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Aim

To conduct a geophysical survey just north of the Fal Estuary in King Harry’s Passage and produce a benthic habitat map using the transect produced by a Side-Scan towfish. Habitat maps provide essential information for coastal management and ecological analysis.

Introduction

 The Fal and Helford are Special Areas of Conservation (SAC)[1] , one of the main reasons why site was surveyed. It was chosen as a SAC for serval reasons including the large number of inlets and bays providing a range of fully marine habitats. As well as, the Atlantic salt meadows (Glauco- Puccinellietalia maritimae) which are an example of saltmarsh vegetation in a ria. This particular physiographic characteristic is restricted to south-west England and west Wales. [2]

Methods

A single-track transect was produced with a Side-Scan sonar in King Harry’s Passage, two videos were also recorded to provide ground-truthing at the start and end of the transect. The second video was also covered by a Van der Veen grab so the substrate at the start of the transect could be accurately classified.

Figure 2. Van Veen grab

Figure 1. Video Probe

Figure 3. Side Scan sonar towfish

Results and Discussion

The Side-Scan sonar revealed a mainly homogenous substrate, with the exception of 5 rocky outcrops shown in figure x. The main disadvantage of using sonar was the disruption caused by passing vessels and the rough weather which produced artefacts on the transect. However, as this information was recorded at the time of the transect the issue was nullified.

Video 1 showed a high abundance of epifaunal species Crepidula femicata (slipper limpet) and common star fish Echinodesmata Asterias Reubens. However, the poor quality of the video made identification of smaller fauna and flora extremely difficult. The video was recorded as the while the boat drifted for five minutes from 50o13.434N, 005o51.372W starting at 11:46UTC.

Video 2 recorded from 50o12.333N 005o02.239W starting at 12:07 and ending at 12:12UTC. The first habitat, which was not covered by the side-scan sonar, was dominated by yellow and red microalgae that was attached to hard substratum, but the combined presence of the algae and poor video quality made any classification of this habitat impossible. After drifting for 2 and a half minutes, there was a sharp gradient into the second habitat which was later classified as ‘Infralittoral coarse sediment’ (SS. SCS. ICS). which was characterised by coarse bioclastic sediments, predominately oyster shells, suggesting that the habitat was adjacent to a main oyster bed.

Using the Marine Habitat Classification for Britain and Ireland3 the site was most closely identified as ‘Infralittoral coarse sediment’ (SS. SCS. ICS) as the sample grab showed a high abundance of infaunal and epifaunal species such as Lanice conchilega (sand mason worm), glycera lapidum and Leucosiidae crab which are characteristic species in this habitat. However, the most abundant species found in this habitat are infaunal species not found in the grab sample. It is possible that the grab sample used was too small to truly identify this habitat and further grab samples would have to be taken to make a definite conclusion regarding this particular habitat.

References

[1] Gov.uk. (2017). Western Channel and Celtic Sea marine area: index map and site packages - GOV.UK. [online] www.gov.uk/government/publications/western-channel-and-celtic-sea-marine-area-index-map-and-site-packages [Accessed Available at: https:// 13 Jul. 2017].

[2] Jncc.defra.gov.uk. (2017). Fal and Helford - Special Area of Conservation - SAC - Habitats Directive. [online] Available at: http://jncc.defra.gov.uk/protectedsites/sacselection/sac.asp?EUCode=UK0013112 [Accessed 13 Jul. 2017].

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