Coastline

The coast, also known as the coastline or seashore, is defined as the area where land meets the

ocean

, or as a line that forms the boundary between the land and the

ocean

or a

lake

. The

Earth

has around of coastline. Coasts are important zones in natural

ecosystems

, often home to a wide range of

biodiversity

. On land, they harbor important ecosystems such as freshwater or estuarine

wetlands

, which are important for bird populations and other terrestrial animals. In wave-protected areas they harbor

saltmarshes

,

mangroves

or seagrasses, all of which can provide nursery habitat for finfish,

shellfish

, and other aquatic species. Rocky shores are usually found along exposed coasts and provide habitat for a wide range of sessile animals (e.g.

mussels

,

starfish

,

barnacles

) and various kinds of

seaweeds

. Along

tropical

coasts with clear, nutrient-poor water,

coral reefs

can often be found between depths of 1 – 50 m.

According to a

United Nations

atlas, 44% of all people live within 150 km (93 mi) of the sea. Because of their importance in society and high concentration of population, the coast is important for major parts of the global food and economic system, and they provide many ecosystem services to humankind. For example, important human activities happen in

port cities

. Coastal fisheries (commercial, recreational, and subsistence) and aquaculture are major economic activities and create jobs, livelihoods, and

protein

for the majority of coastal human populations. Other coastal spaces like

beaches

and seaside resorts generate large revenues through

tourism

. Coastal ecosystems can also provide protection against

sea level rise

and

tsunamis

. In many countries,

mangroves

are the primary source of wood for fuel (e.g. charcoal) and building material. Coastal ecosystems like mangroves and seagrasses have a much higher capacity for

carbon sequestration

than many terrestrial ecosystems, and as such can play a critical role in the near-future to help mitigate climate change effects by uptake of atmospheric anthropogenic carbon dioxide.

However, the economic importance of coasts makes many of these communities vulnerable to climate change which causes increases in

extreme weather

and sea level rise, and related issues such as coastal erosion, saltwater intrusion and coastal flooding. Other coastal issues, such as marine pollution,

marine debris

, coastal development, and marine ecosystem destruction, further complicate the human uses of the coast and threaten coastal ecosystems. The interactive effects of climate change, habitat destruction, overfishing and

water pollution

(especially

eutrophication

) have led to the demise of coastal ecosystem around the globe. This has resulted in population collapse of fisheries stocks, loss of biodiversity, increased invasion of alien species, and loss of heathy habitats. International attention to these issues has been captured in

Sustainable Development Goal 14

"Life Below Water" which sets goals for international policy focused on preserving coastal ecosystems and supporting more

sustainable economic practices

for coastal communities.United Nations (2017) Resolution adopted by the General Assembly on 6 July 2017, Work of the Statistical Commission pertaining to the 2030 Agenda for Sustainable Development
A/RES/71/313
Likewise, the United Nations has declared 2021-2030 the UN Decade on Ecosystem Restoration, but restoration of coastal ecosystems has received insufficient attention.

Because coasts are constantly changing, a coastline's exact

perimeter

cannot be determined; this measurement challenge is called the coastline paradox. The term ''coastal zone'' is used to refer to a region where interactions of sea and land processes occur. Both the terms ''coast'' and ''coastal'' are often used to describe a geographic location or region located on a coastline (e.g., New Zealand's West Coast, or the East, West, and Gulf Coast of the

United States

.) Coasts with a narrow continental shelf that are close to the open ocean are called ''pelagic'' ''coast'', while other coasts are more sheltered coast in a

gulf

or

bay

. A

shore

, on the other hand, may refer to parts of land adjoining any large body of water, including oceans (sea shore) and lakes (lake shore).

Size

The

Earth

has around of coastline. Coastal habitats, which extend to the margins of the

continental shelves

, make up about 7 percent of the Earth's oceans, but at least 85% of commercially harvested fish depend on coastal environments during at least part of their life cycle. As of October 2010, about 2.86% of exclusive economic zones were part of

marine protected areas

.

The definition of coasts varies. Marine scientists think of the "wet" (aquatic or intertidal) vegetated habitats as being coastal ecosystems (e.g. seagrass, salt marsh etc.) whilst some terrestrial scientist might only think of coastal ecosystems as purely terrestrial plants that live close to the seashore (see also estuaries and coastal ecosystems).

Formation

Tide

s often determine the range over which

sediment

is deposited or eroded. Areas with high tidal ranges allow waves to reach farther up the shore, and areas with lower tidal ranges produce deposition at a smaller elevation interval. The tidal range is influenced by the size and shape of the coastline. Tides do not typically cause erosion by themselves; however,

tidal bore

s can erode as the waves surge up the river

estuaries

from the ocean.

Geologists classify coasts on the basis of tidal range into ''macrotidal coasts'' with a tidal range greater than 4 meters (13 feet); ''mesotidal coasts'' with a tidal range of 2 to 4 meters (7 to 13 feet); and ''microtidal coasts'' with a tidal range of less than 2 meters (7 feet). The distinction between macrotidal and mesotidal coasts is more important. Macrotidal coasts lack barrier islands and lagoons, and are characterized by funnel-shaped estuaries containing sand ridges aligned with tidal currents. Wave action is much more important for determining bedforms of sediments deposited along mesotidal and microtidal coasts than in macrotidal coasts.

Waves erode coastline as they break on shore releasing their energy; the larger the wave the more energy it releases and the more sediment it moves. Coastlines with longer shores have more room for the waves to disperse their energy, while coasts with cliffs and short shore faces give little room for the wave energy to be dispersed. In these areas, the wave energy breaking against the cliffs is higher, and air and water are compressed into cracks in the rock, forcing the rock apart, breaking it down. Sediment deposited by waves comes from eroded cliff faces and is moved along the coastline by the waves. This forms an abrasion or cliffed coast.

Sediment deposited by rivers is the dominant influence on the amount of sediment located in the case of coastlines that have estuaries. Today riverine deposition at the coast is often blocked by dams and other human regulatory devices, which remove the sediment from the stream by causing it to be deposited inland. Coral reefs are a provider of sediment for coastlines of tropical islands.

Like the ocean which shapes them, coasts are a dynamic environment with constant change. The

Earth

's natural processes, particularly

sea level rise

s, waves and various

weather

phenomena, have resulted in the

erosion

, accretion and reshaping of coasts as well as flooding and creation of

continental shelves

and drowned river valleys (

ria

s).

Importance for humans and ecosystems

Human settlements

More and more of the world's people live in coastal regions. According to a

United Nations

atlas, 44% of all people live within 150 km (93 mi) of the sea. Many major cities are on or near good

harbor

s and have

port

facilities. Some landlocked places have achieved port status by building

canal

s.

Nations defend their coasts against military invaders, smugglers and illegal migrants. Fixed coastal defenses have long been erected in many nations, and coastal countries typically have a

navy

and some form of

coast guard

.
File:花蓮新社梯田.jpg,

Paddy field

s by the coast of Fengbin, Hualien as viewed from Port Fòrum, with

Montjuïc

and

Port Vell

can also be seen.

Tourism

Coasts, especially those with beaches and warm water, attract tourists often leading to the development of seaside resort communities. In many island nations such as those of the

Mediterranean

, South Pacific Ocean and Caribbean,

tourism is central to the economy

. Coasts offer recreational activities such as swimming, fishing, surfing, boating, and

sunbathing

.

Growth management and coastal management can be a challenge for coastal local authorities who often struggle to provide the infrastructure required by new residents, and poor management practices of construction often leave these communities and infrastructure vulnerable to processes like coastal erosion and

sea level rise

. In many of these communities, management practices such as beach nourishment or when the coastal infrastructure is no longer financially sustainable, managed retreat to remove communities from the coast.
File:Maarianhamina SNV10312 -2B.jpg, A passenger car ferry arrives at the coast of

Mariehamn

, Åland.
File:Tiburon.jpg, Houses close to the coast, like these in Tiburon, California, may be especially desirable properties.

Ecosystem services

Types

Emergent coastline

According to one principle of classification, an emergent coastline is a coastline that has experienced a fall in sea level, because of either a global sea-level change, or local uplift. Emergent coastlines are identifiable by the coastal

landform

s, which are above the high tide mark, such as raised beaches. In contrast, a submergent coastline is one where the sea level has risen, due to a global sea-level change, local subsidence, or

isostatic rebound

. Submergent coastlines are identifiable by their submerged, or "drowned" landforms, such as

ria

s (drowned valleys) and

fjord

s

Concordant coastline

According to the second principle of classification, a concordant coastline is a coastline where bands of different rock types run parallel to the shore. These rock types are usually of varying resistance, so the coastline forms distinctive landforms, such as coves. Discordant coastlines feature distinctive landforms because the rocks are

eroded

by the ocean

wave

s. The less resistant rocks erode faster, creating

inlet

s or

bay

; the more resistant rocks erode more slowly, remaining as

headland

s or

outcrop

pings.

Other coastal categories

* A cliffed coast or abrasion coast is one where marine action has produced steep declivities known as

cliff

s.
* A flat coast is one where the land gradually descends into the sea.
* A graded shoreline is one where wind and water action has produced a flat and straight coastline.

Landforms

The following articles describe some coastal landforms:

*

Bay

*

Headland

*

Cove

*

Peninsula

Cliff erosion

* Much of the sediment deposited along a coast is the result of erosion of a surrounding

cliff

, or bluff. Sea cliffs retreat landward because of the constant undercutting of slopes by waves. If the slope/cliff being undercut is made of unconsolidated sediment it will erode at a much faster rate than a cliff made of bedrock.
* A

natural arch

is formed when a headland is eroded through by waves.
* Sea caves are made when certain rock beds are more susceptible to erosion than the surrounding rock beds because of different areas of weakness. These areas are eroded at a faster pace creating a hole or crevice that, through time, by means of wave action and erosion, becomes a cave.
* A stack is formed when a headland is eroded away by wave and wind action.
* A stump is a shortened sea stack that has been eroded away or fallen because of instability.
* Wave-cut notches are caused by the undercutting of overhanging slopes which leads to increased stress on cliff material and a greater probability that the slope material will fall. The fallen debris accumulates at the bottom of the cliff and is eventually removed by waves.
* A

wave-cut platform

forms after erosion and retreat of a sea cliff has been occurring for a long time. Gently sloping wave-cut platforms develop early on in the first stages of cliff retreat. Later, the length of the platform decreases because the waves lose their energy as they break further offshore.

Coastal features formed by sediment

*

Beach

* Beach cusps
* Cuspate foreland
*

Dune system

* Mudflat
* Raised beach
*

Ria

* Shoal
* Spit
* Strand plain
* Surge channel
* Tombolo

Coastal features formed by another feature

*

Lagoon

*

Salt marsh

*

Mangrove forests

*

Kelp forests

*

Coral reefs

* Oyster reefs

Other features on the coast

* Concordant coastline
* Discordant coastline
* Fjord
* Island
* Island arc
* Machair

In geology

The identification of bodies of rock formed from sediments deposited in shoreline and nearshore environments (shoreline and nearshore ''Facies (geology), facies'') is extremely important to geologists. These provide vital clues for reconstructing the geography of ancient continents (''paleogeography''). The locations of these beds show the extent of ancient seas at particular points in geological time, and provide clues to the magnitudes of tides in the distant past.

Sediments deposited in the shoreface are preserved as lenses of sandstone in which the upper part of the sandstone is coarser than the lower part (a ''coarsening upwards sequence''). Geologists refer to these are ''parasequences''. Each records an episode of retreat of the ocean from the shoreline over a period of 10,000 to 1,000,000 years. These often show Lamination (geology), laminations reflecting various kinds of tidal cycles.

Some of the best-studied shoreline deposits in the world are found along the former western shore of the Western Interior Seaway, a shallow sea that flooded central North America during the late Cretaceous Period (geology), Period (about 100 to 66 million years ago). These are beautifully exposed along the Book Cliffs of Utah and Colorado.

Geologic processes

The following articles describe the various geologic processes that affect a coastal zone:

* Attrition (weathering), Attrition
* Ocean current, Currents
* Denudation
* Deposition (geology), Deposition
* Erosion
* Flooding
* Longshore drift
* Marine sediments
* Saltation (geology), Saltation
* Sea level change
** eustatic
** isostasy, isostatic
* Sedimentation
* Coastal sediment supply
** sediment transport
** Solution (chemistry), solution
** subaerial processes
** Suspension (chemistry), suspension
*

Tide

s
* Wind wave, Water waves
** diffraction
** refraction
** wave breaking
** wave shoaling
* Weathering

Wildlife

Animals

Larger animals that live in coastal areas include Puffin, puffins, Sea turtle, sea turtles and Rockhopper penguin, rockhopper penguins, among many others. Gastropoda, Sea snails and various kinds of

barnacles

live on rocky coasts and scavenge on food deposited by the sea. Some coastal animals are used to humans in developed areas, such as Dolphin, dolphins and seagulls who eat food thrown for them by tourists. Since the coastal areas are all part of the littoral zone, there is a profusion of marine life found just off-coast, including Sessility (motility), sessile animals such as Coral, corals, sponges, starfish, mussels, seaweeds, fishes, and Sea anemone, sea anemones.

There are many kinds of seabirds on various coasts. These include pelicans and cormorants, who join up with terns and oystercatchers to forage for fish and shellfish. There are sea lions on the coast of Wales and other countries.

Coastal fish

Plants

Many coastal areas are famous for their kelp beds. Kelp is a fast-growing seaweed that can grow up to half a meter a day in ideal conditions. Mangroves, Seagrass, seagrasses, macroalgal beds, and salt marsh are important coastal vegetation types in tropical and temperate environments respectively. Restinga is another type of coastal vegetation.

Threats

Coasts also face many Human impact on the environment, human-induced environmental impacts and coastal development hazards. The most important ones are sea level rise, and associated issues like coastal erosion and saltwater intrusion, and

water pollution

, such as Oil spill, oil spills or

marine debris

contaminating coasts with plastic and other trash.

Sea level rise due to climate change

Pollution

The pollution of coastlines is connected to marine pollution which can occur from a number of sources: Marine debris (garbage and industrial debris); the Petroleum transport, transportation of petroleum in tanker (ship), tankers, increasing the probability of large oil spills; small oil spills created by large and small vessels, which flush bilge water into the ocean.

Marine pollution

Marine debris

Microplastics

Global goals

International attention to address the threats of coasts has been captured in

Sustainable Development Goal 14

"Life Below Water" which sets goals for international policy focused on preserving coastal ecosystems and supporting more

sustainable economic practices

for coastal communities. Likewise, the United Nations has declared 2021-2030 the UN Decade on Ecosystem Restoration, but restoration of coastal ecosystems has received insufficient attention.

Statistics

While there is general agreement in the scientific community regarding the definition of coast, in the political sphere, the delineation of the extents of a coast differ according to jurisdiction. Government authorities in various countries may define coast differently for economic and social policy reasons.

Length of coastline

See also

* Beach cleaning
* Coastal and Estuarine Research Federation
* Coastline of the North Sea
* European Atlas of the Seas
* Intertidal zone
* Land reclamation
* List of countries by length of coastline
* List of U.S. states by coastline
* Marine coastal ecosystem
* Nautical chart

References

External links

Woods Hole Oceanographic Institution
- organization dedicated to ocean research, exploration, and education

{{Authority control

Coasts,
Coastal and oceanic landforms
Coastal geography
Oceanographical terminology
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