Sand and Soft Sediments

About Sandy Habitats

Victorian coastal waters are awash with sand. In some areas like Ninety Mile Beach, sand habitats dominate the zone beyond the surf and are interspersed with low profile reef. Given the extent of sandy habitats in Victorian waters it is not surprising that many animals have adapted to dwell in these areas - on, under and even between the grains of sand. The ripples lining a sandy seafloor may look bare and empty, but can be rich and plentiful in animals. One square metre of sand from the subtidal area off Ninety Mile Beach can contain 6,000 individuals. Animals living in the sand such as scallops, prawns and worms are essential prey for many fin fish, skates and rays. A scattering of large rocks, shells and rubble provides anchorage for plants and non-mobile animals like sponges.

Healthy Sands

Wave energy and moving sands may prevent plants and animals from colonising sands off coastal beaches, however in lower energy areas such as inlets and bays, and deeper water, there is greater opportunity for life to establish itself. Because there is often very little growing on bare sand or sediments it is very difficult to visually assess the health of these habitats. Scientists usually have to take sand samples (cores) and analyse the types and abundance of animals in these, as well as determining their chemical and physical properties.

Impacts to these habitats are pollutants including petrochemicals and heavy metals such as lead and cadmium. Shell fish and other filter feeders in these habitats can ingest these pollutants making them unsafe to eat, for both fish and humans, and toxins may reside within sediments for a long time. Excessive nutrients, for example off Werribee sewage plant, may affect sand communities by killing off sensitive species and causing a population boom in other, more resilient species or creating plankton or bacterial blooms. Introduced marine pests such as the sea star, Asterias, are having a huge impact on sandy seafloor communities as they are voracious predators of shell fish and other invertebrates.

Dredging and mining are physically destructive processes that can kill resident animals, modifying the habitat and re-suspend toxins that may be lying in the sediments. Sponges, sea squirts, sea pens and other invertebrate animals often attach themselves to shells, rubble and small rocks in the sand. Because these animals are relatively soft, and cannot move, they can be damaged and killed by dredging and mining (e.g. for scallops or sand) and may take a considerable period to recover.

Sandy Anecdotes