Abundance/scarcity of CFT areas

Geographical factors.

Species of special interest

Biodiversity Action Plan species

On a national scale CFT biotopes cannot be considered scarce. There are large areas of suitable environment around the south-western, western and northern shorelines of Britain. Thus CFT biotopes as an entity can never be considered under threat - their abundance and frequent inaccessibility will ensure this. However there is a geographical difference in the frequency of distribution, in that CFT biotopes are generally scarcer and more scattered on the eastern and southern coasts (this is clear from their prevalence in the various candidate SAC sites - Figure 5).

However, this abundance does not mean that threats to biodiversity can be dismissed. Local biodiversity could be at risk in those areas where CFT biotopes are generally scarce, and in consequence possibly heavily utilised. This is discussed in relation to anthropogenic activities in Section V.

The other consideration is that whilst CFT communities as a whole are abundant, specific CFT biotopes may be relatively scarce. This could relate particularly to those biotopes characteristic of sheltered locations, and those found in areas of reduced or variable salinity. Such biotopes will not only tend to be scarce, but by the nature of their environment, more accessible and more prone to anthropogenic impacts. CFT biotopes will also decrease in abundance with depth (see section II.B) as a consequence of the reduced availability of hard substrata, yet deep communities may be particularly diverse (Jensen & Fredriksen, 1992), and not necessarily protected by their depth. There has recently been concern regarding the impact of deep sea trawling on Lophelia reefs. The representation of these scarcer biotopes in SACs requires attention.

This aspect can be examined in two ways - in terms of the geographical distribution of the MNCR biotopes, and by looking at the distribution of selected individual CFT species. In both cases this has been done by generating distribution maps from the JNCC's MNCR database (Appendix 4). It is appreciated that the information in this database is far from complete both in terms of availability of data, and inclusion of available data in the database.

From the maps in Appendix 4 it would appear that there are no biotopes with a widespread and general distribution around the British Isles, but this must be suspected an artefact of the restricted data input to the database. However, many have clearly regional distributions.

• Some biotopes have a very obvious northern distribution, such as ECR.CFa/CCparCar (Coralline crusts, Parasmittina trispinosa, Caryophyllia smithii, Haliclona viscose, polyclinids and sparse Corynactis viridis on very exposed circalittoral rock - App. 4, Fig.1a) and MCR.XFa/ErSSwi (Erect sponges and Swiftia pallida on slightly tide-swept moderately exposed circalittoral rock - App. 4, Fig 4d)..
• On the other hand there are others which are found only in the south, e.g. MCR.ByH/Flu.Hocu (Haliclona oculata and Flustra foliacea with a rich faunal turf on tide-swept sheltered circalittoral boulders or cobbles - App. 4, Fig. 6b) and MCR.As/MolPol (Molgula manhattensis and Polycarpa spp. with erect sponges on tide-swept moderately exposed circalittoral rock - App. 4, Fig. 8a).
• Yet other biotopes are predominantly on the east coast, such as MCR.ByH/Flu.Flu (Flustra foliacea on slightly scoured silty circalittoral rock or mixed substrata - App. 4, Fig 5c).

In order to conserve a full range of CFT biotopes it is clearly necessary not only that CFTs as a whole are adequately represented in the SACs, but that these SACs are appropriately distributed geographically. This will ensure that the geographically-limited biotopes are all represented. The distribution of Demonstration SACs where ‘reefs’ are a special feature (Papa Stour, Berwickshire and North Northumberland Coast, and Lleyn Peninsula and the Sarnau) provides a fair geographic coverage, but excludes the extreme south west to which a variety of important CFT biotopes and species are restricted. The presence of a number of CFT communities in the Plymouth Sound SAC in part redresses the balance. However, the various Candidate SCAs which are not selected as demonstration sites provide a comprehensive geographic coverage, with Lundy and the Pembrokeshire Islands presenting a diversity of CFT communities in the south west which have already been extensively studied as a result of their Marine Reserve status.

The fundamental reason why biotopes are geographically restricted is not basically that the particular habitats are themselves geographically restricted, but that in different geographical areas these habitats are occupied by species with restricted ranges. Examples of species distributions are shown in the figures in Appendix 4.

• A variety of species have broad general distributions around Britain, and their distribution probably mirrors the overall distribution of CFT biotopes. Such species include Alcyonium digitatum (App. 4, Fig 13c), Cliona cellata (App. 4, Fig 12a), Flustra foliacea (App. 4, Fig 12c), Metridium senile (App. 4, Fig 14d), Nemertesia antennina (App. 4, Fig 13a) Pomatoceros triqueter (App. 4, Fig 16b) and Tubularia indivisa.
• However, there are other species with clearly limited distributions. Eunicella verrusosa (App. 4, Fig 14a) and Balanophyllia regia (App. 4, Fig 15b) are restricted to the south west, Swiftia pallida (App. 4, Fig 14c) to the north west, and Strongylocentrotus droebachiensis (App. 4, Fig 16d) to the far north in the Shetlands.
• Corynactis viridis (App. 4, Fig 15a) is widely distributed up the western seaboard from the Scillies to the Shetlands, but is absent from eastern shores. Other widespread species absent from eastern areas include Pentapora foliacea (App. 4, Fig 12d) and Pachymatisma johnstoni (App. 4, Fig 12b).

Most of the above examples of species with restricted distributions are used to characterise one or more CFT biotopes. The implication is that some CFT biotopes are ecological equivalents of other biotopes, which they replace geographically. Thus MXR.XFa/ErSEun (erect sponges, Eunicella verrucosa and Pentapora foliacea on slightly tide-swept moderately exposed circalittoral rock) is restricted to the south west. In the north west it is replaced by the equivalent MXR.XFa/ErSSwi (erect sponges and Swiftia pallida on slightly tide-swept moderately exposed circalittoral rock), where one sea fan species is replaced by another.

Species of special interest.

CFT communities are extremely diverse, which is one of their attractions for conservation purposes. Notes on habitat and distribution, and illustrations of most common CFT species can be found in Erwin & Picton (1990). However, this very diversity makes the selection of species of special interest an invidious task. Nevertheless some selection and prioritisation is essential, since they will be necessary to help determine the species and the biotopes to be included in the SAC monitoring programmes described in section VI.C.

Selection criteria can be species-specific, and site specific. The former will define a list of species of general interest, the latter will restrict that list to one relevant for each particular SAC. However, the benefits of regional comparisons should be kept in mind (see section VI.C) and SACs in the same area should, where possible, highlight similar lists of species. Hiscock (1998a, section 4.2.2) identifies a number of general selection criteria for species to be included in ACE surveys, and these have been used as a starting point for selecting criteria appropriate to CFT species.

These are not in any rank order - in some cases they may apply more strongly in some SACs that others. Thus, for example, the ‘risk from exploitation’ may well be a local rather than a general phenomenon.

• Species at risk from exploitation.
• Species used to characterise CFT biotopes.
• 'Keystone' species influencing the dynamics of CFT biotopes.
• Species of limited distribution or general rarity.
• Biodiversity action plan species.
• Species known to be in decline.
• Species with limited dispersal powers.
• Long-lived slow growing species.
• ‘Indicator species’ known to be sensitive to environmental change.

• Species present in the area..
• Species near the limit of their geographic range.
• Species at risk from localised impacts.
• Species locally or regionally rare.

This list of criteria is not exhaustive, and not all criteria are of equal weighting. For example it would be mandatory to include Biodiversity Action Plan species in any monitoring programme, but most of the other criteria involve subjective decisions, or there is a lack of definitive information. In most instances species meeting a greater range of criteria would be more likely to merit inclusion. In Table 1 an attempt is made to categorise a selection of CFT species according to the species-specific criteria - neither the list of species, nor the criteria used, should be regarded as exhaustive, and the procedure needs developing in more detail.

This table provisionally identifies certain species as meeting more of the criteria than others. The following species feature under four or more headings - Alcyonium glomeratum, Eunicella verrucosa, Hoplangia durotrix, Leptosammia pruvoti, Pentapora foliacea and Echinus esculentus. Thus they should be regarded as ‘species of special interest’ under this analysis, and should feature in any monitoring and management programmes.

Biodiversity Action Plan species.

The number of CFT species (fairly broadly defined) included in the Biodiversity Action Plan list is fairly small (eight species), and there are no reasons given for their inclusion, nor for the exclusion of other species which might seem equally (or more) eligible. The included CFT species are listed below, with brief details of their occurrence and distribution in the U.K. where relevant, and a few key references. When action plans have been developed for these species, these plans will need to be taken into account for management purposes when the species occur within SACs.

Coelenterates (details mostly from Manuel,1981).

Aiptasia mutabilis: The trumpet anemone, restricted to the extreme south-west of England and Wales. From the intertidal down to about 30 m, in sheltered habitats. Reproduces asexually, and by viviparity (Stephenson, 1935).

Alcyonium glomeratum. A soft coral - red sea fingers (Beldam & Robins, 1971; Robins, 1968). A typical CFT species, found in areas with minimal algal cover and out of light, generally from 10-50 m. Prefers limited wave action. Restricted to south and west coasts.

Amphianthus dohrnii: An anemone, grows epizoically on gorgonians, hydroids and other organic structures (Stephenson, 1935; Carlgren, 1949). In Britain generally grows on Eunicella or Tubularia, from 10 m to deep water. Formerly common in English Channel and around southern Ireland, but now considered rare with few recent records.

Eunicella verrucosa: The pink sea fan (Carpine & Grasshoff, 1975). Restricted to the south and west coasts (App. 4, Fig 14a). On vertical or overhanging rocks from 10-100 m in moderate exposure, a typical CFT species.

Hoplangia durotrix: The Weymouth carpet coral (Best, 1969), a small colonial coral restricted to the coasts of Devon and Cornwall. Occurs out of the light in caves and crevices down to 25 m.

Leptosammia pruvoti: The sunset star coral, a solitary coral (Best, 1969). In North Devon and various localities in the English Channel. In clefts, under cave roofs or in steep-sided gullies, 10-40 m.

Parazoanthus axinellae: A colonial zoanthid, found mainly on organic substrata such as sponges, worm tubes and dead gorgonians, but also on rock. Limited to extreme south west of Britain, in depths of 6-100 m.

Sea urchins

Strongylocentrotus droebachiensis: The northern sea urchin (Britt & Petersen, 1982; Hagen, 1995), restricted to the north east (App. 4, Fig 16d). In sheltered areas, but also those exposed to strong currents.

Next Section                      References