Graphic showing December 1998 La Niña event.

La Niña - a phenomenon characterized by unusually cold ocean temperatures in the eastern Equatorial Pacific, compared to El Niño, which is characterized by unusually warm ocean temperatures in the eastern Equatorial Pacific

label  - a compound or atom that is either attached to, or incorporated into, a macromolecule and is used to detect the presence of a compound, substance, or macromolecule in a sample; also called a 'tag'

labeled - to mark substances in a way that they can easily be identified. In an organism, substances may be labeled using stable isotopes or harmless radioactive components so that they can be traced, analyzed or measured

labial - pertaining to the lips

labium - any lip-like structure

Lacey Act - the Lacey Act, passed in 1900, and amended several times, makes it unlawful to import, export, transport, sell, buy, or possess fish, wildlife, or plants taken, possessed, transported, or sold in violation of any federal, state, foreign, or Native American tribal law, treaty, or regulation

lacriform - tear-drop shaped; also called "dacriform"

lacuna - a cavity ("little lake") in a matrix-like substance. For example, cartilage cells (chondrocytes) are located in lacunae in the cartilagenous matrix; bone cells (osteocytes) are located in lacunae in bone matrix

lageniform - bottle-shaped

A lagoon in Bora Bora. (Photo: Dr. Anthony Picciolo/NOAA)

lagoon - a warm, shallow, quiet waterway separated from the open sea by a reef crest

lagoon slope - the back reef on a barrier or atoll reef

Lakshadweep Islands - an archipelago situated in the Arabian Sea between 08o 00’ N and 12o 30’ N latitude and 71o 00’ E and 74o 00’ E longitude and at a distance of 220 - 440 km from the west coast of India. Lakshadweep is the tiniest Union Territory of India. The coral reefs of the islands are mainly atolls except for one platform reef

lambert - unit of brightness of light

lamina - a thin, flat layer

laminarian - a brown alga in the plant class Phaeophyceae; a kelp

lanceolate - spear-shaped, tapered at both ends

lanceolate - shaped like a lance head

lanciform - lance-shaped

lander system (benthic lander) - a scientific instrument system designed for temporary deployment on the sea floor in order to monitor environmental parameters. It is an unmanned vehicle that falls to the seafloor unattached to a cable, and then operates autonomously on the bottom. At t

Landsat Program - the Landsat Program (NASA) provides the world's scientists and application engineers with a continuing stream of remote sensing data for monitoring and managing the Earth's resources. Landsat 7 has produced an uninterrupted multispectral record of the Earth's land surface since 1972. Along with data acquisition and the USGS archival and distribution systems, the program includes the data processing techniques required to render the Landsat 7 data into a scientifically useful form. Special emphasis has been placed on periodically refreshing the global data archive, maintaining an accurate instrument calibration, providing data at reasonable prices, and creating a public domain level one processing system that creates high level products of superior quality

Artist's rendition of LANDSAT satellite.

Landsat satellite - U.S. satellite used to acquire high-resolution (500-800m) remotely sensed multi-spectral images of the earth's land surface and surrounding coastal regions

langley - unit of solar radiation

lappet - a sensory structure in some jellyfish (Scyphozoa), associated with a rhopalium, which responds to touch (pressure); a fleshy lobe

Microscopic photograph of a crab larva (megalops stage) from a plankton collection.

larva - a sexually immature juvenile stage of an animal's life cycle. However, there are a few exceptions, where the larval form never metamorphoses into the adult stage and is sexually mature (neoteny)

lateral - refers to the side or flank of an animal

lateral display - a type of threat or reproductive behavior exhibited by many species of fishes, in which two male fish align beside each other, spread their dorsal, anal, and pelvic fins, and intensify the coloration of their bodies. These threats are usually accompanied by tail beats and body quivering

lateral line scale - one of a series of scales that bear the pores and tubes of the lateral line system

Note the lateral line of the Caribbean red snapper (Lutjanus purpureus) with 49 to 53 scales, which extend onto the base of the caudal fin. (Photo: U.S. Food and Drug Administration)

lateral line system - a series of sense organs that detect pressure or vibrations along the heads and sides of cyclostomes, fishes, and some amphibians. It consists of a network of sensory hair cell clusters (neuromasts) and small water-filled canals that lie immediately beneath the skin and extend along the sides of its body. This network is sensitive to external motion

latitude - the angular distance between an imaginary line around the Earth, or any spherical body, parallel to its equator and the equator itself; an imaginary line around the Earth parallel to the equator

launch - to start up any computer program by clicking on its icon or selecting it from the Start menu

Law - a description of how a natural phenomenon will occur under certain circumstances; a statement that summarizes the results observed in an experiment that is repeated many times by many different scientists. A scientific law is widely accepted as true or as a fact, such as Newton's Laws of Gravitation

Law of Conservation of Energy - energy can be transferred from one system to another in many forms, however, it can not be created nor destroyed. Thus, the total amount of energy available in the universe is constant

Law of Parsimony (Occam's Razor) - when you have two competing theories which make exactly the same predictions, the one that is simpler is the better; also called "Occam's Razor"

Law of the Minimum - the growth of a population is limited by the resource in shortest supply. Also known as 'Liebig's Law'

lead line - a line with a lead weight on the end used to measure depth. The lead is dropped into the water and marks on the line are read to determine the current water depth. The lead usually has a cavity to return a sample of the bottom type (mud, sand, etc.)

least squares - a statistical criterion for the estimation of the goodness of fit in correlation analysis. Least squares methods aim to minimize the sum of squared differences between the observations and the predictions from a model

lecithotrophic larva - a planktonic larva that gains its nutrition from yolk (semi-crystalline phospholipoprotein granules). In most bony fishes, yolk is supplied by the yolk sac, a bag-like ventral extension of the gut containing yolk granules

lectotype - in taxonomy, one of several syntypes, designated by any author after the original publication of a species name as the 'type specimen' for the taxonomic name. Designated only where there was no original holotype

leeward - referring to the side of an island or reef that faces away from the prevailing wind

lek - a polygynous mating system where a number of males aggregate at a particular site during the breeding period and engage in courtship behavior, especially displays. Females attracted to the site "select " males for mating and subsequent fertilization of eggs. Once mated, the females usually go elsewhere to lay their eggs or to complete gestation. Lekking behavior (also called arena behavior) has been observed among cuttlefish, fishes, birds, antelope, and insects. Lekking species tend to stay at a single lek throughout a breeding season and to return to the same lek site from breeding period to breeding period

lenticel - aerial roots (pneumatophores) of mangroves contain spongy tissue connected to the exterior of the root via small pores called lenticels. During low tide, when lenticels are exposed to the atmosphere, oxygen is absorbed from the air and transported to and even diffused out of the roots below ground. This diffusion of oxygen maintains an oxygenated microlayer around the roots that enhances nutrient uptake.

leptocephalus larva - a long, ribbon-like larval form that is characteristic of eels, tarpons, and bonefishes

lepton - a class of subatomic particles that constitute matter which have no measurable size and do not interact with the strong nuclear force. The charged leptons are the electron, the muon, the tau and their antiparticles. Neutral leptons are called neutrinos

lesion - any pathological or traumatic discontinuity of tissue, or loss of function of a part; a wound or injuryto the tissues

lethal gene - a mutant form of a gene gene whose phenotypic effect eventually results in the death of the bearing organism. Death from different lethal genes may occur at any time, from fertilization of the egg to advanced age. Lethal genes may be dominant, incompletely dominant, or recessive; also called a 'lethal allele'

leucocyte - a cellular component of blood. Leucocytes help to defend the organism's body against infectious disease and foreign materials as part of the immune system; also called "white blood cell"

leuconoid - the body form of highest complexity in sponges. The leucanoid form is highly irregular, displays the greatest degree of folding of the body wall, and has lost radial symmetry. The choanocytes line the pockets formed by the convoluted body wall

leucophore - a colorless chromatophore which contains purines, usually guanine, in the form of small, motile crystals in the cell's cytoplasm

library - in genomics, an unordered collection of clones (i.e., cloned DNA from a particular organism) whose relationship to each other can be established by physical mapping; a collection of cloned DNA fragments representing the genome of a particular organism

LIDAR (Light Detection And Ranging) - a remote-sensing technique that uses a laser light source to probe the characteristics of a surface target. A laser emission may be directed downward from a low flying aircraft. Information about the target is derived from back-scattered reflectance or fluorescence of the target. Chlorophyll pigments in coral reef organisms (e.g., algae, seagrasses, coral), when excited by shorter (blue or green) wavelength light, emit light at longer (red) wavelengths, i.e., it fluoresces

ligand - a molecule, such as a hormone or growth factor, that binds to a specific site on a receptor protein

ligase - an enzyme used to join DNA (DNA ligase) or RNA (RNA ligase) segments together

light emitting diode (LED) - a very small light often used in electronic instrumentation

limits of acceptable change (LAC) - a framework for establishing acceptable and appropriate resource and social conditions in recreation settings. LAC is an approach to balance recreational use of a "wilderness" area with environmental and resource protection needs

limnology - the study of the physical, chemical, meteorological and biological aspects of fresh waters

limoniform - lemon-shaped

limu - general Hawaiian name for all kinds of aquatic plants and soft corals; also terrestrial algae growing in any damp place on the ground, on rocks, and on other plants

limu kohu - the Hawaiian name for the red alga, Asparagopsis taxiformis, an edible species that is no longer common in the Main Hawaiian Islands, but is relatively abundant the shallow waters of some of the Northwestern Hawaiian Islands

line intercept transect - a linear transect protocol where a tape is secured at each end of the transect with the tape draped over the reef in between. Observations are collected on each species and substrate component and their length under the tape

line point intercept (LPI) - a line of specified length (transect) laid out within a study site. Measurements and observations may be taken at specified intervals (points) along the line

line precedence - in taxonomy, when two different names for the same taxon are first published in the same publication, then the one which appears on the earlier line has line precedence. Line precedence does not necessarily mean priority as well. This is determined by the action of the first reviser

lineage - a genetically continuous line of evolutionary descent

linear acceleration - the rate of change of velocity in a linear direction (along a straight line) with respect to time

linear reef - a linear coral formation that is oriented parallel to the shore or the shelf edge

linear regression - regression in which the relationship is linear

linear relationship - a situation in which the best-fitting regression line is a straight line

A NOAA scientist laying out a linear transect line.

linear transect - a line of specified length laid out within a study site. They are generally positioned parallel to the shore along depth contours. Measurements and observations may be taken along the entire surface beneath the line (line intercept transect) or at specified intervals along the line (point intercept transect)

linguiform - tongue-shaped

linkage - the proximity of two or more markers (genes, etc.) on a chromosome; the closer together the markers are, the lower the probability that they will be separated during DNA repair or replication processes, and hence the greater the probability that they will be inherited together

linked genes - genes that are so closely associated on a chromosome that the allelic forms found on a chromosome are inherited together by an offspring at least 80 percent or more of the time

Linnaean tautonymy - in taxonomy,the identical spelling of a new genus-group name and a pre-Linnaean (i.e., before 1758) one-word name cited as a synonym of only one of the species or subspecies originally included in that genus

In the 18th century, Linnaeus made a great contribution to science by developing systems of classification and nomenclature to organize the explosion of information on plants and animals. The tenth edition (1758-59), of Linnaeus's classic work, Systema Naturae, was chosen as the starting point for zoological nomenclature. (Photo: Smithsonian Institution Libraries)

Linnaeus, Carolus - the 18th century Swedish botanist (1707-1778) who established the modern binomial system of biological nomenclature for plants and animals. His non-latinized name was Carl von Linne

The lionfish, Pterois volitans, is a recent invasive species in the western Atlantic Ocean. Like some other members of the scorpion fish family, the lionfish is a venomous animal, possessing venom glands at the base of the dorsal, anal and pelvic fin spines. The venom is injected in a potential predator via the spines. The genus Pterois contains eight species variously referred to as lionfishes, turkeyfishes, or firefishes. The lionfish is an inhabitant of near and offshore coral and rocky reefs. During the day, it seems to prefer shelter under ledges or in caves or crevices. (Photo: Paula Whitfield, NOAA Beaufort Laboratory)

lionfish - the red lionfish (Pterois volitans) is a venemous coral reef fish belonging to the scorpion fish family (Scorpaenidae). Native to the Indian and western Pacific oceans, lionfish are now an invasive species found in the western Atlantic Ocean from southern Florida to New York and Bermuda. They appear to be a reproducing along the southeastern U.S. coast; Other common names are turkeyfish, dragonfish, and firefish

Lionfish Tissue Repository - a large, multi-national collaborative program, jointly managed by NOAA and the Reef Environmental Education Foundation (REEF), intended to maintain and provide tissue samples for research into the ecological and evolutionary processes driving the ongoing invasion of lionfish (Pterois spp.) in the Caribbean and western Atlantic

lipase - an enzyme, secreted by the pancreas and the glands of the small intestine, that breaks down fats into glycerol and fatty acids during digestion

lipid - a group of organic compounds, including the fats, oils, waxes, steroids, and triglycerides, that are insoluble in water but soluble in common organic solvents, and are oily to the touch. Together with carbohydrates and proteins, lipids constitute the principal structural materials of cells

lipophilic  - having an affinity for, attracting, or the ability to adsorb or absorb lipids (fats)

lipopolysaccharide - a compound containing a lipid bound to a polysaccharide

liposome - an artificial, single or multilaminar vesicle, made from a lipid, that is used for the delivery of a variety of biological molecules or molecular complexes to cells, e.g., drug delivery and gene transfer. Liposomes are also used to study membranes and membrane proteins

Listserv ® - the most common kind of maillist found on the internet

lithoherm - a deep-water mound of limestone, usually formed by submarine consolidation of carbonate mud, sand and skeletal debris

lithosphere - the outer solid part of the earth, including the crust and uppermost mantle. The lithosphere is about 80-100 km thick, although its thickness is age dependent The lithosphere below the crust is brittle enough at some locations to produce earthquakes by faulting, such as within a subducted oceanic plate

Lithothamnion ridge - a synonym for algal ridge. The algal genus Lithothamnion is important in maintaining reef integrity by cementing various pieces of calcium carbonate

This sea slug is a denizen of northwest U.S. rocky littoral (intertidal) zones.

littoral - intertidal; between low and high tide levels

Live rock from Tonga, crated for shipping to an aquarist. (Photo: http://www.reefscience.com)

live rock - calcareous rock which is removed from the vicinity of a coral reef with some of the life forms on it still living. These may include bacteria, coralline algae, sponges, worms, crustaceans and other invertebrates. Live rock is commonly used in reef aquaria because it contains bacteria that can help filter the water through nitrification

A liveaboard dive boat designed and constructed with divers and underwater photographers in mind. A vessel such as this may accommodate up to 20 passengers in private cabins, all with full bathrooms. It is fully air-conditioned with a state-of-the-art dive center, and complete photo and video labs with daily E6 processing. Wide dive platforms provide easy water entries and exits. (Photo: Belize Aggressor)

liveaboard - a commercial dive boat with sleeping and eating accommodations. Scuba divers live aboard the boat for several days and usually visit dive locations unaccessible to other divers

This comb jelly (ctenophore) possesses a lobate shape. (Photo: NOAA)

lobate - lobe-shaped

lobe - a rounded projection

local extinction - the complete loss of an organism in a specific part of its range

locomotion - the act of moving, or the ability to move, from place to place

loculus - an anatomical term for any small compartment or recess; a small cavity or space within an organ or in a plant or animal; a calcified area or fiber-filled space within the axial sleleton (axis) of a gorgonian; a space within the gastrovascular cavity between septa

locus - the position of a gene, DNA marker, or genetic marker on a chromosome

logarithmic phase - the steepest slope of the growth curve of a culture; the phase of vigorous growth during which cell number doubles every 20-30 minutes; also called 'log or exponential growth phase'

logarithmic scale - a constant ratio scale in which equal distances on the scale represent equal ratios of increase. For example, in a logarithmic scale, the distance between 10 and 100 is the same as the distance between 100 and 1000, or between 1000 and 10,000. Logarithmic scales are used when the range of numbers being represented is large

long gill net - a gill net that has a float line that is more than 1,000 yd (914 m) in length

long term monitoring - the repeated surveying of organisms, populations, communities, or environmental parameters over time to help us understand a variety of natural processes

longitude - an imaginary great circle on the surface of the Earth passing through the north and south poles at right angles to the equator; "all points on the same meridian have the same longitude"

longline - a fishing line that is deployed horizontally to which baited hooks are attached. A longline may be a bottom longline, i.e., designed for use on the bottom to catch ground fishes, or a pelagic longline, i.e., designed for use off the bottom to catch pelagic fishes such as tuna and swordfish. The longline hauler may be manually, electrically, or hydraulically operated

longshore current - a current that flows parallel to the shore just inside the surf zone. It is also called the littoral current

look bucket - a bucket with a see-through bottom made of glass or plexiglass. The transparent bottom is lowered below the water surface allowing the user to observe underwater features

Loop Current - a warm, swift, ocean current that flows northward between Cuba and the Yucatán peninsula, moves into the Gulf of Mexico, loops clockwise in the eastern Gulf before exiting east into the Atlantic Ocean through the Florida Straits. It is part of the western boundary current system of the North Atlantic subtropical gyre and may extend to great depths. An eddy, or Loop Current ring, separates from the Loop Current and may drift slowly westward into the central and western Gulf of Mexico

This photo of a Lophelia coral garden was taken via a manned submersible on the ocean floor. (Photo: NOAA)

Lophelia reef - a reef formed by Lophelia pertusa, a deep-sea coral found in all oceans except the Arctic Ocean

lophocyte - a mobile cell in sponges that produces collagen

lophophorate - an informal taxonomic unit that includes coleomatic metazoans which possess a specialized filter-feeding organ, the lophophore. Almost all lophophorates are marine organisms and all are suspension feeders. Lophophorates are deutersotomes and are typically considered relatively closely related to chordates and echinoderms. There are three lophophorate phyla: Phoronida, Bryozoa and Brachiopoda

lophophore - a feeding organ possessed by lophorates. It is a disk or horseshoe-shaped structure which surrounds the mouth and bears the tentacles of the Bryozoa (moss animals), Brachiopoda (lamp shells) and Phoronida (horseshoe worms). The tentacles are hollow (coelomic) and covered with cilia which generate water currents that draw food toward the mouth

LORAN (LOng RAnge Navigation) - a navigation system developed in the 1950's based on the time displacement between signals from two or more fixed shore based antennae

A peaceful lotic environment, the Patuxent River, eastern Maryland, in December 2000. (Photo: Mary Hollinger, NOAA/National Oceanographic Data Center)

lotic - refers to a flowing or running body of fresh water, i.e., streams and rivers

low recruitment - a low influx of new members into a population by reproduction or immigration

A small island at the mouth of the Amazon River at low tide. See high tide for contrast. (Photo: Alessandra and Michael)

low tide - the lowest level of the tide; the minimum height reached by each falling tide

A young Acropora palmata colony in St. Croix, U.S. Virgin Islands (Photo: J. Halas)

lower palmata zone - the part of a reef crest that is seaward of the palmata zone. It consists primarily of elkhorn coral (Acropora palmata) at a depth of about 3-6 m in Caribbean reefs

luciferase - the enzyme which activates luciferin, in the presence of ATP, to produce bioluminescence

luciferin - a compound whose activated form emits light. In the presence of the enzyme luciferase and ATP, luciferin is oxidized to produce oxyluciferin and energy given off as cold light (bioluminescence)

lumen - the interior space of a tubular organ, such as a blood vessel or an intestine

lumen - unit of luminous flux

luminous - emitting light.

luminous flux - the rate of flow of light energy

lumisome - in some cnidarians, a small, intracellular membrane-enclosed vesicle which contains all the proteins necessary for bioluminescence

lumper - refers to a taxonomist who focuses more on similarities than differences among taxa, discounting the importance of minor variation among individuals, and who tends to recognize fewer taxa

Blue tangs with lunate-shaped caudal fins. (Photo: NOAA)

lunate - crescent-shaped

lux - unit of illumination equal to one lumen per square meter

lycra - a spandex textile fiber which has unique elastic qualities in that it can be used in very lightweight, durable fabrics of long-lasting elasticity. It has excellent tensile strength, a long flex life, and high resistance to abrasion and heat degradation. Lycra skin coverings are popular with scuba divers as they give some protecion against abrasions and jellyfish and fire coral stings. They also offer (minimal) protection against cold

lysis - the breakdown of a cell caused by rupture of its cell membrane and loss of cytoplasm. Lysis can be caused by viral action, chemical or physical means; to break down

lysosome - a spherical organelle found in animal cells that contains hydrolytic enzymes for breaking down (digesting) complex molecules. They are part of the intracellular digestive system. Lysosomes bud from the cell's Golgi apparatus

lysozyme - a bacteriolytic enzyme found in many animal secretory products. Lysozymes attack the cell wall of gram-positive bacteria leading to the bacterium's death