Brown Tide

Algal Identification


Harmful Algal Blooms

Harmful Algal Blooms in Maryland

​Brown Tide
Aureococcus anaphogefferens

This 2 um pelagophyte produces dense ‘brown tide’ blooms that peak in May-mid-July. Common along the Atlantic seaboard generally in long residence time, high salinity lagoon systems.  Its primary N source is thought to be organic and populations reach sufficient densities to shade out underlying submersed grasses and remain largely ungrazed witin the water column. In embayments on Long Island, NY, this organism caused the collapse of the scallop fishery. This algae contains unique pigments and due to its small size and dense accumulations should be detectable remotely.

The first bloom of this species – also known as a ‘Brown Tide Bloom’ because it turns the water a coffee color -- was identified in Narragansett Bay, Rhode Island in 1985.  Since then it has been identified progressively farther south with Maryland currently its furthest southern extent of Category 3 blooms . While there are no known human impacts from Brown Tide, Brown tide blooms can have serious impacts on shellfish fisheries as well as bay grasses.

Aureococcus was first identified in Maryland’s Coastal Bays during 1998. Subsequent analysis of pigment data, conducted by the University of MD, Horn Point Laboratory, has identified the historic presence of Aureococcus in the Coastal Bays in 1993, 1994 and 1995 (the only years these data were available from the National Park Service). The Maryland Department of Natural Resources continues to conduct Brown Tide monitoring in the Coastal Bays between May and July each year. Data collected since 1999 are available.

Learn more about Brown Tide blooms and their documented environmental impacts.


Brown Tide MapDistribution of Aurecoccus anophagefferens in MD





Chart depicting Annual Occuramce of Brown TideAnnual occurence of Aureococcus (2000-2014)