Brown tides are a regional phenomenon that was first observed in Narragansett Bay, RI and the coastal bays of Long Island, NY in 1985. Recently, the brown tide organism, a minute (ca. 2-3mm) alga (Aureococcus anophagefferens), has caused blooms in New Jersey and Maryland's coastal bays. The organism has been detected in Delaware coastal bays but has not bloomed there.

For the last three years (1999-01), New Jersey coastal bays, especially Little Egg Harbor and Barnegat Bay, have experienced severe brown tide blooms. These blooms, which may turn water a yellow-brown, are not harmful to human health, but may cause significant ecological impacts on shellfish and seagrasses. Brown tides may harm marine life by:

• Reducing shellfish growth,

• Reducing a key link in the food web, and

• Reducing available nursery habitat (submerged aquatic vegetation) for fish and shellfish.

A dense brown tide may have other effects on commercial or recreational uses such as fishing and bird watching. Fish and birds may temporarily move to other areas because they can't see their food. In addition, the color of the water may be aesthetically unpleasing to boaters and swimmers who prefer clearer water.

In 2001, the DEP established the Brown Tide Assessment Project because of limited data on previous brown tide blooms. Results of two years of systematic sampling indicated that significant brown tide blooms recurred in 2000 and again in 2001 since first documented in 1995 and 1997. Brown tide blooms usually occur in June and may extend through August. In 2000, brown tide blooms occurred in June but subsided by July, but in 2001, the blooms began in mid-May and extended through June with a significant secondary bloom in Little Egg Harbor in early September.

Recently, the 2000-01 data were analyzed using the newly developed Brown Tide Bloom Index (Gastrich & Wazniak, 2001). This Index provides a reference of the severity of brown tide blooms by relating concentrations of Aureocococcus to documented natural resources impacts. Similar to those observed in the mid-1990s, the most severe type of blooms, Category 3 blooms, recurred in southern Barnegat Bay, Little Egg Harbor, and Great Bay during 2000 and 2001. Category 3 blooms are greater than 200,000 cells per milliliter and are characterized by a yellow-brown discoloration of the water. These blooms can cause feeding rates of mussels to be severely reduced, recruitment failure and mortality of bay scallops, significant growth failure of hard clams, negative impacts to eelgrass, and negative impacts to other organisms (e.g., copepods and protozoa).

While monitoring confirmed that severe blooms occurred in areas that had experienced them in the past, lower concentrations of brown tide, classified as Category 2 blooms (>35,000 to <200,000 cells per milliliter), occurred in Raritan Bay, northern Barnegat Bay, Great Bay and Great Egg Harbor - areas where brown tide blooms were not expected. Category 2 blooms usually do not discolor the water so they are not as noticeable as heavier blooms, but they have potential negative impacts including: a reduction in growth of juvenile hard clams, reduced feeding rates in adult hard clams, and growth reduction in mussel and bay scallops. Category 1 blooms (<35,000 cells per milliliter) occur at most all monitoring stations throughout the year but have no reported negative impacts.

Although there are numerous hypotheses, the cause of brown tide blooms is not fully understood. Unlike other algal blooms, brown tide blooms are not the usual 'nutrient story' in that they do not seem to be promoted by increases of dissolved inorganic nitrogen (DIN) that may occur as a result of nutrient enrichment from anthropogenic activities. The brown tide alga, Aureococcus, may have a unique niche in that it can utilize a different form of nitrogen, dissolved organic nitrogen (DON). It is hypothesized that a shift in the ratio of DIN to DON may occur in the water column due to changes in groundwater flows - making DON more available to Aureococcus. Alternately, die-offs of other algal blooms, sometimes macroalgae (seaweeds), can make DON more available to Aureococcus and may trigger a brown tide bloom. Long-term datasets in Long Island appear to show that brown tide blooms are positively correlated with higher salinities (>26 ppt) and inversely correlated with groundwater discharges and DIN. In these bays, groundwater is the dominant source of DIN (timed lag groundwater discharge of fertilizers used in earlier decades). During low ground water flows, DIN levels fall while DON levels increase, setting the stage for a bloom because Aureococcus can continue to grow using DON. However, in addition to an analysis of the groundwater flows and inputs, other environmental factors will need to be assessed in order to provide a comprehensive characterization of the problem.

Why do some coastal areas in New Jersey have more severe brown tide blooms than others? Environmental and water quality factors, such as the ones described above, need to be analyzed and compared in both areas having brown tide blooms and those that do not. This should also include an analysis of land uses in the areas where severe brown tides occur.

For additional information about brown tides, please contact Mary Downes Gastrich, Ph.D., Division of Science and Research at mdownesg@dep.state.nj.us.