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Glossary of Terminology: O

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Number of records found : 133


obligate mutualism - a mutualistic relationship where one species cannot survive without the presence of the other

obligatory - obligate or required. For example, an obligatory cleaner fish relies entirely on this feeding mode to obtain nutrients; opposite of facultative

oblique section - a diagonal cross section that is not at right angles to the longitudinal axis of the animal or structure examined

oblong - elongated (stretched) from a square or circular shape

observational learning - a learning process where an animal learns by copying the behavior of other animals

obtuse - blunt or rounded at the end

ocean acidification - ocean acidification occurs when CO2 from the atmosphere is absorbed into the ocean and reacts with water to create carbonic acid. This decreases both ocean pH and the concentration of the carbonate ion, which is essential for calcification by calcifying marine organisms such as corals

Ocean Biogeographic Information System (OBIS) - the marine component of the Global Biodiversity Information Facility. It links marine databases around the world to provide an internet accessible, dynamic interface for comparing species level, geo-referenced biodiversity data in relation to ocean habitats. All Census of Marine Life (CoML) field project data will be managed in and accessible through OBIS (www.iobis.org)

ocean catchment - the term is described as an attempt to quantify the area of ocean that a benthic system may depend on for planktonic food production and supply. This concept of ocean catchment may be used as a basis for examining the spatial scale of pelagic processes which influence benthic systems

Ocean color image of Gulf of Mexico

SeaWiFS (Sea-viewing Wide Field-of-view Sensor) ocean color image of chlorophyll-a in the Gulf of Mexico.


ocean color - a term that refers to the spectral dependence of the radiance leaving a water body

Image of a SeaWiFS

This SeaWiFS (Sea-viewing Wide Field-of-view Sensor) is an ocean color sensor.


ocean color sensor - an instrument for the remote sensing of ocean color, usually from aircraft or satellite

ocean uptake - the process whereby the ocean takes up heat, atmospheric gases, and other chemical species

oceanic - associated with sea-water environment seaward of the shelf-slope break

oceanic crust - that part of the Earth's crust underlying the ocean basins. It is composed of basalt and has a thickness of about 5 km

oceanic island - an island in the ocean formed by breaking away from a continental landmass, volcanic action, coral formation, or a combination of sources

oceanic reef - a reef that develops adjacent to deeper waters, often in association with oceanic islands

oceanodromous - used to describe organisms that migrate only within the ocean, usually from spawning grounds to feeding grounds

Image of ocelli of butterflyfish

These butterflyfish have a prominent ocellus (pl. ocelli), which may serve to deflect predator attacks from the head region of the fish.


ocellus - an eye-like spot, usually surrounded with a ring of a lighter color, e.g. the ocellus toward the caudal peduncle of some butterflyfish. It may function to deflect attacks to the eyes in agonistic encounters.Ocelli are also present in other animal groups, especially insects

ochre - yellowish or yellow-brown color

Image of sea fan (Octocorallia) with brain coral

An octocorallian (sea fan) with brain coral (sceractinian) in the foreground.


Octocorallia - a subclass of the Anthozoa that contains the sea pens, sea pansies, sea fans, whip corals, and pipe corals. Octocorals always possess 8 tentacles and 8 complete septa (hard corals and anemones possess 12 or more tentacles and septa). They are colonial cnidarians whose polyps are connected by a tissue mass called the coenenchyme. This tissue connects the gastrovascular (digestive) cavities of all the polyps in the colony

octopus - in scuba, a backup second stage regulator connected to the first stage, intended for the benefit of other scuba divers in case their air supply should fail. It is the alternate air source that forms the basis for the "buddy" system

ocular - pertains to the eye

Image of fish on Oculina Banks

The Oculina Banks are deep water coral reefs occurring along the shelf edge off the central east coast of Florida. The Oculina varicosa habitat hosts a diverse array of macroinvertebrates and fishes. The habitat also comprises significant spawning grounds for economically important species of reef fishes.


Oculina Banks - a series of deepwater coral pinnacles and ridges, 15 to 30 miles off the east coast of Florida, extending from Ft. Pierce to Cape Canaveral. Formed by a single species of coral, the Ivory Tree Coral, Oculina varicosa, they form pinnacles of up to 100 feet tall, growing below the Gulf Stream at depths of approximately 70 to 100 meters. This is a slow-growing, branching coral often associated with high biodiversity because they provide ideal habitats and spawning sites for numerous species of fishes and invertebrates

odontophore - a tooth-bearing structure found in most mollusks, except bivalves. It consists of several muscles and a cartilage which support the radula and radula sac; the term is also applied to the radula alone

off-reef - a synonym of reef slope

official index - in taxonomy, a list of names or works suppressed or declared invalid by action of the International Commission on Zoological Nomenclature

official list - in taxonomy, a list of names or works which have been conserved or declared valid by action of the International Commission on Zoological Nomenclature

offshore current - any current flowing away from shore

offshore wind - a wind blowing seaward from the land in the coastal area.

oil plume - underwater globules of oil that do not float to the surface of the ocean. Heavy use of chemical dispersants, which breaks up surface oil, is said to contribute to the formation of these plumes, which may pose a threat to the marine ecosystem

oil slick - a layer of oil floating on the surface of water

oil spill  - the accidental release of oil into the environment

oligomer - a molecule of intermediate relative molecular mass, the structure of which essentially comprises a small plurality of units derived, actually or conceptually, from molecules of lower relative molecular mass; a polymer that consists of two, three, or four monomers

oligonucleotide - a short sequence (usually 2-50 bases) of DNA. Oligonucleotides of up to 30 bases are routinely synthesized for use as PCR primers or as probes for their sequence compliments in a complex mixture of DNA

oligotrophic - refers to water bodies with low concentrations of nutrients

omegoid - horse shoe-shaped

omnivore - an organism whose diet consists of a wide variety of foodstuffs, including plants and animals

oncogene - a gene thought to be capable of causing cancer

oncology - the science dealing with the physical, chemical and biological properties and features of cancer, including the causes and progression of the disease

one-gene--one-polypeptide hypothesis - the concept that one gene in DNA codes for a sequence of amino acids in a specific polypeptide

onomatophore - in taxonomy, a specimen which acts as the name bearer; a nomenclatural type (holotype, syntype, lectotype, neotype)

onshore - a direction landward from the sea

onshore wind - a wind blowing landward from the sea in the coastal area

ontogenesis - the entire development of an individual organism from fertilization to completion of its life history

ontogeny - the development, growth, and maturation of an individual

oocyte - a female gametocyte that develops into an ovum after two meiotic divisions; the female reproductive cell, also called an egg or ovum

ooecium - a brood chamber for developing embryos in the Ectoprocta (bryozoans); one of the special zooids of ectoprocts destined to receive and develop ova; an ovicell.

oogamous - characterized by reproducing by the fusion of small motile male gametes and large nonmotile female gametes

oogamy - the union of a large nonmotile egg with a small motile or nonmotile male sperm cell

oogenesis - the process of ovum (egg) development in female animals, in which the diploid number of chromosomes is reduced by half to the haploid number in the ovum

oolite - a sedimentary rock made of spherical or egg-shaped grains of calcium carbonate (ooids). If the ooids are greater than two mm in diameter, the rock may be called a "pisolite"; also called "egg stone"

oolitic limestone - rock composed primarily of petrified corals or the skeletons of other calcareous animals

oolitic sand - a very fine sand made up of tiny egg-shaped oolites. oolites form in Baffin Bay (Texas), the eastern Mediterranean Sea, the Persian Gulf, the waters surrounding the Bahamas, and in Great Salt lake. Oolites are often used in the home aquarium industry because their small grain size

ootheca - an egg mass protected by a surrounding tough covering or a hard foam-like protein covering. Oothecae are made by many insect species and mollusks; an egg case

open circuit scuba - a diving apparatus in which exhaled air is expelled into the water as bubbles; no part is rebreathed by the diver. It is most commonly used in recreational scuba diving

open circulatory system - a circulatory system, characteristic of some invertebrates, e.g., arthropods, in which blood flows through an interconnected system of open sinuses rather than blood vessels. The tissues and cells are directly bathed by the blood for gaseous exchange and nutrient uptake. The circulatory fluid is called the hemolymph

open ocean - the ocean where the water depth exceeds 200m around the boundaries of the major continental land masses. This definition excludes the marginal enclosed and semi-enclosed seas, but includes all ocean regions bordering lesser island systems regardless of water depth

open reading frame (ORF) - the sequence of DNA or RNA located between the start-code sequence (initiation codon) and the stop-code sequence (termination codon)

open sea - that part of the ocean that extends outward from the continental shelf

open system - a system that exchanges energy and matter with its environment

operant conditioning - a learning process where an animal learns by connecting its own behavior with a response from its environment

operator gene - a region of the chromosome, adjacent to the operon, where a repressor protein binds to prevent transcription of the operon

opercular spine - in fishes, a spine projecting from the operculum (gill cover)

operculate - having an operculum

Image of ventral side of fish head

A ventral view of the gill chamber and opercular chamber of a fish. Note the gill (branchial) arches, each with a large number of gill filaments. (Photo: University of California at Davis)


operculum - a lid or flap covering an aperture, such as the gill cover in most bony fishes; the gill cover; also the horny lid closing the aperture of various species of mollusks

operon - a sequence of genes responsible for synthesizing the enzymes needed for biosynthesis of a molecule. An operon is controlled by an operator gene and a repressor gene

ophiopluteus larva - larva of a brittle star (phylum Echinodermata)

opisthobranch - a marine gastropod, many of which have lost or reduced their shell, mantle and gills

opportunistic feeder - a species adapted for utilizing variable, unpredictable or transient environments to obtain food

optical oceanography - the subdiscipline of oceanography concerned with the propagation and interaction of radiation, typically at wavelengths between about 350 and 750 nm, with seawater

optimum - a state that is the best fit for the current situation. All minor changes make the situation worse; in biology, it is the level of some environmental factor, within a species' or population's tolerance range, at which the species or population can function most efficiently or with the greatest positive effect to its physiological or reproductive fitness

optimum allocation - a procedure used in stratified sampling to allocate numbers of sample units to different strata so as to maximize some desirable quantity

Image of sea urchins

The oral surface of some sea urchins. The central opening is the mouth.


oral - pertaining to the mouth

oral cavity - the cavity within the mouth

oral disc - the area around the mouth of an anthozoan polyp that bears from eight to several hundred tentacles

orbit - a bony or cartilaginous eye socket

order - a taxonomic group containing one or more families

organ - a collection of tissues which performs a particular function or set of functions in an animal's body. Organs are composed of tissues, and may be organized into larger organ systems

organ system - collection of organs which have related roles in an organism's functioning. The nervous system, circulatory system, and muscle system are all organ systems

Image of organ-pipe coral

The organ-pipe coral, a reef-building octocoral. (Photo: A. Bruckner, NOAA)


organ-pipe coral - the organ-pipe coral, Tubipora musica, is a reef-building (hermatypic) octocoral

organelle - a structurally discrete component of a cell, e.g., the nucleus or a mitochondrion

organic - refers to those substances produced by the metabolism of a living organism, especially carbon-containing compounds

organic enrichment - the addition of nutrients from organic matter

organic molecule - a molecule that contains one or more carbon atoms

organically polluted - made unfit for living organisms by excess addition of organic matter

organism - any form of unicellular or multicellular life; a living thing that has (or can develop) the ability to act or function independently

organogenesis - the process of formation of specific organs in a plant or animal involving morphogenesis and differentiation

organophosphate - organophosphate compounds are a diverse group of chemicals used in both domestic and industrial settings. Examples include insecticides, nerve gases, ophthalmic agents, and antihelmintics. Organophosphate pollution may adversely effect coral health

orientation - the way an organism positions itself in relation to environmental cues

original description - in taxonomy, the description of a taxonomic group when first established

original diagnosis - in taxonomy, a formal statement of characters which distinguish a taxon from other similar or closely related taxa, published at the time of proposal of a new taxonomic name

original spelling - in taxonomy, the spelling of an available name when first published. The original spelling of a name is to be kept as the "correct original spelling" unless it does not meet the requirements of the International Code of Zoological Nomenclature. An incorrect original spelling is an original spelling that is incorrect. Multiple original spellings are two or more different original spellings for the same name

ornamental - a non-food species that is produced and maintained solely for exhibit purposes in home or public aquaria, or in ornamental garden ponds

Image of white tern

A white tern from Laysan Island, Hawaiian Archipelago. (Photo: NOAA)


ornithology - the scientific study of birds

orphan receptor - a potential receptor gene identified on the basis of nucleotide sequence similarities with known steroid hormone receptors

ortholog - a gene found in different species that evolved from a common ancestral gene by speciation. Normally, orthologs retain the same function in the course of evolution

oscillation - any steady back and forth movements

oscillator - the internal biological clock mechanism that produces a measurable biological rhythm in an organism

Image of cylindrical sponges

Distinct osculi of some Caribbean sponges. (Photo: Copyright Digital Stock Corp.)


osculum - a large opening through which water flows out of a sponge. Sponges may have more than one osculum

osmol - unit of osmotic pressure

osmoregulation - the process of controlling the amount of water in tissues and cells

osmosis - the passage of water through a semipermeable membrane from a solution with a lower concentration of solute to one with a higher concentration of solute

osmotic pressure - the pressure that is needed to counteract the osmotic passage of water molecules across a semipermeable membrane into the more concentrated solute

osmotroph - an organism that obtains nutrients through the active uptake of soluble materials across the cell membrane

osseus - bony

ossicle - one of numerous small calcareous structures that form the exoskeleton of certain echinoderms. Their size,shape and location are highly variable, and they may be movable or fixed in position. They may appear as thin fused plates. In brittle stars they form "vertebrae" in the arms, which with together with their attached muscles, gives the brittle star its serpentine ophiuroid motion. Sea cucumbers hve microscopic ossicles embedded in their dermis. The small, sound transmitting bones in the vertebrate middle ear are also called 'ossicles'

ossified - made or converted into bone

ostium - in sponges, a microscopic pore through which water enters the sponge body

ostracitoxin - a toxin, discharged with mucus into the water, by trunkfishes of the genus Ostracion when they are stressed

otolith - a calcareous structure of the inner ear of some animals, such as fishes, that functions in the detection of changes in gravitational forces relative to orientation. Otoliths are used to determine the age of fishes by counting the number of annual rings deposited

out year - a fiscal year after the fiscal year covered in a budget

outbreak - the sudden appearance of a disease in a specific geographic area or population

outbreak - a sudden appearance or increase in something, such as an outbreak of a particular disease in a coral community

outer slope - a synonym of reef slope. It is sometimes used to represent the lower reef slope

outrigger - a floatation device attached to one or both sides of the hull of a boat to help prevent a capsize

overexploitation - the removal of individuals or biomass from a population at a rate greater than the population is able to compensate for with its own recruitment

overfishing - the removal of marine organisms from the environment at a level that is not sustainable. A reduction of this level would, in the medium term, lead to an increase in the total catch

Overseas Territories (OTs) of the United Kingdom (UK) - The UK’s 14 OTs are located in practically every geographic region of the world, and are home to unique ecosystems, including rare and globally threatened species, many of which are found nowhere else in the world. The OTs are: Turks and the Caicos Islands, Sovereign Base Areas of Akrotiri and Dhekelia, South Georgia and the South Sandwich Islands, Saint Helena, Ascension and Tristan da Cunha, The Pitcairn Islands, Montserrat, Gibraltar, Falkland Islands, Cayman Islands, The British Indian Ocean Territory (BIOT), British Virgin Islands, The British Antarctic Territory, Bermuda, and Anguilla

ovicell - the brood chamber of a bryozoan (Ectoprocta), usually located at the distal end of the maternal zooid.  Embryos are brooded until they develop into non-feeding larvae, which swim briefly, then settle and metamorphose to found a new colony 

ovigerous - carrying eggs or modified for carrying eggs

oviparity - the reproductive mode where eggs are released from the body and later hatch

Image of sea turtle laying eggs

A marine turtle depositiong eggs (oviposition) on a tropical beach. (Photo: Seaturtle Preservation Society of Brevard County, FL)


oviposition - the process of depositing eggs

ovoid - egg-shaped

ovoviviparity - the reproductive mode where the eggs hatch and develop in the female's reproductive tract (or a specialized pouch in the males of some species), are not nourished in any way by the female, and are free-swimming when released from the parent

ovulation - the release of an egg from the ovary

ovum - the mature female germ cell (egg; female gamete)

oxidant - an oxidizing agent

oxidation - the combination of a substance with oxygen. Oxidation can also describe a type of reaction in which the atoms in an element lose electrons and the valence is correspondingly increased

oxidative stress - a process whereby the metabolic balance of a cell is disrupted by exposure to environmental substances, resulting in the accumulation of free radicals, which can damage components of cells' membranes, proteins or genetic material by "oxidizing" them

oxygen isotope ratio (18O) - an expression for the ratio of the 18O to 16O atoms in a sample relative to a standard, defined as: δ18O = (18O/16O sample - 18O/18O standard)/ 18O/16O standard

oxygen isotopes - oxygen atoms that have the same atomic number (protons) but different mass numbers (and different numbers of neutrons). The two stable isotopes of oxygen are 16O and 18O

ozone - a gaseous molecule that contains three oxygen atoms (O3), instead of the usual two (O2). Ozone can exist either high in the atmosphere (stratosphere), where it shields the Earth against harmful ultraviolet rays from the sun, or close to the ground (troposhere), where it is the main component of smog. Ground-level ozone is a product of reactions involving hydrocarbons and nitrogen oxides in the presence of sunlight. Ozone is a potent irritant that causes lung damage and a variety of respiratory problems

ozone shield - the ozone (O3) layer in the stratosphere that gives protection to the Earth's surface because of intense absorption of harmful solar ultraviolet radiation by the gas

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