Algae bloom identified; red tides dissipating

Pictured: drone shots of Cherrystone Creek from Saturday(left) and Sunday(right) shows significantly less ‘red tide’. Photos courtesy of WESR Weather Watcher Andy Dunton.

The harmful algal bloom now affecting waters along Virginia’s Eastern Shore has been identified as Alexandrium monilatum, according to the Chesapeake Bay harmful algal bloom forecasting team, which says recent imagery shows dense patches along the Eastern Shore and across a broad portion of the lower Bay.

The identification is an important update to conditions reported earlier this summer. Scientists had previously been tracking large concentrations of Margalefidinium polykrikoides in the lower Chesapeake. ShoreDailyNews reported Saturday that the bloom had moved toward the Eastern Shore as red tides, fish kills and bioluminescence were being observed along the bayside of Northampton County.

Recent water samples collected by the Virginia Department of Health, the Virginia Institute of Marine Science and volunteers indicate that the current bloom is now dominated by Alexandrium monilatum. NOAA imagery shows dense patches along the Eastern Shore, extending across the Chesapeake toward the Rappahannock River and farther north, along with a smaller patch near the mouth of the York River.

Alexandrium monilatum is a familiar late-summer harmful algal species in the Chesapeake Bay. VIMS says it has appeared almost annually in the lower Bay since 2007, typically when water temperatures are above 77 degrees. The organism can produce reddish water during daylight and intense blue-green bioluminescence at night when the water is disturbed.

VIMS says Alexandrium produces a toxin called goniodomin A and has been associated with deaths of marine finfish, oysters and oyster larvae. Researchers continue studying its effects on marine life and the potential implications for people.

Fish kills, discolored water and foul-smelling water have been reported along the Eastern Shore. The HAB forecasting team said those observations are consistent with the very high chlorophyll concentrations being detected in the bloom. Earlier reports included spot, flounder, menhaden and other fish floating to the surface and washing ashore from Plantation Creek north toward Hungars Creek.

The nighttime glow observed Friday at Smith Beach also fits the characteristics of Alexandrium. VIMS describes the species as capable of producing dramatic glowing waters during dense blooms and has documented similar bioluminescence in the lower Chesapeake and York River.

Conditions appeared to improve somewhat by Saturday. The reddish discoloration known as red tide was much less noticeable and less widespread than it had been Friday, although the latest NOAA imagery continued to show dense algal patches in Eastern Shore waters and elsewhere in the lower Chesapeake.

With a nor’easter expected to affect the region, changing weather could provide some additional relief.

Snyder cautioned that rain can also wash additional nutrients into the water. “The weather — wind and waves — will help break it up and rain will help flush it out a bit, but will also add more nutrient,” Richard A. Snyder, Professor Emeritus at the VIMS Eastern Shore Laboratory said. “Cooler water temps will also help. These are warm water critters.”

VIMS provides a forecasting system that can help aquaculture operators and others working on the Bay anticipate changing conditions. The Chesapeake Bay Environmental Forecast System, or CBEFS, provides current conditions and short-term forecasts for temperature, salinity, dissolved oxygen, pH and other water-quality measurements.

A newer CBEFS harmful algae forecast provides maps showing the estimated probability of encountering a harmful algal bloom, giving shellfish growers and others another tool for making management decisions.

The forecasting team also reported fluorescence farther north in the Maryland portion of the Bay. Samples collected earlier in the week by the Maryland Department of Natural Resources showed a mixture of dinoflagellates rather than the Alexandrium-dominated samples now being reported in Virginia waters.