A History of the Study of Marine Biology

The history of marine biology may have begun as early as 1200 BC when the Phoenicians began ocean voyages using celestial navigation. References to the sea and its mysteries abound in Greek mythology, particularly the Homeric poems “The Iliad” and “The Odyssey”. However, these two sources of ancient history mostly refer to the sea as a means of transportation and food source.

It wasn’t until the writings of Aristotle external from 384-322 BC that specific references to marine life were recorded. Aristotle identified a variety of species including crustaceans, echinoderms, mollusks, and fish. He also recognized that cetaceans are mammals, and that marine vertebrates are either oviparous (producing eggs that hatch outside the body) or viviparous (producing eggs that hatch within the body). Because he is the first to record observations on marine life, Aristotle is often referred to as the father of marine biology.

The Early Expeditions

Capt. CookThe modern day study of marine biology began with the exploration by Captain James Cook external(1728-1779) in 18th century Britain. Captain Cook is most known for his extensive voyages of discovery for the British Navy, mapping much of the world’s uncharted waters during that time. He circumnavigated the world twice during his lifetime, during which he logged descriptions of numerous plants and animals then unknown to most of mankind. Following Cook’s explorations, a number of scientists began a closer study of marine life including Charles Darwin external (1809-1882) who, although he is best known for the Theory external of Evolution external, contributed significantly to the early study of marine biology. His expeditions as the resident naturalist aboard the HMS Beagle external from 1831 to 1836 were spent collecting and studying specimens from a number of marine organisms that were sent to the British Museum for cataloguing. His interest in geology gave rise to his study of coral reefs and their formation. His experience on the HMS Beagle helped Darwin formulate his theories of natural selection and evolution based on the similarities he found in species specimens and fossils he discovered in the same geographic region.

DarwinThe voyages of the HMS Beagle were followed by a 3-year voyage by the British ship HMS Challenger externalled by Sir Charles Wyville Thomson external (1830-1882) to all the oceans of the world during which thousands of marine specimens were collected and analyzed. This voyage is often referred to as the birth of oceanography. The data collected during this trip filled 50 volumes and served as the basis for the study of marine biology across many disciplines for many years. Deep sea exploration was a benchmark of theChallenger’s voyage disproving British explorer Edward Forbes’ theory that marine life could not exist below about 550 m or 1,800 feet.

H.M.S. ChallengerThe Challenger was well equipped to explore deeper than previous expeditions with laboratories aboard stocked with tools and materials, microscopes, chemistry supplies, trawls and dredges, thermometers, devices to collect specimens from the deep sea, and miles of rope and hemp used to reach the ocean depths. The end product of theChallenger’s voyage was almost 30,000 pages of oceanographic information compiled by a number of scientists from a wide range of disciplines. The “Report of the Scientific Results of the Exploring Voyage of H.M.S. Challenger during the years 1873-76” reported, in addition to the fact that life does exist below 550 m/1,800 feet, findings such as:

  • 4,717 new species;
  • The first systematic plot of currents and temperatures in the ocean;
  • A map of bottom deposits much of which has remained current to the present;
  • An outline of the main contours of the ocean basins; and
  • The discovery of the mid-Atlantic Ridge external.

The report is an important work still used by scientists today. In addition to the report, Sir Thomson also wrote a book about the voyage in 1877 titled “The Voyage of the Challenger.” He also wrote one of the early marine biology textbooks “The Depths of the Sea” in 1877.

The Institutions

These expeditions were soon followed by marine laboratories established to study marine life. The oldest marine station in the world, Station Biologique de Roscoff external was established in Concarneau, France founded by the College of France in 1859. Concarneau is located on the northwest coast of France. The station was originally established for the cultivation of marine species, such as Dover sole, because of its location near marine estuaries with a variety of marine life. Today, research is conducted on molecular biology, biochemistry, and environmental studies.

In 1871, Spencer Fullerton Baird external, the first director of the US Commission of Fish and Fisheries (now known as the National Marine Fisheries Service external), began a collection station in Woods Hole, Massachusetts because of the abundant marine life there and to investigate declining fish stocks. This laboratory still exists now known as the Northeast Fisheries Science Center external, and is the oldest fisheries research facility in the world. Also at Woods Hole, the Marine Biological Laboratory (MBL) external was established in 1888 by Alpheus Hyatt, a student of Harvard naturalist Louis Agassiz who had established the first seaside school of natural history on an island near Woods Hole. MBL was designed as a summer program for the study of the biology of marine life for the purpose of basic research and education. The Woods Hole Oceanographic Institute external was created in 1930 in response to the National Academy of Science’s external call for “the share of the United States of America in a worldwide program of oceanographic research” and was funded by a $3 million grant by the Rockefeller Foundation.

An independent biological laboratory was established in San Diego in 1903 by University of California professor Dr. William E. Ritter, which became part of the University of California in 1912 and was named the Scripps Institution of Oceanography external after its benefactors. Scripps has since become one of the world’s leading institutions offering a multi-disciplinary study of oceanography.

Exploration of the Deep Sea

Barton bathysphereTechnology brought the study of marine biology to new heights during the years following the HMS Challenger expedition. In 1934 William Beebe external (1877-1962) andOtis Barton external descended 923 m/3,028 ft below the surface off the coast of Bermuda in a bathysphere external designed and funded by Barton. This depth record was not broken until 1948 when Barton made a bathysphere dive to 1,372 m/4,500 ft. During the interim, Beebe was able to observe deep sea life in its own environment rather than in a specimen jar. Although he was criticized for failing to publish results in professional journals, his vivid descriptions of the bathysphere dives in the books he published inspired some of today’s greatest oceanographers and marine biologists.

In 1960, a descent was made to 10,916 m/35,813 ft in the Challenger Deep external of the Marianna trench—the deepest known point in the oceans, 10,924 m/35,838 ft deep at its maximum, near 11° 22’N 142° 36’E—about 200 miles southwest of Guam. The dive was made in the bathyscape Trieste external built by Auguste Piccard, his son Swiss explorer Jean Ernest-Jean Piccard and U.S. Navy Lieutenant Don Walsh. The descent took almost five hours and the two men spent barely twenty minutes on the ocean floor before undertaking the 3 hour 15 minute ascent.

Bathyscape TriesteThe Trieste’s first dive was made in 1953. In the years following, the bathyscape was used for a number of oceanographic research projects, including biological observation, and in 1957 she was chartered and later purchased by the U.S. Navy. The Navy continued to use the bathyscape for oceanographic research off the coast of San Diego, and later used the Trieste for a submarine recovery mission off the U.S. east coast. The bathyscape was retired following the U.S. Navy’s commission of the Trieste II external, and is currently on exhibit at theWashington Naval Historical Center external.

The Scientists

Rachel CarsonRachel Carson (1907-1964) was a scientist and writer who brought the wonders of the sea to people with her lyrical writings and observations about the sea. Although she was a biologist for the US Fish and Wildlife Service, she devoted her spare time to translating science into writings that would infect the reader with her sense of wonder and respect for nature. She published an article in Atlantic Monthlyin 1937 titled “Undersea” which was followed by a book in 1941 titled “Under the Sea-Wind.”These publications described the sea and the life within it from a scientist’s point of view, but in the words of a naturalist. In 1951, she published “The Sea Around Us” a prize-winning bestseller on the history of the sea. The success of this book allowed her to resign from federal service and write full-time. Shortly after, her focus turned to the negative impact of pesticides, a cause to which she remained devoted to by fighting to raise public awareness until her death in 1964.

Inspired by the work of William Beebe, Dr. Sylvia Earle external (1935-) began her work as an oceanographer at the tender age of 3 when she was knocked off her feet by a wave. She was fascinated by the ocean and its creatures at a very early age growing up near the shore in New Jersey and later in Florida on the Gulf of Mexico. She began her studies with marine botany based on her belief that vegetation is the foundation of any ecosystem. Although she struggled to balance her studies and starting a family, Earle earned her PhD from Duke University external, becoming well known in the marine science community for her detailed studies of aquatic life. Early in her career, and while she was four months pregnant, Earle traveled 30.5 m/100 ft below the surface in a submersible. This was the first of many submersible dives she would make during her career. Her experience living in an underwater marine habitat earned her celebrity status in the scientific community. In 1969, the Smithsonian Institute external released a call for proposals that was circulated in the marine science community for those interested in conducting research while living in an underwater habitat. Earle submitted a proposal describing her intention to use the opportunity to study the ecology of marine plants and fishes in great detail by combining her observations with those of the ichthyologists on board. Unfortunately, the other applicants were male, and the review board deemed Earle’s cohabitation with them inappropriate. Her request to be a part of the Tektite I mission was rejected; however, the Smithsonian later proposed an all-female Tektite II mission external which Earle became a part of. The Tektite II mission received a lot of attention at the time (1970) because of its all female crew.

Following her experience aboard the underwater habitat, Earle developed an interest in deep sea exploration, and in 1979 she broke the record for deep diving at 381 m/1,250 ft below the surface in a special suit called the Jim suit external designed to withstand the pressure. Her record has not been broken. Earle decided to test the Jim suit as part of her research on a book published by National Geographic “Exploring the Deep Frontier”, and out of her frustration that scuba diving techniques only scratched the surface of the ocean. Following this adventure, Earle started two companies that manufacture deep sea exploration vehicles. The continued advancements in the the technology of these vehicles has helped open up areas in the deep sea previously unexplored. During the 1990s, Earle served as Chief Scientist for the National Oceanic and Atmospheric Administration (NOAA) external. She is currently an Explorer-in-Residence with National Geographic external, and, in addition to her research, remains committed to raising awareness on marine environmental issues.

Dr. Robert BallardDr. Robert Ballard (1942-), also a deep-sea explorer, may be best known for finding the Titanic using technologies he helped to develop, including the Argo/Jason remotely operated vehicles and the technology that transmits video images from the deep sea. His earlier deep sea explorations led to the first discovery of hydrothermal vents during an exploration in a manned submersible of the Mid-Ocean Ridge. Ballard founded the Woods Hole Oceanographic Institution’s Deep Submergence Laboratory external and spent 30 years there working on the use of manned submersibles. Ballard has devoted a great deal of time to furthering the field of deep sea exploration. He created a distance-learning program with more than one million students enrolled, taught by more than 30,000 science teachers worldwide. He also founded the Institute for Exploration external located in Mystic, Connecticut for the study of deep-water archaeology which led to the discovery of the largest number of ancient ships ever found in the deep sea. Currently, he is a National Geographic Society Explorer-in-Residence Professor of Oceanography at the University of Rhode Island’s Graduate School of Oceanography external, and Director of the Institute for Archaeological Oceanography external.

The Explorers

Jacques CousteauThe advent of scuba diving introduced other pioneers to the study of marine biology.Jacques Cousteau external (1910-1997) was determined to safely breathe compressed air underwater in order to lenghthen dive times. His work with Emile Gagnan ultimately led to the invention of the regulator which releases compressed air to divers “on demand” (as opposed to a continuous flow). The combination of the Cousteau-Gagnan regulator with compressed air tanks allowed Cousteau the freedom to film underwater, and by 1950 he had produced the Academy Award winning “The Silent World.” By the 1970s he was bringing the underwater realm into millions of homes with his PBS series “Cousteau Odyssey.” Cousteau’s television documentaries won 40 Emmy Awards. Like other oceanography pioneers, Cousteau was criticized for his lack of scientific credentials, however his legacy fostered a greater knowledge and understanding of the devastation caused by threats to ocean health such as pollution of marine resources and resource exploitation.

Hans and Lotte HassCousteau’s Austrian counterpart, Dr. Hans Hass external (1919-), also helped introduce the wonders of the underwater world to the public. Hass and his wife Lotte were both passionate about underwater exploration and protection of the marine environment, and together they produced numerous documentaries and wrote a variety of books on their underwater experiences. During his career as an underwater explorer, Hass also made significant contributions to diving technology. He invented one of the first underwater flash cameras and contributed to the development of the Drager oxygen rebreather which he and Lotte used in 1942 to film “Men Amongst Sharks” and continued to use on diving expeditions aboard their research vessel “Xarifa” in the Red Sea and Caribbean. Hass is also known as one of the first humans to interact with a sperm whale underwater which helped him become a pioneer in the study of marine animal behavior.

The Future

Today, the possibilities for ocean exploration are nearly infinite. In addition to scuba diving, rebreathers, fast computers, remotely-operated vehicles (ROVs), deep sea submersibles, reinforced diving suits, and satellites, other technologies are also being developed. But interdisciplinary research is needed to continue building our understanding of the ocean, and what needs to be done to protect it. In spite of ongoing technological advances, it is estimated that only 5% of the oceans have been explored. Surprisingly, we know more about the moon than we do the ocean. This needs to change if we are to ensure the longevity of the life in the seas—and they cover 71% of the earth’s surface. Unlike the moon, they are our backyard. Without a detailed collective understanding of the ramifications of pollution, overfishing, coastal development, as well as the long-term sustainability of ocean oxygen production and carbon dioxide and monoxide absorption, we face great risks to environmental and human health. We need this research so that we can act on potential problems—not react to them when it is already too late.

Fortunately, thanks to the work of past and present ocean explorers, the public is increasingly aware of these risks which encourage public agencies to take action and promote research. Already the US Commission on Ocean Policy external favors multi-disciplinary research to shape ocean policy. The efforts of public agencies using a multi-disciplinary approach, together with the efforts provided by numerous private marine conservation organizations that work on issues such as advocacy, education, and research, will help drive the momentum needed to face the challenges of preserving the ocean.

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Marine Life

Marine life is the essence of MarineBio, so in this section we explore the science, biology, taxonomy, morphology, behavior, and ecological relationships of marine life that inhabits our ocean

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Mollusca

The Mollusca (pronounced /məˈlʌskə/), common name molluscs or mollusks[note 1] (pronounced /ˈmɒləsks/), are a large phylum of invertebrate animals. There are around 85,000 recognized extant species of molluscs. Mollusca is the largest marinephylum, comprising about 23% of all the named marine organisms. Numerous molluscs also live in freshwater and terrestrial habitats. Molluscs are highly diverse, not only in size and in anatomical structure, but also in behaviour and in habitat. Thephylum is typically divided into nine or ten taxonomic classes, of which two are entirely extinctCephalopod molluscs such as squidcuttlefish and octopus are among the most neurologically advanced of all invertebrates – and either the giant squid or thecolossal squid is the largest known invertebrate species. The gastropods (snails and slugs) are by far the most numerous molluscs in terms of classified species, and account for 80% of the total.

Molluscs have such a varied range of body structures that it is difficult to find defining characteristics that apply to all modern groups. The two most universal features are a mantle with a significant cavity used for breathing and excretion, and the structure of the nervous system. As a result of this wide diversity, many textbooks base their descriptions on a hypothetical “generalized mollusc”. This has a single, “limpet-like” shell on top, which is made of proteins and chitin reinforced with calcium carbonate, and is secreted by a mantle that covers the whole upper surface. The underside of the animal consists of a single muscular “foot”. Although molluscs are coelomates, the coelom is very small, and the main body cavity is a hemocoel through which bloodcirculates – molluscs’ circulatory systems are mainly open. The “generalized” mollusc’s feeding system consists of a rasping “tongue” called a radula and a complex digestive system in which exuded mucus and microscopic, muscle-powered “hairs” called cilia play various important roles. The “generalized mollusc” has two paired nerve cords, or three in bivalves. The brain, in species that have one, encircles the esophagus. Most molluscs have eyes, and all have sensors that detect chemicals, vibrations and touch. The simplest type of molluscan reproductive system relies on external fertilization, but there are more complex variations. All produce eggs, from which may emerge trochophore larvae, more complex veliger larvae, or miniature adults.

A striking feature of molluscs is the use of the same organ for multiple functions. For example: the heart and nephridia (“kidneys”) are important parts of the reproductive system as well as the circulatory and excretory systems; in bivalves, the gills both “breathe” and produce a water current in the mantle cavity, which is important for excretion and reproduction.

There is good evidence for the appearance of gastropodscephalopods and bivalves in the Cambrian period 542 to 488.3 million years ago. However the evolutionary history both of molluscs’ emergence from the ancestral Lophotrochozoa and of their diversification into the well-known living and fossil forms are still subjects of vigorous debate among scientists.

Molluscs have been and still are an important food source for anatomically modern humans. However there is a risk of food-poisoning from toxins that accumulate in molluscs under certain conditions, and many countries have regulations that aim to minimize this risk. Molluscs have for centuries also been the source of important luxury goods, notably pearlsmother of pearlTyrian purple dye, and sea silk. Their shells have also been used as a money in some pre-industrial societies.

Mollusc species can also represent hazards or pests for human activities. The bite of the blue-ringed octopus is often fatal, and that of Octopus apollyon causes inflammation that can last for over a month. Stings from a few species of large tropical cone shells can also kill, but their sophisticated though easily produced venoms have become important tools in neurological research. Schistosomiasis (also known as bilharzia, bilharziosis or snail fever) is transmitted to humans via water snail hosts, and affects about 200 million people. Snails and slugs can also be serious agricultural pests, and accidental or deliberate introduction of some snail species into new environments has seriously damaged some ecosystems.

 

Etymology

The words mollusc and mollusk are both derived from the French mollusque, which originated from the Latin molluscus, from mollis, soft. Molluscus was itself an adaptation of Aristotle‘s τᾲ μαλάκια, “the soft things”, which he applied to cuttlefish.[2] The scientific study of molluscs is known asmalacology.[3]

[edit]Definition

The two most universal features of the body structure of molluscs are a mantle with a significant cavity used for breathing and excretion, and the organization of the nervous system. The most abundant metallic element in molluscs is calcium.[4]

Molluscs have developed such a varied range of body structures that it is difficult to find synapomorphies (defining characteristics) that apply to all modern groups.[5] The most general characteristic of molluscs is that they are unsegmented and bilaterally symmetrical.[6] The following are present in all modern molluscs:[7][8]

Other characteristics that commonly appear in textbooks have significant exceptions:

  Class
Characteristic[7] Aplacophora[9] Polyplacophora[10] Monoplacophora[11] Gastropoda[12] Cephalopoda[13] Bivalvia[14] Scaphopoda[15]
Radula, a rasping “tongue” with chitinous teeth Absent in 20% of Neomeniomorpha Yes Yes Yes Yes No Internal, cannot extend beyond body
Broad, muscular foot Reduced or absent Yes Yes Yes Modified into arms Yes Small, only at “front” end
Dorsal concentration of internal organs (visceral mass) Not obvious Yes Yes Yes Yes Yes Yes
Large digestive ceca No ceca in some aplacophora Yes Yes Yes Yes Yes No
Large complex metanephridia (“kidneys”) None Yes Yes Yes Yes Yes Small, simple

[edit]Diversity

About 80% of all known mollusc species are gastropods (snails and slugs), including the cowry (a sea snail) pictured here.[16]

Estimates of accepted described living species of molluscs vary from 50,000 to a maximum of 120,000 species.[1] In 2009 Chapman estimated the number of described living species at 85,000.[1] Haszprunar in 2001 estimated about 93,000 named species,[17] which include 23% of all named marine organisms.[18] Molluscs are second only to arthropods in numbers of living animal species[16]—far behind the arthropods’ 1,113,000 but well ahead of chordates‘ 52,000.[19] It has been estimated that there are about 200,000 living species in total,[1][20] and 70,000 fossil species,[7] although the total number of mollusc species that ever existed, whether or not preserved, must be many times greater than the number alive today.[21]

Molluscs have more varied forms than any other animal phylum. They include snailsslugs and other gastropodsclams and other bivalvessquids and other cephalopods; and other lesser-known but similarly distinctive sub-groups. The majority of species still live in the oceans, from the seashores to the abyssal zone, but some form a significant part of the freshwater fauna and the terrestrial ecosystems. Molluscs are extremely diverse in tropical and temperate regions but can be found at all latitudes.[5]About 80% of all known mollusc species are gastropods.[16] Cephalopoda such as squidcuttlefish and octopus are among the neurologically most advanced of all invertebrates.[22] The giant squid, which until recently had not been observed alive in its adult form,[23] is one of the largest invertebrates. However a recently caught specimen of the colossal squid, 10 metres (33 ft) long and weighing 500 kilograms (1,100 lb), may have overtaken it.[24]

Freshwater and terrestrial molluscs appear exceptionally vulnerable to extinction. Estimates of the numbers of non-marine molluscs vary widely, partly because many regions have not been thoroughly surveyed. There is also a shortage of specialists who can identify all the animals in any one area to species. However, in 2004 the IUCN Red List of Threatened Species included nearly 2,000 endangered non-marine molluscs. For comparison, the great majority of mollusc species are marine but only 41 of these appeared on the 2004 Red List. 42% of recorded extinctions since the year 1500 are of molluscs, almost entirely non-marine species.[25]

[edit]A “generalized mollusc”

Further information: Mollusc shell
1
2
3
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5
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8
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10
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12
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18
    Digestive & excretory system
    Circulatory & respiratory
    Central nervous system
    Reproductive system
 1 Radula
 2 Mouth
 3 Shell
 4 Stomach
 5 Gonad
 6 Heart
 7 Coelom
 9 Mantle
10 Mantle cavity
11 Anus
12 Gill
13 Foot
15 Pedal nerve cord
16 Gut
17 Visceral nerve cord
18 Nerve ring
A generalized mollusc[26]

Because of the great range of anatomical diversity among molluscs, many textbooks start the subject by describing a hypothetical “generalized mollusc” to illustrate the most common features found within the phylum. The depiction is rather similar to modern monoplacophorans, and some suggest it may resemble very early molluscs.[5][8][11][27]

The generalized mollusc has a single, “limpet-like” shell on top. The shell is secreted by a mantle that covers the upper surface. The underside consists of a single muscular “foot”.[8] The visceral mass, or visceropallium, is the soft, non-muscular metabolic region of the mollusc. It contains the body organs.[6]

 

[edit]Mantle and mantle cavity

The mantle cavity is a fold in the mantle that encloses a significant amount of space. It is lined with epidermis. It is exposed, according to habitat, to sea, fresh water or air. The cavity was at the rear in the earliest molluscs but its position now varies from group to group. The anus, a pair of osphradia (chemical sensors) in the incoming “lane”, the hindmost pair of gills and the exit openings of the nephridia (“kidneys”) and gonads (reproductive organs) are in the mantle cavity.[8] The whole soft body of bivalves lies within an enlarged mantle cavity.[6]

[edit]Shell

Main article: Mollusc shell

The mantle edge secretes a shell (secondarily absent in a number of taxonomic groups, such as the nudibranchs[6]) that consists of mainly chitin and conchiolin (a protein) hardened with calcium carbonate),[8][28] except that the outermost layer in almost all cases is all conchiolin (see periostracum).[8] Molluscs never use phosphate to construct their hard parts,[29] with the questionable exception of Cobcrephora.[30] While most mollusc shells are composed mainly of aragonite, those gastropods that lay eggs with a hard shell use calcite (sometimes with traces of aragonite) to construct the eggshells.[31]

The shell consists of three layers : the outer layer (the periostracum) made of organic matter, a middle layer made of columnar calcite and an inner layer consisting of laminated calcite, that is often nacreous.[6]

[edit]Foot

The underside consists of a muscular foot, which has adapted to different purposes in different classes.[32]:4 The foot carries a pair of statocysts, which act as balance sensors. In gastropods, it secretes mucus as a lubricant to aid movement. In forms that have only a top shell, such as limpets, the foot acts as a sucker attaching the animal to a hard surface, and the vertical muscles clamp the shell down over it; in other molluscs, the vertical muscles pull the foot and other exposed soft parts into the shell.[8] In bivalves, the foot is adapted for burrowing into the sediment;[32]:4 in cephalopods it is used for jet propulsion,[32]:4 and the tentacles and arms are derived from the foot.[33]

[edit]Circulation

Molluscs’ circulatory systems are mainly open. Although molluscs are coelomates, their coeloms are reduced to fairly small spaces enclosing the heart and gonads. The main body cavity is a hemocoel through which blood and coelomic fluid circulate and which encloses most of the other internal organs. These hemocoelic spaces act as an efficient hydrostatic skeleton.[6] The blood contains the respiratory pigment hemocyanin as an oxygen-carrier. The heart consists of one or more pairs of atria (auricles), which receive oxygenated blood from the gills and pump it to the ventricle, which pumps it into the aorta (main artery), which is fairly short and opens into the hemocoel.[8]

The atria of the heart also function as part of the excretory system by filtering waste products out of the blood and dumping it into the coleom as urine. A pair of nephridia (“little kidneys”) to the rear of and connected to the coelom extracts any re-usable materials from the urine and dumps additional waste products into it, and then ejects it via tubes that discharge into the mantle cavity.[8]

[edit]Respiration

Most molluscs have only one pair of gills, or even only one gill. Generally the gills are rather like feathers in shape, although some species have gills with filaments on only one side. They divide the mantle cavity so that water enters near the bottom and exits near the top. Their filaments have three kinds of cilia, one of which drives the water current through the mantle cavity, while the other two help to keep the gills clean. If the osphradia detect noxious chemicals or possibly sediment entering the mantle cavity, the gills’ cilia may stop beating until the unwelcome intrusions have ceased. Each gill has an incoming blood vessel connected to the hemocoel and an outgoing one to the heart.[8]

[edit]Eating, digestion, and excretion

    = Food
    = Radula
    = Odontophore “belt”
    = Muscles
Snail radula at work.

Most molluscs have muscular mouths with radulae, “tongues” bearing many rows of chitinous teeth, which are replaced from the rear as they wear out. The radula primarily functions to scrape bacteria and algae off rocks. This radula is associated with theodontophore, a cartilaginous supporting organ[6]

Molluscs mouths also contain glands that secrete slimy mucus, to which the food sticks. Beating cilia (tiny “hairs”) drive the mucus towards the stomach, so that the mucus forms a long string.[8]

At the tapered rear end of the stomach and projecting slightly into the hindgut is the prostyle, a backward-pointing cone of feces and mucus, which is rotated by further cilia so that it acts as a bobbin, winding the mucus string onto itself. Before the mucus string reaches the prostyle, the acidity of the stomach makes the mucus less sticky and frees particles from it.[8]

The particles are sorted by yet another group of cilia, which send the smaller particles, mainly minerals, to the prostyle so that eventually they are excreted, while the larger ones, mainly food, are sent to the stomach’s cecum (a pouch with no other exit) to be digested. The sorting process is by no means perfect.[8]

Periodically, circular muscles at the hindgut’s entrance pinch off and excrete a piece of the prostyle, preventing the prostyle from growing too large. The anus is in the part of the mantle cavity that is swept by the outgoing “lane” of the current created by the gills. Carnivorous molluscs usually have simpler digestive systems.[8]

As the head has largely disappeared in bivalves, their mouth has been equipped with labial palps (two on each side of the mouth) to collect the detritus from its mucus.[6]

[edit]Nervous system

Simplified diagram of the mollusc nervous system.

Molluscs have two pairs of main nerve cords (three in bivalves) the visceral cords serving the internal organs and the pedal ones serving the foot. Both pairs run below the level of the gut, and include ganglia as local control centers in important parts of the body. Most pairs of corresponding ganglia on both sides of the body are linked by commissures (relatively large bundles of nerves). The only ganglia above the gut are the cerebral ganglia, which sit above the esophagus (gullet) and handle “messages” from and to the eyes. The pedal ganglia, which control the foot, are just below the esophagus and their commissure and connections to the cerebral ganglia encircle the esophagus in a nerve ring.[8]

The brain, in species that have one, encircles the esophagus. Most molluscs have a head with eyes, and all have a pair of sensor-containing tentacles, also on the head, that detect chemicals, vibrations and touch.[8]

[edit]Reproduction

Apical tuft (cilia)
Prototroch (cilia)
Stomach
Mouth
Metatroch (cilia)
Mesoderm
Anus
/// = cilia
Trochophore larva[34]

The simplest molluscan reproductive system relies on external fertilization, but there are more complex variations. All produce eggs, from which may emerge trochophore larvae, more complex veliger larvae, or miniature adults. Two gonads sit next to the coelom, a small cavity that surrounds the heart and shed ova or sperm into the coloem, from which the nephridia extract them and emit them into the mantle cavity. Molluscs that use such a system remain of one sex all their lives and rely on external fertilization. Some molluscs use internal fertilization and/or are hermaphrodites, functioning as both sexes; both of these methods require more complex reproductive systems.[8]

The most basic molluscan larva is a trochophore, which is planktonic and feeds on floating food particles by using the two bands of cilia round its “equator” to sweep food into the mouth, which uses more cilia to drive them into the stomach, which uses further cilia to expel undigested remains through the anus. New tissue grows in the bands of mesoderm in the interior, so that the apical tuft and anus are pushed further apart as the animal grows. The trochophore stage is often succeeded by a veliger stage in which the prototroch, the “equatorial” band of cilia nearest the apical tuft, develops into the velum(“veil”), a pair of cilia-bearing lobes with which the larva swims. Eventually the larva sinks to the seafloor and metamorphoses into the adult form. Whilst metamorphosis is the usual state in molluscs, the cephalopods differ in exhibiting direct development: the hatchling is a ‘miniaturized’ form of the adult.[35]

[edit]Ecology

[edit]Feeding

Most molluscs are herbivorous, grazing on algae. Two feeding strategies are predominant: some feed on microscopic, filamentous algae, often using their radula as a ‘rake’ to comb up filaments from the sea floor. Others feed on macroscopic ‘plants’ such as kelp, rasping the plant itself with its radula. To employ this strategy, the plant has to be large enough for the mollusc to ‘sit’ on; therefore smaller macroscopic plants enjoy less molluscan herbivory than their larger counterparts.[36] Naturally, there are exceptions; the cephalopods are primarily (perhaps entirely) predatory, and the radula takes a secondary role to the jaws and tentacles in food acquisition. The monoplacophoran Neopilina uses its radula in the usual fashion, but its diet includes protists such as the xenophyophore Stannophyllum.[37] Sacoglossan nudibranchs suck the sap from algae, using their one-row radula to pierce the cell walls,[38] whereas dorid nudibranchs and some Vetigastrpods feed on sponges[39][40] and others feed on hydroids.[41] (An extensive list of molluscs with unusual feeding habits is available in the appendix of GRAHAM, A. (1955). “Molluscan diets”Journal of Molluscan Studies 31 (3–4): 144..)

[edit]Classification

Opinions vary about the number of classes of molluscs—for example the table below shows eight living classes,[17] and two extinct ones. Although they are unlikely to form a clade, some older works combine the Caudofoveata and solenogasters into one class, the Aplacophora.[9][27] Two of the commonly recognized “classes” are known only from fossils.[16]

Class Major organisms Described living species[17] Distribution
Caudofoveata[9] worm-like organisms 120 seabed 200–3,000 metres (660–9,800 ft)
Solenogastres[9] worm-like organisms 200 seabed 200–3,000 metres (660–9,800 ft)
Polyplacophora[10] chitons 1,000 rocky tidal zone and seabed
Monoplacophora[11] An ancient lineage of molluscs with cap-like shells 31 seabed 1,800–7,000 metres (5,900–23,000 ft); one species 200 metres (660 ft)
Gastropoda[42] All the snails and slugs including abalonelimpetsconch,nudibranchssea haressea butterfly 70,000 marine, freshwater, land
Cephalopoda[43] squidoctopuscuttlefishnautilus 900 marine
Bivalvia[44] clamsoystersscallopsgeoducksmussels 20,000 marine, freshwater
Scaphopoda[15] tusk shells 500 marine 6–7,000 metres (20–23,000 ft)
Rostroconchia †[45] fossils; probable ancestors of bivalves extinct marine
Helcionelloida †[46] fossils; snail-like organisms such as Latouchella extinct marine

Classification into higher taxa for these groups has been and remains problematic. A phylogenetic study suggests that the Polyplacophora form a clade with a monophyletic Aplacophora.[47] Additionally it suggests that a sister taxon relationship exists between the Bivalvia and the Gastropoda.

[edit]Evolution

[edit]Fossil record

There is good evidence for the appearance of gastropodscephalopods and bivalves in the Cambrian period 542 to 488.3 million years ago. However, the evolutionary history both of the emergence of molluscs from the ancestral group Lophotrochozoa, and of their diversification into the well-known living and fossil forms, is still vigorously debated.

There is debate about whether some Ediacaran and Early Cambrian fossils really are molluscs. Kimberella, from about 555 million years ago, has been described as “mollusc-like”,[48][49] but others are unwilling to go further than “probable bilaterian“.[50][51] There is an even sharper debate about whether Wiwaxia, from about 505 million years ago, was a mollusc, and much of this centers on whether its feeding apparatus was a type of radula or more similar to that of some polychaete worms.[50][52] Nicholas Butterfield, who opposes the idea that Wiwaxia was a mollusc, has written that earlier microfossils from 515 to 510 million years ago are fragments of a genuinely mollusc-like radula.[53] This appears to contradict the concept that the ancestral molluscan radula was mineralized.[54]

The tiny Helcionellidfossil Yochelcionella is thought to be an earlymollusc[46]

Spirally coiled shells appear in manygastropods[12]

However, the Helcionellids, which first appear over 540 million years ago in Early Cambrian rocks from Siberia and China,[55][56] are thought to be early molluscs with rather snail-like shells. Shelled molluscs therefore predate the earliesttrilobites.[46] Although most helcionellid fossils are only a few millimeters long, specimens a few centimeters long have also been found, most with more limpet-like shapes. There have been suggestions that the tiny specimens were juveniles and the larger ones adults.[57]

Some analyses of helcionellids concluded that these were the earliest gastropods.[58] However other scientists are not convinced that Early Cambrian fossils show clear signs of the torsion that identifies modern gastropods twists the internal organs so that the anus lies above the head.[12][59][60]

 
    = Septa
    = Siphuncle
Septa and siphuncle in nautiloid shell

For a long time it was thought that Volborthella, some fossils of which pre-date 530 million years ago, was a cephalopod. However discoveries of more detailed fossils showed that Volborthella’s shell was not secreted but built from grains of the mineralsilicon dioxide (silica), and that it was not divided into a series of compartments by septa as those of fossil shelled cephalopods and the living Nautilus are. Volborthella’s classification is uncertain.[61] The Late Cambrian fossil Plectronoceras is now thought to be the earliest clearly cephalopod fossil, as its shell had septa and a siphuncle, a strand of tissue that Nautilus uses to remove water from compartments that it has vacated as it grows, and which is also visible in fossil ammonite shells. However,Plectronoceras and other early cephalopods crept along the seafloor instead of swimming, as their shells contained a “ballast” of stony deposits on what is thought to be the underside and had stripes and blotches on what is thought to be the upper surface.[62] All cephalopods with external shells except the nautiloids became extinct by the end of the Cretaceous period 65 million years ago.[63] However, the shell-less Coleoidea (squidoctopuscuttlefish) are abundant today.[64]

The Early Cambrian fossils Fordilla and Pojetaia are regarded as bivalves.[65][66][67][68] “Modern-looking” bivalves appeared in the Ordovician period, 488 to 443 million years ago.[69] One bivalve group, the rudists, became major reef-builders in the Cretaceous, but became extinct in the Cretaceous-Tertiary extinction.[70] Even so, bivalves remain abundant and diverse.

The Hyolitha is a class of extinct animals with a shell and operculum that may be molluscs. Authors who suggest that they deserve their own phylum do not comment on the position of this phylum in the tree of life[71]

[edit]Phylogeny

Lophotrochozoa
 

Brachiopods

 
 
 
 
 
 

Bivalves

 
 

Monoplacophorans
(“limpet-like”, “living fossils”)

 
 
 

Gastropods
(snailsslugslimpets,sea hares)

 
 
 

Cephalopods
(nautiloids,ammonites,squid, etc.)

 
 

Scaphopods (tusk shells)

 
 
 
 
 
 
 

Aplacophorans
(spicule-covered, worm-like)

 
 

Polyplacophorans (chitons)

 
 
 
 
Halwaxiids
 

Wiwaxia

 
 

Halkieria

 
 
 

Orthrozanclus

 
 
 

Odontogriphus

 
 
 

A possible “family tree” of molluscs (2007).[72][73] Does not include annelid worms as the analysis concentrated on fossilizable “hard” features.[72]

The phylogeny (evolutionary “family tree”) of molluscs is a controversial subject. In addition to the debates about whether Kimberella and any of the “halwaxiids” were molluscs or closely related to molluscs,[49][50][52][53] there are debates about the relationships between the classes of living molluscs.[51] In fact some groups traditionally classifed as molluscs may have to be redefined as distinct but related.[74]

Molluscs are generally regarded members of the Lophotrochozoa,[72] a group defined by having trochophore larvae and, in the case of living Lophophorata, a feeding structure called a lophophore. The other members of the Lophotrochozoa are the annelid worms and seven marine phyla.[75] The diagram on the right summarizes a phylogeny presented in 2007.

Because the relationships between the members of the family tree are uncertain, it is difficult to identify the features inherited from the last common ancestor of all molluscs.[76] For example, it is uncertain whether the ancestral mollusc wasmetameric (composed of repeating units)—if it was, that would suggest an origin from an annelid-like worm.[77] Scientists disagree about this: Giribet and colleagues concluded in 2006 that the repetition of gills and of the foot’s retractor muscles were later developments, [5] while in 2007 Sigwart concluded that the ancestral mollusc was metameric, and that it had a foot used for creeping and a “shell” that was mineralized.[51] In one particular one branch of the family tree, the shell of conchiferans is thought to have evolved from the spicules (small spines) of aplacophorans; however this is difficult to reconcile with the embryological origins of spicules.[76]

The molluscan shell appears to have originated from a mucus coating, which eventually stiffened into a cuticle. This would have been impermeable and thus forced the development of more sophisticated respiratory apparatus in the form of gills.[46] Eventually, the cuticle would have become mineralized,[46] using the same genetic machinery (engrailed) as most other bilaterian skeletons.[77] The first mollusc shell almost certainly was reinforced with the mineral aragonite.[78]

The evolutionary relationships within the molluscs are also debated, and the diagrams below show two widely supported reconstructions:

Molluscs
Aculifera
 
 

Solenogastres

 
 

Caudofoveata

 
 
 

Polyplacophorans

 
 
Conchifera
 

Monoplacophorans

 
 
 

Bivalves

 
 

Scaphopods

 
 

Gastropods

 
 

Cephalopods

 
 
 
 

The “Aculifera” hypothesis[72]

Molluscs
 
 

Solenogastres

 
 

Caudofoveata

 
Testaria
 

Polyplacophorans

 
 
 

Monoplacophorans

 
 
 

Bivalves

 
 

Scaphopods

 
 

Gastropods

 
 

Cephalopods

 
 
 
 
 
 

The “Testaria” hypothesis[72]

 

Morphological analyses tend to recover a conchiferan clade that receives less support from molecular analyses,[79] although these results also lead to unexpected paraphylies, for instance scattering the bivalves throughout all other mollusc groups.[80]

However, an analysis in 2009 that used both morphological and molecular phylogenetics comparisons concluded that the molluscs are not monophyletic; in particular, that Scaphopoda and Bivalvia are both separate, monophyletic lineages unrelated to the remaining molluscan classes—in other words that the traditional phylum Mollusca is polyphyletic, and that it can only be made monophyletic if scaphopods and bivalves are excluded.[74] A 2010 analysis managed to recover the traditional conchiferan and aculiferan groups, but similarly concluded that the molluscs are not monophyletic, this time suggesting that solenogastres are more closely related to the non-molluscan taxa used as an outgroup than to other molluscs.[81] Current molecular data is insufficient to constrain the molluscan phylogeny, and since the methods used to determine the confidence in clades are prone to over-estimation, it is risky to place too much emphasis even on the areas that different studies agree.[82] Rather than eliminating unlikely relationships, the latest studies add new permutations of internal molluscan relationships, even bringing the conchiferan hypothesis into question.[83]

[edit]Human interaction

For millennia molluscs have been a source of food for humans, as well as important luxury goods, notably pearlsmother of pearlTyrian purple dye, sea silk, and chemical compounds. Their shells have also been used as a form of currency in some pre-industrial societies. Their outlandish forms have helped conjure up tales of mythological sea monsters such as the Kraken. A number of species of molluscs can bite or sting humans, and some have become agricultural pests.

[edit]Uses by humans

Further information: Seashell

Molluscs, especially bivalves such as clams and mussels, have been an important food source since at least the advent of anatomically modern humans—and this has often resulted in over-fishing.[84] Other commonly eaten molluscs include octopuses and squidswhelksoysters, andscallops.[85] In 2005, China accounted for 80% of the global mollusc catch, netting almost 11,000,000 tonnes (11,000,000 long tons; 12,000,000 short tons). Within Europe, France remained the industry leader.[86] Some countries regulate importation and handling of molluscs and other seafood, mainly to minimize the poison risk from toxins that accumulate in the animals.[87]

Photo of three circular metal cages in shallows, with docks, boathouses and palm trees in background

Saltwater pearl oyster farm in Seram,Indonesia

Most molluscs that have shells can produce pearls, but only the pearls of bivalves and some gastropods whose shells are lined with nacre are valuable.[12][14] The best natural pearls are produced by marine pearl oystersPinctada margaritifera and Pinctada mertensi, which live in the tropical and sub-tropical waters of the Pacific Ocean. Natural pearls form when a small foreign object gets stuck between the mantle and shell.

There are two methods of culturing pearls, by inserting either “seeds” or beads into oysters. The “seed” method uses grains of ground shell from freshwater mussels, and over-harvesting for this purpose has endangered several freshwater mussel species in the southeastern USA.[14] The pearl industry is so important in some areas that significant sums of money are spent on monitoring the health of farmed molluscs.[88]

Mosaic of mustachioed, curly-haired man wearing crown and surrounded by halo

ByzantineEmperor Justinian Iclad in Tyrian purple and wearing numerous pearls

Other luxury and high-status products were made from molluscs. Tyrian purple, made from the ink glands of murex shells, “… fetched its weight in silver” in the fourth-century BC, according to Theopompus.[89] The discovery of large numbers of Murex shells on Crete suggests that the Minoans may have pioneered the extraction of “Imperial purple” during the Middle Minoan period in the 20th–18th century BC, centuries before the Tyrians.[90][91] Sea silk is a fine, rare and valuable fabric produced from the long silky threads (byssus) secreted by several bivalve molluscs, particularly Pinna nobilis, to attach themselves to the sea bed.[92] Procopius, writing on the Persian wars circa 550 CE, “stated that the five hereditary satraps (governors) of Armenia who received their insignia from the Roman Emperor were given chlamys (or cloaks) made from lana pinna (Pinna “wool,” or byssus). Apparently only the ruling classes were allowed to wear these chlamys.”[93]

Mollusc shells, including those of cowries, were used as a kind of money (shell money) in several pre-industrial societies. However these “currencies” generally differed in important ways from the standardized government-backed and -controlled money familiar to industrial societies. Some shell “currencies” were not used for commercial transactions but mainly as social status displays at important occasions such as weddings.[94] When used for commercial transactions they functioned as commodity money, in other words as a tradable commodity whose value differed from place to place, often as a result of difficulties in transport, and which was vulnerable to incurable inflation if more efficient transport or “goldrush” behavior appeared.[95]

[edit]Stings and bites

There is a risk of food poisoning from toxins that accumulate in molluscs under certain conditions, and many countries have regulations that aim to minimize this risk. Blue-ringed octopus bites are often fatal, and the bite of other octopuses can cause unpleasant symptoms. Stings from a few species of large tropical cone shells can also kill. However, the sophisticated venoms of these cone snails have become important tools in neurological research and show promise as sources of new medications.

The blue-ringed octopus‘s rings are a warning signal—this octopus is alarmed, and its bite can kill.[96]

When handled alive, a few species of molluscs can sting or bite and, with some species, this can present a serious risk to the human handling the animal. To put this into perspective however, deaths from mollusc venoms are less than 10% of the number of deaths fromjellyfish stings.[97]

All octopuses are venomous[98] but only a few species pose a significant threat to humans. Blue-ringed octopuses in the genus Hapalochlaena, which live around Australia and New Guinea, bite humans only if severely provoked,[96] but their venom kills 25% of human victims. Another tropical species, Octopus apollyon, causes severe inflammation that can last for over a month even if treated correctly,[99] and the bite of Octopus rubescens can cause necrosis that lasts longer than one month if untreated, and headaches and weakness persisting for up to a week even if treated.[100]

Photo of cone on ocean bottom

Live cone snailscan be dangerous to shell-collectors but are useful toneurologyresearchers[101]

All species of cone snails are venomous and can sting when handled, although many species are too small to pose much of a risk to humans. These are carnivorous gastropods that feed on marine invertebrates (and in the case of larger species on fish). Their venom is based on a huge array of toxins, some fast-acting and others slower but deadlier—they can afford to do this because their toxins require less time and energy to be produced compared with those of snakes or spiders.[101] Many painful stings have been reported, and a few fatalities, although some of the reported fatalities may be exaggerations.[97] Only the few larger species of cone snail that can capture and kill fish are likely to be seriously dangerous to humans.[102] The effects of individual cone shell toxins on victims’ nervous systems are so precise that they are useful tools for research in neurology, and the small size of their molecules makes it easy to synthesize them.[101][103]

The traditional belief that a giant clam can trap the leg of a person between its valves, thus drowning them, is a myth.[104]

[edit]Pests

Skin vesicles created by the penetration of Schistosoma. Source: Centers for Disease Control and Prevention

Schistosomiasis (also known as bilharzia, bilharziosis or snail fever) is transmitted to humans via water snail hosts, and affects about 200 million people. A few species of snails and slugs are serious agricultural pests, and in addition, accidental or deliberate introduction of various snail species into new territory has resulted in serious damage to some natural ecosystems.

Schistosomiasis is “second only to malaria as the most devastating parasitic disease in tropical countries. An estimated 200 million people in 74 countries are infected with the disease — 100 million in Africa alone.”[105] The parasite has 13 known species, of which two infect humans. The parasite itself is not a mollusc, but all the species have freshwater snails as intermediate hosts.[106]

Some species of molluscs, particularly certain snails and slugs, can be serious crop pests,[107] and when introduced into new environments can unbalance local ecosystems. One such pest, the giant African snail Achatina fulica, has been introduced to many parts of Asia, as well as to many islands in the Indian Ocean and Pacific Ocean. In the 1990s this species reached the West Indies. Attempts to control it by introducing the predatory snail Euglandina rosea proved disastrous, as the predator ignored Achatina fulica and went on to extirpate several native snail species instead.[108]

Despite its name, Molluscum contagiosum is a viral disease, and is unrelated to molluscs.[109

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Sea Creatures

The term deep sea creature refers to organisms that live below the photic zone of the ocean. These creatures must survive in extremely harsh conditions, such as hundreds of atmospheres of pressure, small amounts of oxygen, very little food, no sunlight, and constant, extreme cold. Most creatures have to depend on food floating down from above.

These creatures live in very harsh environments such as the abyssal or hadal zones, which, being thousands of meters below the surface, are almost completely devoid of light. The water is very cold (between 3 and 10 degrees Celsius, or 37 and 50 degrees Fahrenheit), and has low oxygen levels. Due to the depth, the pressure is between 20 and 1,000 atmospheres. Creatures that live thousands of feet deep in the ocean have adapted to the high pressure, lack of light, and other factors.

 

Barometric pressure

These animals have evolved to survive the extreme pressure of the sub-photic zones. The pressure increases by about one atmosphere every ten meters. To cope with the pressure, many fish are rather small, usually not exceeding 25 cm in length. Also, scientists have discovered that the deeper these creatures live, the more gelatinous their flesh and more minimal their skeletal structure. These creatures have also eliminated all excess cavities that would collapse under the pressure, such as swim bladders.[1]

[edit]Lack of light

The lack of light requires creatures to have special adaptations to find food, avoid predators, and find mates. Most animals have very large eyes with retinas constructed only of cones, which increases sensitivity. Many animals have also developed large feelers to replace peripheral vision. To be able to reproduce, many of these fish have evolved to be hermaphroditic, eliminating the need to find a mate. Many creatures have also developed very strong senses of smell to detect the chemicals released by mates.

[edit]Lack of Resources

giant isopod (Bathynomus giganteus)

At this depth, there is not enough light for photosynthesis to occur and not enough oxygen to support a fish living at higher levels. To survive, these creatures have much slower metabolisms and therefore can survive using little oxygen. They can also go months without food. Most food comes from either organic material that falls from above or from eating other creatures that have derived their food through the process of chemosynthesis (the process of changing chemical energy into food energy). Because of the sparse distributions of creatures, there is always at least some oxygen and food. Also, instead of using energy to search for food, these creatures use particular adaptations to ambush prey.

[edit]Hypoxic environment

Creatures that live in the sub-abyss require adaptations to cope with the naturally low oxygen levels.

[edit]Deep-sea gigantism

Main article: Deep-sea gigantism

Humpback anglerfish:Melanocetus johnsonii

The term deep-sea gigantism describes an effect that living at such depths has on some creatures’ sizes, especially relative to the size of relatives that live in different environments. These creatures are generally many times bigger than their smaller counterparts. The Giant Isopod (related to the common pill bug) exemplifies this. Scientists haven’t been able to explain deep-sea gigantism, with the exception of the giant tube worm. Scientists believe these creatures are much larger than shallower-watertube worms because they live on hydrothermal vents that expel huge amounts of resources. They believe that, since the creatures don’t have to expend energy regulating body temperature and have a smaller need for activity, they can allocate more resources to bodily processes.

There are also cases of deep-sea creatures being abnormally small, such as the lantern shark, which fits in an adult human‘s palm. [2]

[edit]Bioluminescence

Smaller cousins of giant tube worms feeding at ahydrothermal vent

Bioluminescence is the ability for an organism to create light through chemical reactions. Creatures use bioluminescence in many ways: to light their way, attract prey, or seduce a mate. Many underwater animals are bioluminescent—from the Viper fish to theFlashlight fish, which is named for its light.[3] Some creatures, such as the angler fish have a concentration of photophores in a small limb that protrudes from their bodies, which they use as a lure to catch curious fish. Bioluminescence can also confuse enemies. The chemical process of bioluminescence requires at least two chemicals: the light producing chemical called luciferin and the reaction causing chemical called luciferase.[4] The luciferase catalyzes the oxidation of the luciferin causing light and resulting in an inactive oxyluciferin. Fresh luciferin must be brought in through the diet or through internal synthesis.[4]

[edit]Chemosynthesis

Since at such deep levels, there is little to no sunlight, photosynthesis is impossible as a means of energy production, leaving some creatures with the quandary of how to produce food for themselves. For the giant tube worm, this answer comes in the form of bacteria that live inside of it. These bacteria are capable of chemosynthesis and live inside of the giant tube worm, which lives on hydrothermal vents. These vents spew very high amounts of chemicals that these bacteria can transform into energy. These bacteria can also grow freely of a host and create mats of bacteria on the sea floor around hydrothermal vents, where they serve as food to other creatures. Bacteria are a key energy source in the food chain. This source of energy creates large populations in areas around hydrothermal vents, which provides scientists an easy stop for research. [5]

Deep Sea Research

Alvin in 1978, a year after first exploringhydrothermal vents.

Humans have explored less than 2% of the ocean floor, and dozens of new species of deep sea creatures are discovered with every dive. The submarine DSV Alvin—owned by the US Navy and operated by the Woods Hole Oceanographic Institution (WHOI) in Woods Hole, Massachusetts—exemplifies the type of craft used to explore deep water. This 16 ton submarine can withstand extreme pressure and is easily maneuverable despite its weight and size.

However, studying deep sea creatures is problematic, since with the extreme change in pressure, and environment in general, these creatures can’t survive for very long, if at all, on the surface. This makes in depth research difficult because so much of what we want to know about only occurs while the creature is alive. Recent developments have allowed scientists to look at these creatures more closely, and for a longer time. A marine biologist, Jeffery Drazen, has explored a solution, a pressurized fish trap. This captures a deep-water creature, and adjusts its internal pressure slowly to surface level as the creature is brought to the surface, in hopes that the creature can adjust. [6] Another scientific team, from the Universite Pierre et Marie Curie, has developed a capture device known as the PERISCOP that maintains water pressure as it surfaces, keeping the samples in a pressurized environment during the ascent. This allows for close study on the surface without disturbances in pressure to the sample. [7]

[edit]Deep Sea Creatures In Popular Culture

The BBC‘s Blue Planet have featured deep sea creatures, highlighting their peculiar attributes.

[edit]

 


 

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Deep Sea Creatures

The term deep sea creature refers to organisms that live below the photic zone of the ocean. These creatures must survive in extremely harsh conditions, such as hundreds of atmospheres of pressure, small amounts of oxygen, very little food, no sunlight, and constant, extreme cold. Most creatures have to depend on food floating down from above.

These creatures live in very harsh environments such as the abyssal or hadal zones, which, being thousands of meters below the surface, are almost completely devoid of light. The water is very cold (between 3 and 10 degrees Celsius, or 37 and 50 degrees Fahrenheit), and has low oxygen levels. Due to the depth, the pressure is between 20 and 1,000 atmospheres. Creatures that live thousands of feet deep in the ocean have adapted to the high pressure, lack of light, and other factors.

 

Barometric pressure

These animals have evolved to survive the extreme pressure of the sub-photic zones. The pressure increases by about one atmosphere every ten meters. To cope with the pressure, many fish are rather small, usually not exceeding 25 cm in length. Also, scientists have discovered that the deeper these creatures live, the more gelatinous their flesh and more minimal their skeletal structure. These creatures have also eliminated all excess cavities that would collapse under the pressure, such as swim bladders.[1]

[edit]Lack of light

The lack of light requires creatures to have special adaptations to find food, avoid predators, and find mates. Most animals have very large eyes with retinas constructed only of cones, which increases sensitivity. Many animals have also developed large feelers to replace peripheral vision. To be able to reproduce, many of these fish have evolved to be hermaphroditic, eliminating the need to find a mate. Many creatures have also developed very strong senses of smell to detect the chemicals released by mates.

[edit]Lack of Resources

giant isopod (Bathynomus giganteus)

At this depth, there is not enough light for photosynthesis to occur and not enough oxygen to support a fish living at higher levels. To survive, these creatures have much slower metabolisms and therefore can survive using little oxygen. They can also go months without food. Most food comes from either organic material that falls from above or from eating other creatures that have derived their food through the process of chemosynthesis (the process of changing chemical energy into food energy). Because of the sparse distributions of creatures, there is always at least some oxygen and food. Also, instead of using energy to search for food, these creatures use particular adaptations to ambush prey.

[edit]Hypoxic environment

Creatures that live in the sub-abyss require adaptations to cope with the naturally low oxygen levels.

[edit]Deep-sea gigantism

Main article: Deep-sea gigantism

Humpback anglerfish:Melanocetus johnsonii

The term deep-sea gigantism describes an effect that living at such depths has on some creatures’ sizes, especially relative to the size of relatives that live in different environments. These creatures are generally many times bigger than their smaller counterparts. The Giant Isopod (related to the common pill bug) exemplifies this. Scientists haven’t been able to explain deep-sea gigantism, with the exception of the giant tube worm. Scientists believe these creatures are much larger than shallower-watertube worms because they live on hydrothermal vents that expel huge amounts of resources. They believe that, since the creatures don’t have to expend energy regulating body temperature and have a smaller need for activity, they can allocate more resources to bodily processes.

There are also cases of deep-sea creatures being abnormally small, such as the lantern shark, which fits in an adult human‘s palm. [2]

[edit]Bioluminescence

Smaller cousins of giant tube worms feeding at ahydrothermal vent

Bioluminescence is the ability for an organism to create light through chemical reactions. Creatures use bioluminescence in many ways: to light their way, attract prey, or seduce a mate. Many underwater animals are bioluminescent—from the Viper fish to theFlashlight fish, which is named for its light.[3] Some creatures, such as the angler fish have a concentration of photophores in a small limb that protrudes from their bodies, which they use as a lure to catch curious fish. Bioluminescence can also confuse enemies. The chemical process of bioluminescence requires at least two chemicals: the light producing chemical called luciferin and the reaction causing chemical called luciferase.[4] The luciferase catalyzes the oxidation of the luciferin causing light and resulting in an inactive oxyluciferin. Fresh luciferin must be brought in through the diet or through internal synthesis.[4]

[edit]Chemosynthesis

Since at such deep levels, there is little to no sunlight, photosynthesis is impossible as a means of energy production, leaving some creatures with the quandary of how to produce food for themselves. For the giant tube worm, this answer comes in the form of bacteria that live inside of it. These bacteria are capable of chemosynthesis and live inside of the giant tube worm, which lives on hydrothermal vents. These vents spew very high amounts of chemicals that these bacteria can transform into energy. These bacteria can also grow freely of a host and create mats of bacteria on the sea floor around hydrothermal vents, where they serve as food to other creatures. Bacteria are a key energy source in the food chain. This source of energy creates large populations in areas around hydrothermal vents, which provides scientists an easy stop for research. [5]

Deep Sea Research

Alvin in 1978, a year after first exploringhydrothermal vents.

Humans have explored less than 2% of the ocean floor, and dozens of new species of deep sea creatures are discovered with every dive. The submarine DSV Alvin—owned by the US Navy and operated by the Woods Hole Oceanographic Institution (WHOI) in Woods Hole, Massachusetts—exemplifies the type of craft used to explore deep water. This 16 ton submarine can withstand extreme pressure and is easily maneuverable despite its weight and size.

However, studying deep sea creatures is problematic, since with the extreme change in pressure, and environment in general, these creatures can’t survive for very long, if at all, on the surface. This makes in depth research difficult because so much of what we want to know about only occurs while the creature is alive. Recent developments have allowed scientists to look at these creatures more closely, and for a longer time. A marine biologist, Jeffery Drazen, has explored a solution, a pressurized fish trap. This captures a deep-water creature, and adjusts its internal pressure slowly to surface level as the creature is brought to the surface, in hopes that the creature can adjust. [6] Another scientific team, from the Universite Pierre et Marie Curie, has developed a capture device known as the PERISCOP that maintains water pressure as it surfaces, keeping the samples in a pressurized environment during the ascent. This allows for close study on the surface without disturbances in pressure to the sample. [7]

[edit]Deep Sea Creatures In Popular Culture

The BBC‘s Blue Planet have featured deep sea creatures, highlighting their peculiar attributes.

[edit]

 


 

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Marine biology

arine biology is the scientific study of organisms in the ocean or other marine or brackish bodies of water. Given that in biology many phyla, families and genera have some species that live in the sea and others that live on land, marine biology classifies species based on the environment rather than on taxonomy. Marine biology differs from marine ecology as marine ecology is focused on how organisms interact with each other and the environment, and biology is the study of the organisms themselves.

Marine life is a vast resource, providing food, medicine, and raw materials, in addition to helping to support recreation and tourism all over the world. At a fundamental level, marine life helps determine the very nature of our planet. Marine organisms contribute significantly to the oxygen cycle, and are involved in the regulation of the Earth’s climate.[1] Shorelines are in part shaped and protected by marine life, and some marine organisms even help create new land.[2]

Marine biology covers a great deal, from the microscopic, including most zooplankton and phytoplankton to the huge cetaceans (whales) which reach up to a reported 30 meters (98 feet) in length.

The habitats studied by marine biology include everything from the tiny layers of surface water in which organisms and abiotic items may be trapped in surface tension between the ocean and atmosphere, to the depths of the oceanic trenches, sometimes 10,000 meters or more beneath the surface of the ocean. It studies habitats such as coral reefskelp foreststidepools, muddy, sandy and rocky bottoms, and the open ocean (pelagic) zone, where solid objects are rare and the surface of the water is the only visible boundary.

A large proportion of all life on Earth exists in the oceans. Exactly how large the proportion is unknown, since many ocean species are still to be discovered. While the oceans constitute about 71% of the Earth’s surface, due to their depth they encompass about 300 times the habitable volume of the terrestrial habitats on Earth.

Many species are economically important to humans, including food fish. It is also becoming understood that the well-being of marine organisms and other organisms are linked in very fundamental ways. The human body of knowledge regarding the relationship between life in the sea and important cycles is rapidly growing, with new discoveries being made nearly every day. These cycles include those of matter (such as the carbon cycle) and of air (such as Earth’s respiration, and movement of energy through ecosystems including the ocean). Large areas beneath the ocean surface still remain effectively unexplored.

 

 

Birds

Main article: Seabird

Birds adapted to living in the marine environment are often referred to as seabirds. Examples include albatrosspenguinsgannets, and auks. Although they spend most of their lives in the ocean, species such as gulls can often be found thousands of miles inland.

[edit]Fish

Main article: Fish

Fish anatomy includes a two-chambered heart, operculumswim bladderscalesfinslipseyes and secretory cells that produce mucous. Fish breathe by extracting oxygen from water through their gills. Fins propel and stabilize the fish in the water.

Well known fish include: sardinesanchovyling codclownfish (also known as anemonefish), and bottom fish which include halibut or ling codPredators include sharks and barracuda.

[edit]Invertebrates

Main article: Marine invertebrates

As on land, invertebrates make up a huge portion of all life in the sea. Invertebrate sea life includes Cnidaria such as jellyfish and sea anemonesCtenophorasea worms including the phyla PlatyhelminthesNemerteaAnnelidaSipunculaEchiura,Chaetognatha, and PhoronidaMollusca including shellfishsquidoctopusArthropoda including Chelicerata and CrustaceaPoriferaBryozoaEchinodermata including starfish; and Urochordata including sea squirts or tunicates.

[edit]Mammals

Main article: Marine mammal

There are five main types of marine mammals.

[edit]Reptiles

Main article: Marine reptile

Reptiles which inhabit or frequent the sea include sea turtlessea snakesterrapins, the marine iguana, and the saltwater crocodile. Most extant marine reptiles, except for some sea snakes, are oviparous and need to return to land to lay their eggs. Thus most species, excepting sea turtles, spend most of their lives on or near land rather than in the ocean. Despite their marine adaptations, most sea snakes prefer shallow waters nearby land, around islands, especially waters that are somewhat sheltered, as well as near estuaries.[3][4] Some extinct marine reptiles, such as ichthyosaurs, evolved to be viviparous and had no requirement to return to land.

[edit]Fungi

Main article: Marine fungi

Over 1500 species of fungi are known from marine environments.[5] These parasitize marine algae or animals, or are saprobes on algae, corals, protozoan cysts, sea grasses, wood and other substrata, and can also be found in sea foam.[6] Spores of many species have special appendages which facilitate attachment to the substratum.[7] A very diverse range of unusual secondary metabolites is produced by marine fungi.[8]

[edit]Plants and algae

Plant life is widespread and very diverse under the ocean. Microscopic photosynthetic algae contribute a larger proportion of the worlds photosynthetic output than all the terrestrial forests combined. Most of the niche occupied by sub plants on land is actually occupied by macroscopic algae in the ocean, such as Sargassum and kelp, which are commonly known as seaweeds that creates kelp forests. The non algae plants that survive in the sea are often found in shallow waters, such as theseagrasses (examples of which are eelgrass, Zostera, and turtle grass, Thalassia). These plants have adapted to the high salinity of the ocean environment. The intertidal zone is also a good place to find plant life in the sea, where mangroves orcordgrass or beach grass might grow. Microscopic algae and plants provide important habitats for life, sometimes acting as hiding and foraging places for larval forms of larger fish and invertebrates.

 

[edit]Microscopic life

copepod.

Microscopic life undersea is incredibly diverse and still poorly understood. For example, the role of viruses in marine ecosystems is barely being explored even in the beginning of the 21st century.

The role of phytoplankton is better understood due to their critical position as the most numerous primary producers on Earth. Phytoplankton are categorized into cyanobacteria (also called blue-green algae/bacteria), various types of algae (red, green, brown, and yellow-green), diatomsdinoflagellateseuglenoidscoccolithophoridscryptomonadschrysophyteschlorophytesprasinophytes, and silicoflagellates.

Zooplankton tend to be somewhat larger, and not all are microscopic. Many Protozoa are zooplankton, including dinoflagellates, zooflagellatesforaminiferans, and radiolarians. Some of these (such as dinoflagellates) are also phytoplankton; the distinction between plants and animals often breaks down in very small organisms. Other zooplankton include cnidariansctenophoreschaetognathsmolluscsarthropodsurochordates, and annelids such as polychaetes. Many larger animals begin their life as zooplankton before they become large enough to take their familiar forms. Two examples are fish larvae and sea stars (also called starfish).

 

[edit]Marine habitats

Marine habitats
Coral reefs provide marine habitats for tube sponges, which in turn become marine habitats for fishes

Coral reefs provide marine habitats for tube sponges, which in turn become marine habitats for fishes

  Littoral zone
  Intertidal zone
  Estuaries
  Kelp forests
  Coral reefs
  Ocean banks
  Continental shelf
  Neritic zone
  Straits
  Pelagic zone
  Oceanic zone
  Seamounts
  Hydrothermal vents
  Cold seeps
  Demersal zone
  Benthic zone
Main article: Marine habitats

Marine habitats can be divided into coastal and open ocean habitats. Coastal habitats are found in the area that extends from the shoreline to the edge of the continental shelf. Most marine life is found in coastal habitats, even though the shelf area occupies only seven percent of the total ocean area. Open ocean habitats are found in the deep ocean beyond the edge of the continental shelf

Alternatively, marine habitats can be divided into pelagic and demersal habitats. Pelagic habitats are found near the surface or in the open water column, away from the bottom of the ocean. Demersal habitats are near or on the bottom of the ocean. An organism living in a pelagic habitat is said to be a pelagic organism, as in pelagic fish. Similarly, an organism living in a demersal habitat is said to be a demersal organism, as in demersal fish. Pelagic habitats are intrinsically shifting and ephemeral, depending on what ocean currents are doing.

Marine habitats can be modified by their inhabitants. Some marine organisms, like corals, kelp and seagrasses, are ecosystem engineers which reshape the marine environment to the point where they create further habitat for other organisms.

[edit]Intertidal and shore

Tide pools with sea stars and sea anemone in Santa Cruz, California

Intertidal zones, those areas close to shore, are constantly being exposed and covered by the ocean’s tides. A huge array of life lives within this zone.

Shore habitats span from the upper intertidal zones to the area where land vegetation takes prominence. It can be underwater anywhere from daily to very infrequently. Many species here are scavengers, living off of sea life that is washed up on the shore. Many land animals also make much use of the shore and intertidal habitats. A subgroup of organisms in this habitat bores and grinds exposed rock through the process of bioerosion.

[edit]Reefs

Main article: Coral reef

Reefs comprise some of the densest and most diverse habitats in the world. The best-known types of reefs are tropical coral reefs which exist in most tropical waters; however, reefs can also exist in cold water. Reefs are built up by corals and other calcium-depositing animals, usually on top of a rocky outcrop on the ocean floor. Reefs can also grow on other surfaces, which has made it possible to create artificial reefs. Coral reefs also support a huge community of life, including the corals themselves, their symbiotic zooxanthellae, tropical fish and many other organisms.

Much attention in marine biology is focused on coral reefs and the El Niño weather phenomenon. In 1998, coral reefs experienced the most severe mass bleaching events on record, when vast expanses of reefs across the world died because sea surface temperatures rose well above normal.[9][10] Some reefs are recovering, but scientists say that between 50% and 70% of the world’s coral reefs are now endangered and predict that global warming could exacerbate this trend.[11][12][13][14]

[edit]Open ocean

Main article: Pelagic zone

The open ocean is relatively unproductive because of a lack of nutrients, yet because it is so vast, in total it produces the most primary productivity. Much of the aphotic zone‘s energy is supplied by the open ocean in the form of detritus. The open ocean consists mostly of jellyfish and its predators such as the mola mola.

[edit]Deep sea and trenches

The deepest recorded oceanic trenches measure to date is the Mariana Trench, near the Philippines, in the Pacific Ocean at 10,924 m (35,838 ft). At such depths, water pressure is extreme and there is no sunlight, but some life still exists. A whiteflatfish, a shrimp and a jellyfish were seen by the American crew of the bathyscaphe Trieste when it dove to the bottom in 1960.[15]

Other notable oceanic trenches include Monterey Canyon, in the eastern Pacific, the Tonga Trench in the southwest at 10,882 m (35,702 ft), the Philippine Trench, the Puerto Rico Trench at 8,605 m (28,232 ft), the Romanche Trench at 7,760 m (24,450 ft), Fram Basin in the Arctic Ocean at 4,665 m (15,305 ft), the Java Trench at 7450 m (24,442 ft), and the South Sandwich Trench at 7,235 m (23,737 ft).

In general, the deep sea is considered to start at the aphotic zone, the point where sunlight loses its power of transference through the water.[citation needed] Many life forms that live at these depths have the ability to create their own light known as bio-luminescence.

Marine life also flourishes around seamounts that rise from the depths, where fish and other sea life congregate to spawn and feed. Hydrothermal vents along the mid-ocean ridge spreading centers act as oases, as do their opposites, cold seeps. Such places support unique biomes and many new microbes and other lifeforms have been discovered at these locations .[citation needed]

[edit]Distribution factors

An active research topic in marine biology is to discover and map the life cycles of various species and where they spend their time. Marine biologists study how the ocean currentstides and many other oceanic factors affect ocean lifeforms, including their growth, distribution and well-being. This has only recently become technically feasible with advances in GPS and newer underwater visual devices.[citation needed]

Most ocean life breeds in specific places, nests or not in others, spends time as juveniles in still others, and in maturity in yet others. Scientists know little about where many species spend different parts of their life cycles. For example, it is still largely unknown where sea turtles and somesharks travel. Tracking devices do not work for some life forms, and the ocean is not friendly to technology. This is important to scientists and fishermen because they are discovering that by restricting commercial fishing in one small area they can have a large impact in maintaining a healthy fish population in a much larger area far away.

 

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