• Allows precise measurement of densities of the smaller sediment fauna
• No depth or time limitations on sampling
• Field operation relatively simple
• Standard equipment readily available
• Water turbidity unimportant

Will not reliably sample:

Deep-burrowing megafauna

Large, mobile animals (eg. Nephrops)

Large epifauna at low densities (eg. sea pens)

Gives little information on bottom topography or burrow types

Standard sampling area very small (0.1 m² per grab)

Analysis of samples time-consuming and labour-intensive

Equipment needs hard boat to operate. May be unable to access very shallow areas or enclosed inlets

• Allows first-hand observation at close range
• Allows accurate density measurements of sea floor features (burrow openings, sea pens)
• Allows repeated monitoring of fixed study sites
• Benthic samples can be collected (eg. hand-cores, burrow resin casts)
• Equipment readily available, relatively inexpensive compared with ROVs or underwater video
• Can be carried out from small boats or from the shore, allowing access to very shallow or semi-enclosed waters

Strict depth and time constraints

Has potential physical hazards (eg. decompression sickness)

Operations subject to strict legislative controls

Only possible to cover small areas on individual dives

Effectiveness can be limited by water turbidity

• Able to survey large expanses of sea floor quickly
• Allows precise density measurements of features of interest (eg. burrow openings, sea pens)
• No depth or time constraints (in coastal waters)
• Gives much information on sea bed topography and burrow types present, also on behaviour of benthic animals.

Equipment needs hard boat to operate. May be unable to access very shallow waters or enclosed inlets

Equipment readily available but expensive

Analysis of videotapes can be very time-consuming

Not possible to collect benthic samples

Provides no information on smaller sediment fauna

Effectiveness can be limited by water turbidity

Care required in choice of towing path (need to avoid wrecks, rock outcrops and other submarine obstructions)

Remotely-operated vehicles (ROVs

• No time constraints. Depth range limited by length of umbilical but most models can access depths likely to be encountered in UK coastal waters
• Able to cover wide areas (relative to capacity of human divers)
• Mobility allows close-up examination of sea bed
• Give much information on sea bed topography and burrow types present
• Deployment areas less restricted than towed video. Can be used over mixed substrata or in areas with submarine obstructions
• Some models able to collect benthic samples

Equipment needs a hard boat to operate. May be unable to access very shallow waters or enclosed inlets

Equipment very expensive

Precise quantification of sea bed features difficult due to changes in field of view

Effectiveness can be limited by water turbidity (the ROV motors themselves may disturb the bottom sediments)

Provide only limited information on smaller sediment fauna

Sampling of sea floor features is non-random

Acoustic surveys

• No depth (within coastal waters) or time limitations
• Allows substrata to be mapped rapidly over large areas
• Water turbidity unimportant

Equipment needs a hard boat to operate. May be unable to access very shallow waters or enclosed inlets

Equipment very expensive

Results need to be ‘ground-truthed’ by other methods (eg. grab sampling, towed video)

Does not provide details of biological community composition or species abundance

Not able to collect benthic samples