RESEARCH STARTER

Bay of Bengal

The Bay of Bengal, the largest bay in the world, is a significant northeastern lobe of the Indian Ocean, covering approximately 850,000 square miles (2.2 million square kilometers). It is nourished by major rivers, including the Ganges-Brahmaputra-Meghna system and the Irrawaddy, contributing to its ecological diversity. The bay features a complex underwater structure known as the Bengal Fan, formed by ancient tectonic activity and shaped by sediment influx from the Himalayas. Its varied ecosystems include estuaries, coral reefs, and the Sundarbans, home to the largest mangrove forest on the planet, which plays a crucial role in supporting diverse species, including endangered sea turtles and the Bengal tiger.

The Bay of Bengal is also vital for the livelihoods of approximately 450 million people living along its coasts, with a substantial fishery production valued at around $4 billion. However, this rich biodiversity faces threats from industrial development, pollution, and the impacts of climate change, such as rising sea levels and habitat degradation. Initiatives like the Bay of Bengal Large Marine Ecosystem Project aim to address these challenges by promoting sustainable practices and conserving the bay's unique environment. Overall, the Bay of Bengal serves as a crucial ecological and economic resource, reflecting a complex interplay between natural and human forces.

Full Article

  • Category: Marine and Oceanic Biomes.
  • Geographic Location: South Asia.
  • Summary: This major lobe of the Indian Ocean, along with its coral reef, estuarine, and coastal habitats, supports great numbers and diversity of species.

The major northeastern lobe of the Indian Ocean, the Bay of Bengal encompasses about 1,000,000 square miles (2.6 million square kilometers) of ocean fed by such major rivers as the Mahanadi-Brahmani, Godavari, Krishna, and Kaveri from India in the west; the Ganges-Brahmaputra-Meghna system from India and Bangladesh in the north; and the Irrawaddy from Myanmar (formerly called Burma) in the east. Arcing from Sri Lanka and the east coast of India and across the Ganges Delta to Myanmar and the Andaman-Nicobar archipelago, the Bay of Bengal has an average depth of 8,500 feet (2,600 meters), a maximum depth of about 15,400 feet (4,694 meters), and a water volume of about 1.3 million cubic miles (5.6 million cubic kilometers). It is considered the largest bay on Earth.

The floor of the Bay of Bengal is almost entirely made up of the Bengal Fan, a structure first created in the ancient tectonic collision of the Indian Plate and Eurasian Plate, then eroded over eons into a series of underwater canyons by the massive inflow of sediment from the Himalayan headwaters through the Ganges-Brahmaputra-Meghna River system. The Bengal Fan is the largest submarine fan on Earth.

Annual continental runoff of freshwater into the bay, estimated at more than 710 cubic miles (3,000 cubic kilometers), is considerable, and peaks during the monsoon season, June through September. The rivers transport minerals and nutrients into the bay, as well as effluents and other pollutants from the cities, towns, and farms they pass through. Total sediment discharge into the Bay of Bengal is estimated at twenty-four billion tons annually.

Ecology and Species

The Bay of Bengal biome comprises estuaries and wetlands, coral reefs, and such unique zones as the world’s largest salt-tolerant tidal mangrove forest, in the Sundarbans, where river and marine environments merge across the Ganges Delta. Nutrient input from river runoff contributes to the productivity of phytoplankton and zooplankton in these waters. Atoll, fringing, and barrier reefs all occur within the Bay of Bengal coral matrix, supporting substantial communities of sponges, mollusks, crustaceans, echinoderms, and fish.

Key fish species in the Bay of Bengal include the commercially important tuna, including Indo-Pacific bonito (Sarda orientalis), eastern little tuna (Euthynnus affinis), bullet tuna (Auxis rochei), and bigeye tuna (Thunnus obesus); Indo-Pacific king mackerel (Scomberomorus guttatus), Spanish mackerel (Scomberomorus commerson), and Indian mackerel (Rastrelliger kanagurta); fourfinger threadfin, commonly called Indian salmon (Eleutheronema tetradactylum); at least 15 species of anchovy, four species of sardine, and two herring; and tiger prawn (Penaeus monodon).

Sea turtles include the leatherback (Dermochelys coriacea), particularly numerous along the island chains of the Andamans and Nicobars, a prime egg-laying region, and the endangered olive ridley sea turtle (Lepidochelys olivacea). The olive ridley has been known to mass on the beaches of the eastern Indian state of Odisha in numbers of more than half a million during its nesting season. Protection of these nesting grounds includes Operation Olivia, an annual Indian Coast Guard mission along the Odisha coast. The Gahirmatha Marine Wildlife Sanctuary, with mangrove wetlands first protected in 1975, protects this overfished reptile and also helps shield such at-risk fauna as the saltwater crocodile (Crocodylus porosus); eight species of at-risk kingfishers, including the black-capped kingfisher (Halcyon pileata) and pied kingfisher (Ceryle rudis); and resident herons such as Asian openbill (Anastomus oscitans), night heron (Nycticorax nycticorax), and white ibis (Threskiornis melanocephalus).

Mammals thriving in the Bay of Bengal include the dugong (Dugong dugon), which favors the seagrass beds found along the island chains; the Irrawaddy River dolphin (Orcaella brevirostris), preferring estuary zones and the Sundarbans; and cetaceans like Bryde’s whale (Balaenoptera edeni), which inhabit such areas as the submarine canyon known as the Swatch of No Ground. In 2014, Bangladesh established the Swatch of No Ground Marine Protected Area to protect whales, dolphins, sharks, sea turtles, and other marine life in and around the canyon.

Crowning the biological richness of the Bay of Bengal in its northern reaches is the Sundarbans mangrove: Its National Park area in India is a United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage Site, and its entire Indian expanse is a UNESCO Global Biosphere Reserve, while the Sundarbans Reserve Forest in Bangladesh is a Ramsar Wetland of International Importance spanning 2,323 square miles (601,700 hectares). The Sundarbans are vital for migratory fowl. Such apex predators as the greater spotted eagle (Aquila clanga) and Pallas’s fish-eagle (Haliaeetus leucoryphus) winter here and summer in north-central Asia. Indian skimmer (Rynchops albicollis), spotted greenshank (Tringa guttifer), and spoon-billed sandpiper (Eurynorhynchus pygmeus) also rely on the Sundarbans.

Species as diverse as the Bengal tiger (Panthera tigris) and the rare Ganges shark (Glyphis gangeticus) depend on this vast mangrove, with its teeming food supply, prime breeding grounds, and protection from cyclones. Subsistence fishermen here sometimes train the smooth-coated otter (Lutrogale perspicillata) to drive fish into their nets.

Balancing Human Activities

Despite the protected areas within this vast region, much of the coastal habitat is under threat from the energy industry and general urban development, the mangrove timber industry, wet rice cultivation, bird hunting, and aquaculture in the form of shrimp pond farms. Often, the reach of these threats extends outward across the Bay of Bengal. For example, transmission of aquaculture effluents or escaped cultivars that can carry toxins and parasites is likely to be a factor in widespread disease impacts, such as disease outbreaks that can affect farmed and wild marine species. The Network of Aquaculture Centres in Asia-Pacific (NACA) is one of the organizations attempting to move its members toward more sustainable economic pursuits that build habitat protection into their methods and practices.

According to the Council on Foreign Relations in 2023, about 1.4 billion people live in the coastal zone around the Bay of Bengal. The fishery production there is worth about $4 billion. Poverty and population pressures, insufficient governmental planning and control, increased tourism, and insufficient attention to waste management are all threats to the ecology of the region. Due to the low-lying nature of much of the land bordering it, the Bay of Bengal is extremely vulnerable to climate change. As reported by the Council on Foreign Relations, climate change has increased the damage caused by cyclones, and heavy rainfall has caused flash flooding. Drought and soil deterioration are leading to food insecurity.

One cooperative international group focused on these issues is the Bay of Bengal Large Marine Ecosystem Project (BOBLME), an effort by Bangladesh, India, Indonesia, Malaysia, the Maldives, Myanmar, Sri Lanka, and Thailand. A second phase of the project, covering 2023–2028, was launched to implement the region’s Strategic Action Programme. BOBLME aims to help combat the effects of climate change and the overexploitation of marine living resources. According to BOBLME, more than 20 percent of the area’s mangroves have been lost since the 1980s because of expanding agriculture, coastal development, unregulated fishing, and water pollution.


Bibliography

“About NACA.” Network of Aquaculture Centres in Asia-Pacific (NACA), 1 Jan. 2000, enaca.org/?id=1. Accessed 12 Mar. 2026.

“Bangladesh Creates New Marine Protected Area for Dolphins, Whales, Sharks, and Sea Turtles.” Wildlife Conservation Society Bangladesh, 4 Nov. 2014, bangladesh.wcs.org/About-Us/News/articleType/ArticleView/articleId/8633. Accessed 12 Mar. 2026.

“Bay of Bengal Large Marine Ecosystems Phase II.” International Union for Conservation of Nature and Natural Resources (IUCN), 2023, iucn.org/our-work/region/asia/our-work/coastal-and-marine/bay-bengal-large-marine-ecosystems-phase-ii. Accessed 12 Mar. 2026.

Curray, Joseph R. “The Bengal Fan: Morphology, Geometry, Stratigraphy, History and Processes.” Marine and Petroleum Geology, vol. 19, no. 10, Dec. 2002, pp. 1191–1223. doi:10.1016/S0264-8172(03)00035-7. Accessed 12 Mar. 2026.

Kumar, M. Dileep. Biogeochemistry of the North Indian Ocean. Indian National Science Academy, 2006.

“Operation Olivia: ICG Protects over 6.98 Lakh Olive Ridley Turtles along the Odisha Coastline.” Ministry of Defence, 19 May 2025, pib.gov.in/PressReleaseIframePage.aspx?PRID=2129578. Accessed 12 Mar. 2026.

Quader, O. Coastal and Marine Biodiversity of Bangladesh (Bay of Bengal). Space Research and Remote Sensing Organization, 2010.

Sengupta, Debasis, et al. “Surface Freshwater From Bay of Bengal Runoff and Indonesian Throughflow in the Tropical Indian Ocean.” Geophysical Research Letters, vol. 33, no. 22, 28 Nov. 2006. doi:10.1029/2006GL027573. Accessed 13 Mar. 2026.

Shidore, Sarang. “Climate Security and Instability in the Bay of Bengal Region.” Council on Foreign Relations, Apr. 2023, cdn.cfr.org/sites/default/files/report_pdf/Climate%20Security%20and%20Instability%20in%20the%20Bay%20of%20Bengal%20Region_0.pdf. Accessed 12 Mar. 2026.

Verlaan, Philomene A. “Bay of Bengal.” Encyclopaedia Britannica, 2 Mar. 2026, www.britannica.com/place/Bay-of-Bengal. Accessed 12 Mar. 2026.

Full Article

  • Category: Marine and Oceanic Biomes.
  • Geographic Location: South Asia.
  • Summary: This major lobe of the Indian Ocean, along with its coral reef, estuarine, and coastal habitats, supports great numbers and diversity of species.

The major northeastern lobe of the Indian Ocean, the Bay of Bengal encompasses about 1,000,000 square miles (2.6 million square kilometers) of ocean fed by such major rivers as the Mahanadi-Brahmani, Godavari, Krishna, and Kaveri from India in the west; the Ganges-Brahmaputra-Meghna system from India and Bangladesh in the north; and the Irrawaddy from Myanmar (formerly called Burma) in the east. Arcing from Sri Lanka and the east coast of India and across the Ganges Delta to Myanmar and the Andaman-Nicobar archipelago, the Bay of Bengal has an average depth of 8,500 feet (2,600 meters), a maximum depth of about 15,400 feet (4,694 meters), and a water volume of about 1.3 million cubic miles (5.6 million cubic kilometers). It is considered the largest bay on Earth.

The floor of the Bay of Bengal is almost entirely made up of the Bengal Fan, a structure first created in the ancient tectonic collision of the Indian Plate and Eurasian Plate, then eroded over eons into a series of underwater canyons by the massive inflow of sediment from the Himalayan headwaters through the Ganges-Brahmaputra-Meghna River system. The Bengal Fan is the largest submarine fan on Earth.

Annual continental runoff of freshwater into the bay, estimated at more than 710 cubic miles (3,000 cubic kilometers), is considerable, and peaks during the monsoon season, June through September. The rivers transport minerals and nutrients into the bay, as well as effluents and other pollutants from the cities, towns, and farms they pass through. Total sediment discharge into the Bay of Bengal is estimated at twenty-four billion tons annually.

Ecology and Species

The Bay of Bengal biome comprises estuaries and wetlands, coral reefs, and such unique zones as the world’s largest salt-tolerant tidal mangrove forest, in the Sundarbans, where river and marine environments merge across the Ganges Delta. Nutrient input from river runoff contributes to the productivity of phytoplankton and zooplankton in these waters. Atoll, fringing, and barrier reefs all occur within the Bay of Bengal coral matrix, supporting substantial communities of sponges, mollusks, crustaceans, echinoderms, and fish.

Key fish species in the Bay of Bengal include the commercially important tuna, including Indo-Pacific bonito (Sarda orientalis), eastern little tuna (Euthynnus affinis), bullet tuna (Auxis rochei), and bigeye tuna (Thunnus obesus); Indo-Pacific king mackerel (Scomberomorus guttatus), Spanish mackerel (Scomberomorus commerson), and Indian mackerel (Rastrelliger kanagurta); fourfinger threadfin, commonly called Indian salmon (Eleutheronema tetradactylum); at least 15 species of anchovy, four species of sardine, and two herring; and tiger prawn (Penaeus monodon).

Sea turtles include the leatherback (Dermochelys coriacea), particularly numerous along the island chains of the Andamans and Nicobars, a prime egg-laying region, and the endangered olive ridley sea turtle (Lepidochelys olivacea). The olive ridley has been known to mass on the beaches of the eastern Indian state of Odisha in numbers of more than half a million during its nesting season. Protection of these nesting grounds includes Operation Olivia, an annual Indian Coast Guard mission along the Odisha coast. The Gahirmatha Marine Wildlife Sanctuary, with mangrove wetlands first protected in 1975, protects this overfished reptile and also helps shield such at-risk fauna as the saltwater crocodile (Crocodylus porosus); eight species of at-risk kingfishers, including the black-capped kingfisher (Halcyon pileata) and pied kingfisher (Ceryle rudis); and resident herons such as Asian openbill (Anastomus oscitans), night heron (Nycticorax nycticorax), and white ibis (Threskiornis melanocephalus).

Mammals thriving in the Bay of Bengal include the dugong (Dugong dugon), which favors the seagrass beds found along the island chains; the Irrawaddy River dolphin (Orcaella brevirostris), preferring estuary zones and the Sundarbans; and cetaceans like Bryde’s whale (Balaenoptera edeni), which inhabit such areas as the submarine canyon known as the Swatch of No Ground. In 2014, Bangladesh established the Swatch of No Ground Marine Protected Area to protect whales, dolphins, sharks, sea turtles, and other marine life in and around the canyon.

Crowning the biological richness of the Bay of Bengal in its northern reaches is the Sundarbans mangrove: Its National Park area in India is a United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage Site, and its entire Indian expanse is a UNESCO Global Biosphere Reserve, while the Sundarbans Reserve Forest in Bangladesh is a Ramsar Wetland of International Importance spanning 2,323 square miles (601,700 hectares). The Sundarbans are vital for migratory fowl. Such apex predators as the greater spotted eagle (Aquila clanga) and Pallas’s fish-eagle (Haliaeetus leucoryphus) winter here and summer in north-central Asia. Indian skimmer (Rynchops albicollis), spotted greenshank (Tringa guttifer), and spoon-billed sandpiper (Eurynorhynchus pygmeus) also rely on the Sundarbans.

Species as diverse as the Bengal tiger (Panthera tigris) and the rare Ganges shark (Glyphis gangeticus) depend on this vast mangrove, with its teeming food supply, prime breeding grounds, and protection from cyclones. Subsistence fishermen here sometimes train the smooth-coated otter (Lutrogale perspicillata) to drive fish into their nets.

Balancing Human Activities

Despite the protected areas within this vast region, much of the coastal habitat is under threat from the energy industry and general urban development, the mangrove timber industry, wet rice cultivation, bird hunting, and aquaculture in the form of shrimp pond farms. Often, the reach of these threats extends outward across the Bay of Bengal. For example, transmission of aquaculture effluents or escaped cultivars that can carry toxins and parasites is likely to be a factor in widespread disease impacts, such as disease outbreaks that can affect farmed and wild marine species. The Network of Aquaculture Centres in Asia-Pacific (NACA) is one of the organizations attempting to move its members toward more sustainable economic pursuits that build habitat protection into their methods and practices.

According to the Council on Foreign Relations in 2023, about 1.4 billion people live in the coastal zone around the Bay of Bengal. The fishery production there is worth about $4 billion. Poverty and population pressures, insufficient governmental planning and control, increased tourism, and insufficient attention to waste management are all threats to the ecology of the region. Due to the low-lying nature of much of the land bordering it, the Bay of Bengal is extremely vulnerable to climate change. As reported by the Council on Foreign Relations, climate change has increased the damage caused by cyclones, and heavy rainfall has caused flash flooding. Drought and soil deterioration are leading to food insecurity.

One cooperative international group focused on these issues is the Bay of Bengal Large Marine Ecosystem Project (BOBLME), an effort by Bangladesh, India, Indonesia, Malaysia, the Maldives, Myanmar, Sri Lanka, and Thailand. A second phase of the project, covering 2023–2028, was launched to implement the region’s Strategic Action Programme. BOBLME aims to help combat the effects of climate change and the overexploitation of marine living resources. According to BOBLME, more than 20 percent of the area’s mangroves have been lost since the 1980s because of expanding agriculture, coastal development, unregulated fishing, and water pollution.


Bibliography

“About NACA.” Network of Aquaculture Centres in Asia-Pacific (NACA), 1 Jan. 2000, enaca.org/?id=1. Accessed 12 Mar. 2026.

“Bangladesh Creates New Marine Protected Area for Dolphins, Whales, Sharks, and Sea Turtles.” Wildlife Conservation Society Bangladesh, 4 Nov. 2014, bangladesh.wcs.org/About-Us/News/articleType/ArticleView/articleId/8633. Accessed 12 Mar. 2026.

“Bay of Bengal Large Marine Ecosystems Phase II.” International Union for Conservation of Nature and Natural Resources (IUCN), 2023, iucn.org/our-work/region/asia/our-work/coastal-and-marine/bay-bengal-large-marine-ecosystems-phase-ii. Accessed 12 Mar. 2026.

Curray, Joseph R. “The Bengal Fan: Morphology, Geometry, Stratigraphy, History and Processes.” Marine and Petroleum Geology, vol. 19, no. 10, Dec. 2002, pp. 1191–1223. doi:10.1016/S0264-8172(03)00035-7. Accessed 12 Mar. 2026.

Kumar, M. Dileep. Biogeochemistry of the North Indian Ocean. Indian National Science Academy, 2006.

“Operation Olivia: ICG Protects over 6.98 Lakh Olive Ridley Turtles along the Odisha Coastline.” Ministry of Defence, 19 May 2025, pib.gov.in/PressReleaseIframePage.aspx?PRID=2129578. Accessed 12 Mar. 2026.

Quader, O. Coastal and Marine Biodiversity of Bangladesh (Bay of Bengal). Space Research and Remote Sensing Organization, 2010.

Sengupta, Debasis, et al. “Surface Freshwater From Bay of Bengal Runoff and Indonesian Throughflow in the Tropical Indian Ocean.” Geophysical Research Letters, vol. 33, no. 22, 28 Nov. 2006. doi:10.1029/2006GL027573. Accessed 13 Mar. 2026.

Shidore, Sarang. “Climate Security and Instability in the Bay of Bengal Region.” Council on Foreign Relations, Apr. 2023, cdn.cfr.org/sites/default/files/report_pdf/Climate%20Security%20and%20Instability%20in%20the%20Bay%20of%20Bengal%20Region_0.pdf. Accessed 12 Mar. 2026.

Verlaan, Philomene A. “Bay of Bengal.” Encyclopaedia Britannica, 2 Mar. 2026, www.britannica.com/place/Bay-of-Bengal. Accessed 12 Mar. 2026.

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