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News and Resources

Conditions Favorable For Brown Tide Growth in Coastal Bays - July 4, 2010

Dr. Roman Jesien is fascinated by brown tide. Brown tides turn bay water to a characteristic coffee color. They are caused by a microscopic algae (Aureococcus anophagefferens). They were first documented in Maryland in 1998 and have been studied in the coastal bays since 1999.

The organism that causes brown tides on the east coast was first discovered in 1985. Prior to that, brown tide blooms had only been found from Narragansett Bay, Rhode Island to Barnegat Bay, New Jersey. The Maryland Department of Natural Resources began monitoring the distribution of Aureococcus at 15 stations in Maryland’s coastal bays in 1999. Since then, brown tide has been observed in all of the Maryland coastal bays and significant blooms have occurred annually in Newport and Chincoteague Bays.

The coastal bays exhibit environmental conditions conducive to brown tide growth. Brown tides occur when certain algae species reach high concentrations, or "bloom," and discolor water. Some of these algae species can harm some marine life under certain conditions. Scientists call such events "harmful algal blooms," or “HABs.” Not all algal blooms that discolor the water are harmful to the environment.

Development of blooms has been restricted to shallow, relatively well mixed estuaries. Low rainfall, elevated salinities, and elevated nutrients can trigger blooms. Research shows that dissolved organic nitrogen is the preferred nitrogen source and may contribute to sustaining a bloom. Temperature is also a factor. Optimal temperature for growth is 68-77 degrees Fahrenheit, so blooms in the coastal bays usually peak in June and July.

What you may see simply as murky, coffee-colored water captures the attention of Maryland Coastal Bays science coordinator Roman Jesien. "Brown tide is a fascinating opportunistic organism, it can act as plant using simple nitrogen compounds as a food source and, when available, complex nitrogen molecules - something animals do.  We are seeing an increase in large complex nitrogen molecules in the coastal bays, which fuel the brown tide blooms," says Jesien.  

                                                                    

While there are no known human health impacts from brown tides, blooms could have ecosystem-wide impacts if damage to eelgrass and bivalve populations is substantial. The impact on eelgrass appears to be mainly associated with reduced light penetration, as blooms can be so dense that they prevent adequate light from reaching the eelgrass. The impact on bivalves may be by both preventing the animals from feeding on more nutritious forms of algae, and through toxins that may be produced by the algae. Brown tide blooms also coincide with the spawning season of several commercially important bivalves in mid-Atlantic estuaries, thus threatening their reproductive success and population growth.

Strong correlations have been shown between total nitrogen input into estuaries and total phytoplankton production. Of specific interest are the impacts of changing nutrient loads on the abundance and quality of the algal community and whether these loads are related to the proliferation of HABs.

Although scientists have not been able to document specific impacts in Maryland, it is believed that brown tide blooms have limited scallops from re-establishing in the bays, reduced light

to seagrasses, and decreased clam growth.

For more information on brown tides and how you can help to reduce nutrients in the coastal bays, please contact the Maryland Coastal Bays Program at mcbp@mdcoastalbays.org or visit www.mdcoastalbays.org for more information.



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