Without venturing into the sea and through in-situ observations, ocean researchers can now quickly understand how parts of North Arabian Sea turn deep green and straw yellow at times.
The real-time assessment and species identification of algal blooms, which add colour to the oceanic waters, has been made possible by using a satellite-based remote sensing technique. Researchers have also developed an algorithm for the process.
A group of ocean scientists from the Centre for Marine Living Resources (CMLRE), Kochi, of the Ministry of Earth Sciences, who had been tracking the algal blooms in many water bodies, claimed to have perfected the algorithm for identification of Noctiluca scintillans, the algal bloom and a diatom, which gives dark green colour to the oceanic waters.
The team led by R. Dwivedi of CMLRE consisted of researchers from CMLRE, the National Centre for Antarctic and Ocean Research, Goa, and Space Applications Centre, Ahmedabad, has described the “approach for detection of bloom-forming algae N. scintillans and its discrimination from diatoms using moderate resolution imaging spectroradiometer in a mixed species oceanic environment.” The research paper was recently published in the journal Environmental Monitoring and Assessment.
The algorithm could be applied for real-time identification of the algal bloom anywhere in Indian waters, said Dr.K.B. Padmakumar of CMLRE.
The new approach will help ocean researchers in quickly identifying algal blooms without venturing into the water. Efforts are on for identification and discrimination of more algal blooms and associated diatoms, he said.
The present “analysis has been carried out by utilising species-specific response of phytoplankton from remote sensing reflectance spectra obtained with a Satlantic underwater profiling radiometer.” The capability of “species identification in near real time can help in planning field campaigns for guiding the ship to an appropriate location for in situ measurements”, the research paper said.
The bloom, also known as green tide, occurs during the winter–spring (mid February–end March) and spreads to the entire northern half of the basin. Researchers had been regularly monitoring the bloom since 2009. During their cruises, researchers had found the colour of water was remarkably dark green in ocean depths exceeding 2,000 metre.
Though not toxic, it is classified as harmful algal bloom as its spread can lead to depletion of dissolved oxygen in the bloom region. The decay of the high biomass can lead to the release of ammonia and steep reduction in dissolved oxygen, which may force other marine organisms to move to safe regions, he said.
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