Shark Bay

Category: Marine and Oceanic Biomes.

Geographic Location: Australia.

Summary: This World Heritage Area is known for its rare stromatolite community, extensive seagrass beds, and diverse shark population.

Shark Bay lies about 500 miles (805 kilometers) north of Perth, in western Australia, and is renowned for its wide variety of sharks and for its environmental significance. In 1991, Shark Bay became a World Heritage Area due to its natural heritage values, which include the Bay’s stromatolite (single-cell cyanobacteria that date back to the Earth’s creation) community, and otherwise diverse animal life. The biome also is widely known for seagrass beds that are among the largest in the world; the seagrass habitat provides food and shelter to numerous marine life species.

Shark Bay is located near the northern limit of the transition zone between temperate and tropical environments; the surface temperature of the water averages 70–79 degrees F (21–26 degrees C). The area has a semiarid-to-arid climate, with hot, dry summers and mild winters. The rainy season occurs during winter, with annual rainfall averaging 8–16 inches (203–406 millimeters). The western portion of Shark Bay receives more rain than the eastern side, which has semidesert conditions, while the western region is dry mediterranean. The average depth of the water in the biome is 30 feet (9 meters); the deepest sections are approximately 95 feet (29 meters).

The Bay also holds historical significance, as it is the earliest recorded site of European exploration on the western Australian coast. Many of the islands here are named after these explorers, such as Dirk Hartog Island (for a Dutch seaman of 1616). William Dampier gave Shark Bay its name in 1699, when he and his crew were mapping the area. Aboriginal Australians call it Gutharraguda, which means "two bays."

Biodiversity

So named for some of its more prevalent inhabitants, Shark Bay is home to 28 species of shark and six types of ray. The bay has one of the largest populations of tiger sharks in the world. Tiger sharks inhabit inshore waters, deeper offshore areas and reefs, and are the top predator in this marine ecosystem. Their main prey are sea snakes and dugongs, or sea cows, and they also feed on green sea turtles, and various fish, as well as smaller sharks and rays.

Shark Bay is one of the few locations in the world where living stromatolites are found. Since stromatolites have such a long biological history, they serve as an example of Earth’s original life-evolutionary progress. In fact, they are theorized to date back to the Snowball Earth period of the Ediacaran era, more than 650 million years ago. Extremely fragile, and growing only a few tenths of an inch (millimeters) per year, these blue-green algae nevertheless build up rocklike structures as they capture and bind together tiny grains of silt and sediment.

The stromatolites of Shark Bay are found in Hamelin Pool, a semi-enclosed, hypersaline embayment that has twice the salt concentration in its water as the marine norm nearby. The elevated salinity level is a result of limited tidal exchange from the sea, along with high evaporation. Due to their delicate nature, stromatolites are easily destroyed by other creatures that feed on them or simply crush them underfoot. The salinity levels and closed nature of Hamelin Pool provide an excellent environment for the stromatolites to thrive without disturbance, as few other creatures can survive for long in the pool.

Shark Bay also is well known for its wildlife diversity. Shark Bay Marine Park—established in 1990 under the Conservation and Land Management Act within the World Heritage site—is a protected and preserved area that enables animal life to flourish without much human interference. It is home to thousands of sharks and to numerous other aquatic and terrestrial animals. Marine animals thrive in its vast seagrass beds, which span 2,500 square miles (6,475 square kilometers) of the ocean floor. The seagrass beds provide food, shelter, and protection to 60 species of fish and small gastropods, and acts as a food source for the population of the threatened dugong. Shark Bay Marine Park consists of four zones, including recreation and sanctuary areas.

While the dugong is somewhat rare in most parts of the world, Shark Bay is home to 10,000 individuals, which is about one-eighth of the world’s dugong population. Even though the dugongs are a food source for the area’s sharks, they manage to hide and thrive in the dense thickets of the seagrass beds. While seagrass is the dominant marine habitat, plenty of creatures live in the sand and open water as well, such as dolphins, whale sharks, sea turtles, migrating humpback whales, lobsters, shrimp, coral, sea snakes, and more than 300 species of fish. The bay is well-known for the friendly monkey mia dolphins.

Several members of Shark Bay’s animal population live on land; these include wallabies, bandicoots, kangaroos, emus, and mice. More than 100 species of amphibians and reptiles live on the islands, including frogs, lizards, snakes, skinks, and geckos. Shark Bay provides a safe environment for such threatened species as the Shark Bay mouse, banded hare-wallaby, rufous hare-wallaby, western barred bandicoot, and burrowing bettong.

Conservation Efforts

Because of Shark Bay’s population of endangered and native animals, Western Australia’s Department of Environment and Conservation is striving to conserve and protect the Bay for future generations. The Shark Bay World Heritage Area covers approximately 13,670 square miles (35,405 square kilometers), with two-thirds of it a marine habitat. The Australian government is working to remove nonnative animals such as goats, foxes, cats, and rabbits, which threaten both the endangered species and many other native ones.

The government is managing human use of Shark Bay, with strict laws concerning fishing, boating, and camping to further preserve the environment of the animals living in the area. While tourism is encouraged, to bring in funds for the preservation of Shark Bay, the Australian government is strategically developing specific sites and areas that will have the least effect on wildlife.

Climate change is impacting Shark Bay. Warming temperatures and increased river flooding from heavier rain events is altering the composition of microbial species in the Bay, and upsetting the ecosystem of the stromatolites. In addition, the increasing amounts of sediment washing into the Bay inflicts damage on parts of the seagrass meadows. These habitats are complex; the effects will have to be monitored closely to gain information on how to help sustain them.

Bibliography

Berry, P. F., et al., eds. Research in Shark Bay: Report of the France-Australe Bicentenary Expedition Committee. Perth: Western Australian Museum, 1990.

McCluskey, Paul. Shark Bay World Heritage Property Strategic Plan 2008–2020. Perth: Australia Department of Environment and Conservation, 2008.

Richards, Jacqueline D. and Barry Wilson, eds. A Biological Survey of Faure Island, Shark Bay World Heritage Property, Western Australia. Perth: Western Australian Museum, 2008.

"Shark Bay, Western Australia." World Heritage Outlook, 2 Dec. 2020, worldheritageoutlook.iucn.org/explore-sites/wdpaid/67724. Accessed 31 Aug. 2022.

Walker, Gabrielle. Snowball Earth: The Story of the Great Global Catastrophe That Spawned Life as We Know It. New York: Crown Publishers, 2003.