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| Marine habitats |
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| Coastal habitats |
| Ocean surface |
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Theintertidal zone orforeshore is the area abovewater level at lowtide andunderwater at high tide; in other words, it is the part of thelittoral zone within thetidal range. This area can include several types ofhabitats with various species oflife, such assea stars,sea urchins, and many species ofcoral with regional differences in biodiversity. Sometimes it is referred to as thelittoral zone orseashore, although those can be defined as a wider region.
The intertidal zone also includes steep rockycliffs, sandybeaches,bogs orwetlands (e.g., vastmudflats). This area can be a narrow strip, such as inPacific islands that have only a narrow tidal range, or can include many meters of shoreline where shallow beach slopes interact with high tidal excursion. Theperitidal zone is 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 competition and the rapidly changing conditions that come with thetides.[1] 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 highlysaline and drysalt, with drying between tidal inundations.Wave splash can dislodge residents from the littoral zone. With the intertidal zone's high exposure tosunlight, thetemperature can range from very hot with fullsunshine to near freezing in colder climates. Somemicroclimates in the littoral zone are moderated by local features and larger plants such asmangroves.Adaptations in the littoral zone allow the utilization ofnutrients supplied 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 shore can be divided into a spray zone or splash zone (also known as thesupratidal zone), which is above thespring high-tide line and 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 biomes orhabitats, includingestuaries, theneritic zone, thephotic zone, anddeep zones.
Marine biologists divide the intertidal region into three zones (low, middle, and high), based on the overall average exposure of the zone.[2] 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 pools form in depressions that fill with water as the tide rises. Under certain conditions, such as those atMorecambe Bay,quicksand may form.[3]
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;[2] 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 availableenergy in 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 ofsunlight to reach the vegetation to allow substantialphotosynthetic activity, and thesalinity is at almost normal levels. This area is also protected from largepredators such as fish because of the wave action and the relatively shallow water.
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 succession over years rather than decades.
The burrowinginvertebrates that 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 shorelineerosion from high intensity waves.[4] Typical inhabitants of the intertidal rocky shore includesea urchins,sea anemones,barnacles,chitons,crabs,isopods,mussels,starfish, and many marinegastropodmolluscs such aslimpets andwhelks. Sexual and asexual reproduction varies by inhabitants of the intertidal zones.[5]
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.[4]
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.
For privately owned beaches in theUnited States, some states such asMassachusetts use 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 inOrkney andShetland.
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.[6]
In theEast African and West Indian Ocean, intertidal zone management is often neglected of being a priority due to there being no intent for collective economic productivity.[7] 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.[citation needed]
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Intertidal zones are sensitive habitats with an abundance of marine species that can experience ecological hazards associated withtourism andhuman-induced environmental impacts. A variety of other threats that have been summarized by scientists includenutrient pollution,overharvesting,habitat destruction, andclimate change.[8] Habitat destruction is advanced through activities including harvesting fisheries with drag nets and a neglect of the sensitivity of intertidal zones.[9]
