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Making Waves: Episode 32 (August 5, 2009)


… A smaller than expected dead zone in the Gulf of Mexico, but it's still going to be severe
… And New England is hit with an unprecedented red tide

It's Wednesday, August 5th, 2009, and those stories are coming up on this episode of Making Waves from NOAA's National Ocean Service.

(Gulf of Mexico Dead Zone)

We're going to kick things off today with a report that just came out last week about the size of this year’s dead zone in the Gulf of Mexico.

A dead zone is the common name for what scientists call 'hypoxia.' When areas of our estuaries, coasts, or oceans have low levels or no oxygen dissolved in the water, the water is said to be hypoxic. These areas are more often called "dead zones" since most marine life in hypoxic waters either die or -- if they can -- swim away from the area. So a dead zone turns areas in the water that would normally be teaming with life into biological deserts.

So what causes this? Well, dead zones can happen naturally, but the ones that scientists and researchers are most concerned about are those created by or made worse by human activity.

The main thing that fuels the dead zone in the Gulf of Mexico and in many areas is nutrient runoff. These nutrients mainly come from agricultural activity: nutrients, which you know better as fertilizers, are added to crops to help plants grow, but the problem is that all of these nutrients aren’t absorbed by the crops. A lot of the nutrients wash away and are carried in waterways and piped along as wastewater all the way to the ocean.

When these nutrients flow into our rivers and coastal waters, they can stimulate an overgrowth of algae, just like they stimulate the growth of plants on land. The problem is that this often leads to the growth of way too much algae … and when this algae dies, it sinks and decomposes in the water. This decomposition process eats up oxygen … and this cycle can deplete the supply of oxygen available to healthy marine life. In other words, the decomposing algae suck all the oxygen out of the water, and that can cause a dead zone in the water.

The Gulf of Mexico dead zone is a big concern in the U.S. because it’s wreaks havoc on the habitats of species that live there, and it threatens valuable commercial and recreational Gulf fisheries that generate about $2.8 billion annually.

Dead zones occur all over the world. In the U.S. they’re most common along the East Coast, the Gulf of Mexico, and the Great Lakes. I’ll give you one guess where the largest dead zone in the nation is found … Yep, it’s the Gulf of Mexico.

Each year, NOAA provides support for researchers to forecast and measure the dead zone in the Gulf. The forecast this year came out in June, and it predicted that the dead zone could be one of the largest on record – about the size of New Jersey. This prediction was mainly driven by US Geological Survey measurements of the amounts of nitrogen feeding into the Gulf from the Mississippi and Atchafalaya rivers earlier in the spring. Nitrogen is one of the main sources of nutrient pollution. As I mentioned before, the main source of this pollution is from agriculture, but that's not the only source. Nitrogen also comes from things like over-use of fertilizers around homes, discharge from waste-water treatment plants, and overflow from septic systems during storms.

Well, last month, a NOAA-supported survey team led by the Louisiana Universities Marine Consortium measured the actual Gulf dead zone, and it turned out to be smaller than expected, at about 3000 square miles. The researchers also found that the dead zone was quite severe this year. It’s usually limited to water just above the sea floor, but the 2009 dead zone extended closer to the water surface than in most years.

Dr. Nancy Rabelais, the researcher from the Louisiana Universities Marine Consortium who led the expedition to measure the dead zone, said she believed the smaller than expected dead zone is mainly due to unusual weather patterns in the Gulf that mixed up and re-oxygenated the waters.

The director of NOAA’s Center for Sponsored Coastal Ocean Research, Dr. Robert Magnien, said that the smaller size looks good at first glance, but he cautioned that this appears to be related to short-term weather patterns, not a reduction in the underlying cause. He stressed that the smaller area measured by this one cruise doesn’t represent a trend, and it doesn’t diminish the need to find ways to reduce the nutrient runoff problem.

The average size of the dead zone over the past five years, including this cruise, is now 6,000 square miles.

The interagency Gulf of Mexico/Mississippi River Watershed Nutrient Task Force has a goal to reduce or make significant progress toward reducing this dead zone average to 2,000 square miles or less by 2015. The Task Force uses a five year average because the size of the dead zone can vary widely from year to year.


Now let's head up the Eastern Seaboard to New England to talk about a different kind of problem caused by algae.

Early last month, red tide caused a near-complete closure of shellfish harvesting in the state of Maine. Atlantic coastal waters of New Hampshire and much of the north coast of Massachusetts have also been hit hard by blooms of toxic algae.

To give you an idea of the effect of this on the economy, in 2005 harvesting closures caused by red tide resulted in $23 million in lost shellfish sales in Massachusetts and Maine alone.

To help tackle this problem, NOAA recently awarded $121,000 to Woods Hole Oceanographic Institution in partnership with the University of Maine to conduct research cruises to monitor the toxins.

The NOAA emergency funding supports sampling, mapping and forecasting of red tide location and intensity, which will help state managers focus their sampling efforts in areas that have the greatest opportunity to reopen for harvesting. The point of this is to minimize economic impacts in the region while continuing to protect human health from shellfish poisoning.

New England red tide, caused by the toxic algae Alexandrium, produces potent neurotoxins that accumulate in clams, mussels, oysters, and other shellfish. A severe and sometimes fatal illness, called paralytic shellfish poisoning, can occur in humans who eat shellfish contaminated with the toxin. This doesn’t mean, though, that you can’t get shellfish in the store. States have well-established, rigorous shellfish monitoring programs to protect human health, so it’s important to note that commercially available shellfish on the store shelf is safe to eat.

This year's red tide event was consistent with the seasonal forecast issued earlier this year by WHOI and North Carolina State University, which predicted a larger than normal Alexandrium bloom with landfall and effects on coastal resources largely dependent on wind patterns in May, June, and July. This forecast was based on runs of a predictive model, developed over the past decade with support from the NOS National Centers for Coastal Ocean Science's Center for Sponsored Coastal Ocean Research.

NOAA's investment of over $23 million in New England red tide research since 1997 has aided management of these events through new tools for detecting and monitoring red tide, better communication among researchers and managers in the region, and seasonal and weekly forecasts of red tide location and extent.


And that's all for this episode. If you have any questions about this week's podcast, about the National Ocean Service, or about our ocean, send us an email at

Let’s bring in the ocean....

This is Making Waves from NOAA’s National Ocean Service.