• The threat of rising ocean temperatures on marine ecosystems 

While the world watches rising temperatures on land, a more dangerous heatwave is unfolding beneath the ocean’s surface. Marine heatwaves are defined by the duration and intensity of abnormally high ocean temperatures. Sea surface temperature is one of the most common methods used by scientists to measure ocean warming. These heatwaves are driven by a combination of atmospheric conditions, such as high-pressure systems and weak winds, along with changes in ocean circulation that reduce the mixing of warm surface waters with cooler, deeper layers. 

When warm sea surface temperatures persist for at least five days and exceed a threshold beyond the normal range, they are classified as marine heatwaves. During El Niño years, when excessive heat and dry conditions continue, marine heatwaves are more likely to occur. This issue should not be ignored, as the Intergovernmental Panel on Climate Change states that since the 1970s, human activity has been the primary cause of rising ocean temperatures. 

Therefore, as humans, we must pay greater attention and take immediate action to address this issue. Marine heatwaves have severe impacts on marine life. Many of the events that caused extensive coral bleaching and reef deterioration occurred between 2006 and 2015. In 2021, marine heatwaves affected nearly 60% of the world’s ocean surface at least once. 

According to the United Nations Environment Programme, if oceans continue to warm, all of the world’s coral reefs could bleach by the end of the century. In addition, heatwaves can slow the growth of some species, increase the prevalence of diseases in marine organisms, and place stress on mobile species such as shellfish, oysters, and abalone. Marine heatwaves place immense pressure on marine ecosystems, causing coral bleaching and mass deaths of fish, marine mammals, and seabirds. They can also intensify hurricanes and trigger toxic algal blooms. The duration, timing, and depth of temperature changes are key factors that determine how severe these effects are in different regions. 

Marine heatwaves also lead to instability in the food chain, where smaller species may grow out of control while predators lose their prey. For instance, many marine organisms lose their habitats and breeding grounds due to the decline of key species such as coral reefs. As a result, the structure and function of marine ecosystems begin to change, leading to long-term instability. These cascading effects demonstrate that rising ocean temperatures are not isolated events but powerful forces reshaping life beneath the surface.

In the Sri Lankan context, one of the biggest threats facing coral reefs is rising ocean temperature. As mentioned, coral reefs are highly sensitive to environmental changes and increases in temperature can severely impact their health. Additionally, the country has experienced repeated coral bleaching incidents, particularly during global climate anomalies such as El Niño in 1998, 2016, and more recently 2024, highlighting a troubling trend of increasing marine heatwaves. Such events not only reduce biodiversity but also disrupt coastal livelihoods that depend on healthy reef ecosystems. 

Moreover, marine ecosystems in Sri Lanka remain under stress due to the combined effects of ocean warming and acidification, which slow recovery rates. This reflects broader global patterns of ocean-driven ecological transformation. If these trends continue, the long-term sustainability of Sri Lanka’s marine biodiversity and fisheries sector will be at significant risk.

In conclusion, marine heatwaves are changing ocean ecosystems in significant and concerning ways. The impacts extend far beyond individual species and threaten the overall balance of marine life, from coral bleaching to disrupted food webs. As climate change intensifies, these hidden changes will have serious effects on biodiversity, fisheries, and human livelihoods. The future of our seas depends on consistent and immediate action to address rising global temperatures, making it critical to recognise the urgency of this issue

(The author is a volunteer writer of The Pearl Protectors)

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The views and opinions expressed in this article are those of the author, and do not necessarily reflect those of this publication

Picture 01

Dead Menhaden fish washed up on the shores of the upper Texas Gulf Coast on June 9, https://www.nbcnews.com/science/environment/warm-ocean-heat-wave-fall-extreme-weather-polar-ice-rcna89754

Picture 02

Effects & Impacts: Warming oceans & marine heatwaves, https://climateandnature.org.nz/climate-wiki/evidence/marine-heatwaves/

Picture 03

From 2013 to 2016, a mass of sweltering water in the eastern Pacific Ocean, known as the Blob, wreaked havoc on marine ecosystems. This illustration shows how unusually hot the waters were in May 2015, with deepest red representing 3 degrees Celsius above average, https://www.sciencenews.org/article/ocean-extreme-heat-wave-past-climate-new-normal