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What is an intertidal zone?
updated Aug 08
The coastal area that is covered by water at high tide and exposed at low tide is called the intertidal zone.

This zone is rich in lifeforms because of the high concentration of nutrients that flow from the land into the sea. In the shallow waters of the intertidal zone, sunlight penetrates to the bottom so that plants can grow well. In sheltered areas protected from strong waves, even more plants and animals can settle down. A particularly large variety of plants and animals are found in the intertidal zone because the twice-daily change in water levels supports two 'shifts' of activity in the same area.

For example, some animals are active at low tide while aquatic creatures take over at high tide. The tides thus strongly affect the rhythm of life on the intertidal zone.


Incoming tides bring in fresh supplies of oxygen, nutrients and plankton to shallow areas. Seeds of coastal and mangrove plants also float in to colonise new spots. At high tide, filter-feeders gorge while fish can forage in the shallows.

Outgoing tides flush out waste and deliver nutrients to habitats further away from the shore. Floating out with the tide are animals, their eggs and free-swimming larvae, seaweeds, and seeds of seagrass and mangroves. At low tide, some creatures feed on the intertidal flats, safe from aquatic predators (but they still have to look out for land predators!). Aquatic animals take shelter in shallow pools left behind at low tide.

Life by the Moon: The cycle of spring and neap tides profoundly influences life on the intertidal zone. For example, eggs and larvae are usually released at spring tide so that they can be carried far out to sea. More about the tides and what causes them.

The slope of a shore determines the extent of the intertidal zone. A gentle gradient means a larger area is affected by the tides, while a narrow area is affected on a steeper sloping shore. Many of our natural shores have been affected by reclamation. Even where they are not bound by seawalls, the shores have become steeper and the intertidal zone narrower. Nan-made lagoons on our shores and Southern Islands, however, created intertidal zones that are slowly being recolonised by marine life.

The fascinating intertidal zone of
Cyrene Reef is only exposed at super low tides.


The vast seagrass meadows of
Pulau Semakau are revealed at low tide.

Soldier crab burrowing into the sand
just before the tide comes in.
Chek Jawa, Jun 07

A Giant carpet anemone submerged
in water with anemone shrimp.
Changi, Jul 06

A Giant carpet anemone exposed at low tide
Chek Jawa, Feb 02
Links

References
www.flickr.com
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