Home Offshore Estuarine Tidal Time Series Habitat Mapping References

Introduction

The Fal is home to a range of habitats (Maerl beds, subtidal/intertidal shores, sand and eelgrass beds), which are all protected the DEFRA (Department for environment, food and rural affairs), as a SAC (special area of conservation).

This habitat mapping of a small section of the Fal Estuary and the Fal river took place on the 8th of July, at 07:12 UTC.  Five Sidescan transects were taken (all in parallel with each other), covering a reasonably large segment of the area. Although the side scanner gave us insight into interesting areas along the transects, we were unable to determine what was creating these interesting points and so a camera was deployed at two points of interest for ground-truthing.

Chart datum suggested that the sediment type that was present was eel-grass (which was seen at the first video camera drop but not at the second). There were many variables that could disrupt the efficiency and precision of the side scanner so two people were on the lookout for obstructions i.e. buoys, boats etc.

Methods

To provide a large-scale picture of the region on a short timescale, a Subsurface Duel Frequency Analogue Sidescan Sonar with a 75m swath was used. The side scan was towed behind the MTS Explorer along the 5 transects. Data was collected from the 100 kHz survey and printed onto a paper trace; although the sidescan plot allowed indication of points of interest, it was open to interpretation as objects at the surface could have an effect on the sidescan.

Groundtruthing was used to verify the interesting features picked up by the sidescanner. Video imaging of the benthic habitat was carried out along 2 transects on the River Helford and one a little further out (where a grab was also taken). Video was used to supplement the side scan data by ground-truthing habitats, and for species identification (later in the lab). Findings were quantified by calculating the approximate percentage cover of each species.

A Van Veer grab was used to establish the sediment and identify organisms in the habitat at site 2 (50o 06.0N, 5o 06.5W). The video was deployed to determine whether a grab could be performed but also to build an image of the overall habitat. There was cloud cover of 3/8, and a sea state of 0, which made for very clear video recordings. The grab allowed us to determine sediment size and composition (we used sieves on-board the MXS Explorer).

Results

Our group created a poster displaying our findings from the survey, please click on the image to enlarge.

The views expressed here are not representative of the University of Southampton.

Biology Nutrients Physical

Biology Nutrients Physical