Brown Tide occurs when the alga Aureococcus anophagefferens undergoes a harmful algal bloom (HAB). These blooms are essentially an explosive population growth of many single-celled marine plants collectively known as phytoplankton. Aureococcus anophagefferens can bloom in certain densities and turns the water dark brown, hence the term "Brown Tide." No conclusive evidence exists as to whether these blooms have a direct negative effect on human health, but they do cause excessive harm to many estuarine organisms like scallops, clams, and aquatic vegetation.
Aureococcus is a particularly hardy alga and is well adapted to flourish where its competitors find survival impossible. A study by researchers at Lamont-Doherty Earth Observatory and Stony Brook University has focused on the characteristics that make this alga such a successful survivor. The study has shown that the genes responsible for its ability to survive the murky waters are triggered by conditions typical in estuaries marred by excess human activity. While other photosynthetic algae perish in the absence of sunlight, or when they run out of their ideal inorganic nutrients, Aureococcus can survive days without sunlight and derive nutrition from the plentiful organic nutrients on offer, including sewage and lawn fertilizers. "They can exploit the low inorganic nutrient situations that other algae can't, and they continue to grow even when high cell densities shade out light," says study lead author Kyle Frischkorn.
Researchers have discovered the alga has as many as three times the light-harvesting genes as its competitors. Furthermore, it is capable of manufacturing enzymes that can break down organic nitrogen and phosphorus when inorganic nutrients become less available. Being smaller than most, it also needs a smaller amount of these resources to compete.
As part of the study, a strain of Aureococcus was cultivated under conditions of low light, inorganic nitrogen, and phosphorus. As expected, its light-harvesting genes were activated, as was its ability to exploit alternative forms of nitrogen and phosphorous.
A number of significant advances have been made in the battle against these explosive blooms. While the conditions favoring the blooms are understood, little is known about the cell processes occurring inside the alga. A team of scientists led by Mingming Wu has designed a hydrogel-based microfluidic device that screens multiple environmental conditions known to promote algal bloom and allows the team to analyze algal growth. Indications are that as cell density increases, the algae start to form a colony and behave as a group. Once it is understood how the cells communicate with one another, Wu's team will understand why algae form the way they do and possibly reveal a way to halt the communication.The device is a suspended grid of hollow circles, each containing a small sample of algae and covered by a semi-permeable gel membrane. Varying, recorded levels of nitrogen and phosphorous in the ideal bloom fuels are passed through different circles, allowing the team to identify the exact conditions that spark the sudden growth. "We have now a tool in hand that allows us to quickly dissect conditions under which bloom occurs," Wu said. "We plan to make a heat map that will help other researchers predict and diagnose harmful algal bloom conditions."
In other research, Dr. Elizabeth M. Cosper and Kristen L. Drewes Milligan at the State University of New York at Stony Brook, have discovered a number of viruses that can destroy the Aureococcus alga. These viruses occur naturally with the alga and are believed to control its growth. Preliminary results have shown that in each case, the virus was added to cultures containing Aureococcus, the algae were destroyed. "If we know what's happening, then we have the knowledge to perhaps control the blooms," said Dr. Cosper.
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