Southampton University Falmouth 2015

Group 13

© B Carter

Introduction

On June 24, 2015 five transects in Falmouth Bay were surveyed between 08:07 and 12:15 UTC.  The aim was to survey the bedforms and benthic habitats in the bay using a Subsurface Dual Frequency Analogue Side Scan Sonar.  After the transects were mapped, a video camera was put in the water approximately ½ a meter above the sea bed while the boat drifted.  This was done in three different locations chosen from the Side Scan Sonar data to observe the biodiversity and bedforms of these areas.  Using the video footage, changes in biodiversity in the Falmouth Bay can be examined, as the bay is a Special Area Conservation. Seagrass and maerl are of particular interest in this SAC area.  All habitat surveying was carried out using standard protocol according to the National Standard.

Video

After looking at the results of the side-scan sonar we chose three areas of interest to video. By analysing these videos we got a better idea of the flora and fauna on the sea bed. The first area we videoed was on transect three. We found it was a seagrass habitat with small bedforms. Seagrass habitats are important nursery grounds for juvenile fish many of which are greatly important to commercial fisheries. We observed many shoals of small fish. We also saw multiple seastar species and a common cuttlefish. The second location we filmed was a dense kelp habitat with some larger bedforms. We found that many of the kelp fronds were covered in bryozoa and there were many other species of seaweed growing between and on the kelp. At the third location we saw very large well established bedforms consisting of biogenous sediment. We inferred this by observing the abundance of flora and fauna in the troughs of the bedforms. We saw seastars sheltering in the troughs as well as a large edible crab.

Side-Scan

An area in Falmouth Bay was surveyed using a side-scan sonar over five transects. The majority of the surveyed area showed very little vegetation and bed-forms. However, Transect 17 showed a large rock shelf and areas of dense vegetation with no bed-forms.

The bed-forms in Zone 3 were of very similar wavelengths, with four groups of bed-forms randomly chosen with a mean wavelength of 0.98m and a range of 0.21m. The sediments in this zone appear to be medium sands.

Zone 1 shows a large intensity of backscatter showing a rocky outcrop. Closer to shore from this the intensity of backscatter decreases suggesting the substrate has become softer. This is because this is the beginning of a shelf and sediments have settled on the shelf.

Zone 2 shows an area of dense vegetation. This has no bed-forms as the vegetation will have stabilised the sediments.

Figure 107- Spiny starfish – Marthasterias glacialis

Figure 104 - Common cuttlefish - Sepia officinalis

Figure 105 Bryozoans growing on kelp fronds

Figure 106 - Small Shanny well camouflaged against the sand - Lipophyrys pholis

Figure - Habitat 108 - seagrass (Zostera marina)

Figure 109- Habitat 2 - Kelp (Laminaria digitata)

Figure 110 - Habitat 3 - large, well established bedforms. Common seastars found sheltering in the troughs of the bedforms (Asterias rubens)

Disclaimer: The views and opinions expressed are those of the individual and not necessarily those of the University of Southampton or the National Oceanography Centre, Southampton.

Figure- 102 Geophysical Poster of Falmouth Bay - pdf

Species

The common cuttlefish (Sepia officinalis) is a mollusc belonging to the class cephlapoda. They grow to a maximum of 45cm but are usually around 20-30cm (Thecephalopodpage.org, 2015).  A pair of flat fins span the entire length of their mantles, which they undulate rapidly when swimming. In Britain, this cuttlefish is found around southern and western coasts. Elsewhere, the species is found in the eastern Atlantic from the Baltic Sea to South Africa, and also in the Mediterranean (Arkive.org, 2015).

References

Arkive.org, (2015). Common cuttlefish videos, photos and facts - Sepia officinalis | ARKive. [online] Available at: http://www.arkive.org/common-cuttlefish/sepia-officinalis/ [Accessed 2 Jul. 2015].

Encyclopedia of Life, (2015). Spiny Starfish (Marthasterias glacialis) - Information on Spiny Starfish - Encyclopedia of Life. [online] Available at: http://eol.org/pages/598450/overview [Accessed 2 Jul. 2015].

Marlin.ac.uk, (2015). MarLIN - The Marine Life Information Network. [online] Available at: http://www.marlin.ac.uk/speciesinformation.php?speciesID=3770 [Accessed 2 Jul. 2015].

Marlin.ac.uk, (2015). MarLIN - The Marine Life Information Network. [online] Available at: http://www.marlin.ac.uk/speciesfullreview.php?speciesID=3613 [Accessed 2 Jul. 2015].

Marlin.ac.uk, (2015). MarLIN - The Marine Life Information Network. [online] Available at: http://www.marlin.ac.uk/speciesfullreview.php?speciesID=4600 [Accessed 2 Jul. 2015].

Seaweed.ie, (2015). Laminaria digitata. [online] Available at: http://www.seaweed.ie/descriptions/laminaria_digitata.php [Accessed 2 Jul. 2015].

Thecephalopodpage.org, (2015). Sepia officinalis, The Common Cuttlefish - The Cephalopod Page. [online] Available at: http://www.thecephalopodpage.org/Soffic.php [Accessed 1 Jul. 2015].

The spiny starfish (Marthasterias glacialis) belongs to the phyla Echinodermata. They are found from the southwest and west coast of England and the west coast of Scotland. They can grow up 70cm but are more usually found between 25-30cm (Marlin.ac.uk, 2015). It has 5 narrow tapering arms with 3 rows of longitudinal spines along each arm. The spines are white, usually with purple tips. spines are surrounded by specialised minute modified spines (pedicellariae), which are used for protection and to gather food. Marthasterias glacialis can be dirty brown to pale greyish green in colour with purple tips to the arms (Encyclopedia of Life, 2015).

Laminaria digitata is a large conspicuous kelp growing up to 2 m in length commonly found at low water during spring tides on rocky shores. The frond is broad and digitate, glossy and dark brown in colour and lacks a midrib. Found attached to bedrock or other suitable hard substrata in the lower intertidal and sublittoral fringe, down to a maximum depth of 20 m in clear waters. Laminaria digitata flourishes in moderately exposed areas or at sites with strong water currents. It is found on most coasts around Britain and Ireland (Marlin.ac.uk, 2015).

Common eelgrass - (Zostera marina) is a grass like flowering plant with dark green, long, narrow, ribbon shaped leaves 20-50 cm in length (exceptionally up to 2 m long) with rounded tips. Leaves shoot from a creeping rhizome that binds the sediment. Leaves and rhizomes contain air spaces, lacunae, that aid buoyancy. Zostera marina has a wide but patchy distribution in southwest of England, the Solent and Isle of Wight on the south coast, Wales, western Ireland, western and eastern Scotland including Orkney and the Shetland Islands (Marlin.ac.uk, 2015).

Habitat Mapping

© B Carmichael

Figure 111 Cuttlefish Sepia officinalis

Figure 112- Spiny star fish

Figure 113 Laminaria digitata

Figure 114- Common eel grass (Zostera marina)

Figure 103- Site of transects