Within our oceans lies a diverse array of seabed habitats and epifaunal communities. At Ocean Ecology, we use state-of-the art techniques to deliver accurate and efficient solutions to collecting information on the habitats present, one of these methods being acoustic imagery.
What is acoustic imagery?
Acoustic cameras, such as the Adaptive Resolution Imaging Sonar (ARIS) system developed by Sound Metrics, are cutting-edge technology which capture high-resolution, video-like images underwater using high-frequency sound waves. Systems like ARIS can deliver detailed acoustic imagery in real time, making it an invaluable tool for understanding the marine environment in turbid UK waters.
One of the key applications of acoustic cameras is seafloor monitoring. We are able to decipher the broad habitat present and the structural complexities it possesses, which can be utilised alongside optical imagery and geophysical data to build an understanding of the site we are investigating.
Benefits of acoustic imagery
There are several benefits of obtaining acoustic imagery, including;
- Minimal impact to the benthic environment. This not only ensures there is less disturbance to the environment on the whole, but can also be used to survey delicate and protected ecosystems.
- Allows for data to be collected in low visibility or low light conditions. Through manipulation of acoustic feedback we can minimise the ‘noise’ created by suspended particles and put focus onto the structures present.
- Assists other methods of data collection, i.e. optical imagery, to build a more in-depth understanding of the habitat.
- Able to increase measurable parameters i.e. height of structures.
- Provides more accurate acoustic feedback than geophysical data which can be used on a smaller scale.
- Able to gain data across a larger surface area than some methods of optical imagery within one frame.
Sabellaria in acoustic imagery
Taking advantage of the ability to identify structural complexities of benthic habitats using acoustic imagery highlights the use of acoustic monitoring technology in assessing Sabellaria reefs – complex biogenic structures built by a species of reef-forming polychaete worm. These biogenic structures provide increased habitat complexity in areas of soft sediments, providing shelter and feeding grounds for a variety of species.
Sabellaria spinulosa reefs are often found in environments with limited visibility. By deploying an acoustic system, it is possible to gain further clarity on the reef structures present. Ocean Ecology has extensive experience analysing Sabellaria spinulosa using optical imagery, as well as devising methods in reef analysis using acoustic imagery to comply with Annex I habitat analysis criteria. Working with Natural Resources Wales, Natural England and Swansea University these methods were used to provide insight into the extent of Sabellaria reef within the Severn Estuary Special Area of Conservation1.
A recent project in which Ocean Ecology was tasked with collecting visual data on a known Sabellaria spinulosa reef within notoriously turbid waters, demonstrates the benefits of acoustic imagery. With experience of optical imagery within the area, there was a significant gain in data quality by employing acoustic methods, where we were able to determine areas of Sabellaria spinulosa tubes in areas of sediment.
Other applications
We frequently use acoustic cameras to investigate benthic habitats across various projects, from assessing potential impacts of thermal plumes associated with nuclear power station outfalls to confirming the presence or absence of Sabellaria reef at offshore wind farm sites prior to construction. We also use it to complement optical cameras by reviewing ARIS footage collected from ROVs.
Beyond Sabellaria reef monitoring, acoustic imagery technology has a broad range of applications, including marine fish identification. In a collaborative study between Ocean Ecology and Swansea University2, ARIS was demonstrated to be an effective tool for estimating fish size, abundance, and species identification. Unlike traditional optical imaging which relies on visual characteristics, such as colour, sonar-based analysis identifies marine species using features such as fin type, body shape, appendages, schooling behaviour, and swimming patterns.
High resolution acoustic imagery can be a standalone tool and can also be used in conjunction with additional sampling tools, such as eDNA or optical imagery to produce a clear insight into the benthic environment and assemblages under review.
As marine monitoring continues to move toward more efficient and non-invasive methods, acoustic cameras are an increasingly beneficial method of establishing underwater clarity and understanding benthic environments.
References
- Griffin, R.A., Jones, R.E., Lough, N.E.L., Lindenbaum, C.P., Alvarez, M.C., Clark, K.A.J., Griffiths, J.D., Clabburn, P.A.T., Turner, J.A. (2019) The effectiveness of acoustic camera technology for mapping and assessing Sabellaria reef in the Severn Estuary Special Area of Conservation (SAC). NRW Evidence Report No.371
- Jones, R.E., Griffin, R.A., Unsworth, R.K.F. (2021). Adaptive Resolution Imaging Sonar (ARIS) as a tool for marine fish identification. Fisheries Research, 243.
