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Development of Low Budget Survey Equipment and Techniques for Shallow
Water Ecosystems: A Case Study of the Fal Estuary Seagrass beds
Clive Pollittt and Claire Eatock
Authors biographical information
Mr Clive Pollitt, FdSc Marine Science student. Falmouth Marine School. Falmouth, Cornwall,
UK. [email protected]
Dr Claire Eatock. FdSc Marine Science lecturer. Falmouth Marine School. Falmouth, Cornwall,
UK. [email protected]
Claire Eatock is a lecturer and Clive Pollitt a foundation degree student at Falmouth Marine
school. Clive is an engineer interested in promoting marine biology to the general public.
Falmouth Marine School
Killigrew Street
Falmouth
Cornwall
TR11 3QS
United Kingdom
Tel: 01326 310 310
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Abstract
Seagrass beds are one of the many shallow water benthic habitats that need to be regularly
monitored. This project used the seagrass beds in the Fal estuary in Cornwall UK as a test case
to develop inexpensive shallow water habitat surveying equipment that would be suitable for
colleges and amateur conservationists. It came up with four devices; a simple glass bottomed
box that could be mounted on the side of a boat; a video camera mounted on a long extending
pole that could give close-up pictures of the benthos; a photo/video-quadrat made from industrial
shelving material that could record statistical data for benthic habitats and finally an underwater
towed video monitoring system that could be used to cover large benthic areas. With these
pieces of equipment a successful baseline survey of the Fal estuary Seagrass beds was
completed.
Keywords
Benthic, Survey, Seagrass, Volunteer Bio-monitoring.
Introduction
Surveying shallow marine benthic environments is important for conservation groups,
environmental monitoring, water quality control, pollution monitoring and for monitoring global
warming and ocean acidification. (Rhoads 2004) A large amount of marine life is within the
shallow photic zone just beyond the shore and in the inter-tidal zone.
The costs associated with this type of surveying have become prohibitive due the sheer amount
of area to be covered. This has resulted in large areas being infrequently surveyed, if at all, and
environmental and planning decisions cannot be easily made with confidence if current coastal
survey data is not available. An example of this is in the Fal estuary in Cornwall, England where
a Special Area of Conservation (SAC) was established in 1992 as a result of the European
Habitats Directive. The local harbor commissioners are one of the organizations who have been
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made responsible for environmental monitoring of the estuary but have very little current data.
This is a very typical situation in Britain and Europe at large. The reasons for this situation are
the costs involved with environmental surveying which are often outside the budget of small
environmental organizations.
The Fal estuary was made a SAC largely because of the maerl and seagrass beds that are present
within it. There is however very little current environmental habitat survey data available, the
habitat map presently in use being more than 20 years old. (Kevan Cook, Lead Advisor, Marine,
Truro, Natural England, personal communication, 23 September 2010)
Volunteer based monitoring programs have been designed and initiated by many organizations
including Seagrass Watch, (McKenzie 2002) but many have found that these programs are
difficult to sustain. This is largely due to the fact that most Seagrass is below the water for much
of the time and qualified volunteer divers are required to do the surveying. (Short 2009)
Different monitoring options are dependent on the structure and resources available, e.g.
cumbersome methods are not practical for volunteer-based monitoring networks and also the
adequacy of different methods for the various species, which requires knowledge of their growth
rates and basic ecology. (Duarte 2003)
Many types of equipment have been used to overcome the difficulty of using professionally
qualified divers. Professional surveying institutions often overcome this by the use of remotely
deployed video equipment (Potts 1982), which has become a well established tool in many areas
of marine research. (Holme 1984) Towed video sledge techniques provide a means to visually
survey large areas of seafloor without the depth or time constraints usually associated with other
techniques such as scuba diving. (Sisman 1982)
In the past, techniques such as this have been used to monitor the condition of features in
candidate Special Areas of Conservation (SAC) (Magorrian 1996) Towed video sledge data can
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be used to estimate the relative abundance of benthic species using the Visual Fast Count (VFC)
technique. (Kimmel 1985) The main disadvantage of the towed video sledge system is the
potential damage it can cause to the fragile seafloor habitat that it is recording. (Grizzle 2008)
An alternative is to have a Drop Down Video System (DDVS) which is a camera mounted on a
frame, often associated with a quadrat. (Holt, Sanderson 2001) This is lowered to the seafloor
where it remains stationary whilst recording the benthos. The position is given by a Global
Positioning System (GPS) receiver and the equipment is then moved to a new location often on a
pre-set transect. DDVS recording techniques have been used in a variety of applications and are
appropriate for the identification of seabed habitats. (Sanderson et al. 1999)
An underwater Remotely Operated Vehicle (ROV) is a self propelled underwater camera system
often with artificial lighting capable of descending to depths unreachable by divers and is
considered suitable for biotype surveying and monitoring. (Arbour 2004) The ROV is usually
connected to a surface support vessel via a tether cable which controls the ROVs movements
and passes the underwater video image to the operator for control and recording purposes. Due
to their maneuverability these systems are able to acquire great detail of the biotype. Together
with GPS equipment and on-board recorders these systems combine the flexibility of a diver
together with the advantages of remote control.
The disadvantage of ROV, towed and drop down video systems is the expense of the equipment
and of the support vessel, deploying equipment and tethers and the need for highly trained
personnel. (Epstein 2010) These factors usually place these survey techniques out of the reach of
small, low budget surveying organizations and volunteer initiatives. (Short 1984)
The purpose of this project was to develop inexpensive and safe shallow benthic surveying
equipment using basic skills and the recent development of inexpensive high definition digital
video cameras and recording equipment. The Seagrass beds in the Fal estuary were chosen as a
test case.
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1) Aqua-scope
The first device developed was built along the lines of a glass bottomed boat. (See figure1) This
piece of equipment was a large wooden box 75cm high by 75cm long and 40cm wide. The
bottom of the box had a glass water-proof window installed with handles and boat attachment
points placed along the sides of the box. The inside was painted matt black and a removable top
with an observation port were added. It was named the Aqua-scope.
Deployment
When the boat had reached the right location to be surveyed the position and depth were taken
using the boats onboard fish finder and GPS. The Aqua-scope was then placed in position over
the side of the boat and secured with its fastenings. Viewing of the seafloor was simply done by
looking into the viewing port. The boat was allowed to drift and the depth, GPS positions and
benthos were noted as it did so. Still camera and video photography was possible with the
camera placed at the viewing port or lowered to the glass pane where a very wide field of view
was possible.
Results
General observation underwater to a depth of 4 to 5 meters in bright, calm conditions was
possible at slack low tide. (See figure 2) The Aqua-scope was successfully used to map the
position of the major sea-grass beds in the Fal and in particular the St. Mawes Eelgrass meadow
near the Fal entrance.
Four surveys were conducted in the summer months of June, July and September and three
during March using the Aqua-scope. It was also used in conjunction with the other surveying
equipment developed in the project to help observe the performance and deployment of the
equipment.
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Materials and Costs (See table 1)
Capabilities and limitations
The data collected by the Aqua-scope could be considered to be equivalent to the data obtained
from surface snorkeling i.e. a general visual survey of areas of the seafloor where the benthos
type , coverage and location could be observed and recorded manually.
The main limitation of the Aqua-scope was the limited depth to which it can be used and the
inability of the boat to maneuver with it deployed. Any movement by the boat against the tide
resulted in turbulence and bubbles around the observation glass. The weather conditions had t
