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Sunset corals

Leptopsammia prouviti, growing on undercut limestone ledges, Lyme Bay, Southwest England. colin munro photography

Sunset corals (Leptopsammia pruvoti), a little natural history.

Leptopsammia prouviti, growing on undercut limestone ledges, Lyme Bay, Southwest England. colin munro photography

Leptopsammia prouviti, growing on undercut limestone ledges, Lyme Bay, Southwest England.

For most, the word coral conjures up images of living reefs surrounded by shoals of colourful fish, in clear, brightly lit tropical waters.  Whilst this is the type of environment where the vast majority of coral species are found, it is not the exclusive habitat.  That corals are found in the chilly and turbid seas around Britain would probably surprise most of theBritish public.  In fact there are five known species of coral found in shallow waters around the UK.  The two best known species are the Devonshire cup coral, Caryophyllia smithii, and the sunset coral, Leptopsammia pruvoti.  Like all our shallow water corals they are solitary corals (apart from the Weymouth carpet coral, Hoplangia durotrix, which forms small clusters of polyps growing from a basal plate).  They don’t form large, colonial skeletons and hence don’t form reefs.The Devonshire cup coral is familiar to many divers and may even be found intertidally in shady overhangs at the very bottom of the tide.

Leptopsammia pruvoti is rather more enigmatic.  It is known to occur in only a handful of locations around Southwest Britain (The Scilly Isles, Lundy Island, Plymouth Sound, Lyme Bay and Portland Bill) though it is more widely distributed along the Atlantic coast of southern Europe and in the Mediterranean.  Leptopsammia pruvoti belongs to the taxonmic family Dendrophylliidae, a sub-group of corals.  An interesting feature of nearly all (around 91%) Dendrophylliidae corals is that they lack symbiotic zooxanthellae (technically speaking they are azooxanthellate).  At this point you may be asking ‘so why is that a big deal … and what exactly are symbiotic zooxanthellae anyway?’.  A common feature of most reef building corals (hermatypic corals) is the presence of tiny unicellular algae, termed zooxanthellae, living  within their tissues.  This is a symbiotic relationship; Zooxanthellae gain protection and some nuitrients from the coral whilst the coral gets glucose, glycerol and amino acids from the unicellular algae.  One of the key benefits for the coral is that this facilitates the production of large amounts of calcium carbonate, the material from which coral skeletons are formed.  Thus the calcuim carbonate based, skeleton-forming process in corals containing zoozanthellae is ‘turbo-charged’; they are able to produce skeletal material at a greater rate and so can grow to form large, colonial skeletons that meld together and form reefs.  Azooxanthellate corals do not have this advantage, but their lack of dependence on photosynthesising algae frees them to expand beyond the brightly-lit surface waters. Azooxanthellate corals in the family Dendrophylliidae can be found from a few metres depth down to over two thousand metres.  This takes them deep into the aphotic zone, the parts of the ocean completely devoid of light (roughly, below 1000 metres).  It also allows them to colonies niches that are out of direct sunlight, such as caves (e.g. the recently discovered coral Leptoseris troglodyta, troglodyte= ‘cave dweller’, found around Indonesia and the Philippines) or the rock overhangs of Lyme Bay.

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Lyme Bay Reefs.

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

This blog post about the marine life and importance of Lyme Bay Reefs has moved to my marine biology website: Marine-bio-images.com. You can read it here at:

https://www.marine-bio-images.com/blog/lyme-bay-marine-ecology/lyme-bay-reefs/

Lyme Bay, Lane’s Ground Reef: sponge species recovery and opportunities lost

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

This blog post has now moved to my Marine Biology website, Marine-bio-images.com. It can be read at:

Lyme Bay, Lane’s Ground Reef: sponge species recovery and opportunities lost

https://www.marine-bio-images.com/blog/lyme-bay-marine-ecology/lyme-bay-lanes-ground-reef-sponge-species-recovery-and-opportunities-lost/

Lyme Bay, what makes it special?

Lyme Bay, what makes it special?

I’ve published about Lyme Bay marine biological monitoring on my marine-bio-images blog   here and earlier on this blog here, looking at the monitoring of Lyme Bay Closed Area, a Marine protected Area success? Parts 1 and 2 describe the impacts mobile fishing gear, in particular scallop dredging, had been having on the reefs since at least the late 1980s. I describe the impacts of scallop dredging in detail here. I will look soon at the actual monitoring that has taken place since the closed area came in to being in 2008, but before doing so it is probably worth devoting a couple of blogs to describe why Lyme Bay is important and worth protecting; just what makes it special.

What Lyme Bay is not

In seeking to justify protection for the reefs and ‘sell’ the area to the wider public, the concepts of ‘coral gardens’ and ‘charismatic species’ has often been pushed.  Such poetic language may well raise the area’s profile and engender support in the short term, but it has lead to some fairly profound misunderstandings – including within NGOs and Government Agencies – about the bay and the reasons the reefs within are important.

A sediment covered limestone reef in Lyme Bay, Southwest England showing the profusion of sediment tolerant species that grow on such reefs. Colin Munro Photography.

A sediment covered limestone reef in Lyme Bay, Southwest England showing the profusion of sediment tolerant species that grow on such reefs. Image No. MBI001261.

Most of Lyme bay is not visually spectacular, there are few dramatic underwater rock cliffs painted with a riot of colour; nor is it beautiful clear water offering panoramic vistas across the seabed.  The reefs in Lyme bay are mostly low lying and the waters tend to be fairly gloomy and turbid.  As this is essentially a large, open, sandy bay exposed to the prevailing winds, then significant amounts of suspended sediment (at least near-shore, close to the seabed) are the norm.  Whilst winds may ease in summer, it is also prone to strong plankton blooms during May and June, with a second less pronounced bloom in late summer.  Thus underwater visibility rarely exceeds 10 metres (30ft) and frequently may be less than 3 metres (10ft).  The reefs in the bay, though numerous in the centre and east, are mostly discontinuous, forming a patchwork of low rocky outcrops surrounded by sediment.  This means that they tend to be covered by thin veneers of sediment as tide and wave action lifts and sweeps saltating sand across them.  The amount of sand will vary, depending on the size of the reef area, how high the reef rises above the surrounding sediment plain, the strength of tidal streams in that part of the bay and how strong the wind has been recently (and thus how big the waves).  This makes it a rather challenging environment both the underwater photographer and scientist attempting to record visual data.  Low light levels and high levels of suspended sediment producing lots of backscatter from lights making for tricky problems in producing good images.

An area of sediment covered boulder reef, Lyme Bay. The large white sea squirt Phallusia mammillata, and the blue-grey colonial sea squirt Diplosoma spongiforme, both characteristic of Lyme Bay, can be seen in this image. Image No. MBI001264. Colin Munro Photography

An area of sediment covered boulder reef, Lyme Bay. The large white sea squirt Phallusia mammillata, and the blue-grey colonial sea squirt Diplosoma spongiforme, both characteristic of Lyme Bay, can be seen in this image. Image No. MBI001264.

The species that make Lyme Bay different and the effects of the Closed Area

The flip side of this is that the communities on these reefs tend to be rather different from those inhabiting areas with perhaps more visually spectacular ‘clean’ reefs further west.  Species that tolerate a degree of sand and silt cover do well here.  A good example of this is the sponge Adreus fascicularis, a species found almost exclusively on silt-covered horizontal bedrock  Considered rare in UK waters, it is relatively common  on the reefs of Lyme Bay.  Similarly the large solitary sea squirt Phallusia mamillata.  A very distinctive species, the largest sea squirt found around British coasts its striking white colour stands out against the dull sediment.  More associated with silty, sheltered harbours and estuaries it is uncommon or rare on open coasts along the rest of its UK range, but quite abundant within Lyme Bay.  So the factors that make this a difficult environment in which to capture appealing images or gather data on the marine life in quite a significant contribute to Lyme Bay being an interesting and unusual environment. There are other species common here that we simply do not known enough about their ecology to say why they are more abundant in Lyme bay than elsewhere; a good example of this is the colonial sea squirt Diplosoma spongiforme. Though not rare elsewhere, it is abundant in Lyme Bay, forming mats, growing over rocks, seafans and other sponges. Similarly the tassled yellow sponge Iophon hyndmani/Iophonopsis nigricans (the two species are grouped together as very difficult to tell apart underwater) is particularly abundant in Lyme Bay. Indeed the sponge assemblages are frequently very rich and diverse on Lyme Bay reefs; for some reefs such as the boulder reefs (for example Lane’s Ground Reef in the central part of Lyme Bay) they are probably the most obvious characteristic of the reef and may well be the most diverse groups within the reef community there. Unfortunately they are still very poorly described (in part because sponge taxonomy is a difficult subject with field characteristics often not being sufficient for positive identification) and so are certainly under-reported and thus frequently undervalued in terms of the Bay’s conservation value. Yet sponges, being soft tissued and quite often slow-growing species, are amongst the most vulnerable to damage and eradication from areas of reef by mobile fishing gear. Indeed the sharp decline in sponge species occurring on Lane’s Ground Reef between 1995 and 2008 (clearly visible for video footage and still images taken by myself during this time period) was one of the most obvious and disturbing changes in the years before statutory protection from bottom-towed mobile fishing was established for central Lyme Bay.

Boulder reef, Lyme Bay.  The amount of suspended sediment in the water can be clearly seen.  The yellow tassled sponge Iophon hyndmani or Iophonopsis nigricans can be seen in the centre of the image, however the lack of sponges (and other attached life) compared to previous years is clear. Image No. MBI001267

Boulder reef, Lyme Bay. The amount of suspended sediment in the water can be clearly seen. The yellow tassled sponge Iophon hyndmani or Iophonopsis nigricans can be seen in the centre of the image, however it can be seen that many of the boulders are now (2010) bare of sponges and other attached life. Image No. MBI001267

Has there been a recovery of sponge species since the Closed Area was established in 2008? Our study (running from 2008-2010, when funding from Natural England ended) suggested that sponge recovery was beginning. Three years is too short a time in which to expect marked changes in such communities. It would also be foolish to read much in this data, three annual surveys (i.e. data being collected once a year for three years) represent only three data points. There will obviously be good years and bad years, plus a degree of error in any data collected, so a line drawn from three data points must come with huge caveats. Nevertheless, this slight improvement was noticeable. We are hopeful that we will be able to re-start our monitoring programme, albeit in a slightly reduced form, on a voluntary basis in 2013. It will be exciting to see what effects the Closed Area has had on the reef communities after five years.

More information about Lyme Bay, in particular the impacts of scallop dredging and the protected Closed Area, can be found on my marine biology blog www.marine-bio-images.com/blog, and on the marine-bio-images website where numerous reports on the research we have conducted here can be found.

All text and images in this blog copyright Colin Munro 2012.  All images are available to license.    Alternatively you can search all my online stock images at my www.colinmunroimages.com  site through the search box (top right) or on my main website here.

Lyme Bay Marine Protected Area: How effective is it? update

Lyme Bay Marine Protected Area: How effective is it? update

Five days ago the skipper/owner of a Brixham based trawler/scallop dredger, the Kelly Marina II (BM454) was convicted and fined for using towed bottom-fishing gear (apparently scallop dredges) within Lyme Bay Closed Area, a 60 nautical mile exclusion zone for such gear.  This Closed Area was established for conservation reasons (the first and so far only one established for such reasons in U.K. waters), specifically the rocky reefs that occur in the Bay and their associated fauna.  So, given the high profile of this recently established protected area, (widely regarded as a flagship protect and a test area for such marine pretected areas in UK waters), and given the long and protracted process (18 years between concerns being years and statutory protection finally arriving) of establishing this Closed Area, then no doubt the authorities would be keen to show that this is not just the ‘same old routine’.  One imagines they would be keen to show that this was a step change and that they were no serious about conservation.  Given also that it is quite impossible to adequately police such an area then one images that stiff punative fines would be the order of the day to send out a clear message concerning the risks if you get caught breaking the rules.  The difficulty in policing was clearly demonstrated by the fact the evidence of this vessel’s transgression was captured by a Dorset Police helicopter seconded from the Air Surveillence Unit.  One immediately wonders how often this happens when police helicopters are not around.  So, given these factors there would obviously have been a very stiff fine….er no.  The fine was £1000, plus £3000 costs and £15 victim surcharge (what?).  So a grand total of £4015; that’s just a few good days earnings for such a vessel.  now imagine a house burglar stealing televisions.  Let’s say each is worth £150 resale value.  He only does this occasionally, so manages to nick five a month on average; not bad:£750 easily earned.  Then he get’s caught, Damn! But not to worry, his fine is only 350 quid, he’s still £400 in pocket.  Not much of a deterrent is it?  Nor does it send a great message to the majority of fishermen who are abiding by the rules and incurring greater costs by having to steam further to fish outside the Closed Area (thus greater fuel costs, longer steaming time and so shorter fishing times).  The fine was imposed by Weymouth Magistrate’s Court.  You can read further details on the marine management website here.

Lyme Bay Closed Area, a Marine Protected Area success? Part 1.

Lyme Bay Closed Area, a Marine Protected Area success? Part 1.

Dense beds of mature pink seafans (Eunicella verrucosa), some almost a metre across, growing on pristine reef in Lyme Bay.

In 2008, the UK Government Department for Environment, Food and Rural Affairs (DEFRA) closed an area of Lyme Bay, some 60 square miles in extent, roughly 10 per cent of the bay, to mobile benthic fishing gear. By mobile benthic fishing gear I mean gear that is towed across the seabed, i.e. bottom fishing trawl nets and scallop dredges. This closure was brought in to protect fragile seabed habitats and the associated marine life, in particular the subtidal rocky reefs and boulder and cobble reefs, known to occur in the central and eastern part of the bay. We’ve known for a long time, at least the late 1980s, that such heavy gear could be highly destructive to some reef species, especially fragile or soft tissued attached species such as sponges and soft corals. Of greatest concern was the increase in scallop dredging. Changes in the quota system, markets and fish prices had lead to the number of boats working with scallop dredges increasing dramatically in the late 1980s. The number of boats operating solely as scallop dredgers had also increased (vessels will often switch gear thoughout the year as fish species migrate and quotas change); thus the overall intensity of scalloping had rocketed. As far back as 1991, I conducted dive surveys for the Devon Wildlife Trust; we had heard reports from recreational divers of swathes of destruction on previously pristine reef areas. What we found was even more disturbing, not only were areas of reef being scraped clean of attached life, the very stucture of the reef was changing.

Scallop dredger in Lyme Bay. A scallop dredger hauling dredges (4 each side) to emtpy catch.

Amongst the more interesting reef areas in Lyme Bay are the boulder and cobble reefs and the mudstone ledge reefs. Boulder and cobble reefs are basically level boulder fields, most of the boulders are small, roughly football-sized and so the heavy scallop dredges can bounce and rattle across these boulders without getting damaged themselves, picking up the occasional scallop as they go. What also happens though is that the boulders are lifted out of the sediment, rolled along and banged together. As this happens the sponges and soft corals growing on the boulders are ripped off or ground to shreds. The steel teeth of the dredges rake into the sediment as the dredge travels, stirring up clouds of sediment which then subsequently settles on top of the boulders. The attached species that managed to survive intact are then smothered in a layer of sediment, blocking their delicate filter-feeding organs.

 

Mudstone reefs are composed of blue lias clay. This is the same hard, slate-like clay that can be seen in the fossil-rich cliffs that line much of the coast of Lyme Bay. As this clay can easily be shattered by a fossil hunters hammer, the effects of half a ton of toothed dredges being hauled across such ledges by a powerful fishing boat are quite devastating. The ledges simply crumble. Now as any good marine biologist knows, most of the larger attached fauna on reefs are filter feeding organisms – sponges, hydroids, soft corals, bryozoans etc., and as every hydrographer (and diver) knows, currents accelerate around the edges of ledges and promentories due to entrainment. So of course all the life clusters around the edges of ledges where the rich feeding currents are. Grind away the edges and you remove maybe 80% of the attached fauna and – most importantly – virtually all the large colonies. The large colonies are the structure-forming ones that provide new niches for other species, they are often the slow-growing species that can take years to re-establish (where possible), and they are also the ones with the largest reproductive potential: for example, a big seafan colony that’s maybe 15 or 20 years old is going to release many time more eggs or larvae than a little one about 5 years old thats only just reached reporductive maturity. So when the big colonies are removed this alone may drastically affect the ability of a species to maintain or re-establish its population in an area.

Reef badly damaged by scallop dredgers. Lyme Bay. Colin Munro Photography.

Reef badly damaged by scallop dredgers

So to put it mildly, the situation was not good, and was rapidly deteriorating. It only took one boat working across a reef to remove so much life that it would take years for recovery to occur. Six months of boats intensively working an area could (and did) irreversably change the structure of some reefs. As scallop stocks declined on the so-called ‘clean ground’ (areas of sandy seabed) boast began to work closer to the edges of reefs, nibbling away at the edges. Fish finders and echo sounders improved in quality, so skippers could see exactly which way ledges rose up, enabling them to work close around the most rugged ledges and pinnacles. DECCA became standard for position fixing, then was replaced by GPS, allowing every more accurate positioning of where the roughest points to be avoided were, so boats could work into reefs where previously they dare not enter. The power of vessels also increased, so when dredges did become stuck fast on a rocky ledge or large boulder the solution was often to turn on the power and pull free, often with devastating consequences for the reef. I personally witnessed this many times over the years. Boats would dredge right up the the edge of a reef, gradually extending further and further in to it through the day as the edges were ground down or boulders rolled away. Occasionally a dredger would come fast. You could see it stop dead in the water and list over to one side where the dredges on that side were caught. Watching from a couple of hundred metres away you would hear the engine rev, see the vessel sink deeper on the caught side, then suddenly lurch free to carry on around again.

Scallop dredger heeling over as the dredges on one side catch fast on the seabed. Lyme Bay. Colin Munro Photography.

Scallop dredger heeling over as the dredges on one side catch fast on the seabed.

On one occasion (whilst conducting dive surveys on a reef composed of large limestone boulders) we watched twelve dredgers work around in tight circles clipping in to the reef again and again for over six hours. We took position fixes and returned at dusk with stills and video cameras. It was about forty minutes steaming time to reach this offshore reef and the sun was disappearing as we descended to the reef and swum on a bearing towards where we had seen the boats working. It was quite black without lights when we hit the bottom at around 28 metres, visibility was very poor as the water was still full of suspended sediment from the dredgers working earlier. Even so the transition from pristine to ‘worked’ reef was clear cut and the devastating effects of that one day’s dredging were unmistakable. The entire seabed was carpeted in a layer of fine sediment, detached soft corals drifted loosely across the reef, detached seafans lay flat partially buried in sediment, fragments of the plates of ross coral (a bryozoan) littered the reef. Large boulders lay overturned with still attached seafans protruding from underneath. Only isolated patched of undisturbed reef remained where the dredgers had been working. Video footage taken during this dive, showing pristine reef from the start of the dive and damaged reef encountered later in the dive, can be downloaded from the link below (48Mb, plays in Windows Media Player or Quicktime Player).
East Tennants Reef following scallop dredging 2002

 

Thus began a long road to the establishment of protection for the reefs. An 18 year long campaign driven by the Devon Wildlife Trust finally lead to stautory protection for the reefs in 2008. So what has this acheived? I’ll address this in Part 2 of this blog.

Update 10th July 2012, New blog: Lyme Bay, what makes it special?
All images and text (C) Colin Munro Photography.