Controlled by the Moon, the Earth's tides are essential for sea life - but how do they work and what effect do they have on ocean-going creatures?
Overview
How do tides work? The movement of the tides is caused by rotation of the Moon and the Earth. Gravity pulls the Moon and Earth together. As the Earth turns, the Moon pulls at the ocean water directly beneath it, causing the sea water to rise.
The biggest tides of all are called spring tides and they occur when the gravities of the sun and moon pull in unison, that happens immediately after the new moon and after the full moon.
Wildlife
High tides allow bottlenose dolphins to reach the shallows for an unusual team hunting campaign. One dolphin will swim rapidly in a circle ahead of the fish they seek and stir up the mud. This forces the fish directly into the path of the rest of the waiting dolphin group.
In South Africa the tides bring dead fish onto the beach and carry the scent of rotting flesh along the surf zone. This smell attracts small snails who use the water currents like surfers to ride up the beach towards their snack.
Spring tides allow tarpon fish to hunt silversides and snappers in the mangroves. The tarpons are the only predators equipped to survive in the stagnant water caused by the falling tide, they take gulps of fresh air at the surface and then dive down to catch their prey.
On rocky coastlines like Vancouver Island in Canada, spring tides expose vast areas of rock with a wealth of crabs and shellfish for racoons to feast on.
During high tide, thousands of female green turtles come ashore to lay their eggs on the beach. The timing of this means that all the young turtles will hatch out at once. Predators will be overwhelmed and many more of the offspring will be able to reach the sea.
Caribbean flamingoes flock to salty beaches where the tide has fallen and only their favourite foods of shrimp and flies can survive the briny water. The salty habitat also keeps the birds safe from any predators so its an ideal place to breed and raise their families.
The sand bubbler crab in Northern Australia works at break-neck speed to feed as much as possible in between each tide. It passes each grain of sand through its mouth, filtering out all the microscopic animals, then discards the rest as small balls of sand. The crab will clean every grain of sand within a metre of its burrow.
Christmas Island crabs cannot swim or breathe under water so use low tides to lay their eggs and release them into the ocean. The eggs develop far off shore, and in a months time a swarm of baby crabs will return, again choosing the perfect tide.
