However, they are considered the tropical rainforests of the oceans because they provide home and habitat to 25 to 33 percent of all marine life. The World Conservation Union (IUCN) considers coral reefs one of the life-support systems essential for human survival.

Reefs are made up of tiny animals called polyps, which create cup-like limestone skeletons around themselves using calcium from seawater. Reefs form as generation after generation of coral polyps live, build and die, creating habitat for themselves and many other plants and animals.

Coral gets its beautiful colors from algae that cover the polyps. The algae produce oxygen and sugars for the coral polyps to eat while the polyps produce carbon dioxide and nitrogen, which enhances algae growth. If coral polyps are stressed by too-warm sea temperatures or pollution, they lose their algae coating and turn white.

Bleached corals can recover if the stress is temporary -- lasting weeks instead of months. In 2002, extensive bleaching of the Great Barrier Reef led to a five percent permanent mortality rate. Reefs in the Indian Ocean and other parts of the Pacific have been hit even harder by warm ocean temperatures over the past few years.

Reefs face a number of other threats from trawling, blast fishing (the use of dynamite to catch fish), pollution, unsustainable tourism and disease, says Huse. Climate change is the most daunting threat of all, in large part because few people realise the impacts their carbon dioxide emissions are having on the oceans, he says.

Every day, the average person on the planet burns enough fossil fuel to emit 24 pounds of carbon dioxide (CO2) to the atmosphere, out of which about nine pounds is then taken up by the ocean. As this CO2 combines with seawater, it forms an acid in a process known as ocean acidification.

There is no debate about the fact that the oceans are becoming more and more acidic due to climate change, says Scott Doney, senior scientist at the Woods Hole Oceanographic Institution in the U.S.

"What isn't known is how marine life will react," Doney said in an interview.

Coral reefs in tropical areas appear to withstand current and future acidification, but new research shows that the recently discovered cold-water corals are highly sensitive, he says.

Cold-water corals are found at depths of 2,000 to 3,000 metres in the North Atlantic and Southern Ocean and to a lesser extent in the North Pacific. Only discovered about 20 years ago, these corals appear to be quite extensive and full of unusual marine life but their full extent has not been documented. And although nearly all of the known reef sites have been damaged by bottom trawl fishing, ocean acidification may be their worst threat.

Like warm-water corals, polyps in cold-water corals take calcium from sea water to make their limestone skeletons. However, there is much less calcium (actually aragonite, a form of calcium carbonate) available at depth and more acidic sea water dramatically reduces what is available. Corals thus form weaker, thinner skeletons or are unable to form them at all.

The calcium levels have already declined in many parts of the world's oceans and by 2100, 70 percent will no longer be able to support cold corals, says John Guinotte, marine scientist at the Marine Conservation Biology Institute in Washington State.

"Corals have no experience with these conditions and are unlikely to adapt in time," Guinotte told IPS.

While Guinotte only looked at impacts on corals, Doney has learned that many other important marine species like types of phytoplankton and small snails that make shells are similarly affected.

"Before 2100, these species won't be able to form the shells they need to live," he said.

Such highly abundant species are an important part of the marine food chain and impacts on the ocean ecology could be devastating.

"There could be a big hit but we don't what it will be yet," said Guinotte. "What we do know is that by the year 2050, the oceans will be very different than they are now."

Copyright © 2006 IPS-Inter Press Service
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Posted: Apr 11, 2006 8:57pm
Ocean “dead zones” cause sex changes in fish, researchers say
Apr 5, 2006

Ocean “dead zones” cause sex changes in fish, researchers say

March 31, 2006
Courtesy American Chemical Society
and World Science staff

Oxygen depletion in the world’s oceans, caused by pollution, could spark the development of far more male fish than female, threatening some species with extinction, a study has found.

A study found that zebra fish raised in tanks with low concentrations of oxygen were more likely to develop male sexual characteristics—even if they were genetically female. (Courtesy NASA)
The researchers, Rudolf Wu and colleagues at the City University of Hong Kong, said the findings raises new concerns about vast areas of the world’s oceans called “dead zones.” 

In these areas, there isn’t enough oxygen dissolved in the water to support most sea life. 

Fish and other creatures trapped there often die. Those that escape may be more vulnerable to predators and other stresses. 

The new study, Wu said, suggests these zones potentially pose a third threat to these species: an inability of their offspring to find mates and reproduce.

The researchers found that low levels of dissolved oxygen, also known as hypoxia, can induce sex changes in embryonic fish. This leads to an overabundance of males that makes it harder for them to find mates and reproduce.

Low oxygen levels also might reduce the quantity and quality of the eggs produced by female fish, diminishing their fertility, Wu added.

In experiments, Wu and his colleagues found low levels of dissolved oxygen—less than 2 parts per million—reduced the activity of certain genes that control the production of sex hormones and sexual differentiation in embryonic zebra fish. 

As a result, 75 percent of them developed male characteristics. This isn’t as bad as it sounds, Wu said, because zebra fish populations are normally about 60 percent male and 40 percent female—but it’s still a problem.

At least some of the excess “male” fish were actually genetically female, but had male sexual characteristics, Wu said, suggesting the oxygen shortage somehow affects sexual development after the genes are in place. It appears to do so by enhancing testosterone levels, his team reported.

“Reproductive success is the single most important factor in the sustainability of species,” Dr. Wu said. “In many places, the areas affected by hypoxia are usually larger than the spawning and nursery grounds of fish.”

Hypoxia is considered one of major threats to marine life and genetic diversity, Wu said. It occurs when excessive amounts of plant nutrients, particularly nitrogen, accumulate in oceans, freshwater lakes and other waterways. This often occurs as a result of agricultural runoff or pollution, but sometimes happens naturally.

These nutrients trigger the growth of huge blooms of algae. These eventually die, sink to the ocean floor and decompose, a process that removes oxygen from the surrounding water. 

Dead zones are developing along the coasts of the major continents, and they are spreading over larger areas of the sea floor, Wu said. The United Nations Environmental Programme estimates nearly 150 permanent and recurring dead zones exist worldwide, including 43 in U.S. coastal waters.

The study was published March 29 on the Web site of the American Chemical Society journal Environmental Science & Technology. The study is scheduled to appear in the May 1 print issue of the journal.

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