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Ecological Importance of the Sarnau In Cardigan Bay

 
The Sarnau of Cardigan Bay (Sarn Cynfelin, Sarn Badrig and Sarn-y-Bwlch) are unusual shallow sub-tidal reefs, and all three Sarns extend in a general direction of west from the mainland and the longest, St Badrig, extends some 24km offshore. These Sarnau are thought to be relics of glacial moraine deposited during the last ice age and washed clean by the sea to leave mounds and ridges of boulders and cobbles (Foster 1970).

fish

Sarn Cynfelin starts from below the farmhouse at Wallog situated between Borth and Clarach near Aberystwyth and extends some 14 kilometres offshore. It is bisected by a 5 metres deep channel approximately half way along its length. Charted depths as shallow as 1.5 metres have been recorded both near the mid-channel and near to its western prong or outermost extremities, to seaward. Fast tidal streams and strong wave action are reputed to have a profound influence on the marine communities present (Hiscock, 1986) and the reefs are characterised by a large number of species resistant to scour and coverage at times by sand.

Algal communities are dominant on large areas of the reefs with growths of foliose red and brown algae forming dense beds in places. The brown algae Chorda filum and Laminaria saccharina, as well as red algae flourish on or near the reef crowns, while the number of algal species increases with depth. In certain parts of the reefs there are extensive underwater forests of sea-oak (Halidrys siliquosa). Rich, animal dominated, biotopes are found in the deeper parts of the reef, including crustaceans, cnidarians, sponges, and hydroids and encrusting bryozoans.

To the north of the Sarns, on the sheltered sides, lie fine sand habitats, which are reportedly rich in bivalve molluscs (JNCC, 1999). The reefs in summer also support good populations of fish, such as Pollock (Pollachius pollachius), bass (Dicentrarchus labrax), and black bream (Spondyliosoma cantharus).


 Until quite recently only very limited benthic information has been available for Sarn Cynfelin. The Sarn was subject to a brief survey in the early 1980�s when two areas were visited by divers supporting work for the Marine Conservation Society. It was suggested at that time that further investigative work looking into the flora and fauna should continue on Sarn Cynfelin (Hiscock 1986). In 2003 Friends of Cardigan Bay , initiated further survey work in this area, mainly focusing on the Sarn as a potential foraging habitat for the bottlenose dolphin (Tursiops truncatus) and harbour porpoise (Phocoena phocoena). Data obtained from these surveys had highlighted certain areas on this reef as �hotspots� where bottlenose dolphin had on several occasions being observed foraging and feeding. Additionally the Atlantic grey seal (Halichoerus grypus) was also recorded.

Dolphins


It was a recommendation of this report that more survey work was needed and this led to the FoCB Sarns Survey of 2005. The aim of the Sarns Survey 2005 was to focus in a little more detail on Sarn Cynfelyn to further evaluate the area for cetacean activity. In addition it was hoped that a photographic log of feeding dolphin would be possible in order to identify prey species taken. It was also the intention to investigate the benthos of Sarn Cynfelyn by means of diver survey at specific locations where sightings of these animals had been made foraging or feeding.

It may then be possible to correlate the associated foraging behaviour of these animals with the benthic information recorded and a photographic record. In this way it was hoped that a simple picture of preferred prey species for these animals could be built at given locations upon the Sarn. The benthic information was gathered using accredited Seasearch methodologies and would also increase the very limited biological knowledge of this area. This was deemed important for the future management of the SAC and the future protection of a variety of wildlife that frequent the area.


During the 2005 season Friends of Cardigan Bay, in conjunction with local diving clubs, executed a series of dives at chosen locations on the reef. One such target area for benthic survey was a small section of the reef at the mid-channel where the linear formation of the reef is bisected by a deeper gulley. It was at this location that the photograph below was taken showing  a mixture of teleosts, mainly bass (Dicentrachus labrax) and grey mullet (Liza auratus). This, therefore, certainly starts to explain why dolphins may be attracted to this location.


This particular section on the reef ranges from fine sand leading to a, steep cobble and pebble bank. This is reflected in the species diversity with this site having by far the largest species list. There are several types of teleost apparent; sand dwelling e.g. common skate and sand goby; rock and crevice dwelling e.g. corkwing wrasse and tompot blenny; and pelagic e.g. bass and grey mullet. The fact that many of these fish are secondary, if not tertiary predators shows the high productivity of the area (Hughes and Pownall, 2005).

This is likely to be both, indirect, through food bought in with water movements, and direct, through the large number of seaweeds and the local production of larvae or nauplii into the surrounding waters. There are numerous species recorded for this site which as sedentary sexually mature organisms produce vast numbers of larvae at varying times throughout the year, many but certainly not all in the spring. For example, barnacles are recorded as common, a single mature Semibalanus balaniodes, can produce as many as 8000 larvae per year (Fish and Fish, 1989).

Dive Drawing

The species list for this site also records a number of species that are indicators of strong currents e.g. dead man�s fingers and dahlia anemones (Fish and Fish, 1989). This links in to the mooted productivity of the area, this, and the possibility of upwellings and currents, attract fish, and in turn dolphins. This again would appear to make this site a very attractive area for cetaceans.
A Seasearch diving sketch for this site is shown below:
 
The Sarn itself seems to provide a seasonal variety of prey species for a variety of higher animals, certainly sightings records show the presence of the harbour porpoise (Phocoena phocoena) and the atlantic grey seal (Halichoerus grypus), but the Sarn in both summer and winter also seems to support a wide variety of seabirds. Internationally important numbers of common scoter, great crested grebe and red throated diver all moult and winter in the Bay. All three species are widespread in shallow waters, but the most important areas are off Borth and the Sarn with over 900 divers being recorded in December 1995 (Moore, J et al 1996). More recent survey reports available from the summer of 2004 show a variety of seabird species upon Sarn Cynfelyn (see below). Anecdotal reports suggest that assorted skuas also pass through and may be present in the area.

In 2004 the great skua (Stercorarius skua) was reported in August and the long-tailed skua (Stercorarius longicaudus) in May.


Cormorant (Phalacrocorus carbo)
Shag (Phalacrocorus aristotelis)
 Gannet (Morus bassanus)
 Manx shearwater (Puffinus puffinus)
 Storm-petrel (Hydrobates pelagicus)
 Fulmar (Fulmaris glacialis)
 Herring gull ( Larus argentatus)
 Great Black-backed gull (Larus marinus)
 Black-headed gull (Larus ridibundus)
 Kittiwake (Rissa tradactyla)
 Guillemot (Uria aalg)
 Razorbill (Alca torda)
 Sandwich tern (Sterna sandvicensis)
 Eider (Somateria mollissima)
 Common scoter (Melanitta nigra)
 Velvet scoter (Melanitta fusca)
 Red- breasted Merganser (Mergus serrator)
 Great Crested grebe (Podiceps cristatus)
 
 In conclusion the benthic surveys that provided this information, appear to have been invaluable, not only in providing new information on habitat, but also allowing for a better understanding of seabed characteristics and biological content associated with surface sightings. The Sarn itself provides a varied and diverse habitat supporting a wide range of both sessile and mobile species. The sheer complexity of these ecosystems cannot be overstated; the predator/prey relationship at the bottom end of the food chain should lead to high levels of plankton and detritus being present on the Sarn during the summer months. Stronger tidal flows sweeping around, over, and in places through the Sarn, may allow for the distribution of nutrients, and animal detritus for consumption by higher animals e.g. teleosts such as bass, mullet, bream and wrasse. The research has also shown that these areas provide ideal havens for juvenile fish. It is these areas that bottlenose dolphin were observed foraging and feeding.


 From the recent research into the Sarnau, particularly that of Sarn Cynfelin, it would certainly seem that the reefs support a wide range of both flora and fauna. Their inclusion as unique examples of glacial reefs in the European designation of the Pen Llyn ar Sarnau SAC is most certainly fully justified. In addition, the importance of these features to the overall ecology of Cardigan Bay is probably only just started to be fully understood. Only with continued research such as this, can we hope to formulate suitable management plans that may, in turn, confer suitable protection to individual species and the much more complex biotopes.
Article by Phil Hughes.


References
 Admiralty, 1972. All map extracts included in this report are from Admiralty Chart Cardigan Bay Central Part 1972, new edition 1987. Reproductions are by permission of the Controller of Her Majesty�s Stationery Office and the UK Hydrographical   Office (www.ukho.gov.uk). Licence agreement HO 1809/041012/01
 Fish J. D., Fish, S., (1989). A Student�s Guide to the Seashore.  Unwin Hyman Ltd, London, UK. pp.234-238.
 Foster, H. D., 1970. Sarn Badrig, a sub-marine moraine in Cardigan Bay, north Wales. Zeitschrift fur Geomorphologie, 14, p 475-486.
 Hiscock, S. 1986. Sublittoral survey of the mid-Wales sarns (reefs): Sarn Badrig, Sarn-y-Bwlch and Cynfelin patches. July 2nd-9th 1986. (Contractor S. Hiscock, Pembroke) Nature Conservancy Council, CSD Report, No. 696.  p3, 29.
 Hughes, P (Thomas E), 2004. Sarns and Ceredigion Cetacean Surveys 2004 CCW Species Challenge Fund, Marine projects, CCW Grant No: Sc7916
 Hughes, P., Pownall, C.R., 2005. Friends of Cardigan Bay: Sarns Survey 2005. In press.
 J.N.C.C., 1999. Marine Nature Conservation Review, Sector 10. Cardigan Bay and North Wales. Brazier, P. et al 1999. Joint Nature Conservation Committee, coasts and seas of the United Kingdom - MNCR series, Area summaries. pp.58-61.
Moore,J. Taylor,M. Westlake,I. Arnold,H. Condry,B. 1996. Cardigan Bay and the Bottlenose Dolphin, Friends of Cardigan Bay 1996.

 

 

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