The severe heat waves across the globe are taking a toll on the underwater life of oceans. One of the significant effects of these heat waves is on the coral reefs causing bleaching. This phenomenon is caused by rising marine temperatures, endangering the delicate marine ecosystems they support. According to US-based National Oceanic and Atmospheric Administration (NOAA), more than 70.7% of coral reefs worldwide have been impacted by severe heat stress since January 1, 2023. Anshika Singh, a marine consultant on India’s Deep Ocean Mission at National Institute of Ocean Technology (MoES) says, “The health of corals depends on a specific temperature range for reproduction and nutrient cycling. This range varies for different species and locations.
When temperatures rise, the beneficial microbes struggle while the harmful ones thrive. This disrupts the delicate balance corals need to survive.”
El Nino Impact
Corals are a symbiotic partnership bet-ween a tiny animal, the coral polyp, and microscopic algae called zooxanthellae that live within the coral tissue, providing it energy. When water temperatures rise above the normal range for extended periods, the stressed coral expels the algae, losing its vibrant colours and vital source of sustenance i.e coral bleaching.
Wenzel Pinto, a researcher at Nature Conservation Foundation, who is currently doing a nationwide research on coral bleaching, says that the research has only just begun and will require considerable effort in analysing data. Although the ocean temperatures in general are on an upward trajectory, the marine heatwaves are the main causal factor in these mass bleaching events. He says, “These heat waves coincide with the El Nino phase of a cyclical weather phenomenon called the El Nino Southern Oscillation event. All the previous global mass bleaching events occurred during the El Nino too (in 1998, 2010 and 2016), and it seems as though the frequency and intensity are increasing over time — likely due to climate change.”
The ICAR-Central Marine Fisheries Research Institute (CMFRI) recently found that coral reefs in the Lakshadweep Sea have undergone severe bleaching due to prolonged marine heatwaves since October 2023. If the temperature rise continues, it can even lead to the decline of corals in Lakshadweep. With reports suggesting over 84% of corals experiencing bleaching in Lakshadweep, this surpasses the severity of previous events in the islands (1998: 81%, 2010: 65%, 2020: 41.9%).
In 2022, a study by the Zoological Survey of India (ZSI) found massive coral bleaching in the coastal areas of the Andaman sea, bleaching up to 83.6% due to the impact of the El Nino event and increased sea surface temperature in 2016. Sangamesh Uday, project coordinator in Andaman and Nicobar Islands for ReefWatch Marine Conservation, says, “As per our latest survey that was done in the month of May 2024, a visual estimate of about 70-80% of coral bleached at Chidiya tapu, Port Blair.” However, the Department of Environment and Forest, Andaman and Nicobar Islands have on-going restoration projects in the Islands. There are six national parks out of which two are dedicated as marine national parks in the Andaman and Nicobar Islands.
Mitigation
The consequences of coral bleaching are far-reaching. Beyond just the tourist attraction, coral reefs are hotspots of marine biodiversity, providing shelter and food for a vast array of fish, invertebrates, and other marine life. 25% of all known marine species reside in coral reefs. If corals are dead or bleached, they will lose their ability to support this rich biodiversity, disrupting the entire marine ecosystem. Also, they serve as breeding grounds for several commercially important fish species, providing food security and livelihood for coastal communities. Wenzel adds, “Coral reefs protect coastlines from storms which are also increasing as a result of climate change. So, coastlines will be more heavily battered by waves. Further, if the corals stop growing, gradually, the calcium carbonate reef will erode away, being unable to keep up with sea level rise, leading to frequent flooding.”
While some coral bleaching is natural and can be recovered if water temperatures return to normal, the current trend of rising sea temperatures due to global warming is causing more frequent and intense bleaching events. This makes it difficult for corals to recover, leading to widespread reef death. Anshika says, “Abroad, scientists are adopting ‘bio-mimicry’, where they design artificial structures resembling real coral. This is showing promising results. However, India seems to be mostly focusing on coral nurseries, transplanting healthy coral fragments to pollution-free areas.” Recently, concrete triangles have been deployed in many places in India to support coral restoration.
Other Factors
Other than the heat waves, the other concerning factor for coral bleaching is microplastics pollution in the ocean. Anshika says, “While scuba diving for samples in the Gulf of Munnar, I saw bleached corals. While temperature is a culprit, microplastic pollution also plays a major role. Anthropogenic pollution and global warming activities are causing a lot of intervention to the already established balance in marine life.” Although there is a lack of quantifiable data on current plastic levels and their breakdown into methane (a greenhouse gas), microplastic pollution not only harms corals but can also contribute to global warming. Sangamesh adds, “The solution to reducing the temperatures is through a global effort by reducing carbon dioxide emissions, use of fossil fuels etc. At a more local level the improvement of water quality and wastewater management, sustainable fishing and tourism practices, reducing deforestation of mangroves and other trees, is essential.” Wenzel says that there are ongoing efforts to monitor coral bleaching in several locations across India — Lakshadweep, the Andaman islands, the Gulf of Mannar and Palk Bay, the Gulf of Kachchh, Goa, Ratnagiri and Malvan.
The health of corals depends on a specific temperature range for it to do functions like reproduction and nutrient cycling.” — Anshika Singh, marine consultant, National Institute of Ocean Technology (MoES)
Coral reefs protect coastlines from storms which are also increasing as a result of climate change.” — Wenzel Pinto, researcher, Nature Conservation Foundation
Beyond just the tourist attraction, coral reefs are hotspots of marine biodiversity, providing shelter and food for a vast array of fish, invertebrates, and other marine life. 25% of all known marine species reside in coral reefs. If corals are dead or bleached, they will lose their ability to support this rich biodiversity, disrupting the entire marine ecosystem.
