The ‘Sea pens and burrowing megafauna’ biotope complex is represented to varying degrees in several of the candidate SACs around the UK. The quality of information available also varies from area to area, extending in some cases only to a record of sedimentary habitats in which a biotope can be inferred to exist. The 12 ‘demonstration’ SACs with which the UK Marine SACs Project is mainly concerned will be discussed first in detail, followed by a summary of known or likely occurrence in other proposed SACs. It should be borne in mind that the practicalities of surveying benthic environments, especially over large areas, mean that a statement of non-occurrence of a particular biotope usually represents only an assessment based on the currently available information, an assessment which will always be subject to revision in the light of future observations. However, the hydrodynamic or topographic characteristics of a site often preclude the occurrence of a particular biotope (eg. soft mud biotopes are unlikely to exist at an open-coast site subject to strong tidal currents or heavy wave exposure).

The occurrence or non-occurrence of the biotope complex is summarized in the table below.

* Portland Harbour adjoins the Fleet SAC but falls outside its currently-defined boundaries.

Papa Stour in Shetland has a broken, rocky, and in places very exposed coastline. There are no soft-sediment biotopes around the island, although these do exist in the sheltered voes elsewhere in Shetland (Howson, 1988).

The Solway Firth is notable for its estuarine intertidal mudflats. Recent surveys of sublittoral biotopes found no evidence of sea pens or burrowing megafauna (Covey, 1992; Cutts & Hemingway, 1996), although both are well-represented further south in the Irish Sea proper. The biotopes in question have also not been recorded in Morecambe Bay (Emblow, 1992; Rostron, 1992). Mills (1997) notes that benthic sampling undertaken in the Irish Sea off Blackpool, about 30 km from the mouth of the bay, found muddy sands at depths of 25 - 30 m with Virgularia mirabilis, Calocaris macandreae and Goneplax rhomboides. Rostron (1992) found Upogebia deltaura in a dredge sample off the coast of Walney Island. However, this community has not been recorded within Morecambe Bay itself. The Llyn Peninsula is bordered by the Irish Sea to the north and Cardigan Bay to the south. Megafaunally-burrowed sediments occur in both sea areas but have not so far been recorded close inshore to the peninsula, except for one record of Upogebia sp. burrows in the anchorage at St Tudwal’s Road (Hiscock, 1984). To some extent, the presence or absence of the biotope complex in these three SACs on the Irish Sea periphery is a matter of boundary placement, but any representation within them is likely to be marginal.

The Wash in North Norfolk contains large expanses of intertidal and shallow subtidal sediment, but is not known to support either sea pens or burrowing megafauna (Covey, 1991; Hill et al., 1996).

The locations of those candidate SACs believed to contain extensive examples of the ‘Sea pens and burrowing megafauna’ biotope complex are shown in the figure linked below. The sites themselves are discussed individually below. Where there is sufficient information, biotopes are assigned to one of the MNCR categories described above.

‘Demonstration’ candidate SACs in which these biotopes can be found are indicated by solid circles. Non - ‘demonstration’ candidate or possible SACs are marked by open squares. Non-SAC areas supporting the biotope complex are shown by vertical hatching. The distributions of Pennatula phosphorea and Nephrops norvegicus in the North Sea are adapted from Dyer et al. (1982), and Callianassa subterranea from Künitzer et al. (1992).

Entec (1996) carried out an acoustic (RoxAnn^TM) survey of Loch nam Madadh, supplemented by towed video and grab sampling. The outer reaches of this complex loch system, south of the island of Flodday, was found to contain an extensive sediment plain, ranging from shelly mud near Lochmaddy village and Charles Harbour, to finer mud near the mouth of the loch. All three sea pen species were recorded, with Virgularia mirabilis having the most extensive distribution. This occurred commonly on the shallower, shelly mud (6 - 24 m depth), while Pennatula phosphorea and Funiculina quadrangularis were confined to the deeper muds in the outer loch. Nephrops norvegicus and Pachycerianthus multiplicatus were also recorded. These findings are supported by the diving observations of Howson (1991). She found the fine muds at 27 - 40 m depth to be heavily burrowed by Calocaris macandreae and Nephrops norvegicus. Burrowing megafauna were not mentioned in the shallower, shelly mud characterized by Virgularia mirabilis. These observations, summarized the linked figure, suggest that the biotopes CMU.SpMeg, CMU.SpMeg.Fun and CMS.VirOph can be recognized here.

Davies & Hall-Spencer (1996) used the same set of techniques (RoxAnn^TM, ground-truthed by towed video and SCUBA) to survey the benthic biotopes of the Sound of Arisaig SAC. Extensive areas of fine mud in the 30 - 60 m depth range were found in the Sound of Arisaig itself and in Loch Ceann Traigh (figure - not currently available). These sediments were heavily burrowed by megafauna, although only Nephrops norvegicus was specifically mentioned. Howson (1990) recorded Maxmuelleria lankesteri from a site near the mouth of Loch Ailort, with Virgularia mirabilis ‘in moderate numbers’. This may represent biotope CMU.SpMeg, although more detailed information on species composition is clearly needed. Both Davies & Hall-Spencer (1996) and Howson (1990) recorded circalittoral sandy muds with Virgularia mirabilis in shallower water (10 - 37 m), particularly in areas where hard substrata gave way to sediment. The presence of Ophiura spp. and scarcity of attached epifauna (Howson, 1990) indicate that this association represents biotope CMS.VirOph.

This large, virtually land-locked marine inlet contains a diverse range of benthic biotopes, including megafaunally-burrowed fine muds. Species present include Nephrops norvegicus and Goneplax rhomboides (Erwin, 1977). Magorrian et al. (1995) mapped the substrata of the lough using acoustic methods (RoxAnn^TM), supplemented by video and still photography. Areas of very soft, featureless sediment with few burrows occupied large areas in the north of the lough. Firmer muds towards the lough centre supported high densities of Nephrops burrows (figure). The Nephrops grounds were estimated to cover 12 km² of the 22.9 km² surveyed.

The subtidal sediment fauna of this large bay is relatively poorly known. However, several species of burrowing megafauna have been recorded from areas of muddy sand inshore near Aberystwyth, and further north near Pwllheli, the latter area bordering on the Llyn Peninsula SAC (figure). Species present include the crustaceans Upogebia deltaura and Callianassa sp., and the holothurian Labidoplax digitata (Mackie et al., 1995).

Plymouth Sound contains a wide range of both hard and soft substrata (Davies, 1997). Burrowed sediments occur in the sound, and species records indicate that the megafauna may be quite diverse (Marine Biological Association, 1957) (figure). Callianassa subterranea, Upogebia deltaura and U. stellata have been collected from muds just north of the breakwater in the middle of the sound, and the rarely-recorded Axius stirhynchus occurs in the low intertidal on muddy shores. Hiscock & Moore (1986) found burrows of Goneplax rhomboides near Plymouth Hoe. Larvae of Jaxea nocturna are not uncommon in summer in the Plymouth area (Marine Biological Association, 1957), suggesting that this species may occur within the sound. Records of the echiuran Maxmuelleria lankesteri from the south coast of England (Hughes et al., 1996b) suggest that this species might also conceivably be present. There are a few records of the sea pen Virgularia mirabilis from Plymouth Sound (Hiscock & Moore, 1986), but the species does not appear to be common here.

The shallow tidal inlet of the Fleet contains soft mud substrata in its western embayment, but there are no records of the biotopes under consideration here (Dyrynda, 1984). However, the Fleet is connected to the sea via Portland Harbour, which supports the sole known example of the biotope IMU.PhiVir (Philine aperta and Virgularia mirabilis in soft stable infralittoral mud) in southern Britain (Portland Harbour falls outside the currently-defined boundaries of the Fleet SAC, but the community found there will be briefly described because of its regional importance). Dyrynda recorded burrows of Cepola rubescens and Goneplax rhomboides at about 10m depth in the harbour, with Virgularia mirabilis abundant in patches. The anemone Scolanthus callimorphus, otherwise known in the British Isles only from western Ireland, was also recorded here. Sediments were found to consist of 54% silt-clay and 5% organic matter.

Foster-Smith et al. (1996) carried out an acoustic survey of the benthic biotopes of this candidate SAC. Towed video was used to ground-truth the RoxAnn^TM results. A site at the southern edge of the surveyed area was found to have a fine silty sand substratum with beds of Virgularia mirabilis. The acoustic survey indicated that an extensive belt of this biotope runs parallel to the coastline in fairly deep water (50 - 70 m) (figure). The sea bed in the observed area was worked into burrows and mounds. Species responsible were not identified, but Calocaris macandreae and Nephrops norvegicus are likely candidates in this area. The echiuran worm Echiurus echiurus is common further offshore at the St Abbs sewage sludge disposal ground (I. Jack, Scottish Environmental Protection Agency, personal communication), so might also be expected to occur here. The offshore sediment fauna of the Northumberland coast belongs to the classical ‘Brissopsis-chiajei’ community of Petersen (Buchanan, 1963). This corresponds to CMU.BriAchi in the MNCR biotope classification.

Several other candidate or possible SACs are known to support examples of the ‘Sea pens and burrowing megafauna’ biotope complex. The Moray Firth (designated as an SAC because of its bottlenose dolphin population) is an important fishing ground for Nephrops norvegicus, with 1279 tonnes landed in 1995 (Marine Laboratory, Aberdeen). It is likely therefore that other megafaunal burrowers will also occur here. The Loch Alsh/Duich/Long system contains extensive mud and muddy sand plains with Virgularia mirabilis (Connor, 1989). Loch Duich supports particularly good examples of the CMU.SpMeg and CMU.SpMeg.Fun biotopes, with forests of Funiculina quadrangularis and burrows of Nephrops norvegicus, Callianassa subterranea and Lesueurigobius friesii. The head of Loch Duich has one of the largest known populations of the rare anemone Pachycerianthus multiplicatus (figure).

None of the other proposed SACs are known to contain examples of this biotope complex, and the habitat criteria underlying their selection (eg. lagoons, estuaries, reefs) suggest that its occurrence is unlikely.

The ‘demonstration’ SACs discussed above all contain examples of the ‘Sea pens and burrowing megafauna’ biotope complex extending over wide areas of sea bed. In the cases of Loch nam Madadh, Sound of Arisaig, Strangford Lough and Berwickshire/North Northumberland, the geographic extent of the biotope complex has been mapped, whereas in Cardigan Bay and Plymouth Sound its spatial distribution is less accurately known. In none of these SACs has there been a detailed study of sea pen density, the species composition of the burrowing megafauna or their relative abundances. This information can only be gained by field observation using SCUBA, or by detailed analysis of towed camera recording. So far, this has been achieved only in the north-eastern Irish Sea (Hughes & Atkinson, 1997) and in Lochs Sween and Fyne, Argyll (Atkinson, 1989; Howson & Davies, 1991; Nickell et al., 1995b), none of which are located within proposed SACs.

In the absence of data on community composition and species abundance, it is difficult to say at present which of the candidate SACs possess the ‘best’ examples of the biotope complex, ie. those which are most important from a scientific or conservation-related perspective. However, some general assessments based on geographic distribution can be made. Loch nam Madadh and Loch Duich contain the biotope variant characterised by Funiculina quadrangularis, which is unlikely to be found in any of the other SACs. The red band-fish Cepola rubescens is known from Portland Harbour, adjoining the Fleet SAC, and is not known to be present in any other candidate SACs. More detailed information on the megafaunal communities of southern and eastern Britain (ie. Plymouth Sound and Berwickshire/North Northumberland SACs) would be interesting, as our present concept of the biotope complex is derived largely from sites in north-west Britain (sea lochs, Irish Sea), and different combinations of species may be expected to occur elsewhere.

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