Back More
Salem Press

Table of Contents

Biomes and Ecosystems

Indian Ocean

by Alexandra M. Avila

Category: Marine and Oceanic Biomes.

Geographic Location: East Africa, South Asia, and Australia.

Summary: The Indian Ocean connects one-third of the world’s human population and offers vast richness of habitat, yet it is under threat from unregulated runoff and pollutants as well as climate change.

The Indian Ocean is the third-largest of the world’s five main oceans, and comprises approximately one-fifth of the total ocean area of the world. The Indian Ocean rim region is home to around one-third of the world’s population. It is bordered by the Indian subcontinent (from which it derives its name), and the southeast Asian peninsula; Indonesia; Australia; East Africa; and the Arabian Peninsula of western Asia. The southern portion is bordered by the Antarctic or Southern Ocean.

Major marginal seas and lobes, or extensions, of the Indian Ocean include: the Arabian Sea, Red Sea, Persian Gulf, Bay of Bengal, Andaman Sea, and the Great Australian Bight. The Indian Ocean has four access waterways of great significance: the Suez Canal (Egypt), Bab el Mandeb (Djibouti-Yemen), the Strait of Hormuz (Iran-Oman), and the Strait of Malacca (Indonesia-Malaysia).

Factors such as area’s ecological and topographical complexity have led scientists to conclude that the Indian Ocean is generally characterized by unique species and high levels of biodiversity. This is supported by the high level of endemism—species found nowhere else on Earth—that has been recorded in adjacent, shallow habitats.

Climate and Resources

The majority of the continental shelves of the Indian Ocean are somewhat narrow, with an average width of only around 124 miles (200 kilometers), except off the western coast of Australia, where the continental shelf extends to more than 620 miles (1,000 kilometers). Given its vastness, the area’s climate is also diverse. The area north of the Equator has a monsoon climate with semiannual reversing winds, which can bring violent rains to India from June to September. Just south of the Equator is the trade-winds zone, where weather conditions are more consistent year round.

Climate zones here include tropical, temperate, sub-Antarctic, and Antarctic. A large part of the Indian Ocean lies within the tropical and temperate climatic zones, where numerous corals and other organisms that depend upon coral reefs are found. The tropical shore areas are home to ecologically important mangrove thickets that provide breeding and nursing grounds for many marine species. During the winter in the near-Antarctic areas furthest to the south, surface ice formation occurs. However, overall the Indian Ocean is the warmest of the Earth’s oceans.

Tropical fish in the shallow waters off the Maldives in the Indian Ocean. The Maldives are one of several Indian Ocean island groups with shallow fringing reefs that provide habitat for commercially valuable fish.

IndianOcean.jpg

(Thinkstock)

Another important feature of this ocean is the depth of many of its trenches, including the Diamantina Fracture Zone, also known as the Diamantina Trench or Diamantina Deep, and the Sunda Trench, which was formerly known as the Java Trench. These are deep areas of complex topography, featuring troughs to depths that scientists argue range from 24,245 to 26,401 feet (7,390 to 8,047 meters) for the Diamantina Trench and from 23,813 to 25,345 feet (7,258 to 7,725 meters) for the Sunda Trench. Ridges that rise up from the seafloor to 13,123 feet (4,000 meters) in depth also provide unique and varied deep-water habitats across much of the southern part of the region.

The trench areas found in the Indian Ocean are of great ecological and economical importance, with their cold, nutrient-rich upwellings supporting a range of commercial fisheries focused on albacore and bluefin tuna, sharks, whiting, snapper, salmon, rock lobster, deep sea crab, abalone, and other marine types. Tuna coral reefs provide another rich area for large-scale fishing. Madagascar, for example, has extensive reefs of all types off of its coasts, as does India in the Gulf of Mannar reef constellation; other areas blessed with important reef zones include the Andaman Sea; the Arabian Sea and Gulf of Oman; and Maldives, Mauritius, Reunion, Seychelles, and Comoros Islands with shallow fringing reefs.

Marine reptiles of the Indian Ocean include the green, olive ridley, hawksbill, leatherback, loggerhead, and flatback turtles. Marine mammals here feature the endangered dugong, spinner dolphin, humpback dolphin, killer whale, sperm whale, blue whale, and the southern elephant seal.

Birds occur in large numbers in the many island, coastal, and estuarine environments around the Indian Ocean. These range from resident species such as the Mauritius parakeet and kestrel; to shorebirds and waders like heron and ibis; to the far-traveling albatross, lesser frigate, and tern.

Threats

Worldwide, coral reefs are under the threat of depletion due to global climate change; direct human pressures, both commercial and recreational; and inadequate governance, awareness, and political will, something that is especially true in the Indian Ocean. Overexploitation of fishery resources has been reported off the shores of Tanzania and Mauritius, while the coral reefs near Kenya, Tanzania, and Mauritius also suffer from destructive fishing practices. Trampling of coral by fishermen has degraded many reefs in the region.

Coral mining and coral sand mining in Mafia (Tanzania), Comoros, Mauritius, and Madagascar have caused damage to the reefs here. More than 551,156 tons (500,000 metric tons) of coral sand is excavated annually from Mauritius; most beaches in Comoros also have been scarred by this destructive activity. More than 276 tons (250 metric tons) of shells and corals are exported from Tanzania in a typical year. Exploitive collection and coral mining has moved from the depleted areas off of East Africa to the Maldives Islands, where it is used for road construction, and to Sri Lanka and India, where tens of thousands of tons are removed annually for a variety of purposes.

Sedimentation from agricultural practices is yet another ecological concern throughout the region, one that affects the reefs off the coasts of the Seychelles, Dar es Salaam, and Zanzibar. Eutrophication, which is the overabundance of nutrients leading to unsupportable blooms of aquatic plant matter, derives from the runoff of fertilizer and sewage; this has resulted in the disruption of habitats in East African waters, the Arabian Sea, Bay of Bengal, and elsewhere around the Indian Ocean.

Seagrass beds that are found throughout the region—another vital habitat type—are also under pressure, from intensive use of bottom traps and beach seine nets, fishing practices using explosives, sand mining, and dredging off coastlines and in shipping channels. The high degree of water turbidity has driven down the rate of growth of seagrasses off the western coast of India, while recent rapid fluctuations in salinity levels from river runoff have had deleterious effects on the beds near Bangladesh.

Other activities that exact a high environmental cost in the Indian Ocean include petroleum exploration from large reserves of hydrocarbons, especially in the Arabian Sea; deforestation, leading to higher runoff levels; coastal development, which undermines mangrove and seagrass bed habitat; and excessive levels of motorized tourism, which leads to persistently more pollution. Since 1963, approximately 50 percent of India’s mangroves have been destroyed. The government of India in 1984 established Sundarbans National Park, looking to protect one of the world’s biggest and richest mangrove areas.

The Indian Ocean provides major sea routes connecting the Middle East, Africa, and east Asia with Europe and the Americas. Given the significant amount of international trade that takes place throughout the region’s waters, the Indian Ocean is vulnerable to high levels of pollution caused by deliberate waste disposal at sea and by accidental oil spills. This poses a difficult-to-regulate threat to the direct survival of marine organisms and on the ongoing buildup of toxins in the marine ecosystem.

Because the Indian Ocean is bordered by the fast-growing economies of such nations as India, Thailand, and Indonesia, there is a high risk that more industrial, agricultural, and municipal waste and runoff will be released into the Indian Ocean in the future because of a lack of regionally coordinated enforcement of environmental protection standards. Each of these threats is likely to be multiplied or complicated by climate change. The direct impacts of global warming upon the Indian Ocean will likely include rising sea levels; rising air and water temperatures; more and heavier tropical cyclones; altered timing of monsoon season onset; and increasing acidity of seawater and the negative effects of this on coral, mollusk, and lower-food-web species reproduction.

Further Reading

1 

Campbell, M. L. “An Overview of Risk Assessment in a Marine Biosecurity Context.” In Gil Rilov and Jeffrey A. Crooks, eds., Biological Invasions in Marine Ecosystems. New York: Springer, 2009.

2 

Ginsburg, R. N. Global Aspects of Coral Reefs: Health, Hazards, and History. Miami, FL: University of Miami, 1994.

3 

Jameson, Stephen C., John W. McManus, and Mark D. Spalding. State of the Reefs—Regional and Global Perspectives. Townsville, Australia: International Coral Reef Initiative, 2005.

4 

Laipson, E. “The Indian Ocean: A Critical Arena for 21st Century Threats and Challenges.” In E. Laipson and A. Pandya, eds., The Indian Ocean—Resource and Governance Challenges. Washington, DC: Henry L. Stimson Center, 2009.

Citation Types

MLA 9th
Avila, Alexandra M. "Indian Ocean." Biomes and Ecosystems, edited by Robert Warren Howarth, Salem Press, 2013. Salem Online, online.salempress.com/articleDetails.do?articleName=BIOMESECO_101536901271.
APA 7th
Avila, A. M. (2013). Indian Ocean. In R. W. Howarth (Ed.), Biomes and Ecosystems. Salem Press. online.salempress.com.
CMOS 17th
Avila, Alexandra M. "Indian Ocean." Edited by Robert Warren Howarth. Biomes and Ecosystems. Hackensack: Salem Press, 2013. Accessed September 24, 2026. online.salempress.com.