INCOIS identifies nine key algal bloom hotspots along India’s east and west coasts

India’s coastline, rich in biodiversity, is grappling with a growing phenomenon of algal blooms. These events, caused by a sudden surge in phytoplankton biomass, are becoming more frequent and intense owing to environmental and human factors.

In this backdrop, a groundbreaking study, spearheaded by director of the Indian National Centre for Ocean Information Services (INCOIS) T.M. Balakrishnan Nair, identified nine key algal bloom hotspots along India’s east and west coasts.

These are Goa, Mangaluru, Kozhikode, Kochi and Vizhinjam Bay on the west coast and Gopalpur, Kalpakkam, Palk Bay and the Gulf of Mannar on the east coast.

For the first time, researchers have also defined region-specific phytoplankton biomass thresholds for the aforementioned hotspots to detect and classify bloom phases into ‘Likely to Bloom’, ‘Bloom’, ‘Intense Bloom’ and ‘Extreme Bloom’ categories.

The research, done in collaboration with National Institute of Oceanography (NIO) and Berhampur University using cutting-edge satellite data and field reports, showed that factors driving these algal blooms range from nutrient flux during monsoons to coastal upwelling (cooler and nutrient-rich water rising to the ocean surface).

Algae such as diatoms along with dinoflagellates and cyanobacteria dominate these blooms, which have significant ecological implications, said Dr. Balakrishnan. He explained that though phytoplankton is the foundation of the marine food chain, its unchecked growth, often triggered by nutrient enrichment from coastal upwelling or land discharge, can lead to algal blooms.

While some of such algal blooms shore up fisheries, there are also harmful algal blooms (HABs), which disrupt ecosystems, deplete oxygen and produce toxins harming aquatic life and human activities such as fishing and tourism, he said.

Indian coastal waters have been experiencing a rise in algal blooms, but owing to a lack of clear thresholds for Chlorophyll-a (the predominant pigment in marine algae) to identify bloom phases, it could not be identified earlier. The study has also underscored the need for advanced monitoring techniques, including region-specific bio-optical algorithms and enhanced satellite remote sensing.

The southern region of the Indian coast experiences a relatively higher number of blooms in comparison with the northern part. It was also deduced that these blooms occur mostly during the pre-southwest and onset of the northeast monsoon on the east coast. On the west coast, it has been observed that the frequent blooms happen during the southwest and post-southwest monsoon.

Understanding the long-term trends and impact of these phenomena is crucial for preserving marine ecosystems and the livelihoods they support, in view of climate change and human activities exacerbating the frequency and intensity of the blooms. It is also critical for sustainable management of marine resources, fisheries and tourism. said Dr. Balakrishnan.

Other researchers part of the study, titled ‘Determining chlorophyll-a thresholds for characterising algal bloom conditions: An ocean colour remote sensing approach’, are Susmita Raulo, Alakes Sanjiba Baliarsingh, V.V.S.S. Sarma, Sudheer Joseph and Suchismita Srichandan. It has been published in the latest issue of the journal, Science of the Total Environment.

Published – January 23, 2025 08:00 pm IST

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