NOAA tracks harmful algal bloom in lower Chesapeake Bay

Federal scientists are monitoring an active harmful algal bloom in the lower Chesapeake Bay.  A Virginia marine scientist says the greatest concern for the Eastern Shore is its potential effect on fish, shellfish and aquaculture.

NOAA’s National Centers for Coastal Ocean Science said satellite chlorophyll data show blooms in the lower Bay and major rivers along Virginia’s western shore. High concentrations of Margalefidinium polykrikoides have been confirmed by Old Dominion University, the Virginia Institute of Marine Science and the Maryland Department of Natural Resources.

The microscopic organism can turn the water reddish-brown, creating what is commonly called a “mahogany tide.” It can harm fish and shellfish, particularly young fish and oysters.

“The effect on aquaculture and wild fisheries are perhaps the biggest concerns,” said Richard Snyder, professor emeritus at the VIMS Eastern Shore Laboratory.

Snyder said the term “harmful algal bloom,” or HAB, can cause unnecessary fear because it includes many different kinds of algae. Some species produce dangerous toxins, while others primarily threaten marine life.

The Virginia Department of Health says the species commonly associated with seasonal red and brown tides in the lower Bay have not been tied to human health effects. However, they have been linked to fish kills and shellfish die-offs.

For the Eastern Shore, Snyder said the current bloom appears to be concentrated mainly along the Bay’s western side. Lower-Bay circulation tends to keep those waters there, while water containing fewer  nutrients from the Atlantic Ocean is more common along the Eastern Shore’s bayside.

Mixing can sometimes carry blooms toward the Eastern Shore, however. Snyder said Pocomoke Sound also can develop algae blooms because it is relatively enclosed, but it is not known whether a bloom seen there earlier this month contained harmful species.

Snyder said this year’s weather may have contributed to the size of the HAB bloom, but they happen every year. Drought reduced the nutrients washing into the Bay and helped produce unusually clear water earlier this year. When rain returned, it carried accumulated nitrogen and phosphorus from the land into the water.

“The phytoplankton responded, growing rapidly on the bounty, including HAB species,” Snyder said.

NOAA is using satellites to track the bloom’s location and movement, but these images include all phytoplankton (as chlorophyll). HAB blooms are confirmed in suspected locations by analyzing water samples.  Current observations are available through NOAA’s Chesapeake Bay monitoring system. Suspected blooms or fish kills can be reported through the Virginia Department of Health.