Plant science. Animal anatomy. Life Sciences. Developmental Biology. Plant Sciences. Introduction -- 2.
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G igi8. The prospective eignifioioce of the ceDs contamed in the four qoadianti of the primldve limh due m AmHystoma Jour Eipcr Zool 37 Rana or Ambysloma embryos For hosts use meduUaiy-pIatc or roedJ lary fold stages for donors use late ncurulac [dosing folds] or canT tail-bud stages. I Take donor and host out of all membranes and plajx them side by side m grooves m an operating dish. Onent the donor right side up and the host ventral side up Operate m full strength Holtfreter solution,. Dothey beat synchronously?
Take notes Pmctjcx the dissection ttt toc, on t normal cmbiyo first. Proceed as m Experiment 25 but carefully awid mjury to the pre chordal entomesoderm. Scrape off the ectoderm with the tip of the glass needle and the hair loop. Proceed as m Experiments 25 and 27 Carefully separate medullary plate from substrate tiding hair loop and glass needle. Adeluanm H. B a ExperimentEl itadies on the development erf the eye. Experimentil itadief on the development of the eye.
Expenmental studiet on the development of the eye. Abgrtnioiig des Aogenmaterials ond anderer Teilbeilrke in der lledaHaiplatte. Ibtd Detennlcitkxi des Aagttifcnmts bd AnpbitrfetL Aad. How is the determination of the medullary plate of the eye, of the bal anccr, accomplished? If one bears this in mind then the use of this conv'cnient term as defined above will do no harm.
The student is referred to the chapters on mduebon m the books of Huxley and Dc Beer, of Spemann and of Weiss. Spemann s conduswns were confirmed first the optic cup is Instrumental in the formation of the lens second the dependence of the lens epithelium on the optic cup diffcia m different speaes. The presence of a small eye may be doe to an mcom plete extirpation -and a regulation of tbc fragment.
After the embryo has reached the swimming stage fix It m 10 per cent formaldehyde After a few mmutes the lenses will become visible as opaque white structures Note that the epidermis which has grown over the nght tyt has become transparent and forms a normal cornea. JIauusov IL G zgio. Lewis U H Du UlrbdtienDge b der. Host and transplant structures supplemented each other in the formation of a whole new or ganisra This capaatj for integrated inductions has earned for the upper.
Since many of the inductions obtamed by the student will be partial rather than com. Remember that early gastrulae ere very delicate when taken out of their membranes and that your success will depend on careful handling and working under sterile conditions. Readjust the glass bndge if necessary. Operate m full strength Holtfreter solution. Spemann has frequently used the hair loop as a cutting instrument.
Make a number of operations The mortality is high Keep all dishes bghtly dosed Use sterile pipettes and hair loops for inspection. Study the papers of Holtfreter and 6 and try to obtam mdoc tbns with living or dead tissue of adult salamanders brain, rctma or With pieces of medullary plate or ectoderm of A mbysloma which have been tilled by heat or In alcohol wash carefully before implanting There b. Bautzuaxn H. New Htvtn Ytle Urdvenity.
This can be accomplished readily by creating wound surfaces on the td jacent and pressing them together until healing is completed Such twins have been reared through metamorphosis. Sectiomng i! Jour Eiper 2 o 6 L, 45 J Hauscct R. G S. Lithium chloride if added to the sea water m a ccrtam concentration and if applied before gastrulation re nits in eiDgastrulation that is the entoderm grows to disproportion ately large size and instead of mvagmating evaginates.
If an eitcmal agent affects a fundamental physiological activity of all cells then its cffecta arc widespread, and the end effect depend! Label all dishes carefully. Jour Eiper Zotd 67 Amer Jour Anat. C hitp C. Eiper ZoOL, 89 i. Limtuor F E. SrociAiD Ch.
Sttanpb Ges. Ha senes of lectures Ancifimy and ike problem of beba-wvr should be consulted In connection enth this exercise. The gy imming reflex is the first integrated actixtly of an amp hib ia n larra. Swimming is preceded by spontaneous wngglmg motions within the membranes long before hafrhmg CoghiD studied in detail these earhest reflexes and classified them m a number of behaiTor stages p senes shows dearth the progressjon in the complexity of the behavior pattern. The following expcnmenti and observations obtain significance only m the light of these neurological data.
The stu cut. Bbould study the diagrams of the organization of the nervous system in different stages of behavior in Coghfll The ongm of mdependent limb movtments is another example To quote Coghill. The same bolds for jaw movements in feeding gill movements etc Altogether complex activities such as swimming or feeding are not the result of expcnence or learmng but the result of an orderlj sequence of devdopmental steps of the neural mechanisms.
These stages were worked out by Coghill The following dcfimtions arc taken verbatim from DuShane and Hutchinson pp with a few additions. Place one after another in a dish. By gently stroking the narcotized animals with the hair loop, check each day to sec if they are completely immobDlked If not, transfer them to t stronger concentration. CocHiLL, G. Jour Expcf ZoCl. Data on different breeds on the pnnaples and practice of meubatwn on factors influencing hatchabilitj etc. Mount a loo-watt bulb on a wooden base and invert the tin can over it Place the egg over the hole.
Candle in a darkened room. From the seventh day on the chono-aHantoIc circulation can be seen in live cm bryos as an irregular network closely applied to the shclL From the thlr tcenth day on living embryos appear increasingly dark and the line of demarcation against the air chaniber is very sharp and distinct In ero bryos which die during these days this line is indistinct and hasy.
Stages i and 2 arc difficult to handle os donors stage 6 Is too old for donors but may be Uocd os hosts. Mold the cotton into a groove in which the egg will fit Eggs are placed on these "nests dunng the operatioD agar plates stained with Nfle blue sulphate and neutral red for vital staining for preparation of the plates see p I pair of hne scissors 1 pair of large sdssors 6 square cover gla. Ufually It is not feasible in courses of experimental cmbrj-ology to sec tion the transplants Therefore U is suggested that limb pnraordia be used for chorio-allantolc, cocloraic and flank grafts Carliltginous limb skeletons of transplants, days old can easily be stained tn Mo mthm.
Before starting the following cipenments the student should scqtuunt himself thoroughly with the no rmal dcvelopincnt of the duck embryo, from the pnimtxve streak stage to the early somite stage between 12 and 36 hours of incubation. According to this account, a vital stain mark placed on Hensen s node will result m a itain of the entire length of the notochord ind of the floor of the neural tube.
Wetzel was the first to apply Vogt's technique of vital staining to the chick embryo The results are not so satisfactory as in amphlbums. In the chick the stain is taken up by yoDc and fat globules, which break down m cell metabolism As a result the marks fade out more rapidly than b amphibians, in which the pigment granules are the chief camerB of the Etam It IS therefore necessary to apply a deep stain.
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Moisten a small strip of the red and of the blue agar piste with saline solu. Carefully avoid any injury to the shell membrane. Lift the window out with the scalpel and watchmaker forceps. Handle the embryo with watchmaker forceps. Dissect the skin away if necessary Use a very strong light source. Stain Hensen s node following the procedure given on page After 24 hours remove the blastodcmi from the egg Slit the neural tube In the midline with a glass needle hold the embryo with a forceps or turn the.
Place the mart m front of Hensen s node, near it and to the right of the median plane. Make a precise sketch. After 24 hours dissect the embrjo find the stain Notice which parts of the brain are stamed. JiCOBsox W Pasieeli, J AnaL n. Entw'feadi-, ap i. LHhe s laboratory at the Umverslt of Chicago by Hoadlc and Willicr It makrfl use of the highly vascularized chono-allantoic membrane of avian embryos which becomes closcl apphed to the shell membrane and is thus withm easy reach of the cjpenmenter Fig 34 The mem brine of Sj-io-day chid: embryos is suffiaently developed to servT as a substrate The structures whose potenaes are to be tested are placed on the membrane through a window in the shell which is sealed up after the operatioiL The grafts become vascularized and can be reared for days.
The have to be rccos'ered before the chono-allantoic membrane breaks down on the nmeteenth day of mcubation The transplants are complctel isolated from the structures of the host embryo proper, so that inductive effects etc. Mold the cotton into a shallow groove into which the egg will fit Fill 3 watch glasses with sterfle saline solution and coitt them with a lid Keep the third watch glass dry and covered Immedlatclj before operation cover the operation table with sterile towels Dry all stnmienta carefully Place them and all pipettes in a fold of a sterile towel and place the towel to the right of the binocular microscope.
Its rocking movements maj be seen in candling. This is absolutely necessary because otherwise the shell membrane cannot be removed without mjury to the chono aflantoic mem brane. II Candle the donor embryo and mark ita position Place it on a cot ton nest and saw a large square wmdow wound the marked region. Use one to hold the cmbiyo and the other to remove the membranes Work under the low power of the binocular microscope against a dark background. Operate under the bmocular miscroscope and try to place the graft near the blood vessel.
It sometunes sticks to the pipette U this happens then pipette it back into the watch glass with strong squirts and repeat the procedure. Note whether it was a wing or leg bud etc. Repeat the experiment using both wing and leg buds If the matenaJ is scarce scieral buds from the same donor should be taken It a also possible but not advisable to implant 2 grafts in the same host.
Compart with the figures in Murray and E A Hunt Stamuig is not necessary The grafts must be sectioned if liislological studies arc desired. HoAPLar L. Jour Exper Zod. Jour Anit, 59 Jour Exper Zoo! Amer Joor AnaL, 33 With a pair of steriUred scissors cut out the entire area vasculosa with the embryo in its center AVlth the watchmaker forceps or with a wide-mouthed pipette transfer it to a dish with saline solution.
As in Eiperrment 47 with the following modifications 10 p Preparation of the transpilant In cuttmgout thehrabbud leave small strips of tissue somites or adjacent mesodennl attached to the antenor and posterior ends of the base of the bud these will be tucked into the slit The other Umb buds maj be used for further transplan ta bons. Firsts mate a transverae cut behind the nght optic vcside through the head to the midlme Second mate a median cut through the anterior part of the head Tie left eye nmy be used for an other transplantation Fig 36 b.
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The migration of melanophores can be demonstrated by the foDowmg experiment devised by Wilher and Rawles Rupture chorion and amnion over the right wing bud open up a large hole The membranes wili heal ov'cr again With the glass needle make a small but rather deep hole at the base of the wing Vital staimng Is not necessary Return the host to the incubator. AuxutDEt L.
Girtoxoax ScBOE? Intra-coelomic grafts of the eje pninordium of the chici. Jour Eiper ZooL, 74 GoyfiroT E. Rev sulase de sooL, J4! Senorrf, 0 E. The origiQ and morphogeaetJe potcades of rtjeocrates. Grovtl] SuppL It is desirable to run all expenments at constant temperatures. I Prepare and label finger bowls or Petri dishes one for sped mens Prepare a dish for discarded pieces. Exteument sa Reocneration or Short Tka. Sectwn several plananans m the median plane A Fig 38 b Section others m a paramedian plane Discard all pieces of the old pharynx. Observe lateral regeneration. Make an obhque cut and discard the anterior piece.
This asymmetry is clearly expressed m the earher appearance of the left antenor eye The tail blastema is likewise asvTnmetncal The regener ates fllustrate another pomt of general interest the main direction of outgrowth both of head and of tail blastemas is at first perpendicular to the cut surface and not m the mAin ana of the old piece Barfurth was the first to observe this on tail regenerates from obhque scctioiis m amphibian tadpoles and regeneration perpendicular to the cut surface is occasionally referred to as Barfurth a rule In later stages the heads and taila straighten out Rukn has inUrpreted these results on the base of Child s gradient theory.
Each half tends to reconstitute a whole organism Fig 38 d. Run parallel cultures of E and F pieces in well or spring water as controls. Dupliatas cruoata is one of the strangest duplications occurring in animals It is a complete duplication in which two heads and two taHs are present. If necessary reopen the longitudinal cut Make opera Check the operated AnTmAlt on the following days Reopen the tticdian slit if necessarj.
Except for some sea snakes, most extant marine reptiles are oviparous and need to return to land to lay their eggs. Apart from sea turtles, the species usually spend most of their lives on or near land rather than in the ocean. Sea snakes generally prefer shallow waters nearby land, around islands, especially waters that are somewhat sheltered, as well as near estuaries.
The ancient Ichthyosaurus communis independently evolved flippers similar to dolphins. Some extinct marine reptiles, such as ichthyosaurs , evolved to be viviparous and had no requirement to return to land. Ichthyosaurs resembled dolphins. They first appeared about million years ago and disappeared about 90 million years ago. The terrestrial ancestor of the ichthyosaur had no features already on its back or tail that might have helped along the evolutionary process.
Yet the ichthyosaur developed a dorsal and tail fin which improved its ability to swim. During the Mesozoic many groups of reptiles became adapted to life in the seas, including ichthyosaurs , plesiosaurs , mosasaurs , nothosaurs , placodonts , sea turtles , thalattosaurs and thalattosuchians. Marine reptiles were less numerous after mass extinction at the end of the Cretaceous. Marine birds are adapted to life within the marine environment. They are often called seabirds. While marine birds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution , as the same environmental problems and feeding niches have resulted in similar adaptations.
Examples include albatross , penguins , gannets , and auks. In general, marine birds live longer, breed later and have fewer young than terrestrial birds do, but they invest a great deal of time in their young. Most species nest in colonies , which can vary in size from a few dozen birds to millions. Many species are famous for undertaking long annual migrations , crossing the equator or circumnavigating the Earth in some cases. They feed both at the ocean's surface and below it, and even feed on each other. Marine birds can be highly pelagic , coastal, or in some cases spend a part of the year away from the sea entirely.
Some marine birds plummet from heights, plunging through the water leaving vapour-like trails, similar to that of fighter planes. They have air sacs under their skin in their face and chest which act like bubble-wrap , cushioning the impact with the water. European herring gull attack herring schools from above. The first marine birds evolved in the Cretaceous period , and modern marine bird families emerged in the Paleogene.
Mammals from Latin for breast are characterised by the presence of mammary glands which in females produce milk for feeding nursing their young. There are about living and recently extinct marine mammal species such as seals , dolphins , whales , manatees , sea otters and polar bears. Both cetaceans and sirenians are fully aquatic and therefore are obligate water dwellers. Seals and sea-lions are semiaquatic; they spend the majority of their time in the water, but need to return to land for important activities such as mating , breeding and molting. In contrast, both otters and the polar bear are much less adapted to aquatic living.
Their diet varies considerably as well: some may eat zooplankton ; others may eat fish, squid, shellfish, and sea-grass; and a few may eat other mammals. In a process of convergent evolution , marine mammals, especially cetaceans redeveloped their body plan to parallel the streamlined fusiform body plan of pelagic fish. Front legs became flippers and back legs disappeared, a dorsal fin reappeared and the tail morphed into a powerful horizontal fluke.
This body plan is an adaptation to being an active predator in a high drag environment. A parallel convergence occurred with the now extinct marine reptile ichthyosaur. Endangered blue whale , largest animal ever . Bottlenose dolphin , highest encephalization of any animal after humans . Dugong grazing on seagrass.
Primary producers are the autotroph organisms that make their own food instead of eating other organisms. This means primary producers become the starting point in the food chain for heterotroph organisms that do eat other organisms. Some marine primary producers are specialised bacteria and archaea which are chemotrophs , making their own food by gathering around hydrothermal vents and cold seeps and using chemosynthesis.
However most marine primary production comes from organisms which use photosynthesis on the carbon dioxide dissolved in the water. This process uses energy from sunlight to convert water and carbon dioxide  : — into sugars that can be used both as a source of chemical energy and of organic molecules that are used in the structural components of cells. The principal marine primary producers are cyanobacteria , algae and marine plants.
The oxygen released as a by-product of photosynthesis is needed by nearly all living things to carry out cellular respiration. In addition, primary producers are influential in the global carbon and water cycles. They stabilize coastal areas and can provide habitats for marine animals. The term division has been traditionally used instead of phylum when discussing primary producers, but the International Code of Nomenclature for algae, fungi, and plants now accepts both terms as equivalents.
Cyanobacteria are a phylum division of bacteria which range from unicellular to filamentous and include colonial species. They are found almost everywhere on earth: in damp soil, in both freshwater and marine environments, and even on Antarctic rocks. The first primary producers that used photosynthesis were oceanic cyanobacteria about 2. Because oxygen was toxic to most life on Earth at the time, this led to the near-extinction of oxygen-intolerant organisms , a dramatic change which redirected the evolution of the major animal and plant species. Originally, biologists thought cyanobacteria was algae, and referred to it as "blue-green algae".
The more recent view is that cyanobacteria is a bacteria, and hence is not even in the same Kingdom as algae. Most authorities exclude all prokaryotes , and hence cyanobacteria from the definition of algae. Algae is an informal term for a widespread and diverse group of photosynthetic protists which are not necessarily closely related and are thus polyphyletic.
Marine algae can be divided into six groups:. Unlike higher plants, algae lack roots, stems, or leaves. They can be classified by size as microalgae or macroalgae. Microalgae are the microscopic types of algae, not visible to the naked eye. They are mostly unicellular species which exist as individuals or in chains or groups, though some are multicellular.
Microalgae are important components of the marine protists discussed above , as well as the phytoplankton discussed below. They are very diverse. It has been estimated there are ,, species of which about 50, species have been described. They are specially adapted to an environment dominated by viscous forces. Chlamydomonas globosa , a unicellular green alga with two flagella just visible at bottom left.
Chlorella vulgaris , a common green microalgae , in endosymbiosis with a ciliate . Macroalgae are the larger, multicellular and more visible types of algae, commonly called seaweeds. Seaweeds usually grow in shallow coastal waters where they are anchored to the seafloor by a holdfast. Seaweed that becomes adrift can wash up on beaches. Like microalgae, macroalgae seaweeds are technically marine protists since they are not true plants. A seaweed is a macroscopic form of red or brown or green algae. Sargassum seaweed is a brown alga with air bladders that help it float. Sargassum fish are camouflaged to live among drifting Sargassum seaweed.
The unicellular bubble algae lives in tidal zones. The unicellular mermaid's wineglass are mushroom-shaped algae that grow up to 10 cm high. Killer algae are single-celled organisms, but look like ferns and grow stalks up to 80 cm long. Unicellular organisms are usually microscopic, less than one tenth of a millimeter long.
There are exceptions. Mermaid's wineglass , a genus of subtropical green algae , is single-celled but remarkably large and complex in form with a single large nucleus, making it a model organism for studying cell biology. Selective breeding in aquariums to produce hardier strains resulted in an accidental release into the Mediterranean where it has become an invasive species known colloquially as killer algae. Back in the Silurian , some phytoplankton evolved into red , brown and green algae. These algae then invaded the land and started evolving into the land plants we know today.
Later, in the Cretaceous , some of these land plants returned to the sea as mangroves and seagrasses. Marine plants can be found in intertidal zones and shallow waters, such as seagrasses like eelgrass and turtle grass , Thalassia. These plants have adapted to the high salinity of the ocean environment. Plant life can also flourish in the brackish waters of estuaries , where mangroves or cordgrass or beach grass beach grass might grow.
Sea dragons camouflaged to look like floating seaweed live in kelp forests and seagrass meadows . Mangroves and seagrasses provide important nursery habitats for marine life, acting as hiding and foraging places for larval and juvenile forms of larger fish and invertebrates. Plankton from Greek for wanderers are a diverse group of organisms that live in the water column of large bodies of water but cannot swim against a current. As a result, they wander or drift with the currents. They are a crucial source of food for many marine animals, from forage fish to whales. Plankton can be divided into a plant-like component and an animal component.
Phytoplankton are the plant-like components of the plankton community "phyto" comes from the Greek for plant. They are autotrophic self-feeding , meaning they generate their own food and do not need to consume other organisms. Phytoplankton consist mainly of microscopic photosynthetic eukaryotes which inhabit the upper sunlit layer in all oceans.
They need sunlight so they can photosynthesize. Most phytoplankton are single-celled algae, but other phytoplankton are bacteria and some are protists. They form the base of the primary production that drives the ocean food web , and account for half of the current global primary production, more than the terrestrial forests. Diatoms are one of the most common types of phytoplankton. Green cyanobacteria scum washed up on a rock in California. The coccolithophore Emiliania huxleyi. Algae bloom of Emiliania huxleyi off the southern coast of England. Zooplankton are the animal component of the planktonic community "zoo" comes from the Greek for animal.
They are heterotrophic other-feeding , meaning they cannot produce their own own food and must consume instead other plants or animals as food. In particular, this means they eat phytoplankton. Zooplankton are generally larger than phytoplankton, mostly still microscopic but some can be seen with the naked eye. Many protozoans single-celled protists that prey on other microscopic life are zooplankton, including zooflagellates , foraminiferans , radiolarians and some dinoflagellates.
Other dinoflagellates are mixotrophic and could also be classified as phytoplankton; the distinction between plants and animals often breaks down in very small organisms. Other zooplankton include pelagic cnidarians , ctenophores , molluscs , arthropods and tunicates , as well as planktonic arrow worms and bristle worms. Nassellarian radiolarian. Group of planktic foraminiferans. Noctiluca scintillans , a bioluminescence dinoflagellate. Venus girdle , a ctenophore. Tomopteris , a planktonic segmented worm with unusual yellow bioluminescence .
Many marine animals begin life as zooplankton in the form of eggs or larvae, before they develop into adults. Dinoflagellates are often mixotrophic and live in symbiosis with other organisms. Two dinoflagellates at left and a tintinnid ciliate. Euglena mutabilis , a photosynthetic flagellate.
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Some dinoflagellates are bioluminescent. At night, ocean water can light up internally and sparkle with blue light because of these dinoflagellates. The luminescence, sometimes called the phosphorescence of the sea , occurs as brief 0. In researchers found whales carry nutrients from the depths of the ocean back to the surface using a process they called the whale pump.
There whales defecate a liquid rich in nitrogen and iron. Instead of sinking, the liquid stays at the surface where phytoplankton consume it. In the Gulf of Maine the whale pump provides more nitrogen than the rivers. If phytoplankton dies before it is eaten, it descends through the euphotic zone and settles into the depths of sea. Zooplankton make up most of the marine animal biomass , and as primary consumers are the crucial link between primary producers mainly phytoplankton and the rest of the marine food web secondary consumers.
Biogenic ooze, or biogenic sediment, refers to pelagic sediments with at least 30 percent of marine skeletal material. The term ooze was originally used by John Murray , the "father of modern oceanography", who proposed the term radiolarian ooze for the silica deposits of radiolarian shells brought to the surface during the Challenger Expedition.
The remains of single-celled plankton and benthos organisms are major biogenic components contributing to marine sediments. The hard shells or tests are made out of silica opal as in radiolaria and diatoms or out of calcium carbonate as in coral, shellfish, foraminifera and coccoliths. Radiolarians are unicellular with diameters from 0. They are found as zooplankton throughout the ocean, and their skeletal remains make up much of the cover of the ocean floor as siliceous ooze. Due to their rapid species turn-over, they represent an important diagnostic fossil found from the Cambrian onwards.
The elaborate mineral skeleton of a radiolarian is usually made of silica. Diatoms , major components of marine plankton, also have silica skeletons. Coccoliths have plates made with calcium carbonate called coccoliths , which are important microfossils. Shells from a foraminiferal ooze on the deep ocean floor. Marine carbon cycle .
Marine silicon cycle. In a team of microbiologists led by Edward DeLong made a crucial discovery in the understanding of the marine carbon and energy cycles. They discovered a gene in several species of bacteria   responsible for production of the protein rhodopsin , previously unheard of in the domain Bacteria. These proteins found in the cell membranes are capable of converting light energy to biochemical energy due to a change in configuration of the rhodopsin molecule as sunlight strikes it, causing the pumping of a proton from inside out and a subsequent inflow that generates the energy.
Overfishing is occurring in one third of world fish stocks, according to a report by the Food and Agriculture Organization of the United Nations. Ocean acidification is the increasing acidification of the oceans, caused by the uptake of carbon dioxide from the atmosphere.
When carbon dioxide dissolves in water it forms hydrogen and carbonate ions. This in turn increases the acidity of the ocean and makes survival increasingly harder for shellfish and other marine organisms that depend on calcium carbonate to form their shells. Marine pollution results from the entry into the ocean of industrial , agricultural, and residential wastes.
Nutrient pollution is a primary cause of eutrophication of surface waters, in which excess nutrients, usually nitrates or phosphates , stimulate algae growth. Toxic chemicals can adhere to tiny particles which are then taken up by plankton and benthic animals , most of which are either deposit feeders or filter feeders.
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In this way, toxins are concentrated upward within ocean food chains. Many particles combine chemically in a manner which depletes oxygen, causing estuaries to become anoxic. Pesticides and toxic metals are similarly incorporated into marine food webs, harming the biological health of marine life. Many animal feeds have a high fish meal or fish hydrolysate content. In this way, marine toxins are transferred back to farmed land animals, and then to humans.
Phytoplankton concentrations have increased over the last century in coastal waters, and more recently have declined in the open ocean. Increases in nutrient runoff from land may explain the increases in coastal phytoplankton, while warming surface temperatures in the open ocean may have strengthened stratification in the water column, reducing the flow of nutrients from the deep that open ocean phytoplankton find useful.
Estimates suggest something like 9 million tonnes of plastic is added to the ocean every year. It is thought this plastic will need years or more to biograde. Once in the ocean, plastics are shredded by marine amphipods into microplastics. There are now beaches where 15 percent of the sand are grains of microplastic. In the oceans themselves, microplastics float in surface waters amongst the plankton, where they are ingested by plankton eaters. Habitat loss is occurring in seagrass meadows , mangrove forests , coral reefs and kelp forests , all of which are in global decline due to human disturbances.
Shifting baselines arise in research on marine ecosystems because changes must be measured against some previous reference point baseline , which in turn may represent significant changes from an even earlier state of the ecosystem. Areas that swarmed with a particular species hundreds of years ago may have experienced long term decline, but it is the level a few decades previously that is used as the reference point for current populations.
In this way large declines in ecosystems or species over long periods of time were, and are, masked. There is a loss of perception of change that occurs when each generation redefines what is natural or untouched. Biodiversity is the result of over three billion years of evolution. Until approximately million years ago, all life consisted of archaea , bacteria , protozoans and similar single-celled organisms. The history of biodiversity during the Phanerozoic the last million years , starts with rapid growth during the Cambrian explosion — a period during which nearly every phylum of multicellular organisms first appeared.
Over the next million years or so, invertebrate diversity showed little overall trend and vertebrate diversity shows an overall exponential trend. However, more than 99 percent of all species that ever lived on Earth, amounting to over five billion species,  are estimated to be extinct. The dramatic rise in diversity has been marked by periodic, massive losses of diversity classified as mass extinction events. Most diversity and biomass on earth is found among the microorganisms , which are difficult to measure. Recorded extinction events are therefore based on the more easily observed changes in the diversity and abundance of larger multicellular organisms , rather than the total diversity and abundance of life.
Based on the fossil record , the background rate of extinctions on Earth is about two to five taxonomic families of marine animals every million years. The Great Oxygenation Event was perhaps the first major extinction event. Since the Cambrian explosion five further major mass extinctions have significantly exceeded the background extinction rate. Vertebrates took 30 million years to recover from this event. During the sixth century BC, the Greek philosopher Xenophanes BC recognised that some fossil shells were remains of shellfish.
He used this to argue that what was at the time dry land was once under the sea. Later, during the fourth century BC, another Greek philosopher Aristotle — BC attempted a comprehensive classification of animals which included systematic descriptions of many marine species,   and particularly species found in the Mediterranean Sea. The most striking passages are about the sea-life visible from observation on Lesbos and available from the catches of fishermen.
His observations on catfish , electric fish Torpedo and angler-fish are detailed, as is his writing on cephalopods , namely, Octopus , Sepia cuttlefish and the paper nautilus Argonauta argo. His description of the hectocotyl arm , used in sexual reproduction, was widely disbelieved until its rediscovery in the 19th century.
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What the modern zoologist would call vertebrates and invertebrates, Aristotle called "animals with blood" and "animals without blood" he did not know that complex invertebrates do make use of hemoglobin , but of a different kind from vertebrates. He divided animals with blood into live-bearing mammals , and egg-bearing birds and fish.
Invertebrates "animals without blood" he divided into insects, crustacea further divided into non-shelled — cephalopods — and shelled and testacea molluscs. In contemporary times, marine life is a field of study both in marine biology and in biological oceanography. 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. For this reason marine biology encompasses not only organisms that live only in a marine environment, but also other organisms whose lives revolve around the sea.
Biological oceanography is the study of how organisms affect and are affected by the physics , chemistry , and geology of the oceanographic system. Biological oceanography mostly focuses on the microorganisms within the ocean; looking at how they are affected by their environment and how that affects larger marine creatures and their ecosystem.
Biological oceanography takes a bottom up approach in terms of the food web, while marine biology studies the ocean from a top down perspective. Biological oceanography mainly focuses on the ecosystem of the ocean with an emphasis on plankton: their diversity morphology, nutritional sources, motility, and metabolism ; their productivity and how that plays a role in the global carbon cycle; and their distribution predation and life cycle.
From Wikipedia, the free encyclopedia. The plants, animals and other organisms that live in the salt water of the sea or ocean, or the brackish water of coastal estuaries. Killer whales orca are marine apex predators that hunt many large species. Oceans also contain microscopic marine life , such as bacteria and phytoplankton. Elevation histogram showing the percentage of the Earth's surface above and below sea level.
See also: Hydrosphere. The Earth's water cycle. Life timeline. This box: view talk edit. Single-celled life. Multicellular life. Earliest water. Earliest life. Earliest oxygen. Atmospheric oxygen. Oxygen crisis. Sexual reproduction. Earliest plants. Ediacara biota. Cambrian explosion. Earliest apes. See also: Human timeline , and Nature timeline. Further information: Evolutionary history of life and Timeline of evolutionary history of life. Microbial mats are the earliest form of life on Earth for which there is good fossil evidence.
The image shows a cyanobacterial -algal mat. Stromatolites are formed from microbial mats as microbes slowly move upwards to avoid being smothered by sediment. Main article: Marine microorganism. See also: Evolution of cells. Marine microbial loop. See also: Marine bacteriophage and Viral evolution.
Bacteriophages phages. Multiple phages attached to a bacterial cell wall at ,x magnification. Diagram of a typical tailed phage. These are cyanophages , viruses that infect cyanobacteria scale bars indicate nm. In terms of individual counts, tailed phage are the most abundant biological entities in the sea.
See also: Bacterioplankton. Protists according to how they get food. Algae see below. Slime moulds and slime nets. Choanoflagellates , unicellular "collared" flagellate protists, are thought to be the closest living relatives of the animals. Two dinoflagellates. Play media. See also: Microanimal and Ichthyoplankton. See also: Marine fungi , Mycoplankton , and Evolution of fungi. Main article: Marine invertebrates.
See also: Avalon explosion and Cambrian explosion. There has been much controversy over which invertebrate phyla, sponges or comb jellies , is the most basal. Barrel sponge. Egg-shaped cydippid ctenophore.
The Elements of Experimental Embryology
Placozoa have the simplest structure of all animals. Food uptake by Trichoplax adhaerens. Their tentacles sting and paralyse small fish. See also: Embryological origins of the mouth and anus. Further information: Marine worm and Sea worm. See also: Evolution of molluscs and Evolution of cephalopods. Bigfin reef squid displaying vivid iridescence at night.
Cephalopods are the most neurologically advanced invertebrates. Hypothetical ancestral mollusc.