Four things you didn't know lived at the beach
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All around your beach towel, a cornucopia of organisms are living in the sand — sometimes microscopic, and almost always out of sight.
"Australia has about 8,000 sandy beaches. It's really a very extensive and dominant habitat," marine ecologist Alan Jones says.
Despite this dominance, the flora and fauna living on sandy beaches remain largely understudied.
In a great many cases, they are completely unknown to science.
Dr Jones is a senior fellow with the Australian Museum, where he has worked since 1975 as a marine ecologist.
He talked with RN's Off Track about some of the organisms he studied on Australia's sandy beaches.
Amphipods
Amphipods are small crustaceans, mostly less than a centimetre long.
They act as biological cleaners, eating up detritus at the water's edge, including weed and dead animals.
In turn, they are eaten by small fish, and can often be associated with fish nursery areas, providing ample feeding opportunities for the growing fry.
There are well over 100 species of amphipod known form Australian waters, mostly from shallow areas close to shore.
These animals look vaguely shrimp-like. Some have a brood chamber called a marsupium, where the eggs or young can be protected.
Some species are sensitive to light and water pressure, and use these as cues to wriggle out of the sand and surf up and down the water line with the tide.
Diatoms
"One of the huge distinguishing factors about beaches, in a way, is that the beach face has no plants ... that you can see," Dr Jones says.
"There are tiny ones which live beneath the sand grains: diatoms."
Diatoms are tiny, mostly single-celled algae, often green or brown.
Generally, they have a coating of silica, so they've been called algae in glass houses.
There are about 1,000 known species of diatoms in Australia, most of which are microscopic in scale.
Despite their small size, they photosynthesise and are a food source for other tiny organisms.
Ghost crabs
Kelp strandings can be used as habitat and food by many organisms, including a mostly nocturnal crab: the ghost crab.
Sometimes called the stalk-eyed crab for fairly obvious reasons, their eyes are set up on those little sticks to give them better visibility as they scuttle along the sand.
These creatures, which grow up to about 3.5cm, have a semi-permanent burrow in the beach sometimes hundreds of metres away from the water.
The hideaway can be up to a metre deep, and at night, the crabs come out and run down to the water's edge to forage.
Dr Jones says while they're there, they'll also exchange the water in their gill chambers to get fresh water from the tide.
"They have very cunning ways of finding their way back to their burrow," he says.
"They have ways of navigating by the sun or the moon, and also the local topography.
"They seem to remember the bumps in the sand close to their burrows, so they say: 'Hello! I remember this bump! That's my burrow, I'll zap down there and be safe.'"
Isopods
These creatures can often look like terrestrial slaters, and are sometimes called roly-polies or sowbugs.
Dr Jones says they have complicated ways of figuring out which direction to move, including an internal tide clock.
"They're low to the ground, and they can't jump up in the air and check out their situation," Dr Jones says.
"And because the sun and the moon move and don't provide a constant reference point, they need a clock to make them adjust [to the tides]."
Isopods across the globe range in size and live in almost all marine and aquatic environments.
Some species can be up to 50 centimetres in length.
Learn more about the universe of organisms beneath the sand by subscribing to Off Track on iTunes, the ABC Radio app or your favourite podcasting app.
Topics: marine-biology, ecology, biology, science-and-technology, sydney-2000, nsw, australia
