Intertidal zone

"Foreshore" redirects here. For the area in Cape Town, South Africa, seeForeshore, Cape Town.

Theintertidal zoneorforeshoreis the area abovewater levelat lowtideandunderwaterat high tide; in other words, it is the part of thelittoral zonewithin thetidal range.This area can include several types ofhabitatswith various species oflife,such assea stars,sea urchins,and many species ofcoralwith regional differences in biodiversity. Sometimes it is referred to as thelittoral zoneorseashore,although those can be defined as a wider region.

The rocky shoreline ofSaint-Malo,northwestern France, with a stripe of the black lichenHydropunctaria mauraat the high tide line

The intertidal zone also includes steep rockycliffs,sandybeaches,bogsorwetlands(e.g., vastmudflats). This area can be a narrow strip, such as inPacific islandsthat have only a narrow tidal range, or can include many meters of shoreline where shallow beach slopes interact with high tidal excursion. Theperitidal zoneis similar but somewhat wider, extending from above the highest tide level to below the lowest. Organisms in the intertidal zone are well-adapted to their environment, facing high levels ofinterspecific competitionand the rapidly changing conditions that come with thetides.The intertidal zone is also home to several species from many differentphyla(Porifera,Annelida,Coelenterata,Mollusca,Arthropoda,etc.).

The water that comes with the tides can vary frombrackish waters,fresh withrain,to highlysalineand drysalt,with drying between tidal inundations.Wavesplash can dislodge residents from the littoral zone. With the intertidal zone's high exposure tosunlight,thetemperaturecan range from very hot with fullsunshineto near freezing in colder climates. Somemicroclimatesin the littoral zone are moderated by local features and larger plants such asmangroves.Adaptationsin the littoral zone allow the utilization ofnutrientssupplied in high volume on a regular basis from thesea,which is actively moved to the zone by tides. The edges of habitats, in this case the land and sea, are themselves often significantecosystems,and the littoral zone is a prime example.

A typicalrocky shorecan be divided into a spray zone or splash zone (also known as thesupratidal zone), which is above thespring high-tide lineand is covered by water only during storms, and an intertidal zone, which lies between the high and low tidal extremes. Along mostshores,the intertidal zone can be clearly separated into the following subzones: high tide zone, middle tide zone, and low tide zone. The intertidal zone is one of a number ofmarine biomesorhabitats,includingestuaries,theneritic zone,thephotic zone,anddeep zones.

Zonation

Tide pools at Pillar Point showing zonation on the edge of the rock ledge

A rock, seen at low tide, exhibiting typical intertidal zonation, Kalaloch,Washington,western United States.

Marine biologistsdivide the intertidal region into three zones (low, middle, and high), based on the overall average exposure of the zone.The low intertidal zone, which borders on the shallow subtidal zone, is only exposed to air at the lowest of low tides and is primarily marine in character. The mid intertidal zone is regularly exposed and submerged by average tides. The high intertidal zone is only covered by the highest of the high tides, and spends much of its time as terrestrial habitat. The high intertidal zone borders on thesplash zone(the region above the highest still-tide level, but which receives wave splash). On shores exposed to heavywave action,the intertidal zone will be influenced by waves, as the spray from breaking waves will extend the intertidal zone.

Depending on the substratum and topography of the shore, additional features may be noticed. Onrocky shores,tide poolsform in depressions that fill with water as the tide rises. Under certain conditions, such as those atMorecambe Bay,quicksandmay form.

Low tide zone (lower littoral)

This subregion is mostly submerged – it is only exposed at the point of low tide and for a longer period of time during extremely low tides. This area is teeming with life;the most notable difference between this subregion and the other three is that there is much more marine vegetation, especiallyseaweeds.There is also a great biodiversity. Organisms in this zone generally are not well adapted to periods of dryness and temperature extremes. Some of the organisms in this area areabalone,sea anemones,brown seaweed,chitons,crabs,green algae,hydroids,isopods,limpets,mussels,nudibranchs,sculpin,sea cucumber,sea lettuce,sea palms,starfish,sea urchins,shrimp,snails,sponges,surf grass,tube worms,andwhelks.Creatures in this area can grow to larger sizes because there is more availableenergyin the localized ecosystem. Also, marine vegetation can grow to much greater sizes than in the other three intertidal subregions due to the better water coverage. The water is shallow enough to allow plenty ofsunlightto reach the vegetation to allow substantialphotosyntheticactivity, and thesalinityis at almost normal levels. This area is also protected from largepredatorssuch as fish because of the wave action and the relatively shallow water.

Ecology

Main article:Intertidal ecology

See also:Intertidal fishandTide pool

ACaliforniatide pool in the low tide zone

The intertidal region is an important model system for the study ofecology,especially on wave-swept rocky shores. The region contains a high diversity of species, and the zonation created by the tides causes species ranges to be compressed into very narrow bands. This makes it relatively simple to study species across their entire cross-shore range, something that can be extremely difficult in, for instance, terrestrial habitats that can stretch thousands of kilometres. Communities on wave-swept shores also have high turnover due to disturbance, so it is possible to watchecological successionover years rather than decades.

The burrowinginvertebratesthat make up large portions of sandy beach ecosystems are known to travel relatively great distances in cross-shore directions as beaches change on the order of days, semilunar cycles, seasons, or years. The distribution of some species has been found to correlate strongly with geomorphic datums such as the high tide strand and the water table outcrop.

Since the foreshore is alternately covered by the sea and exposed to the air, organisms living in this environment must be adapted to both wet and dry conditions. Intertidal zone biomass reduces the risk of shorelineerosionfrom high intensity waves.Typical inhabitants of the intertidal rocky shore includesea urchins,sea anemones,barnacles,chitons,crabs,isopods,mussels,starfish,and many marinegastropodmolluscssuch aslimpetsandwhelks.Sexual and asexual reproduction varies by inhabitants of the intertidal zones.

Humans have historically used intertidal zones as foraged food sources during low tide.Migratory birds also rely on intertidal species for feeding areas because of low water habitats consisting of an abundance of mollusks and other marine species.

Legal issues

See also:Public trust doctrine

As with the dry sand part of a beach, legal and political disputes can arise over the ownership and use of the foreshore. One recent example is theNew Zealand foreshore and seabed controversy.In legal discussions, the foreshore is often referred to as thewet-sand area.

Beach fishing inEdgartown, Massachusetts

For privately owned beaches in theUnited States,some states such asMassachusettsuse the low-water mark as the dividing line between the property of the State and that of the beach owner; however the public still has fishing, fowling, and navigation rights to the zone between low and high water. Other states such as California use the high-water mark.

In theUnited Kingdom,the foreshore is generally deemed to be owned bythe Crown,with exceptions for what are termedseveral fisheries,which can be historic deeds to title, dating back toKing John's time or earlier, and theUdal Law,which applies generally inOrkneyandShetland.

InGreece,according to the L. 2971/01, the foreshore zone is defined as the area of the coast that might be reached by the maximum climbing of the waves on the coast (maximum wave run-up on the coast) in their maximum capacity (maximum referring to the "usually maximum winter waves" and of course not to exceptional cases, such astsunamis). The foreshore zone, a part of the exceptions of the law, is public, and permanent constructions are not allowed on it. In Italy, about half the shoreline is owned by the government but leased to private beach clubs called lidos.

In theEast Africanand West Indian Ocean, intertidal zone management is often neglected of being a priority due to there being no intent for collective economic productivity.According to workshops performing questionaries, it is stated that eighty-six percent of respondents believe mismanagement of mangrove and coastal ecosystems are due to lack of knowledge to steward the ecosystems, yet forty-four percent of respondents state that there is a fair amount of knowledge used in those regions for fisheries.

Threats

See also:Effects of climate change on oceans

Nutrition (Eutrophic) Pollution in Assateague Island National Seashore, Maryland

Intertidal zones are sensitive habitats with an abundance of marine species that can experience ecological hazards associated withtourismandhuman-induced environmental impacts.A variety of other threats that have been summarized by scientists includenutrient pollution,overharvesting,habitat destruction,andclimate change.Habitat destruction is advanced through activities including harvesting fisheries with drag nets and a neglect of the sensitivity of intertidal zones.

Gallery

• 
  Mussels in the intertidal zone inCornwall,England
• 
  Barnaclesandlimpetsin the intertidal zone near Newquay, Cornwall, England.
• 
  Atidal poolin the intertidal zone during low tide, Sunrise-on-Sea, South Africa
• 
  Unexplained crumbs of sand that appear to have been deposited around stone by escaping air
• 
  Rocks in intertidal zone completely covered by mussels, at Bangchuidao Scenic Area,Dalian,Liaoning Province,China

See also

• Ballantine Scale
• Ecological forecasting
• Littoral series
• NaGISA
• Shorezone
• Tidelands

External links

• Watch the online documentaryThe Intertidal Zone