SEA CUCUMBER (HOLOTHUROIDEA)

Sea Cucumbers are echinoderms from the class Holothuroidea. They are marine animals with a leathery skin and an elongated body containing a single, branched gonad. Sea cucumbers are found on the sea floor worldwide. The number of holothurianpron.: /ˌhɒlɵˈθjʊəriən/ species worldwide is about 1250 with the greatest number being in the Asia Pacific region. Many of these are gathered for human consumption and some species are cultivated in aquaculture systems. The harvested product is variously referred to as trepang, bêche-de-mer or balate. Sea cucumbers serve a useful purpose in the marine ecosystem as they help recycle nutrients, breaking down detritus and other organic matter after which bacteria can continue the degradation process.

Like all echinoderms, sea cucumbers have an endoskeleton just below the skin, calcified structures that are usually reduced to isolated microscopic ossicles (or sclerietes) joined by connective tissue. In some species these can sometimes be enlarged to flattened plates, forming an armour. In pelagic species such as Pelagothuria natatrix (Order Elasipodida, family Pelagothuriidae), the skeleton and a calcareous ring are absent.

The Sea Cucumbers are named for their resemblance to the vegetable Cucumber, but are not related to the Cucumis sativus vine.

Overview

Sea cucumbers communicate with each other by sending hormone signals through the water.

A remarkable feature of these animals is the catch collagen that forms their body wall. This can be loosened and tightened at will, and if the animal wants to squeeze through a small gap, it can essentially liquefy its body and pour into the space. To keep itself safe in these crevices and cracks, the sea cucumber will hook up all its collagen fibres to make its body firm again.

   A sea cucumber in Mahé, Seychelles ejects sticky filaments from the anus in self-defence

Some species of coral-reef sea cucumbers within the order Aspidochirotida can defend themselves by expelling their sticky cuvierian tubules (enlargements of the respiratory tree that float freely in the coelom) to entangle potential predators. When startled, these cucumbers may expel some of them through a tear in the wall of the cloaca in an autotomic process known as evisceration. Replacement tubules grow back in one-and-a-half to five weeks, depending on the species. The release of these tubules can also be accompanied by the discharge of a toxic chemical known as holothurin, which has similar properties to soap. This chemical can kill any animal in the vicinity and is one more way in which these sedentary animals can defend themselves.

If the water temperature becomes too high, some species of sea cucumber from temperate seas can aestivate. While they are in this state of dormancy they stop feeding, their gut atrophies, their metabolism slows down and they lose weight. The body returns to its normal state when conditions improve.

They can be found in great numbers on the deep seafloor, where they often make up the majority of the animal biomass. At depths deeper than 5.5 mi (8.8 km), sea cucumbers comprise 90% of the total mass of the macrofauna. Sea cucumbers form large herds that move across the bathygraphic features of the ocean, hunting food. The body of some deep water holothurians, such as Enypniastes eximia, Peniagone leander and Paelopatides confundens, is made of a tough gelatinous tissue with unique properties that makes the animals able to control their own buoyancy, making it possible for them to either live on the ocean floor or to actively swim  or float over it in order to move to new locations,

In more shallow waters, sea cucumbers can form dense populations. The strawberry sea cucumber (Squamocnus brevidentis) of New Zealand lives on rocky walls around the southern coast of the South Island where populations sometimes reach densities of 1,000 animals per square meter. For this reason, one such area in Fiordland is simply called the strawberry fields.

  Emperor shrimp Periclimenes imperator on a Bohadschia argus sea cucumber

A variety of fish, most commonly pearl fish, have evolved a commensalistic symbiotic relationship with sea cucumbers in which the pearl fish will live in sea cucumber's cloaca using it for protection from predation, a source of food (the nutrients passing in and out of the anus from the water), and to develop into their adult stage of life. Many polychaete worms and crabs have also specialized to use the cloacal respiratory trees for protection by living inside the sea cucumber.

The largest American species, Holothuria floridana, which abounds just below low-water mark on the Florida reefs, has volumes well over 500 cubic centimeters.

Visitors to the Mariana Islands often encounter the local variation, called balate, which litters the seafloor all around the island, including in water as shallow as 3 feet (91 cm). These jet black sea cucumbers are normally 10 to 12 inches (25 to 30 cm) long, 1.5 to 2.0 inches (3.8 to 5.1 cm) in diameter and are often curled up, partially covered with sand from the seafloor.

The most common way to separate the subclasses is by looking at their oral tentacles. Subclass Dendrochirotacea has 8-30 oral tentacles, subclass Aspidochirotacea has 10-30 leaflike or shieldlike oral tentacles, while subclass Apodacea may have up to 25 simple or pinnate oral tentacles and is also characterized by reduced or absent tube feet, as in the order Apodida.

Anatomy

  Conspicuous Sea Cucumber, Coconut Island, Hawaii

Sea cucumbers are typically 10 to 30 centimetres (3.9 to 12 in) in length, although the smallest known species is just 3 millimetres (0.12 in) long, and the largest can reach 1 metre (3.3 ft). The body ranges from almost spherical to worm-like, and lacks the arms found in many other echinoderms, such as starfish. The anterior end of the animal, containing the mouth, corresponds to the oral pole of other echinoderms (which, in most cases, is the underside), while the posterior end, containing the anus, corresponds to the aboral pole. Thus, compared with other echinoderms, sea cucumbers can be said to be lying on their side.

Body plan

The body of a holothurian is roughly cylindrical. It is radially symmetrical along its longitudinal axis, and has weak bilateral symmetry transversely with a dorsal and a ventral surface. As in other Echinozoans, there are five ambulacra separated by five ambulacral grooves, the interambulacra. The ambulacral grooves bear four rows of tube feet but these are diminished in size or absent in some holothurians, especially on the dorsal surface. The two dorsal abulacra make up the bivium while the three ventral ones are known as the trivium.

At the anterior end, the mouth is surrounded by a ring of tentacles which are usually retractable into the mouth. These are modified tube feet and may be simple, branched or arborescent. They are known as the introvert and posterior to them there is an internal ring of large calcareous ossicles. Attached to this are five bands of muscle running internally longitudinally along the ambulacra. There are also circular muscles, contraction of which cause the animal to elongate and the introvert to extend. Anterior to the ossicles lie further muscles, contraction of which cause the introvert to retract.

The body wall consists of an epidermis and a dermis and contains smaller calcareous ossicles, the types of which are characteristics which help to identify different species. Inside the body wall is the coelom which is divided by three longitudinal mesenteries which surround and support the internal organs.

Diet and digestive system

  A sea cucumber atop gravel, feeding

Holothuroidea are generally scavengers, feeding on debris in the benthic zone of the ocean. Exceptions include pelagic cucumbers and the species Rynkatropa pawsoni, which has a commensal relationship with deep-sea anglerfish. The diet of most cucumbers consists of plankton and decaying organic matter found in the sea. Some sea cucumbers position themselves in currents and catch food that flows by with their open tentacles. They also sift through the bottom sediments using their tentacles. Other species can dig into bottom silt or sand until they are completely buried. They then extrude their feeding tentacles, ready to withdraw at any hint of danger.

In the South Pacific the cukes may be found in densities of 33 specimens per square yard (40 per m2). These populations can process 34 pounds of sediment per square yard per year.

A pharynx lies behind the mouth and is surrounded by a ring of ten calcareous plates. In most sea cucumbers, this is the only substantial part of the skeleton, and it forms the point of attachment for muscles that can retract the tentacles into the body for safety as for the main muscles of the body wall. Many species possess an oesophagus and stomach, but in some the pharynx opens directly into the intestine. The intestine is typically long and coiled, and loops through the body three times before terminating in a cloacal chamber, or directly as the anus.

Nervous system

Sea cucumbers have no true brain. A ring of neural tissue surrounds the oral cavity, and sends nerves to the tentacles and the pharynx. The animal is, however, quite capable of functioning and moving about if the nerve ring is surgically removed, demonstrating that it does not have a central role in nervous coordination. In addition, five major nerves run from the nerve ring down length of the body beneath each of the ambulacral areas.

Most sea cucumbers have no distinct sensory organs, although there are various nerve endings scattered through the skin giving the animal a sense of touch and a sensitivity to the presence of light. There are, however, a few exceptions; members of the Apodida order are known to possess statocysts, while some species possess small eye-spots near the bases of their tentacles.

Respiratory system

Sea cucumbers extract oxygen from water in a pair of "respiratory trees" that branch off the cloaca just inside the anus, so that they "breathe" by drawing water in through the anus and then expelling it. The trees consist of a series of narrow tubules branching from a common duct, and lie on either side of the digestive tract. Gas exchange occurs across the thin walls of the tubules, to and from the fluid of the main body cavity.

Together with the intestine, the respiratory trees also act as excretory organs, with nitrogenous waste diffusing across the tubule walls in the form of ammonia and phagocytic coelomocytes depositing particulate waste.

Circulatory systems

Like all echinoderms, sea cucumbers possess both a water vascular system that provides hydraulic pressure to the tentacles and tube feet, allowing them to move, and a haemal system. The latter is more complex than that in other echinoderms, and consists of well-developed vessels as well as open sinuses.

A central haemal ring surrounds the pharynx next to the ring canal of the water vascular system, and sends off additional vessels along the radial canals beneah the ambulacral areas. In the larger species, additional vessels run above and below the intestine and are connected by over a hundred small muscular ampullae, acting as miniature hearts to pump blood around the haemal system. Additional vessels surround the respiratory trees, although they contact them only indirectly, via the coelomic fluid.

Indeed, the blood itself is essentially identical with the coelomic fluid that bathes the organs directly, and also fills the water vascular system. Phagocytic coelomocytes, somewhat similar in function to the white blood cells of vertebrates, are formed within the haemal vessels, and travel throughout the body cavity as well as both circulatory systems. An additional form of coelomocyte, not found in other echinoderms, has a flattened discoid shape, and contains haemoglobin. As a result, in many (though not all) species, both the blood and the coelomic fluid are red in colour.

Vanadium has been reported in high concentrations in holothurian blood, however researchers have been unable to reproduce these results.

Locomotion and exoskeleton

 Pelagic sea cucumbers, often confused with jellyfish, have webbed swimming structures enabling them to swim up off the surface of the seafloor and journey as much as 1000 metres up the water column

Like all echinoderms, sea cucumbers possess pentaradial symmetry. However, because of their posture, they have secondarily evolved a degree of bilateral symmetry. For example, because one side of the body is typically pressed against the substratum, and the other is not, there is usually some difference between the two surfaces. Like sea urchins, most sea cucumbers have five strip-like ambulacral areas running along the length of the body from the mouth to the anus. The three on the lower surface have numerous tube feet, often with suckers, that allow the animal to crawl along. The two on the upper surface have under-developed or vestigial tube feet, and, in some species, lack tube feet altogether.

In some species, the ambulacral areas can no longer be distinguished, with tube feet spread over a much wider area of the body. Those of the subclass Apodacea have no tube feet or ambulacral areas at all, and burrow through sediment with muscular contractions of their body.

However, even in those sea cucumbers that lack regular tube feet, those immediately around the mouth are always present. These are highly modified into retractile tentacles, much larger than the regular tube feet. Sea cucumbers have between ten and thirty such tentacles, depending on the species.

Many sea cucumbers have papillae, conical fleshy projections of the body wall with sensory tube feet at their apices.

Echinoderms typically possess an internal skeleton composed of plates of calcium carbonate. In most sea cucumbers, however, these have become reduced to microscopic ossicles embedded beneath the skin. A few genera, such as Sphaerothuria, retain relatively large plates, giving them a scaly armour.

Reproduction and life cycle

Most sea cucumbers reproduce by releasing sperm and ova into the ocean water. Depending on conditions, one organism can produce thousands of gametes. Sea cucumbers are typically dioecious, with separate male and female individuals, but some species are protandric. The reproductive system consists of a single gonad, consisting of a cluster of tubules emptying into a single duct that opens on the upper surface of the animal, close to the tentacles.

At least 30 species, including the red-chested sea cucumber (Pseudocnella insolens), fertilise their eggs internally and then pick up the fertilised zygote with one of their feeding tentacles. The egg is then inserted into a pouch on the adult's body, where it develops and eventually hatches from the pouch as a juvenile sea cucumber.  A few species are known to brood their young inside the body cavity, giving birth through a small rupture in the body wall close to the anus.

In all other species, the egg develops into a free-swimming larva, typically after around three days of development. The first stage of larval development is known as an auricularia, and is only around 1 millimetre (0.039 in) in length. This larva swims by means of a long band of cilia wrapped around its body, and somewhat resembles the bipinnaria larva of starfish. As the larva grows it transforms into the doliolaria, with a barrel-shaped body and three to five separate rings of cilia. The tentacles are usually the first adult features to appear, before the regular tube feet.

Holothurians as food and medicine

  Dried sea cucumbers in a Japanese pharmacy

To supply the markets of Southern China, Macassan trepangers traded with the Indigenous Australians of Arnhem Land. This Macassan contact with Australia is the first recorded example of trade between the inhabitants of the Australian continent and their Asian neighbours.

There are many commercially important species of sea cucumber that are harvested and dried for export for use in Chinese cuisine as Hoi sam. Some of the more commonly found species in markets include:

• Holothuria scabra
• Holothuria fuscogilva
• Actinopyga mauritiana
• Stichius japonicus
• Parastichopus californicus
• Thelenota ananas
• Acaudina molpadioides
• Isostichopus fuscus

Some varieties of sea cucumber (known as gamat in Malaysia or teripangin Indonesia) are said to have excellent healing properties. There are pharmaceutical companies being built based on gamat. Extracts are prepared and made into oil, cream, or cosmetics. Some products are intended to be taken internally. A single study conducted on an unreported number of mice found intraperitoneal injection of sea cucumber extract to be somewhat effective in high doses (100 mg/kg) against internal pain, but ineffective against externally induced pain. Another study suggested that the sea cucumber contains all the fatty acids necessary to play a potentially active role in tissue repair.

On December 21, 2007, a study published in PLoS Pathogens found that a lectin from Cucumaria echinata impaired the development of the malaria parasite when produced by transgenic mosquitoes.

Commercial harvest

In recent years, the sea cucumber industry in Alaska has increased due to increased export of the skins and muscles to China.

In China, sea cucumbers are farmed commercially in artificial ponds. These ponds can be as large as 1,000 acres (400 ha), and satisfy much of the local demand. Wild sea cucumbers are caught by divers and these wild Alaskan sea cucumbers have higher nutritional value and are larger than farmed Chinese sea cucumbers. Larger size and higher nutritional value has allowed the Alaskan fisheries to continue to compete for market share, despite the increase in local, Chinese sea cucumber farming.

One of Australia's oldest fisheries is the collection of sea cucumber, harvested by divers from throughout the Coral Sea in far North Queensland, Torres Straits and Western Australia. In the late 1800s there were as many as 400 divers operating from Cooktown, Queensland. The main target species today are White Teat Fish, Black Fish and Sand Fish, caught by divers in waters as deep as 40 meters.

Aquaculture

Overexploitation of sea cucumber stocks in many parts of the world, provided motivation for the development of sea cucumber aquaculture in the early 1980s. The Chinese and Japanese were the first to develop successful hatchery technology on Apostichopus japonicus, prized for its high meat content and success in commercial hatcheries.  A second species, Holothuria scabra, was cultured for the first time using the techniques pioneered by the Chinese and Japanese for by India in 1988.  In recent years Australia, Indonesia, New Caledonia, Maldives, Solomon Islands and Viet Nam have also successfully cultured H. scabra using the same technology and has since been expanded to other species.

In art and literature

Sea cucumber (a - Tentacles, b - Cloaca, c - Ambulacral feet on the ventral side, d - Papillae on the back)

Edgar Allan Poe's only novel, The Narrative of Arthur Gordon Pym of Nantucket(1838), includes in its twentieth chapter a long, detailed description of sea cucumbers, which the narrator calls biche de mer.

The first movement of French pianist Erik Satie's Embryons desséchés is titled "D'Holothournie". It is said to emulate the "purring" of the Holothourian.

Sea cucumbers have inspired thousands of haiku in Japan, where they are called namako(海鼠), written with characters that can be translated "sea mice" (an example of gikun). In English translations of these haiku, they are usually called "sea slugs". According to the Oxford English Dictionary, the English term "sea slug" was originally applied to holothurians during the 18th century. The term is now applied to several groups of sea snails, marine gastropod mollusks that have no shell or only a very reduced shell, including the nudibranchs. Almost 1,000 Japanese holothurian haiku translated into English appear in the book Rise, Ye Sea Slugs! by Robin D. Gill.

Nobel laureate poet Wisława Szymborska wrote a poem which mentions holothurians, titled "Autotomy".

Source :

http://en.wikipedia.org/wiki/Sea_cucumber

Sea Cucumber

COASTAL ZONE (GENERAL INTRODUCTION)

A coastlineor seashore is the area where land meets the sea or ocean.  A precise line that can be called a coastline cannot be determined due to the dynamic nature of tides. The term "coastal zone" can be used instead, which is a spatial zone where interaction of the sea and land processes occurs.  Both the terms coast and coastal are often used to describe a geographic location or region; for example, New Zealand's West Coast, or the East and West Coasts of the United States.

A pelagic coast refers to a coast which fronts the open ocean, as opposed to a more sheltered coast in a gulf or bay. A shore, on the other hand, can refer to parts of the land which adjoin any large body of water, including oceans (sea shore) and lakes (lake shore). Similarly, the somewhat related term "bank" refers to the land alongside or sloping down to a river (riverbank) or to a body of water smaller than a lake. "Bank" is also used in some parts of the world to refer to an artificial ridge of earth intended to retain the water of a river or pond. In other places this may be called a levee.

While many scientific experts might agree on a common definition of the term "coast", the delineation of the extents of a coast differ according to jurisdiction, with many scientific and government authorities in various countries differing for economic and social policy reasons.

Formation

 Atlantic rocky coastline, showing a surf area. Porto Covo, west coast of Portugal

Tides 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 deprossosition 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 bores can erode as the waves surge up river estuaries from the ocean.

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 on a coastline.  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.

Like the ocean which shapes them, coasts are a dynamic environment with constant change. The Earth's natural processes, particularly sea level rises, 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 (rias).

Environmental importance

The coast and its adjacent areas on and off shore are an important part of a local ecosystem: the mixture of fresh water and salt water in estuaries provides many nutrients for marine life. Salt marshes and beaches also support a diversity of plants, animals, and insects crucial to the food chain.

The high level of biodiversity creates a high level of biological activity, which has attracted human activity for thousands of years.

Human impacts

Human uses of coasts

 A settled coastline in Marblehead, Massachusetts. Once a fishing port, the harbor is now dedicated to tourism and pleasure boating. Observe that the sand and rocks have been darkened by oil slick up to the high-water line.

 This stretch of coast in Tanzania's capital Dar es Salaam serves as a public waste dump.

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

View of sea coast from top of a hill at Visakhapatnam in India

More and more of the world's people live in coastal regions.  Many major cities are on or near good harbors and have port facilities. Some landlocked places have achieved port status by building canals.

The coast is a frontier that nations have typically defended 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.

Coasts, especially those with beaches and warm water, attract tourists. In many island nations such as those of the Mediterranean, South Pacific and Caribbean, tourism is central to the economy. Coasts offer recreational activities such as swimming, fishing, surfing, boating, and sunbathing. Growth management can be a challenge for coastal local authorities who often struggle to provide the infrastructure required by new residents.

Threats to a coast

Coasts also face many human-induced environmental impacts. The human influence on climate change is thought to contribute to an accelerated trend in sea level rise which threatens coastal habitats.

Pollution can occur from a number of sources: garbage and industrial debris; the transportation of petroleum in tankers, increasing the probability of large oil spills; small oil spills created by large and small vessels, which flush bilge water into the ocean.

Fishing has declined due to habitat degradation, overfishing, trawling, bycatch and climate change. Since the growth of global fishing enterprises after the 1950s, intensive fishing has spread from a few concentrated areas to encompass nearly all fisheries. The scraping of the ocean floor in bottom dragging is devastating to coral, sponges and other long-lived species that do not recover quickly. This destruction alters the functioning of the ecosystem and can permanently alter species composition and biodiversity. Bycatch, the capture of unintended species in the course of fishing, is typically returned the ocean only to die from injuries or exposure. Bycatch represents about a quarter of all marine catch. In the case of shrimp capture, the bycatch is five times larger than the shrimp caught.

It is believed that melting Arctic ice will cause sea levels to rise and flood costal areas.

Conservation

Extraordinary population growth in the 20th century has placed stress on the planet's ecosystems. For example, on Saint Lucia, harvesting mangrove for timber and clearing for fishing reduced the mangrove forests, resulting in a loss of habitat and spawning grounds for marine life that was unique to the area. These forests also helped to stabilize the coastline. Conservation efforts since the 1980s have partially restored the ecosystem.

Types of coast

According to one principle of classification, an emergent coastline is a coastline which 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 landforms, 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 rias (drowned valleys) and fjords.

According to a 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 ocean waves. The less resistant rocks erode faster, creating inlets or bays; the more resistant rocks erode more slowly, remaining as headlands or outcroppings.

Other coastal categories:

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

Coastal landforms

Coastal landforms. The feature shown here as a bay would, in certain (mainly southern) parts of Britain, be called a cove. That between the cuspate foreland and the tombolo is a British bay.

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 then a cliff made of bedrock. (Easterbrook 1999).
• A Natural arch is formed when a sea stacks 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 crevasse 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 off shore (Easterbrook 1999).

Animals

A wide variety of animals live along a typical coast. Some birds nest there, like puffins, sea turtles and rockhopper penguins. Sea snails and various kinds of barnacles live on the coast and scavenge on food deposited by the sea. Most coastal animals are used to humans in developed areas, such as 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.

There are many kinds of seabirds on the coast. Pelicans and cormorants join up with terns and oystercatchers to forage for fish and shellfish on the coast. There are sea lions on the coast of Wales and other countries.

Plants

Coastal areas are famous for their kelp beds. Kelp is a fast growing seaweed that grows up to a metre a day. Corals and anemones are true animals, but live a similar lifestyle as plants do. Mangroves, Seagrasses and salt marsh are important coastal vegetation types in tropical and temperate environments respectively.

Coastline statistics

Coastline problem

Shortly before 1951, Lewis Fry Richardson, in researching the possible effect of border lengths on the probability of war, noticed that the Portuguese reported their measured border with Spain to be 987 km, but the Spanish reported it as 1214 km. This was the beginning of the coastline problem, which is a mathematical uncertainly inherent in the measurement of boundaries that are irregular.

The prevailing method of estimating the length of a border (or coastline) was to lay out n equal straight-line segments of length ℓ with dividers on a map or aerial photograph. Each end of the segment must be on the boundary. Investigating the discrepancies in border estimation, Richardson discovered what is now termed the Richardson Effect: the sum of the segments is inversely proportional to the common length of the segments. In effect, the shorter the ruler, the longer the measured border; thus, the Spanish and Portuguese geographers were using different-length rulers.

The result most astounding to Richardson is that, under certain circumstances, as ℓapproaches zero, the length of the coastline approaches infinity. Richardson had believed, based on Euclidean geometry, that a coastline would approach a fixed length, as do similar estimations of regular geometric figures. For example, the perimeter of a regular polygon inscribed in a circle approaches the circumference with increasing numbers of sides (and decrease in the length of one side). In Geometric measure theory such a smooth curve as the circle that can be approximated by small straight segments with a definite limit is termed a rectifiable curve.

Measuring a coastline

More than a decade after Richardson completed his work, Benoît Mandelbrot developed a new branch of mathematics, fractal geometry, to describe just such non-rectifiable complexes in nature as the infinite coastline.  His own definition of the new figure serving as the basis for his study is:

I coined fractalfrom the Latin adjective fractus. The corresponding Latin verb frangeremeans "to break:" to create irregular fragments. It is therefore sensible ... that, in addition to "fragmented" ... fractusshould also mean "irregular."

A key property of the fractal is self-similarity; that is, at any scale the same general configuration appears. A coastline is perceived as bays alternating with promontories. In the hypothetical situation that a given coastline has this property of self-similarity, then no matter how greatly any one small section of coastline is magnified, a similar pattern of smaller bays and promontories superimposed on larger bays and promontories appears, right down to the grains of sand. At that scale the coastline appears as a momentarily shifting, potentially infinitely long thread with a stochastic arrangement of bays and promontories formed from the small objects at hand. In such an environment (as opposed to smooth curves) Mandelbrot asserts "coastline length turns out to be an elusive notion that slips between the fingers of those who want to grasp it."

There are different kinds of fractals. A coastline with the stated property is in "a first category of fractals, namely curves whose fractal dimension is greater than 1." That last statement represents an extension by Mandelbrot of Richardson's thought. Mandelbrot's statement of the Richardson Effect is:

where L, coastline length, a function of the measurement unit, ε, is approximated by the expression. F is a constant and D is a parameter that Richardson found depended on the coastline approximated by L. He gave no theoretical explanation but Mandelbrot identified D with a non-integer form of the Hausdorff dimension, later the fractal dimension. Rearranging the right side of the expression obtains:

where Fε^-Dmust be the number of units ε required to obtain L. The fractal dimension is the number of the dimensions of the figure being used to approximate the fractal: 0 for a dot, 1 for a line, 2 for a square. D in the expression is between 1 and 2, for coastlines typically less than 1.5. The broken line measuring the coast does not extend in one direction nor does it represent an area, but is intermediate. It can be interpreted as a thick line or band of width 2ε. More broken coastlines have greater D and therefore L is longer for the same ε. Mandelbrot showed that D is independent of ε.

Source :

http://en.wikipedia.org/wiki/Coast

Coastal zone