Marine (ocean) biology is the study of the function, biodiversity, and ecology of the animals and plants that live in the ocean. An organism's function is how it lives and grows in its environment. Biodiversity refers to the wide range of species of plants, animals, and microorganisms such as bacteria that live in the ocean. Ecology is the study of the relationships between organisms as well as the relationships between organisms and their environment. In order to do their work, marine biologists incorporate information and techniques from a broad range of disciplines, including chemistry, physics, geology (the study of rocks), paleontology (the study of fossils), and geography (the study of locations on Earth).
Many factors make the marine environment a unique place for animals and plants to live. The marine environment is fluid, which affects the way organisms move and breathe. A variety of chemicals are dissolved in the water that bathes marine organisms and many have special ways to use these chemicals or to prevent them from entering their bodies. Ocean water is salty, which affects the organism's ability to obtain and hold water in its body. The ocean has relatively constant temperatures, especially compared to land. This means that animals do not need to exert a lot of energy to stay warm. Sunlight generally reaches only the surface layers of the oceans so plants must live in surface waters in order to perform photosynthesis (process where they convert energy from the Sun into food).
History of marine biology
Greek philosopher and natural historian Aristotle (384–322 b.c.e.), is generally regarded as the first marine biologist. Aristotle believed that observation, along with induction and reasoning, would lead to an accurate understanding of the natural world. These pioneering ideas set the stage for the modern scientific method. Aristotle identified, described, and named 24 species of marine worms and crustaceans (animals that have a hard external covering and jointed limbs like crabs, shrimp, lobsters), 40 species of molluscs (clams, scallops, oysters) and echinoderms (a group of invertebrate animals that includes sea stars, sea urchins, and sea cucumbers) and 116 species of fish. He also correctly identified whales and dolphins as mammals (warm-blooded animals that have hair and feed young with milk).
Between Aristotle's time and the Renaissance (about 1500 c.e.), very little work was done in marine biology because most people assumed that Aristotle had already accomplished everything. In the sixteenth century, explorers made many important observations about marine life. Alexander von Humboldt (1769–1859) was a German naturalist who journeyed through Central and South America identifying marine animals and plants. British sea captain James Cook (1728–1779) was a renowned explorer who traveled throughout the Pacific describing and identifying marine organisms.
In the nineteenth century, work in marine biology became more active. British naturalist Charles Darwin (1809–1882) studied many marine organisms during his travels aboard the H.M.S. Beagle (1831–1836). Darwin's work led to the theory of evolution, a theory that the organisms best suited to their environment live and reproduce to eventually form new species while those not suited to the environment will die. His work also led to a theory of how coral reefs form atolls (a type of island) and to a classification of barnacles (a type of crab that attaches itself to hard surfaces) that is still in use today. Edward Forbes was a British naturalist and one of the first scientists to focus his attention on organisms in the ocean. His azoic theory put forward the idea that there was no life at depths below about 1,800 feet (554 meters). Although this theory was accepted as true for nearly a century, it was later proved to be false. The first large expedition to study life in the ocean was undertaken by the British ship H.M.S. Challenger between 1872 and 1876. The biologists aboard found and described a large number of new marine species.
During the twentieth century, great advances in marine biology occurred. Submersible submarines, the Self Contained Breathing Apparatus (SCUBA), and underwater photography allowed scientists to observe life throughout the oceans. Technological advances have led to electronic instrumentation that measure the characteristics of the ocean such as temperature, salinity (saltiness), intensity of light, and concentrations of dissolved gasses that provides important information on the distribution of organisms throughout the oceans. Tracking devices that use satellites (instruments sent into orbit in order to observe Earth) to report the locations of large animals, such as whales, sharks, and tuna, are used to understand migration (travel) patterns. Techniques from the fields of biotechnology (the use of modern equipment and tests to understand biological processes), molecular biology (the study of molecules within cells), neurobiology (the study of nerves), and biochemistry (the study of chemicals that are found in organisms) are used routinely to provide a greater understanding of marine organisms.
Types of organisms studied
Marine biology involves the study of all types of organisms that live in the ocean, from the very small to the very large. The patterns and distributions of microscopic organisms called plankton involve one area of research. Plankton include viruses (small molecules like DNA or RNA that have the ability to reproduce when they are in a host), bacteria, phytoplankton (small plants that float in the ocean water) and zooplankton (small animals that float in the ocean). Another focus of marine biology includes the larger animals called neckton that swim through the water. These animals include marine invertebrates (animals without a backbone) such as squid, most species of fish and marine mammals, such as dolphins and whales. Another group of marine organisms are those that live on the ocean floor. These organisms are called benthic and can include animals and plants as well as microorganisms. Some examples of benthic plants include the giant kelp, sea grasses, and algae (plant-like organisms that photosynthesize, but have simpler bodies without veins) that grow on a thin layer on rocks. Many invertebrates are benthic, like corals, sea anemones, sea cucumbers, sea stars, clams, snails, and crabs. A few fish that live close the bottom of the ocean are also considered benthic, such as halibut and some gobies. Many microorganisms, like bacteria and protozoans, are found in among the sand and clay at the bottom of the ocean.
Important research areas in marine biology
Marine biology contributes a large amount of information to the fields of environmental biology, economics, fisheries research, and biotechnology. Because the field is relatively young, there is still much to be learned from and about the animals and plants that live in the ocean.
Marine organisms influence local environmental conditions and economies. A simple, but powerful example of this is the red tide, which is usually caused by a particular type of phytoplankton called a dinoflagellate. Under certain environmental conditions, these dinoflagellates grow extremely quickly, blooming in bays and near shore regions of the ocean. In some instances they can cause fish kills and infect shellfish with poisonous substances, which could make the people that eat them sick. Much work is underway by marine biologists in order to understand the conditions that cause these harmful blooms so that they can predict their effects and when they will occur.
Many marine biologists study ways to improve mariculture, which is the farming of marine fish, shellfish, and seaweeds. Work includes developing types of animals and plants that are easy and economical to farm. For example, the triploid oyster is an oyster that has a longer harvest period than those found in nature. In addition, work is underway to improve the health of fish raised in pens and to decrease the pollution caused by marine farms.
Much research in marine biology contributes to the fields of biotechnology and molecular biology. Many marine animals and plants have been found to contain chemicals with industrial uses. For example, some phytoplankton produce sunscreens that can be incorporated into lotions. Other marine invertebrates produce chemicals that are mixed with paint to discourage the growth of barnacles on ships and moorings. Molecular probes (special molecules that can identify other molecules) are used in marine ecology to detect the presence of harmful viruses and bacteria on beaches and near-shore waters. Other techniques from molecular biology are used to determine if fish and marine invertebrates have been exposed to poisonous pollutants. Molecular biological techniques are also being used to analyze the DNA (genetic substance) in various marine organisms to try to understand the past relationships among species.
Juli Berwald, Ph.D.
For More Information
Byatt, Andrew, et al. Blue Planet. London: DK Publishing, 2002.
Doris, Helen. Marine Biology (Real Kids, Real Science). New York: Thames & Hudson, 1999.
Levinton, Jeffrey S. Marine Biology: Function, Biodiversity, Ecology. 2nd ed. New York: Oxford University Press. 2001.
Levinton, Jeffrey. "MBRef: A Reference Source for Marine Biology Student Research." Marine Biology Web.http://life.bio.sunysb.edu/marinebio/mbref.html (accessed on August 26, 2004, 2004).
"Marine Biology." SeaGrant: MarineCareers.net.http://marinecareers.net/marbio.htm (accessed on August 26, 2004).
"Marine Organisms." The Marine Biological Laboratory.http://www.mbl.edu/marine_org/index.html (accessed on August 26, 2004).
"Scripps Research." Scripps Institute for Oceanography.http://sio.ucsd.edu/research (accessed on August 26, 2004).
Shaner, Stephen W. "A Brief History of Marine Biology and Oceanography." University of California Extension Center for Media and Independent Learning.http://www.meer.org/mbhist.htm (accessed on August 26, 2004).
MARINE BIOLOGY. Study of life along the seashore, which became known as marine biology by the twentieth century, was first developed and institutionalized in the United States at the end of the nineteenth century. Two distinct traditions contributed to its modern disciplinary form.
First to emerge was marine biology as a summertime educational activity, chiefly designed to instruct teachers of natural history about how to study nature within a natural setting. The notion was first suggested to Louis Agassiz, the Harvard zoologist and geologist, by his student Nathaniel Southgate Shaler. Shaler had conducted highly successful summer field experiences for geology students, and felt that similar experiences could be valuable for biology students. Encouraged by his wife, Elizabeth—a longtime advocate for educational opportunities for the largely female teaching community—Agassiz obtained funding and opened the Anderson School of Natural History in 1873 on Penikese Island, located not too distant from Cape Cod. Following this school, several others offered similar experiences. The Summer School of the Peabody Academy of Sciences (Salem, Massachusetts) sponsored instruction for teachers in marine botany and zoology in 1876, and the Boston Society of natural History, with the support of the Women's Education Association (WEA) of Boston, started its summer station north of Boston at Alpheus Hyatt's vacation home in Annisquam.
The second tradition was European, where several marine stations operated by 1880, most notably the Stazione Zoologica in Naples. This marine biology laboratory was founded by Anton Dohrn in 1872. The "Mecca for marine biology," as Naples was soon known, attracted scholars from throughout the world. Agassiz's son, Alexander Agassiz, imported Dohrn's notion to his summer home near Newport, Rhode Island, offering the latest microscopical tools for researchers. William Keith Brooks, a student of the elder Agassiz, accepted the invitation and completed his doctoral research with the younger Agassiz in 1875. Then, when Brooks obtained a position at America's first graduate university, Johns Hopkins University, one of his first tasks was to create a research laboratory in marine biology. Thus, the Chesapeake Zoological Laboratory was opened in 1878
The first U.S. marine biology laboratory to incorporate both traditions was the Marine Biological Laboratory (MBL), which opened in Woods Hole, Massachusetts, in 1888. It originally offered courses in marine botany and marine zoology for beginning students and teachers. But its original director, C. O. Whitman, had spent time at Naples and, like his colleague Brooks, wanted to create research opportunities in marine biology for more advanced students and researchers. To accomplish the task, Whitman initiated advanced courses in embryology, invertebrate zoology, cytology, and microscopy, all of which began to attract more sophisticated students. By the early twentieth century, the MBL welcomed only advanced students and investigators.
Similar marine biology laboratories were founded on the Pacific Coast. Stanford University established the Hopkins Marine Station in Pacific Grove, California, in 1892. To the north, the University of Washingt on opened a marine station near Friday Harbor (San Juan Islands, Washington) in 1904. Henry Chandler Cowles, an ecologist from the University of Chicago who had done pioneering studies on the sand dunes of Lake Michigan started a course in intertidal ecology, the first such course in the United States.
One additional West Coast laboratory played a critical role in defining the new field of marine biology, albeit by exclusion. William Emerson Ritter, an embryologist from Berkeley, created a laboratory near San Diego, initially named the San Diego Marine Biological Laboratory, in 1903. But Ritter was interested in a more global approach to investigations by the seashore, an approach he never successfully defined. He was successful, however, in attracting the financial resources of the Scripps family, and soon the Scripps Institution for Biological Research was built north of the village of La Jolla. Ritter specifically stated that he had no intention of forming another MBL on the West Coast, preferring to emphasize a comprehensive study of the sea. After he retired, without creating an educational base for the institution similar to the other stations, he was replaced by Thomas Wayland Vaughan in 1924. The La Jolla station was renamed the Scripps Institution of Oceanography, and marine biology disappeared as a focus.
The three major American marine biology stations throughout the twentieth century and into the twenty-first century are the MBL, Hopkins Marine Station, and Friday Harbor Laboratories. By the end of world War I (1914–1918), the stations defined marine biology as the study of life in the littoral zone (also known as the inter-tidal zone), or the area that serves as an interface between the marine and terrestrial environments. Courses at the laboratories helped to divide marine biology into several specialty areas, including invertebrate zoology, ecology, algology, embryology, and invertebrate physiology. Following World War II (1939–1945), this focus shifted somewhat as more research funding was available in the biological sciences, especially in terms of research questions with an application to medicine and to the exciting field of molecular biology. Woods Hole's MBL, for example, has all but abandoned the traditional areas of marine biology for specialized medical and genetic research. Most investigations at the MBL by the end of the twentieth century were laboratory-based studies of cellular and molecular processes, with little fieldwork or studies of marine life. At the same time, largely because the West Coast has a more robust intertidal fauna and flora that is largely unaffected by human intervention, Hopkins and Friday Harbor retain a traditional focus on marine biology.
For the most part, marine biology does not include investigations of the open seas, studies of freshwater marine systems, or inquiries into the country's fisheries. Biological oceanography, a subdiscipline of Oceanography, examines biological questions in the oceans, including studies of marine mammals, marine fisheries, and freshwater sources for the ocean (limnology).
———. "Summer Camp, Seaside Station, and Marine Laboratory: Marine Biology and Its Institutional Identity." Historical Studies in the Physical and Biological Sciences 32, no. 1 (2001).
Maienschein, Jane. 100 Years Exploring Life, 1888–1988: The Marine Biological Laboratory at Woods Hole. Boston: Jones and Bartlett Publishers, 1989.
Origins of Modern Marine Biology. During the last quarter of the nineteenth century, several leading American biologists became interested in establishing a marine station capable of promoting and sustaining advanced research and instruction in marine biology along the lines of successful and influential European biological stations, such as Anton Dorrn’s marine-biology station in Naples (in which four American universities officially participated) or Henri Lacaze-Duthier’s laboratory at
Banyuls-sur-Mer, France. Louis Agassiz, a Swiss-born zoologist, (1807-1873) mounted the first such endeavor at Penikese Island, Massachusetts, in 1873, and during the same period his students Alpheus Hyatt (1838-1902) and Alpheus Packard (1839-1905) established summer programs at the Massachusetts seaports of Annisquam and Salem, respectively. These programs were all short-lived.
The Woods Hole Laboratory. The most influential early research station was the U.S. Fish Commission laboratory, at Woods Hole, Massachusetts, directed by Spencer Fullerton Baird between 1871 and 1887. Created to survey and study the offshore fish populations and to manage a hatchery, this laboratory contributed to scientific knowledge mainly in the classification of fish species and marine ecology.
The Marine Biology Laboratory. Hoping to expand the scope of his laboratory in concert with a coalition of research-oriented universities, Baird drew up a plan that was the basis for the establishment of the Marine Biological Laboratory (MBL) at Woods Hole in 1888, the year after Baird’s death. Under its first director, Charles O. Whitman (1842-1910), who ran the laboratory until 1908, the MBL established a summer program with instruction in invertebrate zoology in 1888, adding marine botany in 1890, general physiology in 1892, and embryology in 1893. The courses were designed to address problems of marine biology but also employ the specific advantages offered by marine biology in order to push ahead the research perspectives of biology generally. The general-physiology course taught at Woods Hole was the first of its kind in the world. Everywhere else physiology was limited to the study of mammals. At Woods Hole in 1899-1900 German-born physiologist Jacques Loeb (1859-1924), conducted his famous experiments on artificial parthenogenesis of sea-urchin eggs, causing unfertilized eggs to develop into new organisms. Embryology courses at Woods Hole took advantage of the specific characteristics of marine eggs, many of which (including those of the sea urchin) have no outer shell and are transparent.
A Pioneering Institution. By giving the study of marine biology the broadest possible focus, the MBL became a leader in experimental biology. Until universities developed their own research facilities, institutions such as the MBL functioned as centers for scientific research and discovery. Following Dorrn’s model, the MBL allocated benches in its laboratory to participating universities, which sent their most promising students to Woods Hole. In addition to Loeb, the earliest researchers at the MBL included geneticists T. H. Morgan (1866-1945), who won a Nobel Prize in Physiology and Medicine in 1933, and E. B. Wilson (1856-1939)—who, like Morgan, had earlier worked in the U.S. Fish Commission laboratory—as well as embryologist Frank R. Lillie (1870-1947) and geneticist Nettie Stevens (1861-1912).
“THE END OF SCIENCE”
By the time he delivered the Lowell Lectures on Light Waves and Their Uses at Harvard University in 1899, Albert A. Michelson had come to believe that the age of great scientific discoveries had come to an end and that the physicist’s future role would be in the realm of refining previously established laws through precise measurement:
What would be the use of such extreme refinement in the science of measurement? Very briefly and in general terms the answer would be that in this direction the greater part of all future discovery must lie. The more fundamental laws and facts of physical science have all been discovered, and these are now so firmly established that the possibility of their ever being supplanted in consequence of new discoveries is exceedingly remote.
Six years after Michelson spoke these words Albert Einstein published his special theory of relativity, overturning all of Michelson’s assumptions about the nature of the universe.
Dean C. Allard, “The Fish Commission Laboratory and Its Influence on the Founding of the Marine Biological Laboratory,” Journal of the History of Biology, 23 (1990): 251-270;
Frank R. Lillie, The Woods Hole Marine Biological Laboratory (Chicago: University of Chicago Press, 1944).
marine biology, study of ocean plants and animals and their ecological relationships. Marine organisms may be classified (according to their mode of life) as nektonic, planktonic, or benthic. Nektonic animals are those that swim and migrate freely, e.g., adult fishes, whales, and squid. Planktonic organisms, usually very small or microscopic, have little or no power of locomotion and merely drift or float in the water. Benthic organisms live on the sea bottom and include sessile forms (e.g., sponges, oysters, and corals), creeping organisms (e.g., crabs and snails), and burrowing animals (e.g., many clams and worms). Seafloor areas called hydrothermal vents, with giant tube worms and many other unusual life forms, have been intensively studied by marine biologists in recent years.
The distribution of marine organisms depends on the chemical and physical properties of seawater (temperature, salinity, and dissolved nutrients), on ocean currents (which carry oxygen to subsurface waters and disperse nutrients, wastes, spores, eggs, larvae, and plankton), and on penetration of light. Photosynthetic organisms (plants, algae, and cyanobacteria), the primary sources of food, exist only in the photic, or euphotic, zone (to a depth of about 300 ft/90 m), where light is sufficient for photosynthesis. Since only about 2% of the ocean floor lies in the photic zone, photosynthetic organisms in the benthos are far less abundant than photosynthetic plankton (phytoplankton), which is distributed near the surface oceanwide. Very abundant phytoplankton include the diatoms and dinoflagellates (see Dinoflagellata). Heterotrophic plankton (zooplankton) include such protozoans as the foraminiferans; they are found at all depths but are more numerous near the surface. Bacteria are abundant in upper waters and in bottom deposits.
The scientific study of marine biology dates from the early 19th cent. and now includes laboratory study of organisms for their usefulness to humans and the effects of human activity on marine environments. Important marine biological laboratories include those at Naples, Italy; at Plymouth and Millport in England; and at Woods Hole, Mass., La Jolla, Calif., and Coral Gables, Fla. Research has been furthered by unmanned and manned craft, such as the submersibleAlvin.
See also oceanography.
See R. Carson, The Sea Around Us (rev. ed. 1961); R. Ballard, Exploring Our Living Planet (1983); M. Banks, Ocean Wildlife (1989); W. J. Broad, The Universe Below (1997).
Marine microbiology refers to the study of the microorganisms that inhabit saltwater. Until the past two to three decades, the oceans were regarded as being almost devoid of microorganisms. Now, the importance of microorganisms such as bacteria to the ocean ecosystem and to life on Earth is increasingly being recognized.
Microorganisms such as bacteria that live in the ocean inhabit a harsh environment. Ocean temperatures are generally very cold—approximately 37.4° F (about 3° C) on average—and this temperature tends to remain the cold except in shallow areas. About 75% of the oceans of the world are below 3300 feet (1000 meters) in depth. The pressure on objects like bacteria at increasing depths is enormous.
Some marine bacteria have adapted to the pressure of the ocean depths and require the presence of the extreme pressure in order to function. Such bacteria are barophilic if their requirement for pressure is absolute or barotrophic if they can tolerate both extreme and near-atmospheric pressures. Similarly, many marine bacteria have adapted to the cold growth temperatures. Those which tolerate the temperatures are described as psychrotrophic, while those bacteria that require the cold temperatures are psychrophilic ("cold loving").
Marine waters are elevated in certain ions such as sodium. Not surprisingly, marine microbes like bacteria have an absolute requirement for sodium, as well as for potassium and magnesium ions. The bacteria have also adapted to grow on very low concentrations of nutrients. In the ocean, most of the organic material is located within 300 meters of the surface. Very small amounts of usable nutrients reach the deep ocean. The bacteria that inhabit these depths are in fact inhibited by high concentrations of organic material.
The bacterial communication system known as quorum sensing was first discovered in the marine bacterium Vibrio fischeri. An inhibitor of the quorum sensing mechanism has also been uncovered in a type of marine algae.
Marine microbiology has become the subject of much commercial interest. Compounds with commercial potential as nutritional additives and antimicrobials are being discovered from marine bacteria, actinomycetes and fungi . For example the burgeoning marine nutraceuticals market represents millions of dollars annually, and the industry is still in its infancy. As relatively little is still known of the marine microbial world, as compared to terrestrial microbiology, many more commercial and medically relevant compounds undoubtedly remain to be discovered.
See also Bacterial kingdoms; Bacterial movement; Biodegradable substances; Biogeochemical cycles
Marine biology is a field of study encompassing all oceanic life, including representatives from each of the taxonomic kingdoms (plants, animals, blue-green algae, fungus, and single-celled microorganisms called protists). Taxonomy is a system used to name organisms based on their evolutionary relationships. Specializations within this field include ecology , environmentalism, parasitology , reproduction, ocean farming, and anatomy. Many ocean-dwelling organisms have yet to be discovered and assigned a taxonomic nomenclature (scientific name). Other specializations are based on ocean regions, such as coastal, coral reef, deep-sea trench, arctic, and open ocean marine biology. This field is strongly rooted in international research and cooperation because ocean wildlife does not necessarily belong to any one government or country. It necessitates a love of the outdoors, and of the ocean in particular, a willingness to work independently at distant locations, good analytical skills, excellent writing skills, and environmental awareness. Strong swimming skills and certification in scuba (a word derived from the acronym for self-contained underwater breathing apparatus) are also mandatory. Marine biologists may seek employment as a teacher, researcher, resource manager for a governmental agency, field biologist in a consulting company, advocate in an environmental organization, or technician in an aquarium or zoo.
For those who have a strong interest in fishes, marine mammals, marine ecology, or any other related field, it is best to obtain a strong background in basic biology and oceanography. Look for colleges with large marine biology departments, preferably located along the coast of an ocean environment that interests you. Search the Internet for information on the field and make contacts with specialists at other institutions. It is extremely important that you join a research lab or intern at an aquarium or on a research boat during your undergraduate college education. Training marine mammals, for instance at a theme park or for biopsychology or communications research, requires knowledge of psychology and possibly of veterinary science. For a career in academics or college professorship, a doctoral degree from a high-level research institute is necessary. If you wish to work at a zoo or teach high school, a master's degree will suffice.
Rebecca M. Steinberg
Moyle, Peter B., and Joseph J. Cech. Fishes: An Introduction to Ichthyology. Upper Saddle River, NJ: Prentice Hall, 2000.
Nybakken, James Willard. Marine Biology: An Ecological Approach. San Francisco: Benjamin Cummings, 2001.
A marine biologist is someone who studies plants, animals, and other organisms of the oceans, ranging from large marine mammals to microscopic plankton . Marine biologists study such subjects as animal behavior and ecology, biomedical uses of the sea, the commercial importance of the ocean's natural resources, and methods for preservation of species and habitats.
The need for marine biologists has increased because of growing interest in conservation of the oceans, and many are employed by private and government environmental protection and resource management agencies. For example, marine biologists are needed to determine catch quotas for species of fish in order to prevent a decline in population. In addition to performing basic research, they present information to governments and industries to aid in resource conservation decisions. As land development increases, marine biologists are needed to determine its effects on surrounding habitats and whether an ecosystem can withstand human invasion. Marine biologists also find work worldwide teaching in colleges, universities, and even some high schools. Many work on oceanographic research vessels and in laboratories from polar to tropical settings.
To be well prepared for a career in marine biology, a strong background in mathematics is crucial. One should also take a wide range of science courses in high school and college, such as biology, chemistry, physics, zoology, geology, marine science, oceanography, and atmospheric science. A working knowledge of computers is increasingly necessary for data collection and analysis. Satellite imaging and global information systems (GIS) are common uses of computers in the field.
Summer courses and internships are available worldwide to provide hands-on experience with marine life, the use of field and laboratory equipment, and other aspects of marine research. Employment opportunities are available from the bachelor to the doctorate level, with greater independence, decision-making responsibility, and income at the higher levels.
Lisa Nicole Saladin and Kenneth S. Saladin
American Fisheries Society Jobs Center Online. <http://www.fisheries.org/jobs.html>.
Castro, Peter, and Michael E. Huber. Marine Biology, 3rd ed. Boston: McGraw-Hill, 2000.
Scripps Institution of Oceanography. <http://www.sio.ucsd.edu/>.
Woods Hole Oceanographic Institution. <http://www.whoi.edu/>.