Glossary of Terminology: M

The glossary is organized alphabetically by page -- A through Z. Literature sources are listed on the References Page.

The entire glossary is also provided as a PDF document. The document includes all terms, photographs, images, and literature sources.

Click here to search the Glossary of Terminology by keyword(s).

Glossary Pages

A | B | C | D | E | F | G | H | I | J | K | L | M
N | O | P | Q | R | S | T | U | V | W | X | Y | Z

Number of records found : 273

macerate - to disintegrate tissues by means of cutting, soaking or enzymatic action to obtain a cell dissociation

macro - a text file containing a sequence of commands that can be executed as one command.

Image of kelp (a macroalgae)

Macroalgae are important habitat on temperate and northern reefs.

macroalgae - algae that project more than one centimeter above the substratum

macrobenthos (macrofauna or macroflora) - benthic organisms (animals or plants) whose shortest dimension is greater than or equal to 0.5 mm

macroevolution - evolution on the grand scale resulting in the origin of higher taxa

macrogamete - the larger of the two gamete types in a heterogametic organism. It is considered as the the female gamete

macromolecule - a large polymer, such as DNA, RNA, protein, lipid or polysaccharide, made up of thousands of atoms

macronutrient - a nutrient, such as a nitrate or phosphate, that is required by plants in relatively large quantities in order to undergo photosynthesis and growth

macrophage - an amoeboid cell capable of moving through tissues, engulfing and destroying dead cells or bacteria. Certain white blood cells are the most aggressive macrophages

macrosmatic - pertains to animals with a well developed olfactory (smell) sense

macula - a dark spot, blemish; the small, highly sensitive area (of the human eye) which is located in the center of the retina. It is responsible for near and fine detail vision

Madden Julian Oscillation (MJO) - a major perturbation of tropical convection which moves and completes a global circuit every 30 to 60 days. It is a dominant cause of intraseasonal variability in tropical equatorial regions

Image of a red starfish

The white spot in the middle of the central disc of the starfish is the madreporite, the opening into the echinoderm+s water vascular system.

madreporite - a perforated platelike structure in most echinoderms that forms the intake for their water vascular systems

maerl - a collective term for two or three species of calcareous algae in the family Corallinaceae. Ground or granulated products from these algae are used as a fertilizer; fine-grained carbonate-rich mud

magenta - reddish purple color

magma - molten rock that forms naturally within the Earth. Magma may be either a liquid or a fluid mixture of liquid, crystals, and dissolved gases

magmatic hotspot - in geology, a hotspot is a location on the Earth's surface that has had volcanism for a long period of time. Geologists have identified some 40-50 such hotspots

magnetic north - the direction a compass needle points when there are no local interfering influences

maillist (mailing list) - a system that allows people to send e-mail to one address, whereupon their message is copied and sent to all of the other subscribers to the maillist. In this way, people who have many different kinds of e-mail access can participate in discussions together

maitotoxin - a neurotoxic compound which is produced by certain marine dinoglagellates and associated with the digestive tract of herbivorous fishes. It is responsible for a form of seafood poisoning in humans eating tropical coral reef fishes

makatea - a fossil coral reef

Image of an octopus

A Pacific octopus (Mollusca) photographed during the NOAA Submarine Ring of Fire expedition, 2002. (Photo: NOAA Ocean Explorer)

malacology - the scientific study of mollusks

Malacostraca  - a class of arthropods in the subphylum Crustacea. The more than 20,000 described species of Malacostraca can be divided into two groups, the Phyllocarida, and the Eumalacostraca. Phyllocarida contains the oldest crustacean known and includes only one living group.The Eumalacostraca consists of all Malacostracan groups other than the Phyllocarida. Eumalacostracans generally possess a well-developed carapace and a long, muscular abdomen. It is the group that contains most of the animals the general public recognize as crustaceans, such as shrimp, crabs, lobsters

maladaptation - an action implemented to reduce vulnerability to climate and/or ocean change that impacts adversely on or increases the vulnerability of other systems, sectors, or social groups

malar - pertaining to the cheek region of vertebrates

Image of dolphin

Dolphins are among the most recognizable marine mammals; this one floats serenely in the Caribbean Sea. (Photo: Copyright Corel Corporation)

Mammalia - a class of warm blooded animals (mammals) whose common characteristics include the presence of hair, milk-secreting glands, a muscular diaphragm between the abdominal and pleural and mediastinal cavities, a lower jaw composed of a single pair of bones, a middle ear containing three bones, and the presence of only a left systemic arch

mammalian dive reflex - the physiological responses, including bradycardia and shutdown of the peripheral circulation, which occurs during dives by an air-breathing vertebrate

mammalogy - the scientific study of mammals

mandible - pertains to mouth parts; the lower jaw

mangal - relating to a shoreline ecosystem dominated by mangrove trees, with associated mud flats

Image of mangrove nursery area

Mangrove nursery area, Puerto Rico.

mangrove - a general name for several species of halophyte belonging to different families of plants (including trees, shrubs, a palm tree and a ground fern) occurring in intertidal zones of tropical and subtropical sheltered coastlines and exceeding one half meter in height. The term is applied to both the individual and the ecosystem, the latter of which is termed mangal. Mangroves provide protected nursery areas for juvenile reef fishes, crustaceans, and mollusks. They also provide a feeding ground for a multitude of marine species. Many organisms find shelter either in the roots or branches of mangroves. Mangrove branches are nesting areas for several species of coastal birds. The root systems harbor organisms that trap and cycle nutrients, organic materials and other important chemicals. Mangroves also contribute to higher water quality by stabilizing bottom sediments, filtering water and protecting shorelines from erosion. They protect reefs from land runoff sedimentation. Conversely, coral reefs protect mangroves and seagrasses from erosion during heavy storms and strong wave action. The nations with the largest mangrove areas include Indonesia (with 21% of global mangroves), Brazil (9%), Australia (7%), Mexico (5%), and Nigeria (5%).The global area of mangroves – 150 000 square kilometers – is equivalent to the area of the state of Illinois, or half the area of the Philippines. About one fifth of all mangroves are thought to have been lost since 1980, and although loss rates are declining, they are still 3 to 4 times higher than average global forest loss estimates

manta tow technique - a technique used to provide a general description of large areas of reef and to gauge broad changes in abundance and distribution of organisms on coral reefs. The technique, widely used in Australia, involves towing a snorkel diver (observer) at a constant speed behind a boat. The observer holds on to a 'manta board' attached to a small boat by a 17-meter length of rope. This person makes a visual assessment of specific variables during each manta tow (2 minutes duration), and records these data when the boat stops, on a data sheet attached to the manta board. The manta tow technique is used to provide a general description of large areas of reef and to gauge broad changes in abundance and distribution of organisms on coral reefs. The advantage of manta tow over other survey techniques is that it enables large areas of reefs to be surveyed quickly and with minimal equipment

Image of cowrie with partially extended mantle

A cowrie, Cypraea sp., with partially extended mantle.

mantle - a membranous or muscular structure in mollusks that surrounds the visceral mass and secretes a shell if one is present

mantle (geology) - the middle layer of the Earth, lying just below the crust and consisting of relatively dense rocks. The mantle is divided into the upper mantle and the lower mantle; the lower mantle has greater density than the upper mantle

mantle cavity - the space between the mantle and the rest of the body parts of a mollusk, which contains several important respiratory and reproductive organs

Image of a jellyfish

The mouth of a jellyfish is at the end of the manubrium, which extends to engulf prey. (Photo: NOAA/Florida Keys National Marine Sanctuaries)

manubrium - the proboscis of a jellyfish: a tubular structure that connects the mouth to the digestive cavity

marae - in the Marquesas, a Polynesian sacred enclosure or a place of worship . In Hawaii, it is called a "heiau"

mareogram - a graphic representation of the rise and fall of the sea level, with time as abscissa and height as ordinate, usually used to measured tides; may also show tsunamis; also called 'marigram'

margin - a boundary, edge or border of a structure or surface

Marianas Archipelago Reef Assessment and Monitoring Program (MARAMP) - a multi-agency effort that began in 2003 with the first cruise to the Mariana Archipelago. The objective of MARAMP is to rapidly evaluate and map the shallow water reef habitats in the Mariana Archipelago. Scientists on board the National Oceanographic and Atmospheric Administration (NOAA) research vessel Oscar Elton Sette use a variety of techniques to study the oceanography and coral, fish, algae, and benthic habitats around most of the islands and offshore banks of the archipelago

Image of farmed shrimp

Shrimp farms and their waste runoff have resulted in the destruction of coastal habitats and added to pollution in critical estuarine waters.

mariculture - the cultivation of marine organisms under controlled conditions; a synonym for marine aquaculture

Marine Aquarium Council (MAC) - an international, not-for-profit organization that brings marine aquarium animal collectors, exporters, importers and retailers together with aquarium keepers, public aquariums, conservation organizations, and government agencies. Its mission is to conserve coral reefs and other marine ecosystems by creating standards and certification for those engaged in the collection and care of ornamental marine life from reef to aquarium

Image of plastic bag stuck on coral

Marine debris, such as this plasic bag, can kill coral. (Photo: NOAA)

marine debris - debris composed primarily of plastics, nets, lines, other fishing gear, glass, rubber, metal, wood and cloth. Sources of debris are people on beaches, storm drains, fishing boats, waste treatment sites, and industrial facilities. These materials have damaging effects on coral reefs

Image of woman with marine iguana

A marine iguana from the Galapagos Islands. (Photo: NOAA)

marine iguana - the marine iguana (Amblyrhynchus cristatus) inhabits the Galapagos Island, an archipelago on the Equator, 800 kilometers west of the Ecuadorian coast. It differs from the mainland iguanas by the shape of the snout and other morphological features. The species probably rafted to the islands many millions of years ago, and developed a new ecological niche.They feed almost exclusively on marine algae and seaweed in the intertidal zone, and some make shallow dives past the breaker zone

Marine Life Conservation District (MLCD) - a designated area for the conservation and replenishment of marine resources. MLCDs allow only limited fishing and other consumptive uses, or prohibit such uses entirely. They provide fishes and other aquatic life with a protected area in which to grow and reproduce, and are home to a great variety of species

Marine Managed Area (MMA) - see: Marine Protected Area

Marine Protected Area (MPA) - any area of the marine environment that has been reserved by federal, state, territorial, tribal or local laws or regulations to provide lasting protection to part or all of the natural or cultural resources within them. Familiar examples of U.S. MPAs include National parks, wildlife refuges, monuments and marine sanctuaries, fisheries closures, critical habitat, habitat areas of particular concern, state parks, conservation areas, estuarine reserves and preserves, and numerous others. Areas which are not MPAs are areas where access is restricted for reasons other than conservation (such as security zones, shellfish closures, sewage discharge areas, and pipeline and cable corridors), or unprotected areas that are logistically inaccessible due to weather, sea state, etc; MPAs are sometimes called Marine Managed Areas (MMA). However, "marine protected area" is a broad, inclusive term which includes both mulit-purpose sites with some restrictions as well as the more restrictive "no take marine reserves."

marine protected area (MPA) spillover - MPA spillover refers two types of movements outside the MPA: (1) adults and juvenile animals swim into adjacent areas, and (2) eggs, larvae and young post-larval stages can drift out from the MPA into the surrounding waters

Marine Protection, Research, and Sanctuaries Act (MPRSA ) - the MPRSA (1972) provides protection for many coral reefs by authorizing NOAA to designate areas as marine sanctuaries and promulgate regulations for the conservation and management of those areas. Since the Act was passed, thirteen sanctuaries have been designated, several of which contain coral reef communities. Coral research, monitoring, and management activities are conducted in these sanctuaries, as well as in the Northwestern Hawaiian Islands Coral Reef Ecosystem Reserve, which is currently (June 2004) under consideration to become the nation’s fourteenth sanctuary

marine reserve - an area in the ocean that isprotected from uses that remove animals, plants, and other organisms, or alter their habitats

Marine Resources Pacific Consortium (MAREPAC ) - MAREPAC is a consortium made up of representatives from nine islands in Micronesia (Marshall Islands, Federated States of Micronesia, Northern Marianas, Guam, Palau, and American Samoa). MAREPAC's mission is to develop regional capabilities, foster collaboration, and disseminate accurate information in support of sound policy development on sustainable use of marine resources of cultural, economic, and scientific value

marine snow - dense concentrations of particulate organic detritus and living organisms whose downward drift appears similar to a snowfall

marine tenure - locally specified entitlements to marine territories and resources claimed and exercised by the ‘guardians’ or "owners" of those territories and resources

maritime climate - a climate strongly influenced by an oceanic environment, found on islands and the windward shores of continents. It is characterized by small daily and yearly temperature ranges and high relative humidity

marker gene - in genetic engineering, an easily identified gene that is inserted into an organism, along with a desired gene. The presence of the marker gene demonstrates that the transformation was successful

marl - fine-grained carbonate-rich mud; a calcareous clay which contains approximately 30 to 65 percent calcium carbonate

Image of salt marsh

Coastal marsh in Monterey Bay National Marine Sanctuary, CA. (Photo: Kip Evans)

marsh - a soft, wet area periodically or continuously flooded to a shallow depth, usually characterized by a particular group of grasses, cattails and other low plants

marsupium - an abdominal pouch where certain animals carry their young, as in some crustaceans and the brood pouch of the male seahorse

MARXAN - software designed to provide decision support assistance for those designing biodiversity reserves or networks of reserves. MARXAN is a decision support tool to consider options in terrestrial and marine reserve design, supporting the implementation of ecosystem-based management (EBM) principles

Mascarene Plateau - a submerged volcanic plateau dominating the western Indian Ocean, extending approximately 2,000 km between Seychelles and Mauritius. It covers an area of over 115,000 square kilometers of shallow water with depths ranging from 8 m to 150 m on the plateau, plunging to depths of 4000 m at its edges. It is the major marine ecosystem of the western Indian Ocean

mass extinction - a catastrophic, widespread perturbation where major groups of species become extinct in a relatively short time

mass spawning - spawning events where many different species spawn simultaneously

mass spectrometer - a laboratory instrument that measures the mass-to-charge ratio of individual molecules that have been converted into ions. This information is then used to determine the masses of the molecules

mass spectrometry - an analytical technique where ions are separated according to their ratio of charge to mass. The atomic weight of the particle can be obtained from the mass spectrum produced

Image of massive coral colony

Scuba divers examine a massive coral colony. (Photo: Australian Institute of Marine Sciences)

massive - having a large compact structure without a definable shape

massive colony - a coral colony that is solid and typically hemispherical in shape

maternal mRNA - messenger RNA found in oocytes and early embryos that is derived from the maternal genome during oogenesis

MATLAB - an integrated technical computing environment that combines numeric computation, advanced graphics and visualization, and a high-level programming language. MATLAB enables one to perform computationally intensive tasks faster than with traditional programming languages

maxilla - pertains to mouth parts; the upper jaw

maxilliped - one of the mouth appendages of crustaceans, situated behind the maxillae. Crabs have three pairs, but many of the lower crustaceans have only one pair

maximum sustainable yield - the maximum number of a food or game population that can be harvested without harming the population's ability to grow back; the largest average catch or yield that can continuously be taken from a stock under existing environmental conditions

mean - a statistical measure of central tendency. The sum of a set of observations divided by the number of observations. It is also referred to as 'arithmetic mean' and 'sample mean'

mean high tide - the level to which the water rose on an average day over a previous period of time (years or decades); the average of all the high tides as calculated over a long period of time

Mean Higher High Water (MHHW) - A tidal datum. The average of the higher high water height of each tidal day observed over the National Tidal Datum Epoch; The average height of the higher of the two daily high tides

mean low tide - the average altitude of all low tides recorded at a given place over a long period of time

mean lower low water (MLLW) - the average of the lowest tide recorded at a tide station each day during the recording period; The average height of the lower of the two daily low tides

mean sea level - the level of the surface of the sea between mean high and mean low tide. It is used as a reference point for measuring elevations; the average height of the sea measured over 18.61 years.

meandroid colony - a massive colony that has corallite mouths aligned in valleys, such that there are no individual polyps

mechanoreceptor - a neurological receptor that responds to mechanical energy, e.g. pressure, touch, and gravity

median - a statistical measure of central tendency. The middle-most value in a set of observations with an equal number of observations lying above and below the median value

median fin - in fishes, an unpaired fin located on the sagittal plane of the body, i.e., the dorsal, caudal and anal fins

Image of medusa stage of jellyfish

A jellyfish (medusa stage) showing its oral or subumbrella surface. The hanging tentacles bear stinging cells, used for food capture.

medusa - the free swimming stage of some corals, jellyfish, anemones, hydroids and comb jellies, shaped like a bell or umbrella and swims by pulsations of the body

medusa bud - one of the buds of a hydroid, destined to develop into a gonophore or medusa. Medusa buds are released from the gonangium through a central opening, the gonopore

medusoid - a body form resembling a medusa; umbrella shaped

megabase (Mb) - unit of DNA or RNA sequence equal to one million (10) pairs of nucleotide bases. Abbreviated Mb

megabyte (mb) - a measure of storage space. One megabyte roughly translates to a million characters of text, or 180,000 words

megafauna - animals exceeding 2 cm in length; a term referring to late Pleistocene large terrestrial mammals whose body weight exceeded 44 kg (100 lbs)

megalops larva - the larval stage in brachyuran crabs that follows the zoea larval stage

megasclere - a large spicule in sponges

meio- - smaller; less than

meiobenthos (meiofauna or meioflora) - benthic organisms whose shortest dimension is less than 0.5 mm but greater than or equal to 0.1 mm

Diagram showing meiosis

Diagram showing the meiotic division of a diploid cell, which in two divisions, results in the production of four haploid daughter cells. This process is also termed gametogenesis because it results in haploid sperm and egg cells.

meiosis - a two-stage type of cell division in sexually reproducing organisms that results in the development of sperm and egg cells . In meiosis, a diploid cell divides to produce four haploid cells, each with half the original chromosome content. In organisms with a diploid life cycle, the products of meiosis are called gametes. In organisms with an alternation of generations, the products of meiosis are called spores

Graphic depicting Melanesia

Map showing location of Melanesia. (Graphic: Melanesian Cultural Heritage Management Identification Study)

Melanesia - a large region of volcanic islands which includes New Guinea, the Solomon Islands, Vanuatu, Fiji, Maluku, the Torres Strait Islands, and New Caledonia. The name "Melanesia" means "black islands", referring to the dark-complexioned inhabitants these islands

melanic - very dark or black color

melanin - a pigment in the skin of animals which determines skin and coat color. It is found in two chemically different forms: eumelanin (which produces brown and black) and phaeomelanin (which produces yellow and red). Melanin also provides protection against the damaging effects of ultraviolet radiation

melanistic - dark or blackish

melanocyte - a cell in the inner layer of the epidermis that produce melanin

melanophore - a chromatophore which contains black and brown pigments called melanin

melon - a lens-shaped fatty deposit lying in the facial depression of many toothed whales, such as the bottle-nosed dolphin. It appears as the bulging forehead just in front of the blowhole. It contains fatty deposits, muscles, and nasal air sacs and passages. The melon is used in focusing a whale's sounds, functioning as an acoustical lens for echolocation.The fatty deposits change shape as the whale is producing sounds

membrane filter - a thin microporous material of specific pore size used to filter bacteria, algae, and other very small particles from water

Memorandum of Understanding (MOU) - an interagency agreement defining the role and responsibility which each agency has in dealing with particular issues

Mendel's Laws of Heredity - the Law of Segregation states that each hereditary characteristic is controlled by two 'factors' (alleles), which segregate and pass into separate germ cells (gametes). The Law of Independent Assortment states that pairs of 'factors' segregate independently of each other when germ cells are formed

Image of Gregor Mendel

Gregor Mendel (1822-1884), the "father" of the science of genetics.

Mendelian inheritance - one method in which genetic traits are passed from parents to offspring. It is named after the Austrian monk, Gregor Mendel, who first studied and recognized the existence of genes and this method of inheritance; a hereditary process explainable in terms of the behavior of chromosomes, e.g., segregation of chromosomes, independent assortment, and homologous exchange of parts

Mendelian population - a natural, interbreeding unit of sexually reproducing organisms sharing a common gene pool

menisciform - crescent-shaped

meristic - pertains to serially repeated structures which can be counted, e.g. scales, vertebrae, fin rays, fin spines, other spines, myomeres, photophores, scutes, laterel line pores, etc

mermaid's purse - an egg case of a shark or ray, usually oblong in shape with horns or tendrils

meroblastic cleavage - incomplete cleavage of the zygote, restricted to the blastodisc, the non-yolky cytoplasm at one end of the egg; typical of teloblastic eggs

merogony - a process that increases the number of infective cells of some parasites. A single large schizont gives rise to a large number of small merozoites that infect other host cells

meroplankton - planktonic eggs and larvae which are temporary members of the plankton community

mesenchyme - in cnidarians, a primitive "connective tissue" located between the epidermis and the gastrodermis. If it contains no cell components, it is termed "mesoglea"; undifferentiated cells of an embryo, derived from mesoderm, which give rise to connective tissue and the circulatory and lymphatics systems; amoebocytic cells often embedded in a gelatinous matrix

mesenterial filament - a thickened rim or ribbon-like extension running along the free border of a mesentery from the end of the actinopharynx downwards. They aid in the capture and digestion of food materials and may also assist in inhibiting substrate competitors

mesenteric filament - the cord of tissue In sea anemones that runs along the edge of incomplete mesenteries and which bear glandular cells and nematocysts; they are used in digestion and become acontia toward the pedal disc

mesentery - a sheet of tissue that envelops, separates, or supports particular organs or body regions; a vertical sheet of tissue that divides the gastrovascular cavity of cnidarian polyps and function also to increase the surface area for digestion and nutrient uptake. Multiple mesenteries are arranged radially within the gastrovascular cavity of cnidarian polyps and are attached to the oral disc.

meso- - a prefix meaning 'middle'

Image of late gastrula

Late gastrula. This photograph is a dorsal view of the embryo, with the anterior being toward the animal pole and the posterior toward the vegetal pole. Note the beginning of the formation of enterocoelic (mesodermal) pouches, from which the mesoderm is derived, on the right and left side of the anterior end of the gastrocoel. A - mesoderm; B - coelom; C - archenteron (Photo: Cell and Developmental Biology Online website (University of Guelph)

mesoderm - the middle of the three germ layers of a triploblastic embryo that gives rise to the skeletal and support, muscular, blood vascular, urogenital and reproductive systems, and contributions to some glands

Image of a green sea anemone

Inner tissues of this Giant Green Anemone (Anthopleura xanthogrammica) are separated by the mesoglea. (Photo: Lisa Eschenbach)

mesoglea - the connective tissue layer between the epidermis and gastrodermis of cnidarians and ctenophores (comb jellies)

mesohyle - the non-cellular gel layer (also called 'mesenchyme') of sponges. It is located between the epidermis (pinacoderm) and the choanoderm, the cell layer that lines the spongocoel. The mesohyle contains either spicules (supportive needles made of calcium carbonate) or spongin fibers (a flexible skeletal material made from protein); also called mesohyl

mesolamella - a collagenous layer that separates the choanochambers of hexactinellid sponges (glass sponges)

mesolecithal - a moderately telolecithal egg, typical of amphibians

mesophotic coral ecosystems (MCEs) - light-dependent coral communities and their associated populations of algae, sponges and other invertebrates, and fishes, that occur in the deepest half of the photic zone (starting at 30-40 m and extending to over 150 m) in tropical and subtropical regions. This zone of dimished light is also referred to as the "twilight zone"

Mesozoic - an era of time during the Phanerozoic eon lasting from 245 million years ago to 66.4 million ago

messenger RNA (mRNA) - an RNA molecule that encodes the amino acid sequence of a protein. It is the mediating template between DNA and proteins. The encoded information from a particular gene is transferred from a strand of DNA by the construction of a complementary template strand of RNA (mRNA) through the transcription process. Next, three nucleotide segments of RNA, called tRNA (transfer RNA), which are attached to specific amino acids, match up with the template strand of mRNA to order the correct sequence of amino acids. These amino acids are then bonded together to form a protein a in a process, called translation. Translation occurs in the ribosomes, which are composed of proteins and a third kind of RNA, rRNA (ribosomal RNA)

metabolic gas - a gas which is released by the body as a result of metabolism. Carbon dioxide is an example of a metabolic gas

metabolism - the sum of all the physical and chemical processes by which living organised materials are produced and maintained (anabolism), and also the destructive transformation processes by which energy is made available for the uses of the organism (catabolism)

metabolite - a substance that takes part in the process of metabolism, which involves the breakdown of complex organic constituents of the organism's body with the liberation of energy for use in bodily functioning. The various compounds that take part in, or are formed by, these reactions are called metabolites

metadata - information about data or other information. Metadata or "data about data" describe the content, quality, condition, and other characteristics of data

metagamy - pertains to a reproductive cycle that alternates between sexual and asexual phases

metagenesis - an alternation of sexual and asexual generations. When metagenesis occurs in cnidarians, the polyp is the asexual generation and the medusa is the sexual generation. A generalized life cycle occurs as follows: medusae produce gametes which unite to form zygotes. Each zygote divides repeatedly and develops into a free-swimming planula larva, which eventually settles and develops into a polyp. Each polyp then asexually produces medusae to complete the life cycle

metagenome - all the genetic material present in an environmental sample, consisting of the genomes of many individual microbial organisms; the comprehensive range of all DNA sequences of a mixed bacterial sample from nature

metagenomics - the application of modern genomics techniques to the study of communities of microbial organisms directly in their natural environments, bypassing the need for laboratory cultivation of individual species

metamere - in biology, any of the homologous segments lying in a longitudinal series that make up the body of certain animals, such as earthworms and lobsters. A metamere is also called a 'somite'

Image of polychaete worm

A polychaete worm exhibiting metamerism. (Photo: Rick Gillis, Ph.D., Biology Dept., University of Wisconsin-La Crosse)

metamerism - in biology, the division of the body into a series of more or less similar segments (metameres), as in an annelid worm or a lobster

metamorphosis - change of body shape, e.g., the change from a larval form to a juvenile or adult form

Image of metanauplius larva

Crustacean metanauplius larva. (Photo: formation des maitres. Physiologie animale, Universite Pierre & Marie Curie, Paris VI.)

metanauplius larva - postnaupliar larva of crustaceans with the same general body and limb morphology as the nauplius, but having additional appendages

metanephridium - a type of excretory tubule in annelid worms. The metanephridium has internal openings called 'nephrostomes' that collect body fluids and conducts them to the outside through external openings, the 'nephridiopores'

metanephros - the final excretory organ that develops in a vertebrate embryo. In birds, reptiles, and mammals it replaces the mesonephros as the functional excretory organ, and develops into the adult kidney

metapopulation - a group of populations, usually of the same species, which exist at the same time but in different places. The dispersed population can replenish one another with migrants

metazoa - multicellular animals having cells differentiated into tissues and organs, and usually a digestive cavity and nervous system

metecdysis - the final stage in arthropod molting in which the new cuticle is hardened

Image of storm

Meteorologists often study violent weather. (Photo: NOAA)

meteorology - the science that deals with atmospheric phenomena, especially weather and weather conditions

meter - a unit of length which constitutes the basis of the Metric System. It is one ten-millionth part of the distance measured on a meridian of the Earth from the equator to the pole. One meter equals 39.37 inches

methane - an odorless gas produced by the decomposition of organic matter

method - a description of how data and information are collected

metric system - a decimal system of measures and weights with the meter and the gram as bases

microarray - in genomics, a tool for studying how large numbers of genes interact with each other and how a cell’s regulatory networks control vast batteries of genes simultaneously. A robot is used to precisely apply tiny droplets containing functional DNA to glass slides. Researchers then attach fluorescent labels to DNA from the cell they are studying. The labeled probes are allowed to bind to cDNA strands on the slides. The slides are put into a scanning microscope to measure how much of a specific DNA fragment is present

microatoll - a circular colonial corallum up to 1 m height and 4 m diameter. Growth is mainly lateral, as upward growth is limited by aerial exposure

microbe - a nonspecific term for small organisms that can be seen only with the aid of a microscope. The term encompasses viruses, bacteria, yeasts, molds,and protists. The term, however, is used most frequently in refererence to bacteria

microbenthos (microfauna or microflora) - benthic organisms whose shortest dimension is less than 0.1 mm

microbial loop - a micro-food chain that works within (or along side) the classical food chain. In the microbial loop the smallest organisms, the heterotrophic bacteria and pico-plankton, use dissolved inorganic material directly as carbon and energy sources. These organi

microbiology - the study of organisms that can be seen only with the aid of a microscope

microbiota - organisms which are invisible, or nearly so, to the naked eye

microecology - the study of the interactions between microorganisms and their environment

microenvironment - a specific set of physical, biological, and chemical factors immediately surrounding the organism

microevolution - relatively minor change in the composition of a species' gene pool over time

microfauna - animals which are invisible, or nearly so, to the naked eye

microflora - plants which are invisible, or nearly so, to the naked eye

microhabitat - a smaller part of a habitat that has some internal interactions allowing it to function self-sufficiently within a generally larger habitat, such as a patch reef in a lagoon

micrometer - an instrument for measuring very small distances

micron (µ) - a unit of length equivalent to a micrometer (µm), one-millionth of a meter or 0.00003937 inch

Graphic of Micronesia

Map of Micronesia. (Graphic: U.S. CIA)

Micronesia - a region situated between the Mariana Trench in the west and the Line Islands in the east. The name "Micronesia" means "tiny islands." the Federated States of Micronesia consists of the states of Yap, Chuuk, Pohnpei, and Kosrae. This region is composed of thousands of small islands, mostly atolls

micronutrient - a nutrient, such as iron, copper, or zinc, that is required in very small amounts by plants in order to photosynthesize and thrive

micropyle - the minute aperture in the egg membrane for the entry of the sperm cell

microsatellites - loci (or regions within DNA sequences) where short sequences of DNA nucleotides are repeated in tandem arrays (the sequences are repeated one right after the other).  The lengths of sequences used most often are di-, tri-, or tetra-nucleotides. In the literature they can also be called simple sequence repeats (SSR), short tandem repeats (STR), or variable number tandem repeats (VNTR). Microsastellites are inherited in a Mendelian fashion. They are widely used in the following applications: forensic identification and relatedness testing; diagnosis and identification of diseases; population studies (by looking at the variation of microsatellites in populations, inferences can be made about population structures and differences, genetic drift, genetic bottlenecks and even the date of a last common ancestor); and conservation biology where they can be used to detect sudden changes in population, effects of population fragmentation, and interaction of different populations. Microsatellites are useful in identification of new and incipient populations

microsclere - a small spicule in sponges

microscopic section - a very thin slice of biological tissue or mineral or other substance for examination under a microscope

microsmatic - pertains to animals with a poorly developed olfactory (smell) sense

microtubule - a long, hollow rod composed of the protein, tubulin. Microtubules make up portions of the cytoskeleton of cells. Microtubules aid in cell support, intracellular transport, and cell proliferation. They are also found in cilia and flagella

microvillus - any of the minute hairlike structures projecting from the surface of certain types of cells

microwave - any electromagnetic radiation having a wavelength in the approximate range from one millimeter to one meter, the region between infrared and short-wave radio wavelengths

Image of tidal pools

Tidal pools in the midlittoral zone. (Photo: Susan Scott)

midlittoral zone - the portion of the intertidal zone that is covered and uncovered by water each day

Image of migrating humpback whales

Humpback whales (Megaptera novaeangliae) migrate from near the poles to tropical waters. (Photo: R Wicklund)

migration - the large-scale movement of a population for some specific purpose

migration corridor - a set route that migratory animals follow when they migrate from one area to another

Millennium Coral Reef Mapping Project (MCRMP) - the Institute for Marine Remote Sensing (IMaRS) at the University of South Florida is funded by the Oceanography Program of the National Aeronautics and Space Administration (NASA) to provide an exhaustive worldwide inventory of coral reefs using high-resolution satellite imagery. The project uses Landsat 7 satellite imagery to map the extent and diversity of coral reefs worldwide at geomorphological levels

milliammeter - an instrument for recording very small electrical currents

millipore filter - a thin membrane composed of cellulose fibers that is used, for example, as a filter in the bacteriological examination of water

Image of salmon testes

The testes of this male adult salmon produce milt when ready to spawn. The milt becomes a liquid, containing sperm cells, and exits through the vent opening to fertilize eggs. (Photo: Pacific Streamkeepers Federation)

milt - the testes of fishes when filled with semen; fish seminal fluid

mimicry - the appearance or characteristics of one organism that copies or "mimics" another in order to gain some advantage; the organism may resemble some other natural object as an aid in concealment

Minamata disease - mercury poisoning of humans from eating contaminated seafood

mineral accretion - a technique used to grow corals on artificial reefs using electricity to accrete minerals thereby cementing coral colonies to the substrate. Applying a low voltage to a metallic structure causes calcium carbonate (CaCO3) to build on the metal, upon which coral larvae can attach, settle and feed. This greatly speeds the coral reef growth process. The voltage is low enough that it can easily be generated by floating solar panels or from wave action

mineral deposit - an accumulation of naturally occurring minerals

mini-atoll - a ring-shaped patch reef with a central area (lagoon) containing sand

mitigation - the act of making less severe or intense; measures taken to reduce adverse impacts on the environment

mitigation plan - a proposal to reduce or alleviate potentially harmful impacts

Mitochondrial DNA (mtDNA) - DNA that is located in the mitochondria of cells. It is inherited only from the female parent

mitochondrial genome - the genetic material of the mitochondria. It is similar in structure to that of the prokaryotic genetic material, formed of a single circular DNA molecule. The mitochondria of sexually-reproducing animals usually comes only from the maternal side, and is essentially the same as that of the mother. Sometimes mitochondria from spermatozoa are also passed on to offspring. Mitochondrial DNA has been studied to trace lineage far back in time

Image of a mitochondrion

Electron micrograph of a single mitochondrion showing the organized arrangement of the protein matrix and the inner mitochondrial membranes. (Photo: U.S. Dept. of Health and Human Services/National Institutes of Health)

mitochondrion - an organelle found in the cells of most eukaryotes. Mitochondria are sometimes described as cellular "power plants" because their primary function is to manufacture adenosine triphosphate (ATP), which is used as a major source of cellular energy

mitogen - any substance that causes cells to begin dividing by mitosis

mitogenome - mitochondrial genome; DNA found in mitochondria, which contains some structural genes and is generally inherited only through the female line

mitosis - the process of nuclear division in eukaryotic cells that produces two daughter cells from one mother cell, all of which are genetically identical to each other. See cell division -

mitotic spindle - a network of fiber-like microtubules that forms in a cell's nucleus during mitosis (nuclear division) which connects the centrosomes to the kinetochores and helps move the chromosomes around

mixed layer - near-surface waters subject to mixing by the action of wind and waves. There is little variation in salinity or temperature at depths below the mixed layer

mixed zone - the populous region of most bank/barrier reefs seaward of the lower palmata zone. It begins at a depth of 6-8 m

MMM (Maximum Monthly Mean SST climatology) - the highest expected (climatological) monthly SST expected at all ocean locations based on 15 years of monthly mean SST data (serves as the input threshold for the Coral Bleaching HotSpot charts)

mode - a statistical measure of central tendency. The number that appears most in a sequence of numbers. A list of numbers can have more than one mode

Modern Synthesis - the synthesis of natural selection and mendelian inheritance

modifier gene - a gene that modifies the effect produced by another gene  

moiety - a component part of a complex molecule

molar - a large flat or ridged-topped tooth adapted for crushing or grinding

molariform - shaped like a molar tooth, being rounded and flattened. In fishes, molariform teeth are used for crushing mollusks and crustaceans

mole - the mass of a compound in grams numerically equal to its molecular weight. Also, the mass of a compound containing Avogadro’s number of molecules

molecular biology - a branch of biology that studies the biology of a cell at the molecular level. Molecular biological studies are directed at studying the structure and function of biological macromolecules and the relationship of their functioning to the structure of a cell and its internal components. Great attention is given to genetic aspects such as replication, transcription and translation

molecular genetics - the study of how genes function to control cellular activities

molecular weight - the sum of the atomic weights of the atoms in a molecule

molecule - a small particle composed of two or more atoms. Molecules are a stable configuration of atomic nuclei and electrons bound together by electrostatic and electromagnetic forces. They have characteristic physical and chemical properties, different from the atoms of which they are composed

Image of an Atlantic deer cowrie (Mollusca)

Atlantic deer cowrie (Cypraea cervus) grazing in the Flower Garden Banks National Marine Sanctuary. (Photo: Frank and Joyce Burek)

Mollusca - an animal phylum that includes bivalves, squids, octopuses and snails. They are distinguished by a muscular foot, a calcareous shell secreted by the underlying body wall (the mantle) and a feeding organ (the radula). Many species are common inhabitants of coral reefs

molt - to shed part or all of a coat or outer covering, such as, shell, feathers, cuticle or skin, which is replaced periodically by a new growth

monaxon - a linear spicule in sponges; a single rod or ray with a pointed, hooked, or knobbed end

Monera - the Kingdom composed of prokaryotic organisms. They have a cell wall, and lack both membrane-bound organelles and multicellular forms. The Archaebacteria, the most ancient of this Kingdom, are so different that they may belong to a separate kingdom. Monera include the cyanobacteria and eubacteria

moniliform - contracted at short, regular intervals like a string of beads; bead-like

monitoring - the systematic collection of data over time

monk seal - an endangered species of seal (Monachus schauinslandi) normally found on the leeward (southwest) sides of the Northwestern Hawaiian Islands, and occasionally sighted in the Main Hawaiian Islands. It is estimated that fewer than 1500 Hawaiian monk seals exist today. The Hawaiian monk seal was officially designated endangered 1976 and is protected by the Endangered Species Act and the Marine Mammal Protection Act. It is illegal to kill, capture or harass monk seals. A critically endangered species of monk seal (Monachus monachus) is found in the Mediterranean Sea. The Caribbean monk seal (Monachus tropicalis) is thought to be extinct

mono- - a prefix meaning one

monoecious - having combined sexes. Individuals of monoecious species contain the reproductive systems of both males and females

monofilament - a single large filament or threadlike structure of a synthetic fiber, such as a monofilament fishing line

monogamy - a male and a female mating only with each other

monomer - in chemistry, a single molecule that is the subunit of a polymer; in genetics, a character determined by a gene or genes at a particular locus

monomorphic - occurring in only one form

monopectinate gill (ctenidium) - in mollusks, refers to having gill lamellae on one side of the ctenidial axis

monophagous - eating one kind of food only

monophyletic group - a group of organisms descended from a common ancestor

monosaccharide - a sugar that does not hydrolyse to produce other sugars; the simplest group of carbohydrates

monotonic function (monotone function) - in mathematics, a function that either never decreases or never increases as its independent variable increases

monotype - in taxonomy, a situation where a genus group taxon is established with only one immediately subordinate taxon, e.g., a genus containing only one species

monsoon - a periodic wind caused by the effects of differential heating, with the largest being the Indian monsoon found in the Indian Ocean and southern Asia

Image of great star coral <i>(Montastraea sp.)</i>

Great star coral (Montastraea cavernosa) is one of four species of Montastraea found at the Flower Garden Banks in the Gulf of Mexico. (Photo: Dr. Stephen Gittings)

Montastraea - a genus of hard (stony) coral that includes the boulder coral and the great star coral

montiform - mountain-shaped

moorish idol - a bony fish species (Zanclus cornutus) in the family Zanclidae. The moorish idol is the only species in the family. It has a long, white, sickle-shaped dorsal fin, two broad vertical black bars on the body, and a yellow-orange saddle across the s

moray eel - any of numerous chiefly tropical, brightly colored marine eels of the family Muraenidae that commonly inhabit coral reefs

morbidity - illness or disease; the incidence and prevalence of a specific disease

morgan - unit of inferred distance between genes on a chromosome

morph - a distinct genetic form or variant of a particular species. For example, a distinct color phase of a species that exhibits more than one color

morphogenesis - a change in the shape or structure of an organism through growth and differentiation

morphology - a branch of biology that deals with the form and structure of organisms, apart from their functions (physiology)

morphometric character - a measurement of a body part, e.g., head length or eye diameter

mortality - the death rate, measured as the number of deaths per a certain population during a specific time period; may describe the population as a whole, or a specific group within a population

morula - a stage of embryonic development in which the cleaving cells (blastomeres) appear as a cluster of blastomeres without a cavity; precedes the blastula stage of embryonic development

mosaic teeth - the series of rows of flat teeth found in rays,skates and some sharks. They are used for crushing hard foods as mollusks and crustaceans; also called "pavement teeth"

motile - capable of self-locomotion in organisms

motu - a coral island in the lagoon of an atoll

mouth brooder (oral brooder) - a fish which broods or protects the eggs or young by taking them into the mouth cavity

mouthparts - a collective term for the appendages around the mouth of crustaceans which are concerned with feeding: mandibles, maxillae and maxillipeds

muciferous - producing or containing mucus

mucophagy - feeding on the mucus of fishes or invertebrates

mucus - a gelatinous material secreted by specialized mucous cells. In corals, it functions in protection from bacterial invasion, food capture, and removal of sediment particles. Mucus is usually moved by cilia (motile hair-like extensions of the cell membrane)

mucus cell - a cell which secretes mucin, which, when mixed with water forms mucus; in cnidarian polyps, mucus trap food particles, removes sediments, lubricates the actinopharynx, protects against dessication, UV radiation, and other environmental stresses; also called mucocyte or mucosecretory cell,

mud - a fine sediment often associated with river discharge and buildup of organic material in areas sheltered from high-energy waves and currents

Image of mudflats

Nutrient-rich mudflats at the Gulf of the Farallones National Marine Sanctuary in California. (Photo: Dan Howard)

mud flat - a relatively level area of fine silt along a shore (as in a sheltered estuary) or around an island, alternately covered and uncovered by the tide, or covered by shallow water

Mullerian mimicry - a form of protective mimicry in which noxious species evolve through convergent evolution to resemble each other

Graphic of multibeam sonar

Hull-mounted multibeam sonar (left) and towed side scan sonar (right) (Graphic: NOAA)

multibeam sonar - sonar signals arriving at a target, or the towfish, from a single source but along different paths. The multibeam sonar system consist of a transducer, motion sensor, gyrocompass, and navigation system. When collected in slightly overlapping swaths (fanlike coverages from sonar scans), multibeam sonars can produce a sonar data set that represents nearly 100 percent acoustic coverage of the seafloor

multimedia - the use of computers to present video, sound, graphics, and text

multimodal distribution - a distribution with more than one mode

Multipurpose Marine Cadastre (MMC) - a multi-agency effort to build a GIS-based marine information system for U.S. waters that provides authoritative geospatial data and supporting information to inform decision making on a range of ocean issues

Multispectral Scanner (MSS) - a scanner system that simultaneously acquires images of the same scene in various wavelength bands

multivariate analysis of variance - an analysis of variance with two or more dependent variables

multivariate community analyses - statistical methods for analyzing physical and biological community data using multiple variables

municipal discharge - discharge of effluent from waste water treatment plants, which receive waste water from households, commercial establishments, and industries in the coastal drainage basin

municipal Sewage - wastes (mostly liquid) originating from a community; may be composed of domestic wastewaters and/or industrial discharges

muon - a charged lepton about 200 times more massive than an electron; an elementary particle with a negative charge and a half-life of 2 microsecond; decays to electron and neutrino, and antineutrino

mutagen - an agent that causes a permanent genetic change in a cell other than that which occurs during normal genetic recombination

mutation - changes in the nature of single genes or segments of chromosomes, which are then inherited by successive generations

mutualism - a symbiotic interaction between two species in which both derive some benefit

Diagram of mycelium

Drawing of the mycelium of a fungus. (Photo: Jon Houseman\BIODIDAC)

mycelium - the mass of filamentous growth (hyphae) from which the vegetative part of a fungus develops

mycophage - an animal which primarily eats fungi

mycosis - any disease caused by a fungus

mycosporine-like amino acids (MAA) - MAAs are a family of compounds which act as nature’s sunscreen in the marine environment. Shallow-water environments of tropical coral reefs are characterized by high levels of ultraviolet-A and ultraviolet-B radiation. Corals have developed an efficient defence against the potential damage of long-term solar irradiation, which often includes the production of natural "sunscreen"-type UV-absorbing compounds and related antioxidants. These compounds in shallow-water corals were identified to be a group of mycosporine-like amino acids (MAAs) having absorption maxima in the range 310-360 nm. MAAs are assumed to be produced by the zooxanthellae in coral tissues, since their biosynthesis involves a biochemical pathway not found in invertebrates. The major distribution of MAAs, however, resides within the coral tissues, suggesting that the algal partner of the mutualistic relationship provides UV protection to the whole of the relationship via MAA translocation. MAAs have been identified in a number of taxonomically diverse organisms such as fungi, marine heterotrophic bacteria, cyanobacteria, eukaryotic algae, marine invertebrates, fishes,and a wide variety of other marine organisms

myocin - a contractile protein found in muscle cells which, together with actin, provides the mechanism for muscle contraction

myoepithelial cell - a contractile cell in cnidarians

myoglobin - an oxygen-binding protein found in the muscle cells of animals. It functions as an oxygen storage unit, providing oxygen to the muscles. Diving marine mammals, such as seals and whales are able to remain submerged for long periods because they have greater amounts of myoglobin in their muscles than other animals do. There is a close chemical similarity between myoglobin and hemoglobin, the oxygen-binding protein of red blood cells

myoneme - in protists, the differentiated threads of ectosarc, which are contractile and perform the function of muscular fibers in the Metazoa; in cnidarians, the myoneme is the contractile portion of epitheliomuscular cellscontained within the cell membrane that anchors it to the mesoglea. They may be diffuse or arranged in circular and longitudinal contracting bands

myotome - any segment of embryonic mesoderm that develops into skeletal (voluntary) muscle in the adult; any of the segmentally arranged blocks of muscle in lower vertebrates, such as fishes

mysid - a small shrimp-like crustacean belonging to the order Mysidacea. Mysids are also called "opossum shrimp" because the females carry their eggs in a pouch beneath the thorax

myxopterygium (clasper) - the copulatory organ or clasper of sharks, rays, skates and chimaeras