(May 3, 2019) An unusual “Mahogany Tide” is affecting Worcester County’s coastal bays and some experts say changes to the average person’s lawn care routine could help to stem the occurrences.

According to a March 19 post from the Maryland Department of Natural Resources, coastal bay areas experienced an unusual bloom of the microscopic algae Prorocentrum minimum last winter.


The microscopic algae Prorocentrum minimum has been blamed for the “Mahogany Tide” seen locally in some coastal bay areas, according to the Maryland Department of Natural Resources.

Large algae blooms, or rapid increases or accumulation in the population of algae, occur when cell counts exceed 3,000 cells per milliliter and can give the water a reddish-brown coffee color. Harmful Mahogany Tides of more than 10,000 cells per milliliter “are typically observed during May in the Chesapeake Bay and April to June in the Maryland coastal bays,” according to the department of natural resources.

“Bloom levels have previously been observed during the winter when unseasonably warm weather occurs, but not like the scale and duration of the bloom this winter,” a department statement said. “Potential harmful effects include decreasing light to bay grasses, as well as contributing to the dead zone when the large bloom of algae dies and decays. This can lead to fish and shellfish kills.”

The species is not known to produce toxins in harmful to humans.

Elevated levels were observed in November and December in the Isle of Wight and Assawoman bays, and the blooms were reportedly caused by “record setting rainfall last year, along with elevated winter water temperatures in November and December.”

The overabundance of algae died in January and February, leading to large accumulations of sea foam in some areas. According to the department of natural resources, “sea foam is a natural occurrence when there is a large amount of organic material from decaying algal blooms in sea waters that are then agitated by wind and waves.”

Samples collected by the Maryland Department of the Environment in February, along with other samples collected by the Assateague Coast Keeper in March and analyzed by the Maryland Department of Natural Resources last month, “indicate Mahogany Tide concentrations are on the rise with the warmer weather.”

Assateague Coastal Trust Executive Director Kathy Phillips said she received reports late last year of “a really mucky foam” being pushed up into certain areas, especially after periods of heavy winds.

Phillips said she drives over Heron Creek on Route 50 every day and “kept noticing the color of the water.” After contacting the department of natural resources, Phillips confirmed the culprit was algae blooms.

“It’s more of a problem for water quality and, if it gets really bad, it can then impact the submerged aquatic vegetation, [and] it can impact crabs and small fish. If it gets bad enough, it can begin to create a dead zone and we might see fish kills,” Phillips said. “If the concentration becomes heavy enough, there is no light getting through the water and that starts to cause problems.”

Ocean City Today last week reported on a bizarre occurrence of sea foam or a similar substance plaguing some Montego Bay residents. Phillips said she tested the water in that area last week and found nothing out of the ordinary.

She said the Mahogany Tide has been seen in the areas of Heron Creek, Manklin Creek, Turville Creek, Greys Creek, and along the St. Martin River.

“We’re also seeing it in the canals in Ocean Pines and Ocean City,” she added.

Phillips said high nutrient levels, including an overabundance of phosphorus and nitrogen, could cause a Mahogany Tide. Other factors include higher-than-usual water temperatures and certain weather conditions.

She said one of the easier ways to reduce nutrient runoff into local waterways is to use alternatives to traditional lawn fertilizers.

“Even if you’re not waterfront, don’t fertilize if there’s rain in the forecast,” Phillips said. “Some of that fertilizer is going to wash off in a heavy rain and it’s going to get into the ditches, it’s going to get into the canals, and eventually it’s going to get out into the bay.”

Assateague Coastal Trust released a document titled “Ten Ways to Keep Your Lawn Green and Protect Our Waterways.”

They are:

1. Your lawn should not be moved any lower than 3 1/2 inches.

2. Lawn clippings should be left on the lawn.

3. No phosphorus fertilizer should be applied, except as indicated by a soil test.

4. Enhanced efficiency controlled release products may be applied at no more than 2.5 pounds per year per 1000 square feet, with a maximum release rate of 0.7 pounds of nitrogen.

5. A single fertilizer application may not exceed 0.9 pounds total nitrogen per square feet.

6. When spreading fertilizer, the application must target the lawn. No fertilizer should get on impervious surfaces.

7. To combat pests, Integrated Pest Management should be used, beginning with over seeding and core aeration. Pesticides should be used only as a last resort after specific pests have been identified. Only natural remedies such as Milky Spore should be used for general application. Other treatments should be used only on a spot-treatment basis.

8. Only corn gluten meal products should be used for pre-emergent weed prevention. Other herbicides should not be used for general application and should be used only on a spot-treatment basis. (If applying fertilizer later in the season, the nitrogen in corn gluten meal must be taken into account, therefore lowering the amount of nitrogen needed later in the season).

9. Do not apply fertilizer within 15 feet of waterways. (ACT suggests no pesticides or herbicides within six feet of waterways as well).

10. Fertilizer and pesticides must not be used within 12 hours of a predicted rain event and also may not be used between Nov. 15 and March 1, due to plants’ inability to soak up nutrients in cold weather.

To report fish kills or other algae-related issues, contact the Maryland Department of Natural Resources Bay Hotline at 877-224-7229.

Josh Davis is an MDDC award-winning editor and reporter at the Bayside Gazette and Ocean City Today newspapers, covering Berlin and Ocean Pines, Maryland. He is the author of three novels, including 'Vanishing is the Last Art' (2012). He lives in Berlin.

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