This glossary was developed as a collaboration between the scientists of the GEOHAB (Marine Geological and Biological Habitat Mapping) and WoRMS (World Register of Marine Species) communities. It was published online on WoRMS from 2010 and comments by users led to additions and corrections. As it was removed after a few years with the intention of being replaced by an improved system it is here republished. The glossary does not intend to provide a review or history of all uses of particular terms, nor how they may be used in other fields of research. The definitions are those recommended for use in marine biology, ecology and geology. Where a term has different uses that the editors feel require clarification, then these will be included.  At present, this glossary excludes terminology specific to the following areas: names of marine species and higher taxa (see WoRMS); place names (see gazetteers at Marine and GEBCO); taxonomy; physiology; archaeology; fisheries; legal and regulatory terms; acronyms. The glossary could be expanded should experts offer to do so and where no existing online peer-reviewed glossary exists.

To search for a word use Ctrl F on keyboard.

Please cite as Costello MJ, Harris P, Pearce B, Fiorentino A, Bourillet J-F, Hamylton S (editors) 2019. A glossary of terminology used in marine biology, ecology, and geology. Version 2.0.


Without life.


The great depths of the oceans, usually considered to be depths of 2000 to 6000 m, a region of low temperatures, high pressure and an absence of sunlight.

Abyssal  Hills

Tract, sometimes extensive, of low (100-500 m) elevations on the deep sea floor.

Abyssal Plain

An extensive, flat, gently sloping or nearly level region at abyssal depths.


Open water habitat of the abyss. Distinct from the benthic (seabed) habitat.


Process of sediment build-up.

Acoustic Backscatter

A method of detecting discontinuities in the water, often used for current and turbidity measurements and for detecting changes in the character of the seafloor.


A process by which species evolve, and by which individuals adapt, their growth and/or behaviour to better survive and grow in a particular environment.

Adaptive Radiation

Process of new species evolving to adapt to different environmental conditions.


The horizontal movement of water, or a property of water through such movement (e.g., temperature change through the movement of water).


Reworking of the sediment by waves and currents.


The collective term for sand, gravel and crushed rock typically used by the building industry. They can be compacted to firmly fill a space and are often bound together with cement (to make concrete) or bitumen (for road surfacing).


A collection of animals or plants gathered or clustered together.


The simplest plants; maybe single-celled (such as diatoms) or quite large (such as seaweeds). Live in salt or fresh water and on land.

Allopatric Speciation

The process through which species arise while separated geographically.


The number of species in a sample.

Aphotic Zone

The part of the water column where light does not penetrate.


Gently dipping seabed surface comprised of sediment found at the base of a slope; commonly the product of slumping (sediment failure) of a steep slope.


The study of historic and prehistoric communities.


A group of adjacent islands.


A neutral substitute for “community” but implying no necessary interrelationships among species; also called species assemblage.


An annular reef enclosing a lagoon in which there are no promontories other than reefs and islets composed of reef material.


Elevation of the seabed over which the depth of water is relatively shallow. Sand banks are sedimentary features longitudinal to the current.

Barrier Islands

Elongate offshore islands or sandbanks oriented parallel to the coastline which may form a lagoon between the island and the coast and which protect the coast from prevailing wave action.


Depression, characteristically in the deep sea floor, more or less equidimensional in shape and of variable extent.


Deep-sea, variously attributed to range from 200 m to 2,000 m or 4,000 m depth.


Seafloor elevations and the variations in water depth; the topography of the seafloor.


The zone of open water below the euphotic (well-lit) and mesopelagic (poorly lit) but above the abysso-pelagic.

Bay, Embayment

A body of water partly enclosed by land.

Beach Draw Down

Removal of sediment deposits from a beach by waves and currents.

Beach  Recharge

Placement of aggregates on beaches to replace that lost by erosion (beach nourishment) or to protect coastal resources.


Sedimentary features of the seabed oriented transverse to flow direction; ripples, dunes and sand waves.

Bedload Transport

The transport of sediments by currents, rolling or hopping along the seabed.

Bejernick’s Law

“Everything is everywhere, the environment selects”. This means that species have the potential to be everywhere over time but that the environment selects which species live in a place. While strictly untrue, there is evidence that it applies relatively more to microscopic than larger organisms.


Associated with the seafloor.

Benthic Boundary Layer

A zone of the water column close to the seabed within which sediment (bedload) transport occurs.

Benthic Ecology

The nature and distribution of organisms on or within the seabed and the interactions between them and their environment.

Benthic Fauna

Animals that live on or within the seabed.


The collection of organisms living on or within the seabed.


A narrow shelf, bank, or ledge at the top or bottom of a slope; in coastal geomorphology a sedimentary feature (ridge) built along the coast, above the level of high tide, by storm wave action.


The turnover of species composition between samples in a geographic area.


The “living community”; formulated in 1877 by Karl Möbius; describes the organisms living in the same habitat, and is a now used synonymously with the term “community”.


The Convention of Biological Diversity definition encompasses the variation within species (genetic, phenotypic), between species, and of ecosystems (habitats, productivity, processes). Most commonly used to describe variation between species.

Biogenic   Habitat

Physical habitat created by living organisms, such as coral reefs, oyster beds, tubeworm reefs, kelp beds, seagrass beds.

Biogeographic Boundary

The area across which species composition changes more rapidly than within a biogeographic region. Not to be confused with habitat boundaries and ecotones.


Mound-shaped deposits of rock and sediment produced by marine organisms. Coral reefs and Halimeda banks are well-known examples.


The mass of organisms in a sample measured as weight.


A large geographic area dominated by a plant life-form that provides physical habitat for other species. Used on land for deciduous forests, tundra, grasslands. Comparable marine biomes are seagrass beds, kelp and mangrove forests, and coral reefs with symbiotic algae.


A spatial representation depicting the boundaries of hierarchical geographic areas considered useful for environmental management.


All living organisms, including fauna and flora, within a defined area.


A zone of transition between core provinces used in an Australian bioregionalisation scheme. Biotones are not simply “fuzzy” boundaries but represent unique transition zones between the core provinces.


A habitat with a characteristic community. Also called facies.


Sediment grains > 256 mm diameter.

Boundary-Layer Currents

Currents at the sediment-water interface.


Neither freshwater nor full-salinity seawater. Typically with 1-20 ppt salinity. See Estuarine.


Organisms that burrow in the substratum, be it sediments or rocks.


A relatively narrow, deep depression with steep sides, the bottom of which generally has a continuous slope, developed characteristically on some continental slopes.


A small, low elevation sandy island formed on the surface of a coral reef.


A narrow sea area, often with strong currents, between island and mainland, between two major islands, or created by currents in seafloor sediment. (e.g., deep-sea channel).


Organisms that create energy from chemical reactions, as distinct from phototrophs which use sunlight.


Seabed on the Continental Shelf dominated by animals, where benthic algae are rare or absent. It is usually seasonally stratified, and the effect of wave action is limited to storms. Typically considered between 50-200 m depth range.


A geographic gradient in some variable, such as a species attribute (e.g., colour).


Particles of between 0.00024 mm to 0.0039 mm in size, or all particles < 0.004 mm in diameter. Smaller than silt. In contrast to silt, clay has colloidal properties (i.e. particles unlikely to settle when floating in a liquid). Mud is comprised of clay and silt.


Sediment grains 64 to 256 mm in diameter

Cold Seep

Area of seafloor where gases and fluids are released but not hot water (hydrothermal vent).


Animals that live as a part of one physically connected colony, such as corals, bryozoans and some tubeworms and tunicates.


Process of organisms establishing themselves in an environment where they were not already present.


Organisms of different species that live together, sharing space or food, whereby at least one partner benefits from the association and neither have detrimental effects on the other (i.e. Not parasitic).


A group of species that are assumed to be interdependent (though this is often not demonstrated). The term can be used in a variety of hierarchies. Communities at larger scales can be progressively subdivided, such as spatially, taxonomically and trophically, to finer scales.

Competitive Exclusion

One species excludes another due to being a superior competitor for a resource.

Competitive Release

The absence of a competitor allows a species to increase in abundance and/or distribution.

Continental Margin

The  submerged  prolongation  of  continental landmass  consisting  of  the  seabed  and subsoil of the continental shelf, slope and rise but not the deep ocean floor.

Continental Rise

A gentle slope rising from the oceanic depths towards the foot of a Continental Slope of between 1 and 2 degrees slope.

Continental Shelf

Seafloor that is the submerged part of a continent, extending from the low water line to a depth at which there is usually a marked increase of slope towards oceanic depths; often generalized to about 200m depth.

Continental Slope

Surface dipping seaward from the continental shelf edge typically with a slope of >2 degrees and extending to the upper limit of the continental rise, or the point where there is a general decrease in steepness.


The vertical movement of water as part of its stirring caused by differences in density.

Coral Reef

(see also “reef”) Reefs developed through biotic processes dominated by corals.  In geology, sedimentary features, comprised of macroscopic skeletal framework, built by the interaction of organisms and their environment, that have synoptic relief and whose biotic composition differs from that found on and beneath the surrounding sea floor.

Coral  Reef  Platform

The flat or nearly flat area of considerable extent, dropping off abruptly on one or more sides, extending around a coral reef in the photic sea surface waters and composed of live and/or dead coral reef.


Narrow geographic areas considered to facilitate the dispersal of species from one area to another across an otherwise unsuitable environment.


In oceanography, an obsolete term which was generally restricted to depths greater than 6,000 m.


Seaward prograding sediment body deposited at the mouth of a river.


A species living on or near the seabed. Commonly used for near-seabed living fish.

Deposit Feeding

Animals that feed on sediments and other material deposited on the seabed.

Digital Terrain Model  (DTM)

Also Digital Elevation Model (DEM). A three-dimensional grid representation of the shape of the earth (seafloor or land) surface.


Biological or ecological diversity is most commonly measured as the number of species, also called species richness. Many other indices of diversity include the relative abundance of species as well as species richness in their calculation. These indices may emphasise the dominance or evenness of the abundance of species in a sample. See alpha, beta, gamma diversity, and biodiversity.

Dominant Species

A species that dominates a sample or area by virtue of its abundance, biomass, size, or conspicuousness.


The process by which surface waters sink to greater depths in the ocean. Important mechanisms are cooling of surface waters and/or addition of salt through the production of sea ice in polar seas.


Sedimentary bedforms larger than ripples, greater than 0.6 m in wavelength and greater than around 10 cm in height. Dunes are mostly asymmetrical in profile, with a gentle up-current stoss slope and a steeper down-current lee slope which may be at the angle of repose of the sediment. Dune crestlines may be either linear (two-dimensional) or non-linear (three-dimensional, barchan-shape) in plan view.  Large dunes may have smaller dunes superimposed upon them. (see also “sand wave”)

Dysphotic Zone

The part of the water column, below the euphotic zone, that receives low levels of sunlight but insufficient to support plant growth; see also mesopelagic.


The combination of species, their interactions, and the physical and chemical processes in their environment in a defined area.


A transition zone between two ecologically distinct areas such as habitats, biotopes or ecosystems.


Form of growth of animals and plants with a tough or hard texture (the crust), over rocks and other materials.


Species only known to occur at one location or area of defined extent, such as a country or sea area.


The collection of organisms living upon the seabed, including animals (epifauna) and plants (epiflora) living on the surface of the seabed or on other animals and plants that live there.


Animals, plants and microbes living on the seabed.


The collection of organisms living in well-lit (euphotic) surface waters of the open ocean; above the mesopelagic.


Animals that can wander, are mobile. As distinct from sessile and sedentary.


Elongated and comparatively steep (sometimes vertical) slope separating flat or gently sloping areas at different average depth.


The seaward portion of a drowned valley system which receives sediment and water from both fluvial and marine sources giving rise to a unique sedimentary regime and areas of variable salinity.


The area between the low and high tide marks, and the supralittoral and sublittoral fringe. Also called mediolittoral, tidal flat, and hydrolittoral.

Euphotic Zone

The upper part of the water column that receives sufficient light to allow plant growth.


Organisms that can live in a wide range of salinities.


The environmental problem of excessive plant growth (e.g. Planktonic or benthic alga) leading to oxygen fluctuations (hypoxia, anoxia, supersaturation), and where dead and rotting plants create a public nuisance. Typically results from the release of nutrients from human activities.


Also called equitability, refers to how the abundance of species is distributed in a sample or group of samples. If all species have equal abundance then evenness is maximised. The inverse of evenness is dominance.


The disappearance of a species from Earth.


The disappearance of a species from a defined geographic area.


Relatively smooth, fan-like, depositional feature normally sloping away from the outer termination of a canyon or canyon system.


Animals; covering both invertebrates and vertebrates.


The unobstructed distance of ocean over which wind has blown to create observed surface waves.


Small particles such as sand and silt.


A long, narrow, deep inlet of the sea between steep slopes, formed by glacial erosion. Sometimes spelt “fiord”.


A strip of relatively flat and normally dry land alongside a stream, river, or lake that is covered by water during a flood.

Food Web

A term used to describe the food relationships between members of a community.

Founder Effects

The consequence of founding parents genes for their progeny. With only a few founders, the species may be considered to have gone through a genetic ‘bottleneck’.


The breakup of an area of habitat such that what was one population of a species is now several disconnected populations which may consequently be at greater risk of extirpation.

Frequency Range (Hz)

The wavelength of sound measured in cycles (wavelengths) per second; one Hertz (Hz) is a sound wave that travels at one cycle per second.


In oceanography, a vertical hydrographic boundary between two water masses which are distinguished by their temperature, salinity and/or productivity.


The total number of species in a large geographic area. See alpha- and beta-diversity.

Gene Flow

Exchange of genes within a population or between populations that reduces genetic diversity.

Genetic Drift

Accumulation of random mutations of alleles over time with a consequent change in genetic make-up.


The natural range (diversity) of geological (rocks, minerals, fossils), geomorphological (landforms, processes), and soil (sediment) features. It includes their assemblages, relationships, properties, interpretations and systems.

Geophysical Anomaly

An abrupt change in the geophysical features of the seabed, potentially associated with wrecks and archaeological sites.


The study of the physics of the earth. Geophysical survey techniques use physical properties themselves (e.g., magnetism) or apply properties to see how the earth affects them (e.g., radar), to determine something about the earth’s structure.

Glacial Outwash

Deposits of material washed out from glaciers by rivers.


The formation, movement and recession of glaciers.


Determination of particle size composition of sediments.


Sediment grains greater than 2mm in diameter.


The behaviour of animals that live in groups, but can survive singly.


Breakwaters used to reduce the rate of transport of beach deposits.


An association or classification for a group of species, often not taxonomically related, that share or use a resource in a similar way (e.g., sediment living macrofauna, gelatinous zooplankton), or live in the same part of the environment (e.g., plankton, benthos).


Narrow channels of one to tens of metres in width, created by moving water.


Seamount having a comparatively smooth flat top formed by wave erosion, coral reef growth, or aerial erosion and subsequent subsidence below the sea level. .


The environment where an individual, species or group of species live that can be repeatedly found in nature.


Pertaining to depths of the ocean greater than 6000 m.


Open water habitat of the hadal region. Below the abyssal.


Inlet with a port facility.

Haul-Out Site

A site where seals come onto the shore or sandbanks.


Local circular depression, often steep-sided, of the seafloor.


Epoch of geologic time spanning the last 11,700 years from the end of the Pleistocene Epoch (and the end of the last ice age) to the present.

Hydrocarbon Seep

Feature of the seafloor where hydrocarbons are being released through the seabed sediments.

Hydrodynamic Processes

Processes associated with waves, tides and currents.

Hydrothermal Vent

A hot water spring on the ocean floor.


Animals that live close to the seabed but are not usually on it (i.e., epibenthos, epifauna) or in it (i.e., endobenthos, infauna). Typically used for crustaceans but in theory could include other taxa. The term demersal is used for fish.


The arrival of organisms to a place, which may result in their establishment (colonization).


Animals living within sediments.


Always submerged, below the low-tide within the euphotic zone. Seabed often dominated by algae, with variable water column temperatures.


Semi-enclosed area of the coast. Related terms include sea lough (Ireland), sealoch (Scotland), fjord, fjiard, ria, voe.


Animals that live within other organisms but are not considered parasitic. Similar to commensal (“living with”) but usually used where the relationship has yet to be determined.


Generally within 5 km of the coastline and < 50 m depth. Same as coastal seas. In the UK, the term ‘Inshore’ applies specifically to the area within 6 nm of the coast where marine activities are managed at a local or regional scale.


Organisms living in the space between grains of sediments. See also meiofauna.

Intertidal Zone

The area between the high-water mark and low-water mark that is submerged at high tide and exposed at low tide. Often used synonymously with seashore.

Island Biogeographic Theory

Holds that the number of species in a location is a result of the interaction between the number colonizing and going extinct, such that that islands that are larger and near a mainland source for colonist will have more species than smaller and more remote or isolated islands. This balance between colonization and extinction is also termed ‘Species equilibrium theory’.


Land surrounded by water.


Relatively small (500 to 1000 m tall) isolated elevation of a rounded shape; a small seamount. Larger than a sea-hill.


A speed of one nautical mile (nm) per hour.


A shallow marine (sometimes brackish to hypersaline) coastal water body, receiving little – if any – fluvial input, separated from the sea by a restricted inlet usually having a sill.

Latitudinal Gradients

Changes in the number (richness) of species with latitude.


Between upper and lower tidemarks, exposed to air at the lowest tides. In marine ecology is equivalent to intertidal and seashore. In wider literature may refer to coastal land and subtidal areas down to 200m.

Littoral    Drift

The net movement of material along the shore under the influence of prevailing waves and currents.


Ecological patterns across geographic areas.


Fauna typically retained on a 1 mm sieve, visible but not usually identifiable to species level by eye.


Also known as a fluxgate gradiometer. A remote sensing instrument capable of identifying subsurface archaeological features by measuring the difference in their magnetic properties against the surrounding soils.

Managed Retreat

Areas where the sea is allowed to inundate sites formerly protected by sea defences.

Marine Protected Area (MPA)

Defined by the IUCN as “any area of intertidal or subtidal terrain, together with its overlying water and associated flora, fauna, historical and cultural features, which has been reserved by law or other effective means to protect part or all of the enclosed environment”. See IUCN for updates.


Large animals easily identified by eye without magnification; e.g. Mammals, birds, fish, sharks, turtles, lobsters, starfish. Larger than macrofauna.


Fauna retained on a 0.1 mm sieve but that pass through a 1 mm sieve. Smaller than macrofauna.


Referring to the poorly lit open water habitat below the epipelagic (euphotic) and above the bathypelagic. Also called the twilight zone.


A population that exists in a connected complex of spatially discrete populations, such as in habitat fragments.


Bacteria and small unicellular organisms not visible to the naked eye or retained on standard sieves.

Mid-Domain Effect

The proposition that the environment constrains species ranges such that more ranges will overlap in the tropics, and thus more species will occur there.


Measures to minimize, reduce or eliminate impacts.


Sediment grains < 0.063 mm diameter. Includes silt and clay.

Multibeam Data

Bathymetric and backscattered data derived from multibeam echo sounder.


Narrow channels of water forming the entrance to inlets, often with shallow sills and called Rapids.

Neap Tide

The minimum amplitude of the astronomical tide (every 14 days between the full and new moon).


An aquatic organism, such as whales, turtles, fish, squid, and krill (euphausiids) that can swim powerfully enough to move against currents.


Pertaining to the water column overlying the continental shelf.

Net Transport

The residual movement of sediment after its oscillatory movement on tidal currents, or under the influence of waves.


The collection of organisms living on the sea surface (epineuston) or within the top 20cm of the surface (hyponeuston).


The range of environmental conditions (such as temperature, salinity, nutrients) within which a species can exist and reproduce. Sometimes defined as everything a species is or does. The preferred (or fundamental) niche is the one in which the species performs best in the absence of competition or interference from extraneous factors.


Defined as unwanted sound and is usually measured in decibels (dB) referenced to an acoustic source frequency dB(A).

Nursery Ground

An area of importance for juvenile animals and plants.


Referring to the open ocean, away from coastal waters.


Open ocean distant from land, typically with stable water column characteristics (stenothermal, stenohaline), permanently stratified, beyond freshwater influence, without benthic algae. Generally > 5 km from the coastline.


An animal that eats both animal and plant food.

Open Coast

Any part of coast not an island or inlet.


Sediment (often sand) deposited on top of local sediments OR deposits of soil and rock that are removed to gain access to ore deposits at open cast mines.


Areas of rough water (relatively higher surface waves) generated by sudden changes in seabed topography, such as sandbanks and deeps.

Oxygen Minimum Zone

Area of the ocean with seasonal or permanently low oxygen conditions.


Earlier stone age period (‘old stone age’).


Sediment that exhibits attributes of a previous depositional environment, but also attributes of the modern environment.


Organisms that feed on a host but do not normally lead to its death.


Female animals that can produce fertile eggs without fertilization from sperm.


Sediment grains 4 mm to 64 mm diameter based on the Cailleux and Wentworth classification.


Organisms, relating to or living in the water column of seas and oceans (as distinct from benthic). Includes nekton and plankton.

Phanerogame  meadow

Extended or patchy areas of seagrass in the Mediterranean Sea colonized by Posidonia oceanica (L.), and/or Cymodocea nodosa (Ucria), In other areas formed by the seagrasses Posidonia, Zostera, or related species.


Organisms (chemoautotrophs) that generate energy using sunlight. See chemoautotroph.


The apparent characteristics, outward features, or appearance of ecological communities often characterized by dominant species.


The physical geography of the land and seabed. See terrain, topography.


Microscopic free-floating plants that drift in sunlit surface waters.


High tower or spire-shaped pillar of rock or coral, alone or cresting a summit. It may extend above the surface of the water. It may or may not be a hazard to surface navigation.


The collection of organisms, often microscopic, that are suspended freely in the water column.


Flat or nearly flat area of considerable extent, dropping off abruptly on one or more sides.


Epoch of geologic time during the Quaternary period extending from the end of Pliocene epoch around 2.6 million years ago up to the beginning of the Holocene epoch, 11,700 years ago.


The collection of organisms that live on the ocean surface.


Small (1-10’s m) circular depressions in the seafloor caused by the release of a gas or liquid (e.g., hydrocarbon seeps).


From the Russian word for “lake”, an area of open water surrounded by sea ice.

Primary Production

Production of organic matter by converting light or chemical energy from primary materials, such as photosynthesis and chemosynthesis.


Reworking of the sediment by waves and currents towards deeper ocean due to sea level fall.


Period of geologic time extending from the end of Pliocene epoch around 2.6 million years ago up to the present; a collective term for the Holocene and Pleistocene epochs.

Rapoport’s Rule

The proposition that species geographic ranges increase with latitude and elevation (and perhaps depth), and thus there are more species in the tropics.


A biogeographic region defined by an assemblage of species distinct from other regions, with characteristic endemic (geographically rare or localized) species. Distinct from habitat which is characterised by its dominant species (often common species), and biome (see above).


The re-establishment of marine populations in an area from which they had been lost.


The influx of new members into a population by either reproduction or immigration.


Hard substrata raised from the seabed that provide a substratum and/or cover for marine life. May be formed by rocks, coral, shells, tube-worms, and other organisms. Also, used in hydrography to refer to hard substrata that may be a hazard to safe navigation.

Reef Ridge

Long, narrow elevation with steep sides composed of live or dead coral.

Relaxation Effect

The consequence of habitat fragmentation that splits populations such that some are extirpated, and thus the species richness declines following fragmentation. Island Biogeographic Theory predicts a loss of species richness due to a decreased habitat area.

Relaxation Time

The time required for species and populations to adjust to changed environmental conditions.


Sediments that were originally deposited under different environmental conditions than those occurring today. See also “palimpsest”. The term is also used for relict populations of a species “trapped” in an environment that is a refuge of former more widespread environmental conditions that allowed the species a wider distribution range.


The variation in the elevation (or depth) of the seafloor.


(a) Long, narrow elevation with steep sides. (b) Long, narrow elevation often separating ocean basins. (c) Linked major mid-oceanic mountain systems of global extent.


Ecologically is a ‘hard substrata’ with an epibiota but where infauna is absent or rare.

Rough Ground

Areas of seabed where there are boulders or biogenic reefs.


The roughness or irregular texture of the seabed.


Broad pass, resembling in shape a riding saddle, on a ridge or between contiguous seamounts.


Sediment grains 0.063 mm to 2 mm diameter.

Sand Dunes

See “Dune”.

Sand Waves

Replaced by the term “dune” in modern usage. Undersea ‘sand dunes’ that may be static or move under the influence of waves and tides and are sub-perpendicular to the current.


Animals that feed on dead animal material, and sometimes also drift algae.


A seabed feature elevated more than 100 m high from the surrounding seabed. Smaller than a knoll and seamount.


An underwater mountain greater than 1000 m in relief above the sea floor, characteristically of volcanic origin and conical form.


Undersea landscapes. Topographic features that reoccur geographically (e.g., seamounts, estuaries, canyons, plains).


Animals that do not normally move, but can if required (e.g. Sea anemones, mussels).


Ecologically are so-called ‘soft substrata’ with infauna, and usually some epibiota.

Sediment Processes

Processes that affect the creation, erosion, transport and deposition of sediments.

Sediment Sink

A site where there is a net accumulation of sediment.

Sediment Transport

Movement of sediment in the water column or on the seabed.

Seismic Data

Acoustic data derived from a low frequency (less than 12 kHz) seismic sound source, typically using compressed air or electric pulses, that produce an image of sediment layers comprising the seabed.

Seismic Waves

Pressure waves generated by volcanic eruptions, earthquakes or explosions that propagate through the earths’ crust; waves that are detected and recorded by seismographs.


Animals attached to the substratum.


Offshore hazard to surface navigation that is composed of unconsolidated material such as gravel or shell.

Side Scan Sonar

An acoustic remote-sensing method of identifying seabed features using a sonar tow-fish that emits sound waves at a low angle of incidence to the seabed.


Seafloor barrier of relatively shallow depth restricting water movement between adjacent basins. In oceanography, the sill depth signifies the depth of water that a water mass must achieve in order to pass between basins.


Particles of between 0.0039 mm to 0.0625 mm in diameter. Larger than clay, smaller than sand. Mud is comprised of clay and silt.


Derived from the phrase “sound navigation and ranging”; method or equipment for determining the water depth by underwater sound (echolocation).


A deep embayment located between offshore islands and the mainland or between islands.


Process of a species being formed from other species.

Species Richness

The number of species that occurs in an area or collection of samples.

Species Saturation

The idea from Island Biogeography Theory that the number of species in an area has a maximum determined by the race of local colonization and extinction; such that if a new species becomes established then an existing species will go extinct.

Species Turnover

The change in species composition over time and/or space. See beta-diversity.

Splash  or  Spray Zone

Area of upper seashore not submerged at high tide but sprayed at high tide by breaking waves.

Spring Tide

The maximum amplitude of the astronomical tide (every 14 days corresponding with the new and full moon)


Organisms limited to a narrow range of salinities. The opposite of euryhaline.

Stepping Stones

Small areas of a habitat that enable a species to disperse across an otherwise unsuitable environment.

Storm  Surge

A major rise in sea level above the normal range due to episodic events such as low atmospheric pressure and high winds.


A channel or gap between an island and the mainland, or two headlands.


Area of upper seashore where loose seaweed and other floating debris is deposited by the falling tide.


In water, where one or more horizontally extended water masses lie on top of each other. They are separated by boundaries based on differences in temperature (thermocline), density (pycnocline) and/or salinity (halocline). See also Front.

Subduction Zone

Adjacent to active plate margins, a place where ocean crust collides with and is subducted beneath continental crust or another ocean to create a ridge and ocean trench complex.


Below the littoral, never exposed to air. Same as subtidal. Includes the infra- and circa- littoral.

Sublittoral Fringe

Transition zone where littoral and sublittoral species occur, sometimes determined by differences in neap and spring low tides.


A substance used as a food source by organisms or enzymes. This usage has been extended to any surface a plant or animal lives upon, whether biotic or abiotic materials. Ecological use favours use of substratum (singular) and substrata (plural) where the surface is for attachment rather than a food source.


Surface (singular) to which an organism grows on or amongst. Substrata is plural.


Uppermost part of shore affected by wave splash but not regularly submerged by the sea. Also called the supratidal, epilittoral, splashzone, spray zone, littoral fringe, and strandline.


A measurable entity that is used to represent, or substitutes for, a more complex element of biodiversity that is more difficult to measure.

Suspension Feeding

Animals that feed on water-borne particulate material, which may include plankton.


A low lying marshy area, such as between sand dunes.


Organisms that both benefit from their association.

Sympatric Speciation

Species that evolve within the same geographic area, perhaps due to specialization on different food resources or seasonal differences in growth or reproduction.

Taxon (Taxa)

A distinct category of organism at any level in the taxonomic hierarchy from species to family to kingdom. Taxa is plural.


Relatively flat horizontal or gently inclined surface, sometimes long and narrow, which is bounded by a steeper ascending slope on one side and by a steeper descending slope on the opposite side.


The physical land surface and seabed.


Derived from the land, as in terrigenous sediment. Usually siliciclastic rather than calcareous  or  calciclastic.

Tidal Range

The amplitude of the tides in a particular area due to astronomical (gravitational forces of the sun and moon) forcing .


The form, relief, shape and texture of the earth’s surface, including the seabed.


Long, narrow, characteristically “V”-shaped in section, very deep and asymmetrical depression of the sea floor, with relatively steep sides.

Trophic Level

The position of an organism in the food chain or “food pyramid,” determined by the number of transfers of energy that occur between the non-living energy source and that level.


Long depression of the sea floor characteristically flat bottomed and steep sided and normally shallower than a trench.


A very fast moving oceanic wave, initiated by an underwater disturbance, such as an earthquake, volcanic eruption or slumping (Japanese for “harbour wave”).


Animals that live in tubes.

Turbidity Current

A dense mixture of suspended sediment and water that flows down-slope under the influence of gravity. Normally constrained to the continental slope and attributed to the formation of submarine canyons.


An oceanographic process by which water rises from the lower depths upwards into shallow surface waters.


Animals that move around.


Animals outside of their normal habitat or environment. They may be searching for new habitats  or  mates.


Relatively shallow, wide depression, the bottom of which usually has a continuous gradient. This term is generally not used for features that have canyon-like characteristics for a significant portion of their extent.


The geographic separation of a population or biota by climatic and/or geological events, typically resulting in the formation of new species.

Water Mass

A volume of water that has defined salinity and/or temperature characteristics.

Wave Refraction

Modification of the angle of waves by seabed features.

Wave Rose

A method of showing the size and direction of waves based on the frequency of occurrence in different quadrants of the compass.


Removal of fine material from coarse ones by winds or currents.


Horizontal areas of vertical height above, and depth below, sea level which has a characteristic fauna and flora. Also called étage.


Planktonic animals; i.e. Animals that live in the plankton and which are unable to move against regional currents.


Further reading

Costello M.J. 2009. Distinguishing marine habitat classification concepts for ecological data management. Marine Ecology Progress Series 397, 253-268.

Harris, P. T. and E. K. Baker, Eds. 2012. Seafloor Geomorphology as Benthic Habitat: GeoHab Atlas of seafloor geomorphic features and benthic habitats. Amsterdam, Elsevier, 947 pp.

International Hydrographic Organization 1953. Limits of oceans and seas. International Hydrographic Organization Special Publication No. 23, 39 pp.

International Hydrographic Organization 2008. Standardization of undersea feature names. Guidelines proposal form terminology. International Hydrographic Bureau, Bathymetric Publication No. 6, 24 pp.

Lincoln RJ, Boxshall GA, and Clark PF. 1998. A dictionary of ecology, evolution and systematics. 2nd  Edition. Cambridge University Press, Cambridge.

Foucault A. and Raoult J.-F., 2001. Dictionnaire de Géologie. Guides pédagogiques Régionaux, 5e éd. Dunod, Paris, 379 pp.

Michel J.-P. and Fairbridge R.W., 1980. Dictionary of Earth Science English-French French- English. Dictionnaire des Sciences de la Terre Anglais-Français Français-Anglais. In: Michel&Fairbridge (Editor). Masson Publishing USA, New York, pp. 411.

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