Marine Bio-images 

Lyme Bay Closed Area Monitoring

Marine Bio-images diving surveyor Lin Baldock counting species within a quadrat , Lyme Bay Closed Area monitoring programme. Copyright Colin Munro
Marine Bio-images diver Dr Lin Baldock counts marine species with random quadrats at station 1 as part of the diving study investigating the changes occurring within the seabed communities now that these cobble reefs have been closed off to towed bottom fishing gear such as trawl nets and scallop dredgers. Photograph Colin Munro, 2009.
Introduction

In 2008, DEFRA closed an area of Lyme Bay some 60 square miles in extent to mobile benthic fishing gear, i.e. bottom trawling and scallop dredging. This closure was brought in to protect fragile seabed habitats, in particular subtidal rocky reefs and areas of boulder and cobble reefs and their associated flora and fauna, from damage caused by such gear. Numerous studies conducted by ourselves and others had demonstrated that such habitats were particularly vulnerable to physical damage by mobile fishing gear. Marine Bio-images is part of the consortium (lead by Plymouth University) conducting a monitoring programme to study the recovery of the newly protected area of seabed. We have designed and are conducting the monitoring of cobble reef areas. This is being conducted by SCUBA diving, conducting random quadrat counts, belt transect surveys and photo-monitoring around fixed stations established within and outside the new closure. This study began in September 2008. It is scheduled for completion in 2011.

Background

Concerns about the effects of towed bottom fishing gear on the rocky and cobble reefs within Lyme Bay, and their associated fauna, have been expressed since the late 1980s. In response to these concerns and several studies indicating damage (e.g. Munro, 1992; 1993; Devon Wildlife Trust, 1998) a voluntary agreement was negotiated by the Devon Wildlife Trust whereby bottom fishing towed gear would not operate within three vulnerable reef areas, known as Beer Home Ground, Lane's Ground and Saw-tooth Ledges. This agreement came in to effect in 1995. The agreement was considered a partial success, with many fishermen abiding by it. However this abiding by the agreement was not universal, and damage continued to be recorded.

As a consequence, in July 2008 a larger area of 60 square miles within Lyme Bay was closed to all towed bottom gear fishing by Statutory Instrument. This area enclosed to three existing voluntary areas.

In particular, regular scallop dredging activity was believed to be causing significant degradation of habitat and loss of epifaunal species within rocky reef and mixed ground (areas comprising mixtures of boulders, cobbles, pebbles, shells and shell and stone gravel).
Lyme Bay seabed badly damaged by scallop dredging copyright Colin Munro
An area of cobble reef within Lyme Bay badly damaged by scallop dredging. This formed of towed fishing gear used over rocky reefs leaves the area largely devoid of life with large amounts of broken rock.
Pristine area of cobble reef within Lyme Bay, undamaged by scallop dredging. Copyright Colin Munro
A nearby area of relatively pristine cobble reef, untouched by scallop dredgers. Larger, longer-lived species such as the axinellid sponge Axinella dissimilis (yellow sponge, centre) and the large sea squirts Phallusia mammillata (white sea squirt, centre foreground) flourish on the undisturbed reef.
The reefs of Lyme Bay

The 'hard ground' within Lyme Bay comprises a mixture of low limestone ledges, mudstone ledges, boulder reefs and boulder, cobble and pebble patchworks. The deeper reefs (between 20 and 30 metres depth) support diverse communities of sponges, hydroids, soft coral, gorgonions, bryozoans and ascidians (sea squirts). The fauna communities present can be very different between different reefs, depending on the location, size, depth and relief. Cobble and small boulder reefs tend to support high densities of sponges, hydroids, anemones, tube worms and solitary and colonial ascidians.

Outer Saw-tooth Ledges reef, Lyme Bay. This is a reef composed or level limestone bedrock with undercut ledges. A rich seabed community of seafans (Eunicella verrucosa), dead men's fingers soft corals (Alcyonium digitatum), sponges and bryozoans carpets the upper faces of the rock. Copyright Colin Munro
Outer Saw-tooth Ledges reef, Lyme Bay. This is a reef composed or level limestone bedrock with undercut ledges. A rich seabed community of seafans (Eunicella verrucosa), dead men's fingers soft corals (Alcyonium digitatum), sponges and bryozoans carpets the upper faces of the rock. Image: Colin Munro
Boulder and cobble reefs: Lane's ground
Lane's Ground reef, Lyme Bay. Undamaged area. Lane's Ground is an area of cobble reef, comprising small boulders, cobbles, pebbles, gravel and sand. Due to it's low profile it has suffered extensive damage due to mobile fishing gear. Benthic trawls and scallop dredges will turn and roll small boulders and cobbles, destroying the fragile species growing on them. They will also mobilise large amounts of fine sediment, which then settles on the rock and attached species. as many of these are filter-feeding organisms they are effectively smothered by this layer of sediment. The above picture (taken in 2009) represents one of the remaining relatively undamaged areas. A wide range of colourful branching and encrusting sponges can be seen covering the boulders and cobbles. Now that all ofLane's Ground is protected by law from mobile fishing gear it is hoped that damaged areas will recover with species re-colonising from the relatively pristine areas. Image: Colin Munro
Lane's Ground reef, Lyme Bay. Undamaged area. Lane's Ground is an area of cobble reef, comprising small boulders, cobbles, pebbles, gravel and sand. Due to it's low profile it has suffered extensive damage due to mobile fishing gear. Benthic trawls and scallop dredges will turn and roll small boulders and cobbles, destroying the fragile species growing on them. They will also mobilise large amounts of fine sediment, which then settles on the rock and attached species. as many of these are filter-feeding organisms they are effectively smothered by this layer of sediment. The above picture (taken in 2009) represents one of the remaining relatively undamaged areas. A wide range of colourful branching and encrusting sponges can be seen covering the boulders and cobbles. Now that all ofLane's Ground is protected by law from mobile fishing gear it is hoped that damaged areas will recover with species re-colonising from the relatively pristine areas. Image: Colin Munro
Probably the best known (and most studied ) of these is known as 'Lane's Ground' reef. This is a narrow strip of 'hard ground' that runs parallel to the shore, approximately 3 nautical miles south of Lyme Regis. Such areas are especially vulnerable to damage by mobile fishing gear. Being relatively low lying they present little physical impediment to dredges or rock-hopper trawls (these are trawl nets fitted with large rubber discs along the footrope at the mouth of the trawl net, allowing the net to ride over small boulders without snagging). The smaller boudlers and cobbles present can also be overturned and rolled by the gear passing across them and consequently soft bodied or fragile attached animals are destroyed. Much of Lane;s Ground reef has been very badly degraded between 1990 (when I first started diving there) and 2008. However the substrate, boulders and cobbles, still remains and pockets of relatively pristine reef can still be found. There is therefore good reason to be optomistic that the reef will recover over time now that the use of trawls and dredges across it is banned.
Colin Munro, 30th March 2010. This is a new section that will be expanded over the coming weeks