Lyme Bay Reefs

As I’ve been writing a fair amount about Lyme Bay and the Lyme Bay Closed Area protection and its effects recently, I thought I’d post a small selection of images to illustrate why the reefs of Lyme Bay are so important.

Sunset corals,Leptopsammia pruvoti, growing on the Saw-tooth Ledges Reef, Lyme Bay, Southwest England. Colin Munro Photography. www.colinmunrophotography.com

Sunset corals,Leptopsammia pruvoti, growing on the Saw-tooth Ledges Reef, Lyme Bay, Southwest England.

Sunset corals are one of the very few species of true corals (i.e. stony, or scleractinian, corals, the sort that are responsible for spectacular reefs in tropical waters). It is a solitary coral, where each polyp attaches to the underlying rock and grows seperately, so does not form colonies or reefs. They do however grow in quite dense clusters and are quite beautiful. Sunset corals are rare in UK waters, known to occur at only a handful of locations. The saw-tooth ledges reefs in Lyme Bay support one of the densest populations found around the UK and also the easternmost population known in UK waters.

 Lane's Ground Reef, a circalittoral boulder reef rich in sponges and and ascidians, within Lyme Bay Closed Area, Lyme Bay, southwest England. Colin Munro Photography. www.colinmunrophotography.com

Lane’s Ground Reef, a circalittoral boulder reef rich in sponges and and ascidians, within Lyme Bay Closed Area, Lyme Bay

Lane’s Ground Reef is a boulder reef known for its rich assemblage of sponge species. In recent years these appear to have undergone a significant decline, attributed to bottom trawling and scallop dredging, however since the establishment of the Closed Area, from which trawlers and scallop dredgers are banned, there are now signs of a recovery.

Cliona celata is one of the most distinctive sponges found in UK waters. Colin Munro Photography. www.colinmunrophotography.com

Cliona celata is one of the most distinctive sponges found in UK waters

The boring sponge, Cliona celata, is one of the most distinctive sponges in UK waters, with its brilliant sulphur yellow colouring and large size. In fact much of the sponge is hidden as, through a process still not fully understood, it bores in to limestone and sandstone. Apart from this ‘massive’ form shown here, the sponge also occurs in a purely boring form where only the circular yellow oscules can be seen protruding from the rock surface. It is believed that the sponges ability to bore into hard limestone is due to chemicals released, possibily acids.

Large, mature pink seafans, Eunicella verrucosa, growing on the East Tennants Reef, Lyme Bay, SW England. Colin Munro Photography. www.colinmunrophotography.com

Large, mature pink seafans, Eunicella verrucosa, growing on the crest of a rock slab, East Tennants Reef, Lyme Bay.

Pink seafans, Eunicella verrucosa, are the only seafan (gorgonion) species known to occur in English waters. The East Tennants Reef supports one of densest and most extensive populations of seafans in the English Channel. The seafans found here are notable for their large size in addition to the high density found here.

A perfectly camouflaged Tritonia nisodnheri nudibranch feeding on a seafan (Eunicella verrucosa) polyp. Colin Munro Photography. www.colinmunrophotography.com

A perfectly camouflaged Tritonia nisodnheri nudibranch feeding on a seafan (Eunicella verrucosa) polyp

The nudibranch (seaslug) Tritonia nilsodnheri feeds exclusively (as far as we know) on the polyps of of gorgonions and soft corals. The processes on its back strongly resemble seafan polyps and so it is almost perfectly camouflaged on its host. It has been proposed that its pink coloration comes from feeding on pink E. verrucosa seafans. Like E. verrucosa it comes in two colour morphs, pink and white. In English waters where seafans are mostly pink (a small percentage are white) so most Tritonia are also pink. In this picture the Tritonia can be seen sucking the soft polyp tissue out from within the harder calyx that surrounds each polyp.

For more information about Lyme Bay Closed Area and the work we have been doing there to understand the changes occurring following establishment of statutory protection in 2008, read the blogs on my Marine Bio-images website.

Lyme Bay Closed Area Monitoring

Lyme Bay Closed Area Monitoring: what we have learned so far

For more background on Lyme Bay reefs. Lyme Bay: what makes it special?

And finally, for a clearer understanding of why scallop dredging is so damaging. Scallop dredging, whay is it considered so damaging to reefs?

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Marine habitat mapping

One of Marine Bio-images’ areas of expertise is Marine Habitat Mapping. We have undertaken a great many mapping studies in the past 20 years, these include biotope mapping of the isle of Scilly sublittoral soft sediments, biotope mapping of the littoral and sublittoral habitats of the Dornoch Firth, biotope mapping of Plymouth Sound soft sediment and reef areas, habitat mapping within Lyme Bay, and habitat mapping of the sublittoral within Lamlash Bay No-take Zone (Isle of Arran).  We use a variety of techniques, depending on depth, turbidity and the size and scale of the features to be mapped.  We have particular expertise in combining drop-down and towed camera systems with diver spot surveys.  This technique is highly cost-effective, providing a wide coverage (using camera systems) along with very detailed data collected by divers.

Dense bed of brittlestars (Ophiothrix fragilis), Lyme Bay, Southwest England, UK. Dense aggregations of brittlestars are a distinctive feature of Lyme Bay.

Dense bed of brittlestars (Ophiothrix fragilis), Lyme Bay, Southwest England, UK. Dense aggregations of brittlestars are a distinctive feature of lyme Bay.

We also use acoustic techniques, including side scan sonar, to provide detail on the seabed releif and likley sediment type.  For soft sediment areas we will ground truth this by grab sampling.

Habitats are subsequently mapped using GIS to produce detailed geo-referenced habitat maps for the features of interest.

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Lyme Bay Closed Area Monitoring: what we have learned so far.

After almost 18 years of research, campaigning and negotiation, statutory protection for the most vuulnerable reefs in Lyme Bay became a reality in 2008.  This was deemed necessary as, despite voluntary agreements, it was apparent the damage to the reefs was still occurring.  The questions that needed to be addressed then became:

  • how will the species on the reefs respond?
  • How long will full recovery take?
  • Will the species that appear to have been hardest hit, the sponges, the seafans, the soft corals, the larger sea squirts, re-establish themselves in a few years or will other species colonise the reefs first?

Between summer 2008 and summer 2010 we undertook a monitoring programmme looking at the species present and how there numbers were changing.  In that time we have just started to get the first tantalising glimpse of the changes occurring.

We have now been able to publish our report on the monitoring work we undertook looking at the changes that occurred on boulder reef communities. The full report (as a PDF) can be downloaded Here: Lyme_Bay_Closed_Area_Monitoring_2008-2010_MBI.

However, as this is a fairly lengthy document it seemed a good idea to summarise what we’ve found so far in a fairly non-technical way, so here goes.

Before describing our findings it’s worth going over a description of Lyme Bay and a bit of background regarding the concerns about bottom fishing towed gear and earlier attempts at achieving a degree of protection.  This helps explain some of our reasoning in survey design and interpretation of the data. (If you only want to read the outcomes then skip down to What we have found so far? near the bottom)

Lyme Bay is a large, open, south-facing bay in Southwest England, opening into the English Channel (see study layout map, below).  The West of the Bay is predominantly fine sediment seabeds, fine sands or mud.  The waters in the west also tend to be more turbid.  This is in part due to the tides are being weaker in the western part of the Bay (allowing fine sediments to settle out of the water column) and also because much of the rock here is soft, rapidly eroding sandstone.  But mostly it is because of the two major rivers, the Teign and the Exe, which flow in to the western side of Lyme Bay carrying large sediment loads which are then deposited in the Bay.

Tidal streams are markedly stronger and no rivers flow into the eastern part of Lyme Bay.  The seabed here is much rockier and sediment tends to be much coarser.  The greater amounts of exposed bedrock, in particular the high rocky ledges, and stronger currents, generally results in richer assemblages of filter feeding animals such as larger erect sponges, gorgonians, soft corals.

Map depicting the Closed Area (yellow); pre-existing Voluntary exclusion areas (Closed Controls: light green) and our monitoring station locations (red polygons).  The pre-existing voluntary exclusion areas were agreed between local fishermen and the Devon Wildlife Trust between 2001 and 2006.  They were partially successful but not all vessels appeared to abide by the agreement and damage to the reef habitats continued, hence the statutory closed area was created.

Map depicting the Closed Area (yellow); pre-existing Voluntary exclusion areas (Closed Controls: light green) and our monitoring station locations (red polygons). The pre-existing voluntary exclusion areas were agreed between local fishermen and the Devon Wildlife Trust between 2001 and 2006. They were partially successful but not all vessels appeared to abide by the agreement and damage to the reef habitats continued, hence the statutory closed area was created.

The reefs of greatest concern in relation to damage from scallop dredges and trawlers were located a little to the east of the centre of the Lyme Bay.  They lie in a band between (roughly) 20 and 24 metres below chart datum (approximately 22 – 29 metres actual depth depending on the state of the tide).  Back in 1992 the Devon Wildlife Trust began getting reports of damage to reefs caused by rockhopper trawls and in particular scallop dredges.  We then conducted a series of diving surveys, documenting the damage occurring here for the first time.  After many years of negotiation, Devon Wildlife Trust and local fishermen reached an agreement whereby bottom towed fishing gear would not operate within two vulnerable reef areas, known as Lane’s Ground and Saw-tooth Ledges.  This agreement came in to effect in 2001.   Two other reef areas, known as Beer Home Ground and the East Tennants Reef, were subsequently added in 2006.  This was a considerable achievement by both Devon Wildlife Trust and local fishermen, and the agreement was largely adhered to.  The problem was it wasn’t adhered to by everyone, and one or two scallop dredgers passing through such an area will cause damage that will linger for years.  So, 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 the four existing voluntary areas.

At this point the need to begin monitoring of how the newly protected area responded to this protection was recognised.  The question was, how to design the monitoring?  Ideally monitoring would have commenced several years before the statutory protection came in to place, allowing a time series of before and after comparisons . However that had not happened and nothing could be done about that now.  Comparison of change in reef habitats inside and outside of the protected area is another approach, but the problem here is that (as described above) conditions and habitat vary markedly across the bay to the east and west and it was very unlikely that similar habitats existed to the east or west of the closed area box, or that species would reproduce, settle, grow and interact in similar ways east or west of the Closed Area box as they would inside the box.  South (offshore) of the box conditions were very different; the water was deeper and the seabed mostly sedimentary, thus it could not be used for comparison either.  There are also the four existing voluntary protected areas to consider.   One possibility is to compare existing voluntary protected areas with areas in the new Closed Area.  If this approach is taken two important factors must be taken in to account.  The first consideration is that each of the voluntary protected areas was very different to the others, in terms of habitat and the species assemblage they support.  By way of example, if one considers Lane’s Ground Reef and East Tennant’s Reef (See map above).

An isolated seafan (Eunicella verruucosa) on Lane's Ground Reef.  This is a very large seafan for Lane's Ground, most are typically around half this size. Marine Bio-images.

An isolated seafan (Eunicella verruucosa) on Lane’s Ground Reef. This is a very large seafan for Lane’s Ground, most are typically around half this size. note that there are no other seafans in sight; this is typical of their sparse distribution on Lane’s Ground. Note also the small boulders that form the reef. The relative instability in stormy seas are probably factors that limit the size of seafans here.

East Tennants Reef is slightly deeper, exposed to slightly stronger currents and is composed of large slabs of limestone, whereas Lane’s Ground is composed of small boulders on patches of sand, gravel and stones.  Lane’s Ground supports relatively few seafans, somewhere in the order of 1-10 per 100mm2.  No large seafans are found on Lane’s Ground Reef, presumably due to a combination of greater exposure to wave action (as shallower), reduced feeding currents and reduced stability of the smaller boulders.

Dense cluster of large seafans (Eunicella verrucosa) typical of East Tennants Reef.  Marine Bio-images.

Dense cluster of large seafans (Eunicella verrucosa) typical of East Tennants Reef. note also the large, stable limestone slabs to which they are attached, and also the numberous (white, background) soft corals Alcyonium digitatum which are also much larger and more numerous here than at Lane’s Ground Reef. This helps illustrate the uniqueness of each reef in Lyme Bay and why treating either the entire Closed Area or all voluntary closuures (Closed Controls) as a single treatmment or entity would not work.

East Tennant’s Reef, in contrast, supports very high densities of large seafans, averaging several hundred per  100mm2, mature colonies being 4-5 times the size of those on Lane’s Ground.  Thus the biomass and reproductive capacity of seafans on East Tennant’s Reef will be many times greater than that on Lane’s Ground and, as conditions are clearly much more favourable to seafans here, it would be unsurprising if settlement, early survivorship and growth rates were higher here also.  So we can see that it is not possible to treat all pre-existing voluntary areas as one condition or ‘treatment’ to compare with newly protected areas outside.  The second factor to consider is that the differences between the existing voluntary protected areas and the newly protected Closed Area beyond their borders were subtle.  Remember the statutory protection was established because the voluntary protected areas were not being fully complied with.  Thus they will not be uniformly ‘better’ than the areas outside; rather they are a patchwork of relatively pristine and recovering areas (the degree of recovery depending on how long ago they were established, 2002 or 2006) and of damaged areas due to recent incursions.

The hypothesis we were required to test under the funding from Natural England was that:
Over time, species assemblages within sites in the new statutory closure but outside the pre-existing voluntary closures would change to more closely resemble those in the pre-existing voluntary closures and become less similar to sites where fishing by towed bottom gear was still permitted.

From what we already know about the Bay and about the voluntary closures we  can Immediately see problems here:  both in comparing what’s happening inside the Statutory Closure to what’s happening outside and in comparing the voluntary closures to the areas of the new statutory closure outside the voluntary closures.

Lane's Ground Reef is a linear reef, running east-west, composed of a matrix of boulder reef patches interspersed with sand and gravel patches. marine Bio-images

Lane’s Ground Reef is a linear reef, running east-west, composed of a matrix of boulder reef patches interspersed with sand and gravel patches.

Like all the reefs in Lyme Bay, Lane's Ground Reef is not one continuous area of similar habitat, rather it is a complex matrix of ribbons of boulder reef interspersed with patches of coarse sand and gravel.  This is further complicated by the fact that trawlers and scallop dredgers have fished across the reef, creating wide swathes of degraded reef.  In order to ensure meaningful comparisons our monitoring stations needed to be located on areas of boulder reef that did not appear degraded.  It can be seen that these formed only small areas within the Lane's Ground voluntary closure and so careful pre-selection of suitable areas was required before haphazardly dropping our station markers within those areas. arine Bio-images

Like all the reefs in Lyme Bay, Lane’s Ground Reef is not one continuous area of similar habitat, rather it is a complex matrix of ribbons of boulder reef interspersed with patches of coarse sand and gravel. This is further complicated by the fact that trawlers and scallop dredgers have fished across the reef, creating wide swathes of degraded reef. In order to ensure meaningful comparisons our monitoring stations needed to be located on areas of boulder reef that did not appear degraded. It can be seen that these formed only small areas within the Lane’s Ground voluntary closure and so careful pre-selection of suitable areas was required before haphazardly dropping our station markers within those areas.

This is the approach we took.

  1. We elected to work with one Voluntary Closed area only, Lane’s ground reef, as (as described above) the differences between the different voluntary closed areas was far greater than any likely change in species’ abundances due to cessation of fishing  in the three years of the study.  To mix habitats through treating multiple voluntary closures as single treatments would simply create vast amounts of ‘noise’  and introduce many other factors than may be responsible for differences in response, other than cessation of fishing, and so making it impossible to interpret the data. This also meant we could very tightly define the habitat we were studying, in terms of seabed composition, relief, depth, tidal streams and wave exposure, all factors we were aware would markedly modify the species assemblage and so potentially compromise our interpretation.  There were a couple of other factors in our selection process.  Being relatively level with only small boulders present, Lane’s Ground Reef was relatively easy for trawlers and scallop dredgers to work; there were no ledges or large rocky outcrops on which to come fast or damage gear.  The fact that it was level also made it much easier to extract reliable data; it is hard to get good quatitative data from reefs with ledges, overhangs, steep slopes etc simply because of the logistics of laying and counting withing transects and quadrats.  We also had very good historical data on Lane’s Ground Reef.  Numerous surveys (many by ourselves) had been conducted there over the previous 18 years, thus we had a very good handle on the habitat, the species we were likely to find and their distribution.  This hugely aided our survey design.   A final, but very important consideration was that Lane’s Ground Reef had been identified previouusly as especially important for its sponge assemblages.  Now we knew that sponges amongst the most vulnerable to mobile fishing gear and there was a lot of anecdotal evidence and comparative video suggesting that sponges had declined markedly on Lane’s Grouund over the past decade.  But the boulder reef habitat was still largely intact, so this seemed an ideal testing ground to find out whether they would recover once physical disturbance cesed.
  2. The aim, within the hypothesis to be tested, was to compare relatively pristine sites (the voluntary closures) with the newly protected sites within the Closed Area and also with the unprotected areas outside the Closed Area.  But we knew the voluntary closures were not pristine and contained many areas similarly damaged to those within the new closure.  Clearly, simply randomly assigning areas within the voluntary closure would not achieve this, so instead we elected to conduct a pre-survey of Lane’s Ground voluntary closure to identify relatively pristine areas, from within in which our ‘pristine’ comparisons would be haphazardly located (i.e. a random stratified approach).  This proved to be more important than we had expected; significant tracts of Lane’s Ground voluntary closure appeared markedly degraded (i.e. showing clear signs of physical damage or markedly reduced numbers of epifaunal species compared to historical surveys of the reef), with relatively pristine areas appearing no more than small ‘islands’ dotted across the reef.
  3. Comparing with areas outside the statutory Closed Area, as the contract required, proved most problematic.  In the end we elected to compare with areas running along the same depth contour as Lane’s Ground Reef, where similar boulder reef habitat occurred immediately outside the Closed Area.  This was a difficult choice.  Selecting areas immediately outside left our study open to criticisms of ‘edge effects’ such as ‘fishing the line’ (where fishermen tend to work along the edges of a protected area more so than further afield).  Yet as we knew, conditions varied markedly as one travelled east, west or south of the Closed Area, and that similar habitat was very difficult to find outside the Closed Area, thus rendering data from further afield unsuitable for comparison.

The layout of the study is shown here.  Four monitoring stations were located within Lane’s Ground Reef (what had been the old voluntary closure and was now referred to, conforming with the terminology defined by Plymouth University, as the Closed Control), three within the new Closed Area, but outside of the voluntary closure (termed the New Closure) and three just outside of the new Closed Area, termed the Open Controls.  So, testing the hypothesis

What have we found so far?
So, what we found was the hypothesis (comparing station outside the Closed Area to those within) didn’t work – essentially because the underlying assumptions were incorrect, namely that the conditions outside of the Closed Area were similar to those inside.  Even when carefully selecting habitat type the results demonstrate that environmental conditions outside of the Closed Area are too dissimilar for meaningful comparisons (in terms of change likely to be due to bottom fishing effects) to be made.  Given what we already knew about the Bay this was no great surprise.  The data also suggested that the New Closure and the Closed Controls were also different when one looked at all the species studied, but with a fair degree of overlap when individual species were studied.  Again this was not terribly surprising.  What we, however, did see was a certain amount of change in both New Closed and Closed Controls.  Now three years (essentially three data points on our time series) is a very short timescale for the species we are looking at, but what it does suggest is that both new closures and existing voluntary closed areas may be responding to the cessation of trawling and dredging.  Again this is not hugely surprising. We know that the existing voluntary closure had suffered from incursions and so was not pristine at the start of the study;  areas not impacted by direct disturbance (i.e. trawls or dredges passing directly over) are likely to have suffered indirectly from the effects of increased sediment plumes as gear passed nearby and mobilised seabed sediments.  As most of the species of concern (sponges, hydroids, soft corals, gorgonians, sea squirts) are filter feeding organisms it is quite likely this had a deleterious effect on them.   Thus even areas that we had pre-selected as relatively pristine may have deteriorated due to the proximity of mobile fishing gear.  This may seem like a bit of a failure, but it is useful as there is often considerable pressure to design studies that are statistically elegant but do not take in to account the complexities and variability of the real environment.

Signs of recovery?
Perhaps the most exciting of all is the possible early signs of sponge assemblage recovery.

Sponges, in particular erect branching sponges, are possibly the most vulnerable of the prominent species found in Lyme Bay.  They are soft bodied and easily destroyed by physical contact.  They are also filter feeders and so likely to suffer from significant increases in sedimentation.  Many are believed to be very slow growing, studies at Skomer and Lundy Island Marine Nature reserves indicate that axinellid sponges (a significant group of erect branching sponges) suggest they are very long lived.  Sponge assemblages have also previously been identified at one of the most notable features of the reefs in Lyme Bay, with Lane’s Ground Reef highlighted as previously supporting particularly rich sponges assemblages and that these rich sponge assemblages were, probably more than any other feature, what made the reefs of such high conservation importance, with many unusual or rare species and others not yet fully identified.   Thus determining whether sponge assemblages recover, and over what timescale, is fundamental to identifying whether the protection afforded to Lyme Bay is a success.

Lyme Bay Closed Area Monitoring.  Change in erect branching sponges 2008 - 2010 within diver transects.

Change in erect branching sponges 2008 – 2010 recorded within diver transects at Open Controls (outside closed Area), New Closures (within Closed Area but outside old voluntary closures) and Closed Control (within Lane’s Ground pre-exisiting voluntary closure). Note the marked jump in mean numbers between 2008 (the start of our study and the first year of the statutory closure) and 2009. Although there is some drop back in 2010 numbers are still notably higher than 2008.

We believe this work is extremely important.  The opportunity to conduct such a study as Lyme Bay affords us comes only very rarely.  Lyme Bay Closed Area is the first such closed area established for conservation purposes in England’s waters.  Furthermore, there are few areas of coastal seabed as well studied as Lyme Bay, thus although we don’t have the ideal pre and post closure monitoring we do possess a wealth of data on what these reefs used to be like almost 20 years ago.  Given the uniqueness of this opportunity and the very encouraging signs in the data from the first three years it would seem essential that the monitoring is continued.  Currently, although the signs are both encouraging and more or less exactly what we would expect given what we already know about Lyme Bay they are, with only three years data, simply an indication of where change might be heading and no more.  Consequently we are now actively seeking funding to restart monitoring in 2013.

[Rockhopper trawls: bottom trawls fitted with extra large rubber discs on the footrope, allowing them to bounce or roll over boulders and small rock outcrops and so work rocky seabeds that other trawls could not]

 

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Diver surveys and Scientific diving services

A Marine Bio-images diver conducts species counts within random quadrats on the seabed in Lyme bay, Southwest England.

A Marine Bio-images diver conducts species counts within random quadrats on the seabed in Lyme bay, Southwest England.

Much seabed data can be collected remotely nowadays, but sometimes, when detailed biological data, high quality images or detailed inspection is required, the only practical solution is to use professional scientific divers.  Marine Bio-images can provide HSE qualified dive teams comprising highly experienced diving marine biologists. Our divers are both very experienced SCUBA divers and biologists with many years experience in underwater data collection, survey and sampling.  To discuss a diving project call +44(0)7926478199 or email marine bio-images here.

Marine Bio-images diving biologist collecting sediment core samples for infauna analysis, particle size analysis and analysis for carbon content.   Colin Munro

Marine Bio-images diving biologist collecting sediment core samples for infauna analysis, particle size analysis and analysis for carbon content.

A Marine Bio-images scientific diver videos along a survey transect line as part of a no-take-zone monitoring programme.  West Scotland. Colin Munro.  Marine Bio-images

A Marine Bio-images scientific diver videos along a survey transect line as part of a no-take-zone monitoring programme. West Scotland.

Marine Bio-images diver Colin Munro preparing to dive with Sony EX1 HD video camera to recoding impacts of trawl gear on the seabed.

Marine Bio-images diver Colin Munro preparing to dive with Sony EX1 HD video camera to recoding impacts of trawl gear on the seabed. image (C) Holly Latham

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Remote video and stills survey and monitoring

Marine Bio-images drop stills camera and video system being deployed from a RIB as part of our monitoring of Lamlash Bay no-take zone

arine Bio-images drop stills camera and video system being deployed from our rigid inflatable boat as part of our monitoring of Lamlash Bay no-take zone

Our lightweight drop camera system can be used as a drop video system, drop stills camera system or a combined video and stills camera system. Remote video is very useful for providing a rapid overview of marine habitats and structures and for mapping extensive features (e.g. seagrass beds, reefs and wrecks) however even HD video is poor for producing detailed species lists and counts. This is because most HD produces stills images less than 1 megapixel in size and, because of the nature of video capture, these often suffer from motion blur. By combining video with regular high resolution (10 megapixel) stills snapshots which are sharp and well lit we are able to conduct rapid mapping of underwater features and simultaneously produce high quality stills suitable for detailed analysis.

Our drop camera system is lightweight, small enough to be carried as personal luggage on airlines, does not require external power and the topside unti is fully waterproof so can be deployed from small open boats. It currently has a working depth of 0-45m. Deeper systems can be supplied with a little notice.

I will add seabed stills and video footage shortly, meanwhile you can contact me for further info at colin-m@marine-bio-images.com

 

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Lyme Bay Closed Area Monitoring

Lyme Bay Closed Area Monitoring. 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.

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.

Final Report covering diver monitoring 2008-2010 now available here.

Introduction

In 2008, DEFRA closed an area of Lyme Bay, southwest England, some 60 square miles in extent to all 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. This was a hugely important step; the first such area in England closed specifically for nature conservation purposes, and the culmination of 18 years of data collection, eductaion and campaigning by organisations such as the Devon Wildlife Trust.  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 was part of the consortium (lead by Plymouth University) conducting a monitoring programme to study the recovery of the newly protected area of seabed. our particular study focussed on the monitoring of cobble reef areas. We chose to do this by SCUBA diving. This decision was based on our long experience in survey and monitoring, and are knowledge of the area.  Most of the species of interest are quaite small small and difficult to spot and the three-dimensional nature of the habitat and the relatively turbid waters of the bay there was no way of collecting the required data remotely with the necessary accuracy. The study collected data on species at 10 fixed stations, 4 stations within pre-existing voluntary closues (also inside the new statutory closure), 3 stations within the new statutory closure (but outside the pre-existing voluntary closures) and 3 outside the new stautory closure. At each station 8 0.25m sq. quadrat counts were conducted and larger species were counted within an 8m belt transect. This study began in September 2008 and ended in August 2010; three annual data sets being collected. the final report has now been completed and we waiting to hear from DEFRA when the report will be published.


View Larger Map

Map depicting the Closed Area (yellow); pre-existing Voluntary exclusion areas (light green) and our monitoring station locations (red polygons). The pre-existing voluntary exclusion areas were agreed between local fishermen and the Devon Wildlife Trust between 2001 and 2006. They were partially successful but not all vessels appeared to abide by the agreement and damage to the reef habitats continued, hence the statutory cosed area was created.

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 Closed Area Monitoring. An area of boulder reef within Lyme Bay badly damaged by scallop dredging.  Scallop dredges,  when used over rocky reefs leaves the area largely devoid of life with large amounts of broken rock.  Even a single pass by such gear can cause large amounts of damage and recovery may take many years.

An area of boulder reef within Lyme Bay badly damaged by scallop dredging. Scallop dredges, when used over rocky reefs leaves the area largely devoid of life with large amounts of broken rock. Even a single pass by such gear can cause large amounts of damage and recovery may take many years. Photograph Colin Munro.

The reefs of Lyme Bay

The ‘hard ground’ (as most local fishermen call it) 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.

 Lyme bay Closed Area Monitoring. 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.  (C) Colin Munro

A nearby area of relatively pristine cobble reef, I took this image some years ago, before scallop dredgers had made major inroads in to Lane’s Ground Reef. 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. In years to come Axinella dissimilis, a long lived and slow growing species, would become rare on the reef.

 Lyme Bay Closed Area Monitoring.  This photograph (taken in 2009) shows an area of relatively undamaged area of Lane's Ground Reef, one of the few patches still untouched by trawls and dredges.  A wide range of branching and encrusting sponges can be seen covering the boulders.

This photograph (taken in 2009) shows an area of relatively undamaged area of Lane’s Ground Reef, one of the few patches still untouched by trawls and dredges. A wide range of branching and encrusting sponges can be seen covering the boulders.

Lane’s Ground Reef

The best known (and most studied ) of these boulder reefs in Lyme Bay is 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. Lane’s Ground is an area of boulder 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. The relatively flat reef presents little obstacle to scallop dredgers, there are no large rock outcrops on which to snag 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. 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.  Although Lane’s Ground was one of the initial voluntary exclusion areas agreed in 2001, damage continued.  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.

The next part of this blog will provide more detail on our study methodology and its findings.

Lyme Bay Monitoring Study: Lyme Bay Closed Area - Measuring Recovery of Benthic Species in cobble reef habitats. marine Bio-images

Lyme Bay Monitoring Study: Lyme Bay Closed Area – Measuring Recovery of Benthic Species in cobble reef habitats. Marine Bio-images

Final Report covering diver monitoring 2008-2010 now available here.

Back to Marine bio-images website

 

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