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Mobtown Beat

In Bloom

Everything you ever wanted to know about the algae causing the Inner Harbor stench

Fish killed in the Inner Harbor by the recent bloom and crash of prorocentrum minimum algae.

By Chris Landers | Posted 6/10/2009

The fire department called it the night of May 25, but the Maryland Department of the Environment (MDE) had been receiving calls about the smell even before the dead fish showed up.

The next morning there were an estimated 3,200 of them in the Inner Harbor, mostly menhaden, but with other species mixed in. Most of them floated near the Maryland Science Center, but they were also spread across the south shore of the harbor from Domino Sugar to the HarborView building, according to a memo sent out by MDE.

The Inner Harbor algae bloom has become an annual sign of approaching summer. The only thing remarkable this year was the smell, which reached as far north as Charles Village and lingered for days. The culprit was Prorocentrum minimum, a long-time and largely innocuous resident of the Chesapeake Bay. It is considered largely harmless, but the organism's recent bloom and subsequent die off provide visible evidence that all is not well in the delicate ecosystem of the harbor.

"In a perfect system, these algae would sort of continue on at optimal levels, not in these bloom-like conditions" explains Mark Trice, program chief of water quality for Maryland's Department of Natural Resources.

Fed by nutrients in the water, supplemented by storm runoff, sewage, and fertilizer from farms, the algae simply grow too numerous to sustain themselves; when they run out of things to eat, they die, and the decomposition of the algae eats up oxygen in the water. The menhaden and other fish become the indirect victims of P. minimum's rapid growth and subsequent crash.

"You can actually consider it like your lawn," Trice says. "These algae are little plants. If you feed your lawn more nitrogen, more phosphorous, more fertilizer, you're going to have more grass. It's the same thing with algae. If you start pumping more nutrients through point sources such as wastewater treatment plants or non-point sources such as agriculture or runoff from lawns, then it's going to fuel these blooms."

P. minimum, and the bloom known locally as Mahogany Tide after the distinctive color of the bloom, occurs around the world. Patricia Glibert, of the Horn Point Laboratory on the Eastern Shore, says that world-wide, there appears to be a correlation between P. minimum blooms and areas of high nutrient pollution. Weather plays a part as well.

"The spring blooms in recent decades," Glibert says, "have been larger than they have been in prior years, although different years have different characteristics. This has been a particularly wet year--a lot of the blooms are associated with [increased] freshwater flow and the nutrients that come with that."

Allen Place, a professor at University of Maryland's Biotechnology Institute, who works out of the Columbus Center on the north side of the harbor, largely agrees with Trice and Gilbert on the crash's cause, although he holds the door open for the possibility that a virus was responsible for the death of the algae.

"There may be other things out there that are causing it to crash," he says, "but the bottom line is it just overtakes all the resources."

P. minimum move to the top of the water during the day for sunlight, then drop down at night to avoid predators like the menhaden. Because of winds in the harbor, they tend to be blown into clumps between the piers, causing an even higher concentration of the algae.

Place cites research based on water samples taken over the past 20 years by the Department of Natural Resources. They show that the characteristic signature of diatoms ("Diatoms are kind of these good grasses of the ocean, basically" he explains) have decreased and the signature of dinoflagellates (a particular type of single-celled organism), like P. minimum have increased.

He gives a reporter a look at a sample of prorocentrum under a microscope in an upstairs laboratory at the Columbus Center.

A young man carrying sample bottles of various species offers an assessment as he hands one of them over: "Prorocentrum isn't very interesting."

Place doesn't exactly agree with him, but he has other dinoflagellates to fry. Save for indirect victims like the menhaden of the harbor, P. minimum is believed to be non-toxic to humans and other species. Other dinoflagellates are not.

If there is a rock star of the algae world, it is likely Pfiesteria piscicida. Widely publicized after a late '90s bloom caused a fish kill in the southern Chesapeake and subsequently linked to health problems in humans, pfiesteria made headlines and was the subject of the book And the Water Turned to Blood, which the Library Journal described thusly: "roused by pollution, a tiny organism in the Chesapeake waters threatens to make the Ebola virus look like a picnic."

Place says he can't speak to the human health effects of pfiesteria, but believes that in the case of the fish kill, popular wisdom has convicted the wrong dinoflagellate. Place found samples of another toxic algae along with pfiesteria in samples from fish-kill areas, and right now he's waiting for Karlodinium veneficum to bloom down at the harbor.

P. minimum, Place says, is not very harmful by itself. At lower densities of the algae, it is fairly trouble free. Karlodinium on the other hand, has a toxin. "It's not a very good plant," he says.

Because P. minimum blooms often precede K. veneficum, Place has been testing the water regularly, and saw the P. minimum grow.

"You can tell immediately because you get this brownish-red color in the water," he says. "It's not new, it's kind of anticipated."

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Tags: polluted harbor, algae, sewage

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