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There's Plenty Of Fish In The Sea - And Algae Are Choking Them

Updated: Jun 15, 2023

Is Algae bad news for the Indian coasts?

Finding Nemo's Body by Aveera Juss

There are many threats currently facing our ocean - warming, acidification, deoxygenation, pollution, overfishing, habitat degradation, eutrophication, and sea level rise. All of these issues are not only a detriment to Earth’s biodiversity but also pose a serious threat to the livelihoods and health of millions of people across the globe. Eutrophication, the excessive richness of nutrients in large bodies of water due to land run-off, is a major threat to human health and is becoming increasingly problematic for India’s Exclusive Economic Zone.

India’s two seas, which are land-locked in the northern regions, create an interesting climatic pattern, resulting in seasonal monsoons on either coast. The combination of warmer seasonal temperatures, nutrient run-off and lower salinity from heavy rainfall, and bottom-water upwelling provides ideal conditions for algal bloom events.

Algal blooms occur with relative frequency across the globe in both marine and freshwater environments. A bloom occurs when the environmental conditions allow for the rapid and prolific growth of photosynthetic algae called phytoplankton. The types of phytoplankton typically responsible for these kinds of blooms are diatoms and dinoflagellates. Some of this phytoplankton produce toxins that can directly harm the surrounding wildlife and bioaccumulate and magnify in certain organisms that humans like to eat, like shellfish. The three most common toxic phytoplankton that humans are exposed to cause paralytic, amnesic, and diarrhetic shellfish poisoning. Some regions of the Atlantic have been exposed to neurotoxic phytoplankton.

In addition to the direct threats to human health via consumption, blooms of certain species' composition or size can mean disaster for the local environment. Dubbed a Harmful Algal Bloom, or HAB, these tiny organisms can reproduce so rapidly that they block sunlight from penetrating the water. The lack of sunlight renders photosynthesis impossible and aquatic plants die. If the phytoplankton itself isn’t immediately toxic to the fish, they often die as a result of clogged gills or lack of food. The phytoplankton themselves eventually die, as all things do, resulting in a massive boom of microbial activity. As the microbes decompose the dying and dead plant material, the dissolved oxygen levels in the water drop dramatically, killing anything left in the water.

HABs only occur when a combination of very specific parameters align. Specifically, those conditions that encourage photosynthetic activity, such as nitrogen, iron, warm water, low salinity, etc. And unfortunately, human activities tend to result in these favourable conditions.

The Indian Seas, the Arabian Sea and the Bay of Bengal, have seen a 15% increase in algal blooms in the past two decades. This increase is likely due to anthropogenic nutrient enrichment, or cultural eutrophication, from coastal aquaculture farming, discharged ballast water, and urban drainage. Additionally, increased sea surface temperatures and changes in monsoon frequency and intensity due to climate change can affect the occurrence of HABs.

(Also Read: Feeding the Future)

More frequent HABs are nothing but bad news for the coastal regions of India. HABs have the capacity to indiscriminately eradicate marine life in an area where roughly 3.5 million people rely on marine life for food and livelihood. And unfortunately, there doesn't seem to be much that can be done about it. Sea surface temperatures are likely to continue warming, and surface waters may become more and more oxygen depleted. And so long as monsoons continue in regions of development, nutrients will continue to run into the ocean. HABs will occur with more relative frequency. Fish will die. People will fall ill. And the cycle will continue.

Given our understanding of the conditions that allow for HABs, the best we can do is increase our monitoring capabilities to ensure the fisherfolk’s livelihoods are not completely wiped out. Currently, the Ministry of Earth Sciences with the Centre for Marine Living Resources and Ecology is coordinating a national monitoring program in the Indian Exclusive Economic Zone. Additionally, the implementation of nature-based solutions, such as artificial oyster reefs and mangrove restoration, may help limit some of the factors that facilitate HABs. By trapping run-off water and the nutrients rich sediments, mangroves can sequester some of the nitrogen, phosphorus and iron before it reaches the ocean. Further, nearshore artificial oyster reefs can filter out phytoplankton and nutrient-rich sediments before they have the opportunity to flourish.

Through research cruises and laboratory experimentation, the bloom dynamics, species composition, and location can help scientists understand where and when a HAB may occur. This data can then be used to strategically implement such nature-based solutions, strengthen regional coastal resilience, and better prepare the public for incoming hazards.


D’Silva, M. S., Anil, A. C., Naik, R. K., & D’Costa, P. M. (2012). Algal blooms: a perspective from the coasts of India. Natural Hazards, 63(2), 1225–1253.

Hallegraeff, G. (2017, November 3). Call to Contribute to Global Harmful Algal Bloom Status Reporting. Ocean Biodiversity Information System.

Kahn, M. A. (2000). Anthropogenic Eutrophication and Red Tide Outbreak in Lacustrine Systems of the Kashmir Himalaya. Acta Hydrochimica Et Hydrobiologica, 28(2), 95–101.

Padmakumar, K. B., Menon, N. R., & Sanjeevan, V. N. (2012). Is Occurrence of Harmful Algal Blooms in the Exclusive Economic Zone of India on the Rise? International Journal of Oceanography, 2012, 1–7.

Woods Hole Oceanographic Institute. (2019). HAB Species, organized by syndrome. U.S. National Office for Harmful Algal Blooms.

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