Shell Beach is not your common sand beach - it's a beach made of trillions of tiny shells, all from one type of animal.

WA’s shell beach is a 110km stretch of the Coral Coast made almost entirely of cockle shells, between 7-10m deep. L’Haridon Bight in Shark Bay is home to billions of tiny coquina bivalve shells. This shallow, hypersaline (∼ 60‰), benthic marine environment, is dominated by the cockle Fragum erugatum (Mollusca, Bivalvia, Cardiidae). The proliferation of this particular species has resulted from the high water salinity (salt concentration) in this area, the tolerance levels of this cockle and no natural predation.

Photo by Manuel Caminero, 2013.

The characteristic rounded shells of cockles are bilaterally symmetrical, and are heart-shaped when viewed from the side with numerous radial ribs. There are more than 200 living species of cockles, with many more fossil forms. Cockles are a synchronous hermaphrodite which typically burrow using their ‘foot’ (a protruding aperture of their mantle), and feed by siphoning and filtering plankton from the surrounding water.

Similar to its close relatives the giant clams (Tridacnidae), Fragum erugatum possesses symbiotic zooxanthellae, which may facilitate survival in the hyperosmotic environment of Shark Bay. The association facilitates a large population size (but short life expectancy), allowing it to dominate a unique, hypersaline, oligotrophic environment.

Shark Bay World Heritage Discovery & Visitor Centre

Although shells are washed ashore continuously, large-scale deposition of the accumulated infratidal coquinas, largely composed these cockle shells, occurs periodically in major storm events. Shell beach has provided a long-term tropical cyclone record from the Indian Ocean region. Multiple shore-parallel ridges record a tropical cyclone history, which are responsible for deposition of the ridges.

First depositions were thought to have occurred here about 4000-6000 years ago. Over time, the shell deposits have cemented to form soft coquina limestone which is being utilised at the local coquinite quarry.

Shark Bay World Heritage Discovery & Visitor Centre

It is 1 of only 2 beaches in the whole world that is completely made up of shells! Pretty extraordinary if you ask me! The effect is brilliant; a long, snow-white beach bordered by aqua blue ocean waters. This little bivalve has created a spectacular feature of Western Australia’s Coral Coast.

Bibliography:

Berry, P.F. & Playford, P.E. (1997) Biology of modern (Mollusca, Bivalvia, Cardiidae) in relation to deposition of the Hamelin Coquina, Shark Bay, Western Australia, Marine & Freshwater Research 48( 5), 415-420.

Morton, B. (2000) The biology and functional morphology of Fragum erugatum (Bivalvia: Cardiidae) from Shark Bay, Western Australia: the significance of its relationship with entrained zooxanthellae, Journal of Zoology 251(1), 39-52.

Nott, J. (2011) A 6000 year tropical cyclone record from Western Australia, Quaternary Science Reviews 30(5), 713-722.