Algae: It's that green stuff that marks the waterline of your boat. It gives the boat ramp its slimy texture at low tide. It's the scum around the edges of your favorite fishing pond as well as the muck that threatened to tangle the Olympic sailing course this summer in China. Usually only a nuisance, algae can thrive when sunlight and nutrients abound, multiplying rapidly till these microscopic organisms actually tint the water with their presence.

Unfortunately, several algae species produce powerful toxins that can kill fish, cause Paralytic Shellfish Poisoning in humans, and harm pets and livestock that swim in or drink the water during a bloom. Scientists call this a Harmful Algal Bloom. Mariners know these as "red tides," though the color of the water varies with the species from brown, to golden, or red in salt water, while in fresh water the blooms are often bright green or even blue.

MOTE MARINE LABORATORYMote Marine Laboratory researchers launch a Slocum Glider, an autonomous underwater vehicle that "flies" underwater using small changes in buoyancy along with its wings to move forward.

In June 2005 the worst red tide in 30 years idled shellfish beds in New England from Maine to Cape Cod. The closure lasted more than one month and cost the shellfish industry approximately $3 million per week. In Florida, red tides harm the tourism industry when officials are forced to close beaches to prevent beachgoers from coming in contact with the red tide toxin.

People who swim during an algal bloom often break out in a rash. The toxin can also become airborne, particularly in the crashing surf of a beach. Inhaling the toxin can cause an itchy throat or more serious respiratory complications, especially among asthmatics.

BLOOM WARNING

Just like beachgoers, boaters should avoid swimming in algal blooms. Simply traveling through large blooms can subject boaters to toxins stirred up by the boat's passing. Personal watercraft riders in particular can be exposed to airborne toxins, probably from being so close to their own wakes.

Unlike beachgoers, boaters don't have lifeguards to warn them away from areas affected by harmful algal blooms. Most boaters are on their own when deciding whether to swim in tinted waters. But that is slowly changing.

Boaters can avoid harmful algal blooms in the Gulf of Mexico thanks to a website http://www.csc.noaa.gov/crs/habf/ developed by the National Oceanic and Atmospheric Administration (NOAA). Using satellites that offer cell count observations of the algal species Karenia Brevis, NOAA can identify and warn the public of harmful algal blooms.

From the Web, boaters and others who use the Gulf of Mexico can view satellite images of blooms that have been confirmed to contain toxic algae by researchers on the ground or on the water. Accompanying the photos are a description of the bloom, usually posted within 24–48 hours of its discovery.

NOAA/UNIVERSITY OF MADISON-WISCONSINWhen severe algae blooms appear in satellite photos like this one of Lake Erie taken in June 2005, researchers respond, testing afflicted waters for the presence of toxins and posting warnings.

Also in the Gulf, Florida's Mote Marine Laboratory researchers, working closely with NOAA, Rutgers University researchers, and others, have developed a red tide detector known as the BreveBuster, a self–contained spectrometer that can identify the harmful species of algae by its own unique "color" or spectra which comes from the blend of pigments used to capture sunlight for conversion into food. The device is named after the species of dinoflagellate, K. Brevis, that produces a neurotoxin that makes people sick.

Dr. Gary Kirkpatrick, a senior scientist at Mote, and his team have deployed two BreveBusters in Charlotte Harbor and one about 20 miles offshore in the Gulf. These three buoy mounted instruments serve as an informal warning system to the Port Charlotte/Fort Myers area, giving the local shellfish growers the advance warning they need to either harvest or move their crop before the harmful bloom arrives.

"We don't have a red tide index for the public yet," says Kirkpatrick. A simplified index similar to a weather service UV index or air quality rating would help convey the severity of a red tide outbreak to the public. Right now, the information produced by the BreveBusters requires interpretation by researchers. But don't rule out an index or similar simple rating in the future.

In 2006, Kirkpatrick's team installed two more instruments linking to NOAA's ocean data buoy service.

In addition, Kirkpatrick's team has fitted the BreveBuster to an autonomous underwater vehicle (AUV) built by Rutgers University researchers that can travel on a two week, unmanned mission and report back its location and the amount of K. brevis in the water at that location by satellite every two hours. These AUVs could be used to confirm the presence of toxic algae in blooms spotted by satellite, eliminating the need for researchers to head out to the blooms by boat to collect samples manually.

"One of our missions is to mitigate the harmful effects of red tide," says Kirkpatrick. Reducing the harm caused by algal blooms is central to much of the research being done all over the country. "We want to reduce their impact. Our information is not quite ready for the public, but other users are taking note."

NOAA provides information on harmful algal blooms in the form of bulletins in many locations. Boaters can check the website http://www.csc.noaa.gov/crs/habf/resources.html for information about their areas.

NOAA/UNIVERSITY OF MADISON-WISCONSINImaging equipment is used to monitor algae as it develops.

As for taking direct action to reduce the extent of algal blooms, researchers have explored several options including spraying the water with a slurry of clay and water, ozone treatment, chemicals, and biological controls, including bacteria and viruses that feed on the algae and reduce the population. Of these, biological controls look the most promising because the pathogen would disappear after the bloom died off, whereas chemicals might persist and cause more environmental harm than good.

But such methods are impractical today owing to the need to maintain a living supply of algae for the pathogens to prey on. In addition, researchers are wary of any attempt to kill off a bloom because the end result might be more toxin in the water all at once instead of over time. For now, learning how to predict harmful algal blooms so that people can stay away from affected areas remains the focus of the research.

AVOIDING HARMFUL BLOOMS

In the Great Lakes and other freshwater estuaries, blue green algae scums can represent extremely high concentrations of microcystin. Accidentally swallowing small amounts of water during a bloom can cause serious harm.

If no scums are visible, but water shows a strong greenish discoloration such that you can't see your feet when standing knee deep, you want to avoid bathing, immersing your head or any ingestion of the water.

Avoid waterskiing in visible scums or waters with a strong greenish coloration because of the potentially substantial risk of exposure to airborne toxins.

If sailing, windsurfing or undertaking any other activity likely to involve accidental immersion, wear clothing that is loose fitting. The use of wet suits for water sports may result in greater risk of rashes as the algal material trapped in the wet suit will be in contact with the skin for longer periods of time.

After coming ashore, shower or wash to remove any algae.

In saltwater, Red Tide toxins are directly related to the amount of algae in the water as measured in cells (individual algae) per liter or gallon. Normal levels of 10–100 cells in a gallon of water cause no detectable problems. But when blooms occur the toxins begin to effect sea life.

When cell counts get up to about 5,000 cells per liter, or approximately 15,000– 20,000 per gallon, shellfish that siphon water in the bloom become toxic to humans.

Shellfish beds are closed at this threshold. When cell counts get to 100,000 to 500,000 cells per gallon, fish kills occur.

At one million cells per gallon the bloom becomes visible in the water by eye and by satellite. The water is very toxic to fish, and shellfish are highly contaminated. There is also a high incidence respiratory problems.