Glossary of Terms

Glossary of terms used in this web application.


the collective term for sand, gravel and crushed rock.
Aggregate extraction
the removal of marine aggregate from the seabed by means of a dredger
All-in cargo
a cargo taken aboard a dredger without alteration of the Gravel:sand ratio by screening
a group of small crustaceans recognised by their laterally compressed bodies
Anchor dredge
a non-quantitative dredge used to sample organisms from the seabed
segmented worms
under human influence
soft-bodied animals that include sea-squirts. Generally attached to rocks.
the processes of recolonisation and growth that lead to the re-establishment of a community following disturbance


small crustaceans encased in a calcareous shell, usually attached to shells and rocks on the seabed
the topography of the seabed
material that is placed on beaches to supplement the sand, pebbles and rocks
Beam trawl
a trawl that is held open with a beam – commonly used for collection of fish and shellfish on the surface of the seabed and in the near-surface sediments
sand sheets, ribbons and sand waves on the seabed
Benthic ecology
the nature and distribution of organisms on the seabed
Benthic fauna
animals that live on the seabed
the community of animals and plants that live on the seabed
the range of species that comprise a particular community or habitat
Biogenic reefs/concretions
aggregates of species that together form a hard substrate
Biological Traits
characteristics of an organism that control its vulnerability to disturbance and ability to recolonise and grow
the mass (weight) of organisms in a community
a distinctive community of interdependent organisms that characterise a particular habitat type
Bipinnaria larva
the early planktonic larval stage of a starfish
Bivalve mollusc
a mollusc with two hinged valves (shells)
Brachiolaria larva
the late planktonic larval stage of a starfish
Branchial basket
the gas-exchange and filtration feeding system of tunicates (sea-squirts)
larval development of offspring takes place within a brood pouch
mainly colonial animals that can form encrusting growths or leaf-like colonies attached to rocks and stones on the seabed
the process whereby an animal reproduces asexually as an outgrowth from the body of the parent
Byssus drifting
a mechanism whereby certain juvenile bivalve molluscs migrate by means of sequential attachment and detachment of byssus threads
Byssus threads
threads secreted from the foot of bivalve molluscs to attach themselves to substrata


Characterising genera
organisms that together account for the similarity of samples from a particular community
large stones-boulders (cf Folk classification)
Cohort analysis
analysis of the size-frequency of individuals in a population to estimate growth rate, age and recruitment
Colonial animal
organisms produced asexually which remain associated with each other to form a colony.
the establishment of marine communities by organisms
Community composition
the relative species variety, population density and biomass
Consent process
the regulatory process by which consent for a dredging licence is obtained
Conservation status
an assessment of the significance of an area for wildlife resources and habitats protected under conservation law
shellfish such as crabs, lobsters and prawns
the larva of an ectoproct bryozoan
Cypris larva
a late-stage larva of a barnacle


Dependent species
species that depend on the presence of other species for their occurrence in a particular habitat
Deposit feeders
organisms that feed on fragmented particulate organic matter deposited on the seabed or within the deposits– detritivores
Designated habitats
habitats protected under Directive 92/43/EEC The Habitats Directive
Designated species
species protected under Directive 92/43/EEC The Habitats Directive
fragmented organic matter, derived from the decomposition of plant & animal remains
simple plant cells that can occur in chains. They form the main component of the phytoplankton and also occur on the surface of the seabed and in shallow sediments
Dispersal potential
the degree to which the animal can be dispersed in the larval stage
a method of expressing the relative contribution of different species to the population density of a community
the part of the dredge pipe that is in contact with the seabed and houses the centifugal pump
the action of removing material from the seabed
Dredge ‘zoning’
management of marine aggregate dredging such that dredging is confined to small zones within the licence area.
Dredging footprint
the area of seabed that is affected by dredging
Dredging intensity
the frequency that a particular area of seabed is dredged
Duration of Impact
the time over which an impact occurs used as a component of risk assessment for environmental resources


organisms such as starfish, sea urchins and sea cucumbers
the planktonic larva of a sea urchin (Echinoid)
a community of organisms & their physical environment acting as an ecological unit
an organism that lives as a parasite inside the body of another (the host)
the process by which relatively slow-moving and sedentary organisms are drawn in by a suction pump
Environmental Impact Assessment (EIA)
an assessment of the environmental resources, their sensitivity to disturbance and proposals to minimise disturbance as required under the EU environmental impact Directive.
animals or plants that live on the surface of the seabed
Epibiotic or epizoic
living attached to the surface of another organism, without any detriment or benefit to the host
animals that live on the surface of the seabed
growth of animals and plants on the surface or rocks shells and stones
growing on the surface of rock
attached to sand particles
the reproductive part of the body of polychaetes that contains the gametes and which swarm into the water column at a single episodic event at the end of the life of the adult
Equilibrium communities
communities with a slow rate of growth and reproduction (‘k-strategists’) that are often controlled by complex biological interactions
External fertilisation
gametes from both genders are released freely into the water column where fertilisation takes place


animals both invertebrates and vertebrates
the potential number of gametes (reproductive units) produced
organisms that feed by filtering suspended particulate matter from the water column
small particles such as sand and silt discharged or mobilised by the dredging and sorting processes
Fisheries resources
all aspects of the nature and abundance of exploitable fish and shellfish
demersal fish such as plaice, sole and flounder
Folk system
a system of classification of sediments based on particle size composition (Folk, 1954). See Figure 1.
Food web
a term used to describe the food relationships between members of a community


reproductive units (male or female)
plural of genus
the taxonomic discrimination comprising the first half of the scientific name of an organism
reproductive organ – source of gametes
having separate sexes (cf. hermaphroditic)
the particle size composition of deposits
coarse material of a size between coarse sand and pebbles (cf Folk classification)
Growth ring
a method of estimating the age of an organism based on annual variations in growth. Used mainly on mollusc shells


the summed physical and biological features of an area that distinguish it
Hamon grab
a type of grab used for sampling seabed deposits
the animal can produce both male & female gametes either at the same time or sequentially
pertaining to the movement of water
small plant-like colonies of polyps that live attached to stones and shells on the seabed


In situ material
material in an undisturbed condition on the seabed
animals that live within the deposits on the seabed
Intermediate genus
a genus which may recover to an adult population within an intermediate period of time
Intertidal mudflats
areas of seabed that are alternately covered and uncovered by the tide and which comprise mainly muds
a measure of the ability of an organism to tolerate environmental stress
animals without backbones worms, molluscs etc.


Joint Nature Conservation Committee (JNCC)
-The Joint Nature Conservation Committee is the UK Government's wildlife adviser, undertaking national and international conservation work on behalf of the three country nature conservation agencies English Nature, Scottish Natural Heritage and the Countryside Council for Wales.
the young post-larval stages of animals
Key faunal species
animal components considered of importance in defining the community
stages that hatch from eggs
Larval mode
the type of larva – whether short-lived, lecithotrophic, or planktotrophic
Lecithotrophic larvae
larvae that are provided with yolk and use this as an energy resource rather than feeding on external sources
Licence Area
the area of seabed within which a licence for aggregate dredging has been granted
Life history
the life stages through which an animal or plant progresses from “birth” to death
the period from “birth” to death


larger animals generally defined as those retained on a 1mm mesh sieve
Marine Aggregates
sand and gravel deposits on the seabed
Marine Protected Areas
areas designated under the 1998 OSPAR Annex V on the Protection & Conservation of the Ecosystems & Biodiversity of the Maritime Area
the ‘jellyfish’ stage in the life-cycle of hydroids
a late larval planktonic stage of a crab
measures to reduce or eliminate impacts
a large group of animals including snails, bivalves and squid
Muddy sands
sands that contain a proportion of mud
Multivariate Analysis
a statistical procedure that compares similarities and differences between communities using many different features including the type and number of organisms


Natura 2000
a European network of SACs, SPAs and other protected sites
Nauplius larva
an early stage larva of crustaceans such as barnacles
Neap tide
the minimum amplitude of the tide (each 14 days between the full and new moon)
Nursery ground
and area of importance for juvenile animals including invertebrates and fish
Obligate cross-fertilising hermaphrodite
animals that can produce both male & female gametes but require external cross-fertilisation in order to reproduce
a ‘soft coral’. These typically grow attached to wrecks, cobbles & other hard surfaces
Ophiopluteus larva
the larva of a brittle-star
Opportunistic species
small fast-growing organisms with a high rate of growth and reproduction (‘r-strategists’) that rapidly recolonise deposits
deposits (often sand) deposited on top of local sediments


organisms that live in the water column
animals and plants that drift in the water column
Planktonic phase
the time that an organism (larva) spends in the plankton
an organism that feeds on planktonic material in the water column.
a simple larval form found in some invertebrate groups such as hydroids
the visible material settling to the seabed following discharge from a dredger
Plume morphology
the shape and configuration of dispersing sediment plumes associated with dredging
a group of marine worms with numerous bristle-like chaetae
Population density
the numbers of organisms in a community
use of food species (prey) by predators
Predation pressure
the extent to which food resources are depleted by animals that prey on them
Primary production
fixing the energy of sunlight into carbon by plants
the yield per unit area. In the case of Fisheries this is often expressed as the value per km² per year


factors that can be measured in a precise way. This contrasts with qualitative, which is a more subjective assessment quantity or quality
the re-establishment of marine communities by organisms
an assessment of the ability of a community to recover following disturbance
the successful colonisation and survival of an organism
Reef assemblage
a group of organisms that are interdependent and which are either attached to a rocky substrate or form one by accretion.
statutory agencies involved in the regulation and consent for aggregate dredging
the recovery and restoration of seabed sediments, topography and biological communities
Risk assessment
a process of assigning ‘risk’ of impacts on resources
Robust genus
a genus that is resilient and may recover within a short period
Ross worm
common name of Sabellaria spinulosa, a species that forms biogenic reefs by accretion that in turn support a range of dependent species
Rough ground
areas of seabed where there are boulders or biogenic reefs


Sabellid worms
marine worms that live in a tube and filter water through a crown of tentacles
Special Areas of Conservation (Habitats Directive)
Sand waves
seabed ‘sand dunes’ that may be static or move under the influence of waves and tides
adjustment of gravel content with mesh screens
organisms that live on or within deposits on the seabed and are unable to move
a measure of response of organisms and habitats to impacts based on the relative robustness and recoverability.
Serpulid worms
a group of polychaete worms that live in a calcareous tube attached to stones and shells
Sexual maturity
the age at which an animal is capable of reproduction
a general term that includes molluscs (whelks, scallops, mussels, cockles etc) and crustaceans (crab, lobster, shrimps)
Side scan sonar
a remote-sensing method of identifying seabed features
Special Protection Areas (Habitats Directive)
Spatial variability
variations in space
Spawning habitat
areas or communities selected for release of eggs
Species inventory
the total species complement of a particular sample or deposit type
Spring tide
the maximum amplitude of the tide (each 14 days corresponding with the new and full moon)
asexual budding individuals of some polychaete worms. Also a term for the tubes that connect hydroid colonies
the type of material on the seabed
Suction-trailer dredger
a method of dredging where material is taken from the seabed by a centrifugal pump whilst the vessel is underway


Tadpole larva
the larval stage of an Ascidian (sea-squirt)
a distinct category of organism such as species, genus or family
Temporal variability
variations with time
features of the biology of an organism such as size, age, and reproductive biology
Traits Diagram
the diagrammatic format used in this report to summarise traits that are relevant to vulnerability and recoverability of marine organisms
a method of fishing using a towed net (trawl)
vessels engaged mainly in fishing by trawl (beam or otter trawl)
Trochophore larva
a free-swimming larval form found in some polychaete worms
Trophic level
a step in the food web from one level to another
Trophic models
estimates of the flow of material (or energy) from one level in the food web to another


Veliger larva
a larval form typical of molluscs with lobed ciliated extensions of the body and a small shell
animals with backbones fish, birds and mammals
the degree to which animals are vulnerable to physical disturbance
Vulnerable genus
a genus which is sensitive to disturbance and which may take a long time for recolonisation and growth
removal of fine material from coarse ones by winds or currents
Zoea larva
a planktonic larval stage of crustaceans (prawns and crabs)
the component polyps that comprise colonial organisms such as bryozoans, hydroids and colonial ascidians
the early stage of development after fertilisation of an egg