What
is an intertidal zone?
updated
Dec 2019
At the edge of
land and sea, there is a zone that is submerged at high tide, but
is dry and exposed to air at low tide. This coastal area affected
by the tides is called the intertidal zone. More about
the tides.
This intertidal zone is rich in life because high concentrations of
nutrients flow from the land. Sunlight penetrates the shallow waters,
allowing organisms that rely on sunlight to grow well on the shore
bottom. These include plants, seaweeds and corals. These in turn shelter
and feed other life. In areas sheltered from strong waves, an even
wider variety of life 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. |
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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.
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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 dry intertidal
flats or in shallow pools left behind at low tide, safe from aquatic
predators who leave for deeper waters (but they still have to look
out for land predators!).
Different kinds animals are also active during the daytime and night-time.
The intertidal zone is often busier after the sun sets, when it's
cool and dark.
The influence of the tides results in zones of different lifeforms
on a sea shore. More about zonation. |
Soldier crab
burrowing into the sand
just before the tide comes in.
Chek Jawa, Jun 07 |
A carpet anemone
submerged
in water with anemone shrimp.
Changi, Jul 06 |
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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. Such
large shallow areas allows a wider variety of ecosystems and thus
richer biodiversity.
Unfortunately, such shallow areas are among the first to be buried by reclamation. The resulting reclaimed shore
is often steeply sloping with a narrow intertidal, or bound by seawalls.
But some marvelous natural intertidal areas have escaped development.
While some man-made lagoons and seawalls are slowly being recolonised
by marine life.
Although many shores are easily accessible, most of Singapore's best
shores remain an unintended secret. Extreme low spring tides are brief
and happen only during a few months in a year, usually well before
sunrise. (Thus, the intertidal is not often exposed to full sun at
low spring tide. This perhaps is one reason why Singapore's intertidal
is so rich.) Nevertheless, enjoyable exploration is possible on some
not-so-low tides during daylight, when guided shore walks are held
at various locations. More about the tides and visiting our shores. |
Links
References
- Tan, Hugh
T.W. L.M. Chou, Darren C. J. Yeo and Peter K.L. Ng. 2007. The
Natural Heritage of Singapore.
Second edition. Prentice Hall. 271 pp.
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