According to the Seafood Research Institute, the phenomenon is recorded in the eastern part of Cat Ba Island.
Red tide is a common name for a phenomenon also known as an algal bloom (large concentrations of aquatic microorganisms), an event in which estuarine, marine, or fresh water algae accumulate rapidly in the water column and results in discoloration of the surface water. It is usually found in coastal areas.
When the algae are present in high concentrations, the water appears to be discolored or murky, varying in color from purple to almost pink, normally being red or green. Not all algal blooms are dense enough to cause water discoloration, and not all discolored waters associated with algal blooms are red. Additionally, red tides are not typically associated with tidal movement of water, hence the preference among scientists to use the term algal bloom.
Some red tides are associated with the production of natural toxins, depletion of dissolved oxygen or other harmful effects, and are generally described as harmful algal blooms. The most conspicuous effects of these kinds of red tides are the associated wildlife mortalities of marine and coastal species of fish, birds, marine mammals, and other organisms.
In Cat Ba, the red tide is caused by an algae species named sea sparkle or Noctiluca scintillans. This kind of algae has bloomed massively since late March.
N. scintillans itself does not appear to be toxic, but as they feed voraciously on phytoplankton high levels of ammonia accumulate in these organisms which is then excreted by N. scintillans into the surrounding area, which may add to the neurotoxic chemicals being produced by other dinoflagellates, such as Alexandrium spp. or Gonyaulax spp., that do result in the death of other aquatic life in the area.
Experts say that red tide may continue developing so close watch on this phenomenon is a must.
Mr. Bui Trung Nghia, Chairman of Cat Ba Island District, says that red tide only appears on a narrow area so it does not affect catching and aqua-cultural activities.
However, the local government has warned residents about this phenomenon and urged them to take initiative of preventing possibly harmful effect of red tide. Minh Vuong