Envision Marine Ltd (ENVISION) were commissioned by Natural England to undertake this study which aimed to assess the distribution and condition of subtidal maerl communities within four areas of the Falmouth Bay to St Austell Bay Special Protection Area (FBSAB SPA).
Sidescan sonar and underwater imagery surveys were carried out by the Cornwall Inshore Fisheries and Conservation Authority (CIFCA) and ENVISION. ENVISION analysed the video and still imagery to quantify live and dead maerl cover, classify habitats, and assess conservation features. Data interpretation combined geophysical data with the biological sample information to produce predictive maps of benthic habitat distribution.
Results from the analysis of 53 video tows and 524 still images are presented. Sandy habitats were recorded in nearshore habitats with seagrass patches. Further offshore areas were dominated with kelp and macroalgal communities on rock, interspersed with sand, coarse sediments, and maerl, and coarse sediments common in greater depths. The extent of maerl was patchy in distribution, with smaller patches often sheltered by rocky habitats. From Old Wall to Bizzies maerl is found in small pockets amongst rock habitats. Within Gerrans Bay maerl habitat is predicted in larger expanses, particularly in the southwest. Maerl is found to lesser extents in inshore areas within Veryan and Mevagissey Bays. Where maerl was recorded, the condition and proportion of live maerl was found to be in favourable (healthy) condition. No invasive species were recorded, and anthropogenic impact was minimal.
The study produced benthic habitat distribution maps, along with recommendations for refining maerl classification, assessment of maerl biotopes, and future habitat mapping. Findings contribute to the conservation and management of marine habitats within the FBSAB SPA.