Marine Heatwaves

Marine Heatwaves



Why in the News?


Scientists from the ICAR-Central Marine Fisheries Research Institute (CMFRI) have documented an extensive bleaching phenomenon affecting the coral reefs in the Lakshadweep Sea due to marine heat waves. Surveys conducted across different Lakshadweep Islands indicate a significant portion of hard coral species experiencing severe bleaching, mainly caused by prolonged marine heatwaves impacting the area since late October 2023.


About Marine Heatwaves

  • Marine heatwaves refer to prolonged periods of unusually warm sea surface temperatures in oceanic regions. These events can have significant ecological impacts on marine ecosystems, including coral reefs, fisheries, and marine life.
  • It happens when the surface temperature of a specific area of the ocean increases by 3 or 4 degrees Celsius above the usual temperature for a minimum of five consecutive days.


Why are Marine Heatwave incidents on the rise in the Indian Ocean?


  • The Indian Ocean has experienced a rapid increase in temperature, rising by 1.2°C per century from 1950 to 2020, with projections indicating even swifter warming at a rate of 1.7-3.8°C per century from 2020 to 2100. This heightened warming has resulted in a notable surge in marine heat waves across the region.
  • Various climate phenomena, such as strong El Niño events and positive phases of the Indian Ocean Dipole (IOD) have played a role in initiating and amplifying marine heatwaves in the Indian Ocean. These climate modes can disrupt ocean-atmosphere interactions, leading to unusually high ocean temperatures.
  • The broader context of climate change, marked by escalating greenhouse gas emissions and global warming, has exacerbated the frequency, severity, and duration of marine heat waves globally, including in the Indian Ocean. Projections from climate models suggest that without significant emission reductions, the Indian Ocean could experience prolonged marine heatwave conditions by the century’s end.
  • Following a marine heatwave in May 2020, an underwater investigation revealed that 85% of the coral reefs in the Gulf of Mannar near the Tamil Nadu coast experienced bleaching.


Adverse impact of Marine heatwaves 


  • Coral Bleaching: One of the most immediate and severe consequences is coral bleaching, where corals expel the algae living in their tissues, leading to loss of color and vital nutrients. This phenomenon weakens the corals and makes them more susceptible to disease, ultimately resulting in widespread coral mortality and degradation of coral reef ecosystems.
  • Distribution of Marine Species: Marine heatwaves can disrupt the distribution and abundance of marine species, leading to shifts in species composition and ecosystem dynamics. Some species may thrive in warmer conditions, while others may struggle to survive or migrate to cooler waters, causing disruptions in food webs and biodiversity.
  • Harmful Impact on Marine Ecosystem: Marine heatwaves can trigger harmful algal blooms (HABs), which produce toxins that can harm marine life and pose risks to human health through the consumption of contaminated seafood. These blooms can lead to mass mortalities of fish, shellfish, and other marine organisms, as well as economic losses for fisheries and coastal communities.
  • Economic Impact:  Marine heatwaves can lead to economic setbacks due to their repercussions on fisheries and aquaculture. For instance, the abalone harvest in Northern Western Australia suffered damage during a marine heatwave in 2011, resulting in financial losses.
  • Marine food chain: Marine heatwaves exert a significant influence on the oceanic food chain by disrupting its foundation, impacting ecosystems, and potentially affecting global food resources. Studies suggest that these heat waves modify microorganisms, notably phytoplankton, which play a vital role at the bottom of the marine food chain.


About Coral Bleaching


  • Coral bleaching is a phenomenon in which coral reefs lose their vibrant colors and turn white due to the expulsion of symbiotic algae called zooxanthellae from their tissues. These algae provide corals with essential nutrients through photosynthesis and contribute to their coloration. 
  • Factors such as increased water temperatures, pollution, and environmental stress can cause corals to expel these algae, leaving them bleached and vulnerable to disease and death. 
  • Coral bleaching is a sign of coral stress and can result in widespread damage to coral reef ecosystems, disrupting marine biodiversity and impacting coastal communities that rely on reefs for food, tourism, and coastal protection.


Why is Coral bleaching in Lakshadweep?


  • Temperature Increase: The Degree Heating Week (DHW) in Lakshadweep has surpassed a critical threshold, with the Lakshadweep Sea consistently experiencing temperatures one degree Celsius above the average since October 27, 2023. Apart from elevated atmospheric temperatures due to global warming, changes in ocean currents also contribute to unusually high water temperatures.
  • Marine Heat Waves: Lakshadweep has been experiencing marine heatwaves since October 2023. If the water temperatures do not decrease, the coral bleaching could lead to the demise of Lakshadweep’s coral reefs. While coral bleaching events have occurred in the Lakshadweep Sea in 1998, 2010, and 2015, the current event’s scale is unprecedented.

About Degree Heating Week (DHW)

  • Degree Heating Week (DHW) is a metric employed to assess the cumulative heat stress experienced in a particular region over the preceding 12 weeks. It involves aggregating all instances where the temperature surpasses the threshold for coral bleaching within this timeframe.


Measures to tackle the problem of Marine heatwaves


  • Sustainable Fisheries Management: Implementing sustainable fishing practices to reduce stress on marine ecosystems and prevent overexploitation of fish stocks. This includes establishing marine protected areas and implementing quotas and regulations to ensure the long-term health of fisheries.
  • Coastal Adaptation and Resilience: Investing in coastal infrastructure and habitat restoration projects to enhance the resilience of coastal communities to the impacts of marine heatwaves and sea-level rise. This can include building seawalls, restoring mangrove forests, and implementing green infrastructure solutions to mitigate flooding and erosion.
  • Climate Change Mitigation: Taking action to reduce greenhouse gas emissions and mitigate the drivers of climate change, such as transitioning to renewable energy sources and implementing energy efficiency measures.
  • Fostering Stakeholder Participation and Resilience: Raising awareness among policymakers, researchers, industries, and local communities is essential for building resilience to marine heat waves. Coordinated responses and collaborative efforts can facilitate the implementation of measures to protect coastal communities and ecosystems. Additionally, diversifying livelihoods and adapting economic activities can help mitigate the adverse impacts of heat waves.
  •  Advance Early Warning Systems: Implementing monitoring programs to track sea surface temperatures and detect the onset of marine heatwaves. Early warning systems can alert coastal communities and resource managers to take proactive measures in response to rising sea temperatures.


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Prelims based Question


Q1. Consider the following statements regarding Corals:

  1. Corals survive well in pollution-free and clear water.
  2. Corals can withstand high-temperature ranges.

Choose the correct answer using the codes given below:

(a). 1 Only

(b). 2 Only

(c). Both 1 and 2

(d). Neither 1 nor 2




Mains based Question


Q1. Discuss the factors contributing to the rise of marine heatwaves in the Indian Ocean and their implications on marine ecosystems. How can these heatwaves be effectively monitored and managed to mitigate their impacts?


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