[Global] Red tide is a common name for a phenomenon also known as a harmful algal bloom which occurs when populations of aquatic microorganisms rapidly increase. When it is caused by some species of dinoflagellate algae, the bloom takes on a red or brown color.
These algae, known as phytoplankton, are single-celled protists, plant-like organisms that can form dense, visible patches near the water’s surface.
Not all algal blooms are dense enough to cause water discoloration, and not all discolored waters associated with algal blooms are red.
In some stages of their life cycle, dinoflagellates are free swimming. The movement of red tide is not affected by tide action.
Some red tides including those occurring in the Gulf produce natural toxins and deplete of dissolved oxygen. These frequently kill marine and coastal species of fish, birds, marine mammals, and other organisms.
Red tides in the Gulf of Mexico are a result of high concentrations of the dinoflagellate Karenia brevis, microscopic marine algae that occur naturally but normally in lower concentrations. In high concentrations, its toxin paralyzes the central nervous system of fish so they cannot breathe.
Gulf of Mexico red tide is a natural phenomenon, but the exact cause or combination of factors that result in a red tide outbreak are unknown.
Because red tide causes economic harm outbreaks are carefully monitored. The Florida Fish and Wildlife Conservation Commission provides an up-to-date status report on the red tide in Florida. The National Oceanic and Atmospheric Administration’s National Ocean Service provides a public conditions report identifying areas where HABs may affect human health.
Humans can become seriously ill from eating oysters and other shellfish contaminated with red tide toxin. Karenia brevis blooms can also cause coughing, sneezing, tear production, and itching in beachgoers, boaters and coastal residents. People with severe or persistent respiratory conditions, like chronic lung disease or asthma, may experience stronger adverse reactions. The human illnesses caused by HABs, though rare, can be debilitating or even fatal.
HABs have been reported in every U.S. coastal state, and their occurrence may be on the rise. HABs are a national concern because they affect not only the health of people and marine ecosystems, but also the ‘health’ of local and regional economies.
The occurrence of red tides in some locations, including the Gulf of Mexico, appears to be entirely natural. These algal blooms are a seasonal occurrence resulting from coastal upwelling, a natural result of the movement of certain ocean currents.
Other HABs appear to be a result of increased nitrates and phosphates, which can be abundant in agricultural run-off. Coastal water pollution produced by humans and systematic increase in sea water temperature have also been implicated as contributing factors. Other influences such as iron-rich dust influx from large desert areas are thought to play a major role in causing red tides.
View original article at: Red tide a natural catastrophe