BROWN TIDES

Where has Aureococcus anophagefferens been found?
Prior to 1999, brown tide blooms had only been found from Narragansett Bay, Rhode Island to Barnegat Bay, New Jersey. The Delaware Inland Bays program tested for it in summer 1998, and found Aureococcus in Little Assawoman Bay. Subsequent sampling revealed Aureococcus in Assawoman Bay, MD. In spite of very low counts, the occurrence of Aureococcus in Little Assawoman and Assawoman Bays was significant because:

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  • Aureococcus had never been found in this area before; 

  • the coastal bays may provide an optimal environment for blooms; and 

  • blooms could have ecosystem-wide impacts if damage to eelgrass and bivalve populations is substantial.

In response to these findings, the Maryland Department of Natural Resources began monitoring the distribution of Aureococcus in Marylandís coastal bays in 1999 at 15 stations during the spring and early summer.  Since that time Brown Tide has been found in all of the Maryland Coastal Bays.  Maryland DNR continues to monitor Brown Tide blooms in the coastal bays each year.

Monitoring
Results:

The bloom conditions observed are of concern, but it is currently unclear whether they were prolonged enough in duration to result in significant impacts to bivalves and seagrasses. Assessments of possible impacts to living resources are being explored. 

Ongoing seagrass and shellfish monitoring programs in this area will continue. Maryland DNR continues to work closely with researchers at University of Maryland and Old Dominion University to better understand the factors that control the growth of this organism in the coastal bays.

In 1999, cell counts identified the algae at modest levels (100,000-200,000 cells/ml) in all major coastal bays and tributaries, except Sinepuxent. Significant levels (greater than 200,000 cells/ml) were observed at Ocean Pines, Tingles Island, Trappe Creek and Taylors Landing stations. a bar graph showing brown tide counts in 1999 from late May to mid July

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Survey results from 2000 sampling reveals cell densities greater than 200,000 cells/ml at Green Run Bay and Tingles Island and densities greater than 500,000 cells/ml at Newport Bay (645,070 cells/ml) and Public Landing (867,003 cells/ml). All the high cell counts were recorded in mid-May through mid-June. By late June, cell densities at all stations had decreased considerably to less than 35,000 cells/ml. a bar graph showing brown tide counts in 2000 from May 8th to July 10th

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In 2001, Category 2 Brown Tide blooms (35,000 - 200,000 cells/ml) were seen in late May in Trappe Creek (112,723 cells/ml), Newport Bay (121,949 cells/ml) and Public Landing (96,286 cells/ml) and in mid-June at Green Point (76,669 cells/ml) and mid-Chincoteague Bay near Public Landing (94,872 cells/ml). Category 3 Brown Tide blooms (>200,000 cells/ml) were observed during mid-June in the Newport Bay (494,158 cells/ml), Public Landing (680,793 cells/ml) and Tingles Island (268,923 cells/ml) areas. See the weekly bloom progression at Public landing.
a bar graph showing Brown Tide, Aureococcus anophagefferens, counts from April 24th to July 11th, 2001

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2002 results showed Category 2 blooms throughout the entire coastal bays except southern Chincoteague Bay and Greys Creek.  Category 3 blooms were documented at the Fenwick Ditch, Newport Bay, Public Landing, Tingles Island and aquaculture sites. 

a bar graph showing Brown Tide counts from April 23rd to October 22, 2002

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Results for 2003 through June 6 indicate that the northern bays, Isle of Wight and Assawoman Bays, are experiencing Category 1 blooms while the lower St. Martin River and Newport Bay have seen Category 2 blooms. Chincoteague Bay has been experiencing a Category 3 bloom.

a bar graph showing Brown Tide, Aureococcus anophagefferens, counts from April 14th to June 4th, 2003

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In 2004, Brown Tide bloomed in the southern bays.  Category three blooms developed at Green Point, Public Landing and Tingles Island.  The bloom at Public Landing lasted for over a month.  Green point has now had a Category three bloom two years in a row and appears to have increased in bloom intensity over time.  Category two blooms were documented at Newport Bay site and were also likely at the Trappe Creek and Nixon sites although bi-monthly sampling did not capture it).

* Adjusted BT counts refers to an adjustment factor that was applied to monoclonal results (new analysis technique starting in 2004) to make them comparable to previous years polyclonal results as well as thresholds established using polyclonal methods. 

View unadjusted monoclonal count data.

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Cool spring temperatures during 2005 kept Aureococcus from blooming in May. However, rapidly increasing water temperatures in early June led to a brief bloom in the southern bays, where water temperatures quickly exceeded the optimum growth range for Brown Tide and the bloom crashed around June 8 (see DNR's continuous monitoring data at Public Landing).  Low level category two blooms were recorded at nearly all the stations south of the Ocean City Inlet. Category three blooms were likely at Public Landing and Taylorís landing although count data are not available.  

* Adjusted BT counts refers to an adjustment factor that was applied to monoclonal results (new analysis technique starting in 2004) to make them comparable to previous years polyclonal results as well as thresholds established using polyclonal methods. 

View unadjusted monoclonal count data.

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For more information contact Cathy Wazniak (410-260-8638) 
or Dave Goshorn (410-260-8639) in DNRís Tidewater Ecosystem Assessment Division.

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