Red tides have been observed in the earth's waters for centuries. Native Americans along
the west coast of the United States learned long ago to identify red tides based on the bioluminescent signatures, similar to the light produced by fireflies, of certain algae living in the nearby ocean. As
it turns out, these particular bioluminescent algae also have a reddish pigmentation, hence the term "red tides," and produce toxic compounds that make red tide events in that region so dangerous.
Of the thousands, perhaps millions, of species of marine algae in the world, only a small handful are known to be sufficiently toxic to cause concern.
Most algae exist harmlessly, using sunlight to produce complex carbohydrates from carbon dioxide and water. Algae are at the base of the marine food web, and it is here that the toxic species, largely
unrecognized, are consumed with their nontoxic cousins by small zooplankton. These zooplankton are then eaten by larger organisms, starting a cascade that can travel up the food chain with deleterious
effects on fish, birds, sea lions and whales, and on unsuspecting humans who dine on the affected fish. Shellfish also consume the toxic algae over time, concentrating the toxins to extremely high levels
before they, in turn, are eaten by humans. There is an increasing awareness in the scientific community that red tide events are growing in magnitude and severity, and are occurring in more and more
geographically dispersed locations. There are five different types of red tides worldwide, and not all of the algae that produce these harmful effects feature the telltale red pigmentation. Thus it is
possible to have a deadly "red tide" event without the water actually turning red. For this reason, scientists now tend to label these events "harmful algal blooms" (HABs) rather than red tides. In
addition, most of the algae that manufacture toxic compounds do not emit bioluminescent signals like those on the U.S. west coast, and thus are not so easily identified. It is all too frequent that HAB
events are only conspicuous once marine animals experience unexpectedly high mass mortality rates or when human illness, and even death, can be traced to toxins associated with HABs. Scientists cannot be
certain that red tide events are actually becoming more geographically dispersed, but there is ample evidence that many areas, free of red tides throughout history, have recently begun to experience these
events. Similarly, scientists cannot state definitively that HABs are occurring with greater frequency and for longer durations. However, there is considerable concern that eutrophication, such as that
caused by fertilizer runoff or by leakage from septic systems placed too close to coastal waterways, plays a significant role in "feeding" red tide algae. Marine algae populations are thought to be limited
by the availability of nitrogen or, less likely, by phosphorus or iron. If these nutrients are being supplied in excess via eutrophication, more algae, including the algae that produce toxins, can grow.
One of the most prevalent types of red tide events is referred to as paralytic shellfish poisoning (PSP). Algae associated with PSP manufacture a toxic compound that blocks sodium channels, the basis for
nerve conduction in animals, including humans. People who consume shellfish that have been filter feeding on the algae that make PSP toxins experience symptoms that include numbness and general paresthesia
(burning, tingling or itching) in the face, throat and extremities, and, in extreme cases, death via respiratory failure. PSP toxins, known scientifically as saxitoxins, are produced by algae
from arginine and acetate. What scientists do not know is which of the algae's genes are involved in this manufacturing process. Discovering these genes is the focus of my research team at BBSR. Why spend
time identifying the saxitoxin genes? We know that only a few species of algae make the toxin and that they appear periodically in the water. Relatively simple laboratory experiments have shown us that both
toxin content (i.e., toxin per cell) and toxin composition (the ratio of different saxitoxin ingredients) are affected by growth conditions, such as water temperature and the availability of nitrogen.
However, because we lacked the molecular tools to analyze the saxitoxin genes, scientists know virtually nothing about the basic cellular and molecular mechanisms that are at the heart of environmentally
mediated toxin production. Using the modern tools and techniques of molecular biology, we are now able to identify which species of algae are toxic and to determine if they are experiencing growth
conditions that favor high or low levels of toxin production. Even more importantly, these technologies can now be expanded to real-life situations. For example, we are collaborating with other laboratories
to develop buoys equipped with robotic devices that sample the surrounding water at timed intervals. Each sample is pulled into the buoy, where another robotic device extracts DNA and analyzes it for the
presence or absence of saxitoxin genes. In a more complex scenario, the robot performs tests to determine whether the mRNAs necessary to direct the synthesis of the enzymes that are required for toxin
production are present. In an even more complicated test, the robot determines if the enzymes themselves are present. The device then relays the information to shore, indicating whether or not shellfish in
the area are currently safe to consume. Our overall research goal is to make it safer for humans worldwide to eat seafood, and to help unlock the mysteries behind blooms of algae in the ocean, whether
they are toxic or not. So why do we conduct this research in Bermuda? First, the potential for HABs to occur in this area is very real. For example, algae known to produce toxins responsible for ciguatera
poisoning were identified in Bermuda in 1996 by scientists attending the International Symposium on Harmful Algae. A recent case of ciguatera poisoning on the island further reinforced this potential,
although at present it remains just a theoretical possibility. Second, red tide research provides an opportunity for BBSR scientists to study internationally significant issues using the tools of
molecular biology. As the scientific community recognizes the need to work at the molecular level when dealing with larger issues, such as global climate change, it is vital for BBSR to continue to develop
its infrastructure in this area, both intellectually and physically. Research on red tides provides a funding platform for enhanced molecular studies; together with the addition of the new Michael R. Naess Laboratory,
it will allow us to move forward into other areas with potentially greater rewards. |
