What are intertidal zones

Intertidal zone - Intertidal zone

"Foreshore" forwards here. For the area in Cape Town, South Africa, see Foreshore, Cape Town.
Coastal area only exposed at low tide
For a broader representation of this topic, see Coastal Zone.

The Intertidal zone , also as foreshore or Coast known , is the area above water level at low tide and under water at high tide (in other words, the area within the tidal range). This area can include different types of habitats with different ways of life, such as: B. starfish, sea urchins and many types of coral. Sometimes it is referred to as a coastal zone, although this can be defined as a larger region.

Bancao Beach in the Philippines at low tide, shows the tidal zone about 200 m from the beach

The known area also includes steep rocky cliffs, sandy beaches or wetlands (e.g. extensive tidal flats). The area can be a narrow strip, as on Pacific islands, which have only a narrow tidal range, or it can include many feet of shoreline where shallow beach slopes interact with high water excursions. The Peritidal zone is similar but slightly wider and extends from above the highest tide level to below the lowest.

Organisms in the intertidal zone are adapted to an environment with extreme loads. Several species from different phyla (Porifera, Annelida, Coelenterata, Mollusca, Arthropoda, etc.) also live in the intertidal zone. Water is available regularly with the tide, but varies from fresh with rain to highly saline and dry salt, drying in between tidal floods. Wave syringes can remove residents from the riparian zone. With the high exposure of the intertidal zone to sunlight, the temperature can range from very hot with full sunshine to near freezing in colder climates. Some microclimates in the coastal zone are tempered by local features and larger plants such as mangroves. Adaptation in the coastal zone allows the use of nutrients that are regularly supplied in large quantities from the sea, which is actively transported into the zone by tides. Habitat edges, in this case land and sea, are often significant ecologies themselves, and the coastal zone is a prime example of this.

A typical rocky shore can be divided into a spray zone or splash zone (also known as the supratidal zone), which is above the high tide line of the source and only covered with water during storms, and a tidal zone that separates the high and low tidal extremes. On most of the banks, the intertidal zone can be clearly divided into the following sub-zones: high water zone, medium water zone and low water zone. The intertidal zone belongs to a number of marine biomes or habitats, including estuarine, nerite, surface, and depth zones.


Tidal pool at Pillar Point with zoning on the edge of the ledge
A rock, seen at low tide, with typical tidal zoning, Kalaloch, Washington, western USA.

Marine biologists divide the tidal region into three zones (low, medium, and high) based on the total average exposure of the zone. The low water zone, which borders the shallow tidal zone, is only exposed to the air at low water and is mainly marine in character. The middle tidal zone is regularly exposed and flooded by average tides. The flood zone is only covered by the highest floods and spends much of its time as terrestrial habitat. The high tidal zone is adjacent to the splash zone (the region above the highest still tide level but which receives wave splashes). On banks exposed to strong waves, the tidal zone is affected by waves because the spray from waves expands the tidal zone.

Depending on the subsoil and the topography of the bank, additional features can be identified. On rocky banks, tidal pools form in depressions that fill with water when the tide rises. Under certain conditions, e.g. For example, in Morecambe Bay, quicksand can form.

Low tide zone (lower coastal area)

This sub-region is largely underwater - it is only exposed for long periods of time during low tide and extreme low tide. This area is full of life; The most notable difference between this sub-region and the other three is that there is much more marine vegetation, especially seaweed. There is also great biodiversity. Organisms in this zone are generally not well adapted to periods of drought and extreme temperatures. Some of the organisms in this area are abalone, sea anemones, brown algae, chitons, crabs, green algae, hydroids, woodlice, limpets, clams, nudibranchs, sculpin, sea cucumbers, sea lettuce, sea palm trees, starfish, sea urchins, shrimp, snails, sponges, surf grass Tube worms and pustules. Creatures in this area can grow larger as more energy is available in the localized ecosystem. In addition, due to the better water coverage, the marine vegetation can become much larger than in the other three tidal sub-regions. The water is shallow enough to allow plenty of sunlight to get into the vegetation to allow significant photosynthetic activity, and the salinity is close to normal. This area is also protected from large predators such as fish due to the wave action and relatively shallow water.


The tidal region is an important model system for the study of ecology, especially on wave-lashed rocky banks. The region is rich in biodiversity, and the tidal zoning results in areas of species being compressed into very narrow bands. This makes it relatively easy to study species across their entire coastal range, which can be extremely difficult, for example, in terrestrial habitats that can stretch for thousands of kilometers. Communities on wave-lashed shores also have a high turnover due to disturbances, so that it is possible to observe the ecological sequence over years rather than decades.

The burrowing invertebrates that make up large parts of the sandy beach ecosystems are known to travel relatively long distances in the coastal direction as the beaches change in the order of days, crescent cycles, seasons, or years. The distribution of some species was found to be strongly correlated with geomorphic data such as the flood stream and the water table.

Since the foreshore is alternately covered by the sea and exposed to the air, organisms that live in this environment must have adaptations for both wet and dry conditions. Hazards include being smashed or carried away by rough waves, exposure to dangerously high temperatures, and drying out. Typical inhabitants of the intertidal rocky shores include sea urchins, sea anemones, barnacles, chitons, crabs, woodlice, clams, starfish and many marine gastropod mollusks such as limpets and whelks.

Legal issues

As with the dry, sandy part of a beach, legal and political disputes can arise over the ownership and use of the foreshore. A recent example is the foreshore and seabed controversy in New Zealand. In legal discussions, the foreland is often referred to as the Wet sand surface .

For privately owned beaches in the United States, some states, such as Massachusetts, use the low water mark as the dividing line between state ownership and beach owner ownership. However, the public still has fishing, poultry and navigation rights for the zone between low and high tide. Other states like California use the high water mark.

In the United Kingdom, the foreshore is generally considered Crown property, although there are notable exceptions, particularly what is several fisheries is designated which may be historical documents dating back to the time of King John or earlier and the Udal Law, which is common in Orkney and Shetland.

In Greece, according to L. 2971/01, the coastal zone is defined as the area of ​​the coast that can be reached by the maximum climbing of the waves on the coast (maximum wave run-up on the coast) in their maximum capacity (maximum relative to the "normally maximum." Winter waves "and of course not exceptional cases such as tsunamis etc.). The coastal zone, part of the exemptions from the law, is public and no permanent structures are allowed.

Other media

The intertidal zone was used as the title for Stephen Hillenburg's old comic book. The comic played "Bob The Sponge," which became SpongeBob SquarePants.

Picture gallery

  • Seashells in the intertidal zone in Cornwall, England.

  • Inexplicable crumbs of sand that seem to have been deposited around stone by escaping air.

  • Rocks in the intertidal zone completely covered by shells, in Bangchuidao Scenic Area, Dalian, Liaoning Province, China.

See also


External links