Harmful algal blooms (HAB), lethal for human beings and marine ecosystems alike, are steadily increasing in intensity in the Indian waters. Researchers have found out that the toxic blooms had increased by around 15 per cent over the last 12 years in Indian seas.
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, according to scientists.
These findings form part of the research data that was generated by a team of marine life experts, including K.B. Padmakumar and V. N. Sanjeevan of the Centre for Marine Living Resources and Ecology, Kochi and N.R. Menon of the Cochin University of Science and Technology, as part of a national programme of the Centre.
The researchers had monitored the harmful blooms and tried to identify the factors causing the bloom, dynamics of bloom formation, spread and its ecological consequences on marine ecosystems. The potentially toxic micro algae recorded from the Indian waters included Alexandrium, Gymnodinium, Dinophysis, Coolia monotis, Prorocentrum lima and Pseudo-nitzschia.
Toxic blooms have been reported from over 30 countries, including India. The first recorded observation on algal blooms in India was in 1908.
The blooms turn lethal for human beings when they consume marine organisms that feed on such algae. Incidents of paralytic shell fish poisoning, following an algal bloom, was reported in 1981 from Tamil Nadu, Karnataka and Maharashtra. Three persons lost their lives and 85 were hospitalised in Tamil Nadu.
In a similar incident at Vizhinjam in Kerala in 1997, seven persons died and around 500 were hospitalised. These people had consumed a mussel, which had fed on toxic algae. Another bloom that hit Kerala in 2004 resulted in nauseating smell emanating from the coastal waters extending from Kollam to Vizhinjam. More than 200 persons suffered from nausea and breathlessness for short duration due to the foul smell. The bloom also resulted in massive death in the region, scientists said.
Scientists had collected algal samples from 1,880 stations during the last 12 years as part of the study. They had also recorded the presence of 422 species of micro algae, including 35 harmful ones. Noctiluca scintillans was the dominant and frequently occurring algae during summer monsoon. While Cochlodinium, Gymnodinium, Gonyaulax and Ceratium bloomed frequently, blooming was an annual affair for Trichodesmium. However, the Noctiluca bloomed at intervals.
It was the Arabian Sea that experienced the most number of blooms over the decades. The Bay of Bengal recorded blooms by and large during the northeast monsoon when cyclonic storms occurred in the region. Global warming and the resultant storminess could also influence the frequency of bloom formation in the Indian seas, scientists said.
Upwelling, formation of mud banks, nutrient discharges from estuaries and run-off from the land during southwest and northeast monsoons cause some algae blooms in coastal waters.
The changing patterns of nutrient ratio of the coastal and the open ocean waters due to anthropogenic activities, increased aquaculture operations leading to enrichment of coastal waters, dispersal of toxic species through currents, storms, ship ballast waters and shell fish seeding activities were some of the factors triggering the blooms, they said.