An algal bloom is a rapid increase or accumulation in the population of algae in freshwater or marine water systems, and is recognized by the discoloration in the water from their pigments.
Cyanobacteria were mistaken for algae in the past, so cyanobacterial blooms are sometimes also called algal blooms. Blooms which can injure animals or the ecology are called “harmful algal blooms” (HAB), and can lead to fish die-offs, cities cutting off water to residents, or states having to close fisheries.
Across the planet, blooms have wrecked local ecosystems. Algae can paralyze fish, clog their gills, and absorb enough oxygen to suffocate them. Whales, turtles, dolphins and manatees have died, poisoned by algal toxins, in the Atlantic and Pacific. These toxins have infiltrated whole marine food chains and have, in rare cases, killed people.
The Gulf of Oman turns green twice a year, when an algae bloom the size of Mexico spreads across the Arabian Sea all the way to India.
The coastal States of India may not suffer from the massive algal bloom that has been reported from the Arabian Sea.
Ocean-watchers had earlier reported that a bloom of the size of Mexico, which originated in the Gulf of Oman, had reached the Arabian Sea and feared that it could reach Indian shores.
The algae blooms pose a number of threats to Oman, whose fishing and trading ships have plied these waters for centuries. Thick blooms reduce visibility, making it difficult for divers to repair undersea gas infrastructure. It can also clog the intake pipes of the desalinization plants that produce up to 90 percent of the country’s fresh water.
Those at the Indian National Centre for Ocean Information Services, (INCOIS), Hyderabad, confirmed that the algal species green Noctiluca scintillans had bloomed. The presence of the green algae gives deep green colour to the ocean in the areas of spread.
The current bloom was unlikely to impact the coastal States of the country. The researchers use remote sensing technique for the identification of the bloom species. In-situ studies were also carried out earlier by deploying research vessels to understand the various phases of the algal bloom.
Though the extension of the bloom towards Gujarat coast varies annually, typically it remains about 15 km away from the shore.
When Noctiluca cells degrade, associated detritus in the form of particulate organic carbon sinks to deeper waters. During this process, decomposition occurs by the microbes and oxygen that is dissolved in water is consumed for their oxidation.
The decomposition reduces dissolved oxygen from the water column and causes adverse effect on fish.
Secondly, degrading Noctiluca cells release ammonia in the water increasing toxic level and it causes fish mortality.
Earlier studies in the bloom area had indicated that there was no significant increase in ammonia or decrease in dissolved oxygen during degrading stage of the bloom in the off shore waters of Gujarat.
There were 80 harmful blooms between 1998 and 2010 in the Indian seas against the 38 that took place between 1958 and 1997. The number of such blooms was just 12 between 1917 and 1957.