Dorset's seabed secrets revealed

By Sue Paz BBC Dorset

The first phase of the project was an acoustic survey

Shipwrecks, gravel dunes and ancient river beds have been revealed on the Dorset seabed by new seabed mapping.

DORset Integrated Seabed study (DORIS) is a collaborative seabed mapping project.

It involves Dorset Wildlife Trust, the Maritime and Coastguard Agency and Channel Coastal Observatory.

DORIS will produce a detailed seabed habitat map covering over 800 sq km (497.12 sq mi) from Swanage to Abbotsbury.

The project, which puts Dorset "at the forefront of marine mapping in the UK", has been made possible by a biodiversity grant of £300,000.

[Biodiversity is the variation of life forms within an ecosystem - all plants, animals and micro-organisms.]

The money came from Viridor Credits Environmental Company, through the Landfill Communities Fund, to Dorset Wildlife Trust, and will help fund a seabed habitat map to identify important marine conservation features in Dorset.

A clearly visible, meandering river channel has been discovered

The Maritime and Coastguard Agency will use the map to update navigation charts, while the Channel Coast Observatory will provide information to coastal engineers.

Dorset Wildlife Trust will use it to identify important and vulnerable seabed habitats.

Peter Tinsley, Marine Conservation Officer at Dorset Wildlife Trust, said: "It's something we've been wanting to do for a long time.

"We don't have a lot of information about habitats - where they are, how much of each particular habitat there is and what condition they're in.

"We chose the area between Abbotsbury and Swanage, partly because it's an area where very little information has been gathered in the past.

"And also because the information that we did have from local divers in some of the more shallow areas seemed interesting - so we decided to investigate further."

Acoustic survey

The first phase of the project was an acoustic survey. This was carried out in early 2009.

Peter said: "It's a three dimensional survey which uses sound waves and indicates the shape of the seabed, highlighting things like ledges and sand waves.

"From this we were able to identify the areas we wanted to have a closer look at using remote video and stills cameras [the next phase].

"You can lower these cameras down into the sea and leave them there for as long as you like.

"Depending on the depth of the water a diver can only stay underwater for about half an hour at a time - so remote cameras are much more effective."

Local volunteer divers are also involved in the DORIS project

So far the seabed mapping project has provided images of well-known features, such as the Shambles Bank and the wreck of the Aeolian Sky.

There have also been some surprising finds, including a river channel cutting though bedrock, about eight miles due south of Lulworth Cove.

Peter said: "It's been under the sea for about 12,000 years and its meandering shape is still clearly visible, which is amazing.

"The project has certainly got a lot of people interested."

Peter explained that there is very little sediment on the seabed in Dorset which means that a lot of the rocks are completely exposed.

He said: "Geologists will learn a lot about how rock layers are structured. They can get a lot more information from looking at them on the seabed, then they can on land."

Volunteer divers, taking part in the Seasearch project [for divers who have an interest in what they see under water], are also using the DORIS data to locate new survey sites.

The region has recently been put forward by Natural England as a draft Special Area of Conservation because of the high quality of its reef habitats.

Peter said: "This was based on existing data, so information from the seabed mapping will further back the case.

"There has never been a greater demand for reliable seabed information like this.

"The Marine and Coastal Access Bill, soon to go through its second reading in the House of Commons, will pave the way for marine spatial planning and for the creation of marine protected areas; both will benefit from the sort of detailed maps DORIS will produce.

"This should lead to more sensible and sustainable use of our marine resources, for the benefit of marine wildlife and those whose livelihoods depend on the sea."