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Geophysics

MTS Xplorer was used to collect side scan data on the 07-07-2017. Data was collected from site 6 in the Helford River (as shown below on map) and used to create a benthic habitat map.

Methodology

Using a Konsberg sidescan sonar set to 100khz, four transects were taken at the mouth of Helford River. Three methods of habitat mapping were used to identify boundaries on site 6: sidescan sonar, a grab and video data. A swath was taken and  the print out was then cut into the different transects and possible habitat boundaries were identified, measured and overlaid onto the track plot map.

Results

Four habitats were identified using the three videos of the seafloor and a grab:

Habitat a (50’05.7N, 05’05.0W) showed a rocky substrate with coarse sand and maerl gravel. The area was dominated by echinoderms such as Ophiura spp. and Ophiocomina nigra along with red algae (Chrondrus crispus and Coralinaceae spp) and brown algae. Using the Marine Habitat Classification for Britain and Ireland (Connor et al., 2004) the site was classed as SS. SMP. Mrl. Pcal. Nmix (Maerl Beds), though it should be noted that little/no live maerl was observed.

Conclusions

Four habitats were observed using the videos, but the sidescan only showed three distinct areas. A reason for this may be due to the similarity between habitats b and c. Though visually different their sediment composition is the same, which may make them indistinguishable using the sidescan.

Due to the camera quality it was difficult to identify species of fauna and macrophyta, as well as whether any live maerl was visible. Though the quality was sufficient to note borders between habitats, which could mostly be confirmed by the sidescan.

References:

Marine Geophysics Data Acquisition, Processing and Interpretation. Guidance notes, English Heritage.

P.J. Hayward and J.S. Ryland, 2012. Handbook of the Marine Fauna of the North-West Europe

A summary of achievements of the MESH Project, 2008

David W. Connor, James H. Allen, Neil Golding, Kerry L. Howell,

Louise M. Lieberknecht, Kate O. Northen and Johnny B. Reker, 2004

The Marine Habitat Classification for Britain and Ireland Version 04.05 JNCC, Peterborough

ISBN 1 861 07561 8

Connor, D. W., Allen, J. H., Golding, N., Howell, K. L., Lieberknecht, L. M., Northern, K. O., Reker, J. B., 2004, The Marine Habitat Classification for Britain and Ireland Version 04.05. In JNCC (2015) The Marone Classification for Britain and Ireland Version 15.03 [Online] [2017, 11th July] Available from: www.jncc.defra.gov.uk/MarineHabitatClassification

Figure 1: Map of site location in respect to Falmouth

Habitat b (50’05.7N, 05’05.0W) displayed fewer rocky areas with far coarser sands with abundant maerl gravel and frequent shell fragments. There were fewer organisms compared to habitat 1, with a sparse arrangement of red/brown algae. The site was classed as SS. SMX (sublittoral mixed sediment).

Habitat c (50’05’7N, 05’06.2W) was classed the same as habitat b (sublittoral mixed sediment), sharing a similar sediment composition. However, red/brown algae were more common, notably Chondrus crispus. Another difference was that the some of the dead maerl appeared to be intact among the maerl gravel.

Habitat d (50’05’7N, 05’06.2W) was mostly absent of life, algae was rare among the coarse sand and maerl gravel. Numerous shells were present in high densities. The only fauna observed were two grabs (one a hermit, the other could not be identified). Due to the sediment composition, this site was also classed as SS. SMX (sublittoral mixed sediment).

This can be seen in more detail on the poster, shown below, produced in the Geolab:

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