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Making Waves: Episode 77 (June 23, 2011)

You're listening to Making Waves from NOAA's National Ocean Service. I'm your host, Troy Kitch.

A couple of episodes ago I told you about our photo contest for World Ocean Day on June 8th. Wow, did we get a lot of submissions. We received over 400 photos from NOS fans here in the U.S. and around the world – from as far away as India and Indonesia. The response was truly amazing.  We picked a few of our favorites and posted them in a gallery on our website, but we had such a hard time picking just a few. So we decided to go ahead and post ALL of the images on our Flickr page at Trust me – it's worth your time to check this out.

Dead Zone Forecast
You know the record setting flooding along the Mississippi River this year? Besides the visible damage caused by the flooding river to towns and property and crops … there's a less-visible problem that we may see down the road as flood waters flow into the Gulf of Mexico.
This is one of the lesser-known side effects of the flooding: as all of that excess floodwater washes over densely populated areas and fields where crops are grown, it absorbs lots and lots of nutrients – chemicals like nitrogen and phosphorus – that come from fertilizers used to grow plants, runoff from urban areas, and wastewater.  These nutrients are carried downstream and eventually end up in the Gulf.
Now, you may think of nutrients as good things, right? We add nitrogen and phosphorus-rich fertilizers to our gardens to make our plants grow better, after all. Well, as is often the case in life, too much of a good thing can be a bad thing.
Here's the problem. As the water from the Mississippi River flows into the Gulf of Mexico … it takes with it all of the nitrogen and phosphorus and other nutrients picked up along the way. Just as nutrients help plants grow in your garden, the nutrients in the Gulf of Mexico carried from inland sources help algae in the water grow in great quantities. There are two problems with this. First, algae can grow in such vast numbers that it can block out sunlight that plants like sea grass need to survive. Second, when these large blooms of algae eventually die off, the decaying process can suck up most of the oxygen in the water in that area.
This can lead to areas with very little oxygen left in the water. It's a condition called hypoxia, but you'll often hear these oxygen-starved areas of water called 'dead zones.' Some creatures can escape out of these zones to water with more oxygen, but many plants and animals can't get out of the area and die.
Hypoxia is a continuing problem in the Gulf of Mexico. Each year, the size of the 'dead zones' in the Gulf vary, which has a lot to do with the quantities of nutrients that are picked up from inland sources, carried down the river, and dumped into the body of water.  Even when there's not a flood, there
are still large quantities of nutrients picked up by the river as it flows through urban areas and farmland.
But as you might imagine, flooding leads to more nutrients in the water.
And so it goes with this year's unprecedented flood season. A new forecast released last week predicts, in fact, that this year's Gulf of Mexico's hypoxic zone may be the largest ever recorded.
Scientists are predicting the area could measure between 8,500 and 9,421 square miles, or an area roughly the size of New Hampshire. If it does reach those levels it will be the largest since mapping of the Gulf "dead zone" began in 1985. The largest hypoxic zone measured to date occurred in 2002 and encompassed more than 8,400 square miles.
The actual size of the 2011 hypoxic zone will be released following a NOAA-supported monitoring survey led by the Louisiana Universities Marine Consortium between July 25 and August 6. This annual forecast is delivered by a team of NOAA-supported scientists from the Louisiana Universities Marine Consortium, Louisiana State University and the University of Michigan. It's based on Mississippi River nutrient inputs compiled annually by the U.S. Geological Survey.
Check our show notes for more details.

Red Tide
Now we're going to shift from talking about algal blooms that lead to 'dead zones' to algal blooms that produce toxins. You probably know these better as 'red tides.'

Now, algae are usually harmless and very important because they're food for many animals…but at times when they bloom out of control, some types of algae start to produce powerful toxins that kill fish and make shellfish dangerous to eat. These toxins threaten marine ecosystems, they're bad for human health, and they cost local and regional economies millions of dollars every year through fishery closures, and recreation and tourism losses because vast swaths of water have to be closed off until the threat passes.

But why do some species of algae produce toxins? It's a long-running mystery. Scientists have suggested that possible functions of the toxins include aiding prey capture, deterring grazers, or inhibiting growth of neighboring algae. Now, new NOAA-funded research points to a new possibility.

Last week, researchers at Texas A&M University published a paper in the Proceedings of the National Academy of Sciences on why so-called "red tide" algae in the Gulf of Mexico produce toxins. Graduate student Reagan Errera and oceanography professor Lisa Campbell in the College of Geosciences identified a trigger for production of brevetoxin, the potent neurotoxin found in a common type of harmful algae found in the Gulf of Mexico called Karenia brevis. The new study suggests that as red tides move onshore and mix with fresher water, the Karenia cells must adjust rapidly to the change in salinity. As they adjust, brevetoxin within the cell increases to allow cells to keep their water and salt content more in balance.

In their report, the researchers demonstrate that brevetoxin production increases dramatically when cells are shifted from higher concentrations of salt typical of the open ocean to lower salinity typical of coastal waters. In fact, the study says, the transition to lower salt environment triggered a 14-fold increase in brevetoxin.

What can this new research do for us? Quay Dortch, program manager for NOAA's Ecology and Oceanography of Harmful Algal Blooms, said that "now that we have a plausible explanation for why Karenia brevis produces toxins, it will help coastal managers, public health officials, and others prepare for and respond to the impacts. We now understand that maximum toxicity will occur in the zone near the coast where shellfish are harvested and where people are exposed to toxic aerosols, especially when near-shore salinities are low."

And that's good news...

…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 — or if you have an ocean fact you'd like answered — send us a note at
This is Making Waves from NOAA's National Ocean Service.