Why in News? ICAR-Central Marine Fisheries Research Institute (CMFRI) has found that coral reefs in Lakshadweep Sea have undergone severe bleaching due to prolonged marine heatwaves.

What are Coral Reefs? Corals are sessile animals attached to ocean floor. When polyps die, their skeletons are used as foundations by new polyps. These stony coral skeletons, over thousands and millions of years, form complex coral reefs (or sea rainforests). Almost all of Lakshadweep’s islands are coral atolls, with their soil largely derived from corals, and extant coral reefs around them.

What is Coral Bleaching? When Corals, because of thermal stress, expel their microscopic algae (responsible for food production), making their tissues transparent and exposing their white skeleton, it is called coral bleaching.

Measuring the Temperature of Corals-Scientists use Degree Heating Week (DHW) indicator (calculated in celsius-weeks (CW))to measure accumulated heat stress (when sea surface temperatures exceeds 1-degree Celsius above maximum mean temperature)in an area over past 12 weeks, by adding up any temperature exceeding the bleaching threshold during that period. Values above 4-degree CW cause significant coral bleaching. Lakshadweep has crossed this threshold.

Are Marine Heat Waves a Problem for Lakshadweep Alone? No, as per Indian Institute of Tropical Meteorology (IITM), Pune, marine heatwaves are impacting complete Indian Ocean. An underwater survey showed that 85% of corals in Gulf of Mannar near Tamil Nadu coast got bleached after 2020 marine heatwave.

What is the Impact of Marine Heatwaves? They threaten livelihoods of coastal communities, tourism and fisheries sectors, and critical marine habitats, including seagrass meadows which experience impaired photosynthesis, reduced growth, and hindered reproductive functions. Coral deaths also lead to accumulation of organic matter, preventing new coral formations and impacting an island’s overall structure.