Mahogany tide losses raise serious concerns for Shore’s oyster growers

Editor’s note: We would like to clarify our use of the name ‘red tide’ for the past week’s Harmful Algal Bloom (HAB) event. While ‘red tide’ is generic phrase for any type of reddish water from an algae bloom event, this particular event is more accurately called a mahogany Tide. Why is this important? A red tide is more specifically caused by a related organism common to the Gulf of Mexico that is harmful to not only fish and shellfish, but also mammals, including humans. The mahogany tide, a dark reddish brown bloom in the Chesapeake is caused by two different species, both affect fish and shellfish but are considered not to be harmful to humans.

Concern is growing across the Eastern Shore’s aquaculture industry over potentially significant oyster losses linked to the harmful algal bloom, or Mahogany tide, that has affected portions of the Chesapeake Bay and Eastern Shore waters in recent weeks.

Forty-nine people attended a meeting Wednesday evening hosted by the Virginia Cooperative Extension to discuss the bloom, its effects on oyster growers and the process of determining the economic damage to the industry.

Representatives from Virginia Cooperative Extension, VDACS, the U.S. Department of Agriculture’s Farm Service Agency, the Virginia Institute of Marine Science, Virginia Tech’s Seafood Agricultural Research and Extension Center and Old Dominion University participated in the meeting.

A major focus was determining the extent of oyster mortality and putting a dollar figure on the losses.

VIMS faculty provided growers with information on sampling oysters to determine mortality rates and develop a more accurate picture of losses. Faculty members at the Virginia Tech Seafood AREC will work with growers to calculate the broader economic impact on the aquaculture industry.

Old Dominion University researchers are continuing efforts to monitor and map the bloom and improve the ability to track future harmful algal events.

The meeting follows several weeks of unusual conditions in the lower Chesapeake Bay. ShoreDailyNews reported last week that red or reddish-brown water, fish kills and later bioluminescence had been observed in bayside waters of Northampton County as a large harmful algal bloom moved toward the Eastern Shore. While we initially reported it was a red tide, it was actually a Mahogany tide, which refers to algae blooms with the Alexandrium monilatum and Margalefididium polykrikos identified last week.

Subsequent sampling identified the bloom affecting Eastern Shore waters as being dominated by Alexandrium monilatum. VIMS says the organism produces the toxin goniodomin A and has been associated with mortality in marine finfish, oysters and oyster larvae. Recent satellite imagery showed dense patches of the bloom along the Eastern Shore and across a broad portion of the lower Chesapeake Bay.

While visible Mahogany tide conditions had diminished considerably in some areas by the weekend, the economic consequences for oyster growers may take considerably longer to determine.

Aquaculture producers who have experienced losses are being urged to report them to the USDA Farm Service Agency office in Accomac. Officials said documenting those losses is important so the damage can be quantified as officials determine whether conditions could support a USDA disaster declaration.

The effort now underway will combine information from individual growers with scientific sampling and economic analysis to establish how widespread the losses are and their total financial impact on Virginia’s aquaculture industry.