Coral Bleaching in the Indian Ocean and Artificial Reef Restoration
1. What Is Coral Bleaching?
Corals are small marine animals (polyps) that live in large colonies and secrete hard calcium carbonate skeletons, the structure we recognize as a reef. Their color comes from symbiotic algae called zooxanthellae, which live inside coral tissue and supply the coral with most of its energy through photosynthesis. When sea temperatures stay too high for too long, corals become heat-stressed and expel these algae, a process called “bleaching” because the coral loses its color and turns white. Bleached coral is not dead: if the water cools down in time, the coral can regain its algae and recover. But if the heat stress persists (measured by scientists as “Degree Heating Weeks,” or DHW), the coral starves and eventually dies.
2. Why Coral Reefs Matter?
Reefs cover under 1% of the ocean floor but support roughly 25% of all known marine species.
Coastal fishing communities depend on reef-associated fish stocks for food and livelihood.
Reefs act as natural breakwaters, reducing wave energy and protecting shorelines from erosion and storm surge.
Reef tourism (diving, snorkeling) is a significant income source in many coastal regions.
3. The Fourth Global Bleaching Event (2023–2025)
From early 2023 to mid-2025, the world experienced its fourth global coral bleaching event (GCBE4), the most extensive on record. Bleaching-level heat stress affected roughly 84% of global reef area across the Pacific, Atlantic, and Indian Ocean basins, with mass bleaching confirmed in at least 83 countries and territories, according to NOAA and the International Coral Reef Initiative (ICRI). The event was driven by sustained marine heatwaves and record sea-surface temperatures (SST), intensified by the 2023–24 El Niño.
Indian Ocean impacts:
Lakshadweep, India: CMFRI recorded severe, widespread bleaching from October 2023 onward; even relatively heat- tolerant species such as Porites lutea were affected.
Gulf of Mannar and Palk Bay, Tamil Nadu: live coral cover fell from 37% (2005) to 27.3% (2021), compounded by the 2016 bleaching event, overfishing, and algal overgrowth.
Maldives: the 2024 thermal anomaly reached record SSTs of about 31.5°C; live hard coral cover in central atolls dropped by over 40% on average (up to 57% at one lagoon reef).
Chagos Archipelago: up to 85% of coral bleached at some sites (April–June 2024), with roughly 23% average coral mortality recorded afterwards.
Fig. 1. Live coral cover trend, Gulf of Mannar, Tamil Nadu (source: SDMRI/ICRI — see Ref. 5).
4. Artificial Reefs: A Restoration Tool:
Artificial reefs are engineered underwater structures, concrete blocks, steel frames, or mineralised structures, placed on the seabed to provide hard settlement substrate for coral, algae, and invertebrates. They function as habitat while natural reefs recover, giving fish shelter, breeding grounds, and feeding areas. In India, the Department of Fisheries has sanctioned 937 artificial reef units across 11 coastal states/UTs (₹176.81 crore) under the Pradhan Mantri Matsya Sampada Yojana (PMMSY).
Why plain concrete reefs matter?
Most artificial reefs deployed in India, and globally, are not Bio rock but simple precast concrete or stacked-boulder structures, and they remain the backbone of reef restoration for good reason. Concrete units are inexpensive to fabricate at scale, need no ongoing power supply or maintenance (unlike Biorock's electrical current), and can be mass-produced in standard shapes (rings, triangles, cubes) suited to local fabrication yards. At Mithapur, Gujarat, artificial reefs have been built since 2012 by stacking limestone and basalt boulders into stable conical modules; at Rameshwaram, Tamil Nadu, 300 precast concrete modules in triangle, rectangle, and ring shapes were deployed for under ₹40 lakh. This low cost and simplicity is what has allowed India to scale artificial reef placement nationally under PMMSY, covering 11 states, in a way that power-dependent technologies like Biorock, which require continuous low-voltage current, cannot easily match. Concrete reefs also deliver a fast fisheries benefit even before any coral grows on them: their hard surfaces and cavities immediately attract fish seeking shelter and feeding grounds, and CMFRI estimates a single 300 m³ reef unit can support 25–30 non-mechanised fishing boats, translating into a documented two- to three-fold rise in catch rates for small-scale fishers. Concrete reefs also help curb bottom trawling in near-shore waters, since trawl nets cannot be dragged through them, giving damaged seabeds a mechanical break from destructive fishing alongside the biological recovery the reef supports.
Biorock (mineral accretion) technology:
Biorock, also called Seacrete, passes a safe, low-voltage electrical current through seawater via a submerged steel structure. This causes dissolved minerals to crystallise as calcium carbonate (CaCO₃) on the frame, similar in composition to natural reef material and roughly concrete-strength. Coral fragments attached to Biorock structures have been recorded growing four to six times faster than on natural substrate, since the coral doesn't have to expend energy building its own skeleton.
Fig. 2. Simplified schematic of Biorock artificial reef technology.
5. India Case Studies:
Gulf of Kachchh, Gujarat: the Zoological Survey of India (ZSI), with the Gujarat Forest Department, installed the country's first Bio rock structure off Mithapur in January 2020. By 2024, five Biorock units and 2,310 artificial reef structures (over 5,800 sq m) were in place, reintroducing staghorn coral (Acropora), locally extinct for roughly 10,000 years.
Gulf of Mannar and Palk Bay, Tamil Nadu: SDMRI's long-term transplantation programme using concrete frames restored live coral cover at Koswari Island from a post-bleaching low of 17.6% (2016) to 19.6% within a year; restored corals reached sexual maturity within about four years.
Rameshwaram, Tamil Nadu: roughly 300 artificial reef modules deployed about 3 nautical miles offshore at 6 m depth, benefiting fishers from eight coastal villages.
Mandvi, Kutch, Gujarat, The ClimaCrew project:
Alongside its established seaweed cultivation and marine-advisory work in Gujarat and Maharashtra, ClimaCrew has reportedly extended into artificial reef installation, with a project off Mandvi Port, Kutch.
A regional newspaper report (VAVAD Daily, Bhuj edition, p.4, see Ref. 13) describes an artificial reef project roughly 5 km off Mandvi Port, Kutch, with about 60 reef/fish-shelter units.
The reef work reportedly sits alongside, rather than apart from, ClimaCrew's core seaweed business. On the seaweed side, the company works with coastal communities in Gujarat, Andhra Pradesh, Tamil Nadu, and Maharashtra to farm Kappaphycus alvarezii and process harvested Sargassum sourced from fishermen, training over 800 individuals to date, and processes the harvest at a plant in Lote-Chiplun, Maharashtra, into extracts used in agriculture and food processing. The company's site-selection process for that cultivation relies on satellite and oceanographic data to identify coastal stretches with the right seabed and water conditions for cultivation modules to take hold. Rebuilding hard substrate through artificial reef units is one way of improving those grounds: reef structures can help dampen wave energy, curb sediment resuspension, and give a shifting seabed a fixed anchor point, conditions that a newly installed reef zone could, over time, help make more favorable for adjacent seaweed Modules.
ClimaCrew, a platform that draws on satellite and oceanographic data, including NASA GIS feeds, to shortlist candidate coastal patches, with marine biologists then verifying sites on the water; cultivation farms of this kind operate at Mundra, Gujarat, among other locations. The Mandvi reef deployment has been reported in connection with DP World's Marine Services business and the Indian Network on Ethics and Climate Change (INECC), which have partnered with ClimaCrew on related coastal restoration work.
Fig. 3. Precast artificial reef units at a fabrication yard, Gujarat.
Fig. 4. Close-up of a single precast reef unit; holes aid marine settlement.
Fig. 5. Reef units being craned onto a barge for deployment near Mandvi, Kutch.
6. What the Evidence Shows:
Habitat enhancement: artificial reefs reliably attract algae, barnacles, oysters, and fish, sometimes hosting higher fish densities than adjacent natural reefs.
Accelerated local recovery: Biorock and coral transplantation measurably speed coral growth and cover recovery at the restoration-site scale (metres to hectares).
Scale limitation: restoration to date covers a small fraction of degraded reef area. Scientists describe artificial reefs as a tool to restore small areas and support heat-sensitive species locally, not a substitute for reducing ocean-wide thermal stress.
7. Outlook:
NOAA confirmed GCBE4 likely ended in mid-2025, but background sea-surface temperatures remain well above levels recorded 25–30 years ago, so recurrent bleaching is expected. Going forward, artificial-reef and Biorock interventions are increasingly being paired with heat-tolerant coral genotype selection, reef-fish protection (to limit algal overgrowth), and reduced local stressors such as sedimentation and pollution.
References:
[1] NOAA - “World's Fourth Mass Coral Bleaching Event Likely Ended in 2025.” National Oceanic and Atmospheric Administration (NESDIS). June 2, 2026.
[2] GCRMN/ICRI - “The most intense global coral bleaching event on record has likely ended.” Global Coral Reef Monitoring Network. June 8, 2026.
[3] Business Standard - “Explained: How coral bleaching threatens Lakshadweep's marine ecosystem.” Business Standard. May 6, 2024.
[4] Down To Earth - “Rising temperatures trigger widespread coral bleaching in Gulf of Mannar & Palk Bay.” Down To Earth. May 28, 2024.
[5] ICRI - “Coral reefs of the Gulf of Mannar, Tamil Nadu, India: Decadal changes in status and management paradigms” (report by SDMRI and Tamil Nadu Government). International Coral Reef Initiative. January 22, 2025.
[6] GCRMN - “New report highlights the impact of the Fourth Global Bleaching Event in the Chagos Archipelago.” Global Coral Reef Monitoring Network. February 5, 2025.
[7] Coral Reefs (journal) - ecological impact assessment of the 2024 bleaching event across Maldivian atolls. Springer - Coral Reefs journal. 2026.
[8] Mongabay India - “How are degraded coral reefs restored in India?” [Explainer]. Mongabay India. May 2026.
[9] Scroll.in - “How India's coral reef restoration efforts are paying off.”
Scroll.in. June 1, 2026.
[10] The Tribune - “Explainer: Artificial reefs - engineering interventions to rehabilitate India's aquatic resources.” The Tribune. 2025.
[11] UN SDG Partnerships - “Coastal habitat rehabilitation, Gulf of Mannar, Tamil Nadu, India” (SDMRI project record). United Nations Sustainable Development Goals Partnership Platform. n.d.
[12] Drishti IAS - “Coral Restoration Through Biorock.” Drishti IAS. 2024.
[13] “Artificial Reef Project Will Become Important in Marine Life Conservation” (Gujarati). Print article, p.4, describing the DP World/INECC-backed, ClimaCrew-installed artificial reef project off Mandvi Port, Kutch. VAVAD Daily, Bhuj edition. Date on clipping partially legible (“td. 4”; month/year not visible). (print source; no URL available)
[14] Tracxn - ClimaCrew company profile (used to cross-check founder name “Devleena Bhattacharjee” against the newspaper report). Tracxn. 2026.
[15] YourStory - “How this deeptech startup is driving seaweed cultivation along the western coast of India” (background on ClimaCrew's Gujarat/Maharashtra coastal work). YourStory. January 21, 2026.
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