Remote sensing of kelp: novel methods for mapping and monitoring wild kelp resources

The executive summary from a report for The Crown Estate, piloting novel methods for mapping and monitoring kelp resources in the northeast Atlantic.

Executive summary

Kelp (Laminariales) are large brown, habitat-forming macroalgal (seaweed) species. Their large biogenic structure and ‘forest-like’ nature provide nursery and feeding grounds for a rich diversity of associated flora and fauna, many of which are critical to ecosystem functioning and commercial fisheries. Kelps, like many other macroalgal species worldwide are under threat: climate change, ocean acidification, anthropogenic pollution, overfishing and invasive species are just some of the pressures that have been reported to negatively impact these and other macroalgae.

 
Kelps are also under an old, but growing threat: wild harvesting. Harvesting of seaweeds from natural populations has been in practice for hundreds of years, particularly in the northeast Atlantic. Now, however, the rate at which kelps are harvested from the wild is increasing due to rising consumer demand for seaweed and seaweed derived products. Currently, kelp resources are understudied, largely due to the logistics of trying to access the kelp forest habitat in the shallow, rocky sublittoral fringe. In the light of these shortcomings, there is a need for a standardised, rapid monitoring protocol to obtain baseline information of wild kelp resources, and ensure sustainable harvesting of said resources. Remote sensing technologies in the form of satellite and aerial imagery, underwater imagery, LiDAR (Light detection and ranging) and sonar (Sound navigation and ranging) have been applied to monitoring submerged aquatic flora, including kelp with varied degrees of success.

 
The present study used a combination of multibeam sonar information and species distribution modelling to map kelp distribution and abundance along a 35 km2 stretch of the Dorset coast. Using data obtained from United Kingdom Hydrography Office (collected as part of their regular surveys), ground-truth information gained from field surveys and species distribution modelling, we pilot a novel monitoring and mapping methodology for kelp. In addition, we have identified several complications, which currently limit the expansion of the method outlined in this study, but offer remedies to these potential pitfalls.

 
We found the high resolution acoustic data very effective for mapping kelp distribution. A critical component of this acoustic data is a measure of the amount of acoustic energy being received by the sensor (aka backscatter). The importance of backscatter information for mapping and monitoring kelp resources has been highlighted as a crucial component of the predictive model. While choosing suitable study sites we found many areas were absent of backscatter information, despite being a typical component of multibeam sonar data. Additionally, while attempting to expand the coverage of the predictive model, difficulties were encountered as backscatter information from different vessels / echo-sounders could not be harmonised. An inability to combine backscatter data from different sources limits the transferability of the model. A standardised data collection protocol is therefore required to ensure harmonisation of backscatter information and transferability of the predictive model. The method piloted in this study exhibits a potential low-cost solution to the data deficit of kelp resources, offering a rapid assessment technique which could be used to inform sustainable management of wild stocks.

Citation

Bennion, M., Yesson, C., Brodie, J. (2017) Remote sensing of kelp: novel methods for mapping and monitoring wild kelp resources. A report for The Crown Estate. (PDF)

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Lulworth Cove, Dorset

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