Discover the different types of seabed ecological survey, and which survey is the best fit for your project.

Seabed ecological surveys help identify and record the habitats and/or species in a given location, to help inform impact assessments, site management decisions and conservation policy development.

From drone and hovercraft surveys to grab sampling and DDV, there are many types of seabed survey. How can you know which survey is right for your project?

The diagram above provides an overview of the type(s) of seabed survey you will need, depending on the location of your project, and the type of data required. Follow the links below to discover more about each survey type:

Drone surveys

Drones, or Unmanned Aerial Vehicles (UAV) can provide aerial imagery of your survey site in a relatively short time. A drone can provide high-resolution georeferenced imagery and elevation data, and allow for high-level habitat mapping.

Pros

• Can cover a larger area in a shorter space of time than hovercraft or on-foot surveys
• Only one surveyor is needed

Cons

• Drones require a licence to operate, and depending on location may be restricted by no-fly zones or need equipment unlocked by the manufacturer
• If there is a need to purchase the drone, this can be a significant upfront cost
• Poor weather conditions can limit drone flying and quality of data

Hovercraft surveys

Hovercraft can travel over water and mudflats to allow for both habitat mapping and core sampling in otherwise inaccessible intertidal areas.

Pros

• Hovercraft allow access to the lower shore not accessible on foot
• Hovercraft allow more in-depth biotope mapping than drone surveys

Cons

• Operating costs can be high compared to other methods
• Use of hovercraft can be restricted, e.g. in areas with wintering waterbirds

^{A survey hovercraft}

Walkover surveys

A walkover, or on-foot habitat mapping, involves survey staff mapping biotopes on the shore with handheld GPS. 

Pros

• Walkover surveys provide detailed and precise biotope mapping and identification
• Walkovers can also detail wider evidence at the site e.g., anthropogenic disturbance
• Walkovers typically cause lower levels of disturbance to bird and mammal populations than hovercrafts

Cons

• At least two surveyors are needed for each walkover
• Walkovers have higher safety implications in tidal and mudflat areas than with a drone
• Walkovers generally achieve lower area coverage over time (approximately 1 km / hour)

Core sampling

Core sampling allows the collection of sediment cores, both mud and sand for infaunal, particle size or chemical analysis in intertidal areas. Cores can be various sizes depending on requirements, though the typical standard size is 0.01 m².

Pros

• Core samplers are lightweight, easy to use, and generally inexpensive  

Cons

• Core sampling can only happen at low water when intertidal sediment is exposed.
• It can be difficult to collect a viable core in areas with compacted mud or high gravel content

Quadrat sampling

Quadrat sampling allows for quantification of fauna in rocky shore habitats, used to estimate population abundance, density, frequency, and distribution.

Pros

• Quadrat sampling provides a quantifiable estimation of fauna
• Quadrats can be many sizes to meet survey requirements
• Quadrats are generally lightweight, easy to use and inexpensive

Cons

• Quadrats are not suitable for studying mobile fauna
• Quadrats require highly accurate in-situ faunal identification by surveyors (unless samples are taken for later analysis)

^{A surveyor carrying out quadrat sampling}

Van Veen grab sampling

Van Veen grab samplers are used to obtain bottom samples from the seabed. They are generally used in intertidal areas or shallow subtidal in soft, muddy and/or sandy sediments.

Pros

• A smaller grab than the Day and Hamon, Van Veen can be hand operated
• Van Veen does not require a large vessel with A-frame or winch capacity
• Van Veen can be operated in shallower areas

Cons

• Van Veen is ineffective on seabed with high gravel or cobble content

Day grab sampling

Day grab is used to obtain bottom samples from the seabed. It is typically used in mud or sandy sediment, and is larger than a Van Veen, with a 0.1 m² standard grab size.

Pros

• Day grab provides a quantifiable estimation of infauna (species living in sediment)

Cons

• Day grab provides limited sampling of epifauna (species living on the seabed).
• Day grab is ineffective on seabed with high gravel or cobble content

Hamon grab sampling

Hamon grab is used to obtain bottom samples from the seabed in coarser sand, gravel or cobble sediments. Grabs come in various sizes, though the typical mini-Hamon collects 0.1 m² samples. Hamon is regularly used for aggregate benthic monitoring, given the typical nature of the seabed in these areas.

Pros

• Hamon provides a quantifiable estimation of infauna (species living in sediment)

Cons

• Hamon provides limited sampling of epifauna (species living on the seabed)
• Hamon is not suitable for sampling in fine or muddy sediments

Drop-down Video (DDV)

Drop-down Video (DDV) can be used in all habitats, especially in rocky areas when grab sampling is not possible. The live top-feed allows for monitoring of the footage throughout the survey.

Large and small DDV systems are available depending on requirements and survey locations. For example, ABPmer’s bespoke DDV can simultaneously record video and high-resolution stills. Our smaller system has excellent functionality for surveying quay walls and vertical structures as it can be hand-held.

Pros

• DDV has wide range of uses in terms of location and habitat type
• DDV is non-destructive technique, ideal for sensitive habitats

Cons

• DDV cannot sample infauna (species in sediment)
• Video quality can be limited by underwater visibility
• The evaluation of video material can be labour intensive

^{Sabellaria reef discovered through DDV}

Diving surveys

Scientific diving surveys are regularly used when detailed inspection is required, and remote sensing is not suitable.

Diving surveys can obtain data from all habitats, and are particularly useful in sensitive habitats such as subtidal reefs, which can be easily damaged by other techniques and cannot be physically sampled using a grab. 

Pros      

• Diving can provide in-depth data collection and species identification

Cons

• Diving can have a higher associated cost than other methods
• Diving represents a greater risk to health and safety than remote sensing techniques

Prepared by Vicky West and Andrew Pearson, ABPmer marine ecology specialists

Main photo: Andrew Pearson

ABPmer’s ecological surveyors regularly coordinate and undertake pre and post-consent monitoring for coastal and marine developers. As an integrated consultancy and survey company, ABPmer offers a unique service to those operating in the marine environment.