Indicator Details

Harmful Algal Blooms

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Harmful algal blooms present but small in 2009

There were much fewer harmful algal blooms in the Maryland portion of the bay this year compared to previous years. However, Prorocentrum minimum bloomed throughout the summer in different regions. Prorocentrum is a dinoflagellate that blooms in mid-salinity waters (see Summer forecast for more information). The optimum temperature range for this species occurs in the spring and fall, and as such the majority of blooms were recorded in April and May. In spring we forecasted summer Prorocentrum bloom conditions based on a model that incorporates river flow and water quality. The forecast predicted P. minimum blooms in the Patapsco and the Patuxent River starting in March, and while those blooms did occur, they occurred later in the summer. This could be related to the delayed river flow that occurred this spring. P. minimum was also predicted to occur in the lower Potomac in May and this bloom was indeed recorded. See the Forecast Accuracy page for more information. 

In the spring, scientists forecasted low to moderate Microcystis bloom severity in the Potomac River. Scientists estimated that 9% of samples collected in Mattawoman Creek would contain cell densities at bloom concentrations (i.e., greater than 10,000 cells mL^-1). However, while Microcystis was found in the Potomac River, a bloom did not occur this year. In contrast to the Potomac River, blooms in the Transquaking River occurred from April to September, and at times reached very high densities.

 

There were smaller, localized blooms in several Virginia tributaries but no major blooms. The Elizabeth River continues to have Cocclodinium polykrikoides blooms each year. 

Of concern this year is the detection of Alexandrium monilatum in the lower York River. Alexandrium monilatum was first reported in the York River in 2007 and at a site in the lower Chesapeake Bay. This species has not been seen prior to 2007 in Virginia rivers and the lower Chesapeake Bay in monitoring data that goes back to 1985.  It is a chain-forming species that is considered a toxin producer (able to produce an ichthyotoxin). It is a cyst producer and by invading these various estuaries, it may leave these cysts in the local river sediment, to later re-populate the waters in following years. This species was identified again in the York River in 2008 and 2009, and also in the lower James River in 2008. Its presence these past 3 years is good evidence that it is becoming established within these waters and to expect its presence at these sites in coming years.

There were several macroalgal blooms in the bay, most notably an initially unknown red, moss-like algae in Tangier Sound. Scientists collected samples of this algae and have found it to be Syridia, a red macroalgae native to Chesapeake Bay. It is known to occur in eutrophic (high nutrients) systems. The bloom covered large areas of aquatic grasses around Tangier, forcing watermen to either clear it out of their rakes or fish in other areas. More information can be found on the Bay Daily Blog.

 

 

 

Acknowledgements:
HAB data provided by Cathy Wazniak (MD DNR), macroalgal bloom data provided by Tom Pelton (Chesapeake Bay Foundation). Peter Tango provided the Microcystis forecast and Jon Anderson provided the Prorocentrum forecast.

For more information, see MD DNR Harmful Algal Blooms page and the Harmful Algal Blooms newsletter.