PLYMOUTH FIELD COURSE 2019
Habitat Mapping
The photo collection from the habitat mapping research is available in the slide show to the right.
Please visit the youtube link below for the full video compilation, including the photo collection and additional videos taken during the research.
The video includes more details on the pictures as well as video clips of research procedures.
HABITAT MAPPING IN THE PLYMOUTH SOUND
The Plymouth Sound and estuaries were designated as a SAC on the 1st of April 2005,
due to habitat features such as Atlantic salt meadows, reefs, sandbanks, mudflats
and sand flats, as well as its role as a home to many of Europe’s threatened marine
species such as Allis shad (Alosa alosa) and subtidal seagrass (Zostera marina).
Our survey was carried out either side of the Torpoint Ferry chains, it is important
to survey habitats in busy maritime areas such as this to study the effects that
frequent dredging and constant mechanical disturbance have on the biota. Other anthropogenic
impacts on the estuary include contamination of toxic synthetic and non-
SIDESCAN SONAR
Our survey set out to map the benthic habitat in a small fragment within the Special Area of Conservation (SAC) of the mouth of the River Tamar, Plymouth UK. This was carried out by plotting 3 parallel transects, with a longitudinal distance of 100m from each other, using a subsurface Dual Frequency Analogue Side Scan Sonar operating at 100kHz. The side scan was deployed at a depth of 2m, with a swath wide of 75m either side, however the large amount of noise on the portside overpowered the sonar, producing an unreadable image. Ground trothing methods, including deployment of a camera and van Vee grabs, were carried out on coordinates that had been identified from the side scan image. Using the video footage from the camera, and examining the contents from the grabs, fauna can be visually identified.
Figure 1 (right): Surface Contour plot of the area surveyed by Sidescan sonar correlated to transect lines. Data was collected across 3 collocated transects, with altitude highlighted.
ECOLOGICAL SAMPLING
Initial video analysis uncovered significant domination of Crepidula fornicata across the benthos, as supported by the ecological grab samples which revealed high numbers of shell fragments at both locations (not quantified as only full specimens identified) but only 4 complete shells in comparison to 28 complete shells between grab, although a greater standard error is seen at Grab 1. This may be due to physical pressure applied by the action of the chains, although in order to substantiate this theory a wider range of ecological samples are required from a greater distribution of locations both surrounding the chains and from elsewhere within the estuary. Tubeworm abundance is most conserved between grab samples with 9 at Grab 1 and 10 at Grab 2, with greatest variation in Crepidula fornicata as discussed. Much of the footage revealed high sediment load covering approximately 90% of the benthos where shell fragments did not dominate.
In conclusion, a low biodiversity observed surrounding the Torpoint ferry chains is theorized to be the result of anthropogenic disturbance of the seabed and may contribute to a reduction in genetic resilience across the community under future changing physiological stress (Tillman and Downing, 1994). Organisms with low resistance/minimal solid protection such as Zostera marina observed elsewhere are at increased vulnerability to physical damage and subsequently not seen at either grab location despite being observed elsewhere in the Plymouth Sound management area where disturbance is much less.
References:
Tillman, D; Downing, J. 1994. Biodiversity and Stability in grasslands. Nature 367.
Pages 363-
Plymouth MPA. (2019). Plymouth Sound & Tamar Estuaries -
Langston, W.J., Chesman, B.S., Burt, G.R., Hawkins, S.J., Readman, J.W. and Worsfold, P., 2003. Characterisation of the South West European Marine Sites: Plymouth Sound and Estuaries cSAC, SPA. Occasional Publication of the Marine Biological Association 9.
Figure 2 : Bar chart indicating the biodiversity and abundance of species across each Grab sample. A higher abundance of shell fragments are observed at Grab 2 while living individuals appear to be more numerous at Grab 1.
Figure 3: Average size of slipper limpets for Grab 1 and Grab 2 with standard error bars. Note differing size of samples.
VIDEO ANALYSIS
The quality of video footage was somewhat limited by environmental parameters and
a high level of turbidity, explicitly a high octant cloud cover reducing solar irradiance
at the River surface alongside high sediment load re-
All data used to create the results on this page can be found on the University of Southampton FTP Server.