The Aquatic and Wetland Invertebrates of Wetland Trust Land at East Guldeford and Pannel Valley, East Sussex

The aquatic and wetland invertebrates of Wetland Trust land at East Guldeford and Pannel Valley, East Sussex

C. M. Drake

2010

Dr C. Martin Drake Orchid House Burridge Axminster Devon EX13 7DF Contents Summary ...... 1 Introduction ...... 1 Methods...... 2 Sampling ...... 2 Analysis...... 2 Results and recommendations ...... 5 East Guldeford ...... 5 Species richness ...... 5 Rare species ...... 5 Comparison with other sites in Walland Marsh ...... 7 Management ...... 7 Pannel Valley ...... 12 Species richness ...... 12 Rare species ...... 12 Management ...... 13 References ...... 15 Acknowledgements ...... 15 Appendix 1. Raw data for East Guldeford...... 16 Appendix 2. Raw data for Pannel Valley...... 19 Appendix 3. Environmental variables at East Guldeford...... 23 Appendix 4. Environmental variables at Pannel Valley...... 24 Appendix 5. Status definitions ...... 25

Summary Aquatic and marginal invertebrates were sampled at ten ditches on two blocks of grazing marsh at East Guldeford and Pannel Valley on 18-19 June 2010. The fauna at East Guldeford was exceptionally rich in nationally rare or scarce species (29 altogether) and had high species-richness when compared with brackish ditches nationally. The main management recommendations were to keep present levels of brackishness and reduce the length of grass- dominated ditches by making slightly deeper sections along the length of the internal ditches. Occasional drying-out of some ditches was not thought to be a problem. If water levels are raised, then the bank slope of the new water’s edge must be kept gentle.

The fauna of Pannel Valley was relatively poor for a southern marsh. There were few nationally scarce or rare species, and the number of species of all statuses was unexceptional. The raised-water area with very low levels of grazing had a slightly poorer fauna than one shallow scrape and three ditches in cattle-grazed pasture. The main management recommendation was to soften the profiles of the currently steep banks to encourage a wider margin of emergent and mat-forming vegetation. Introduction East Guldeford is an area of grazing marsh in Walland Marsh. The area surveyed comprises five fields and nearly 5km of ditches. The pasture used to be intensively grazed by sheep but, after a recent change in ownership, grazing has been relaxed. The ditches are typical of this part of Walland Marsh. They include a few moderately steep-sided examples and others that were not deeply dug or slubbed out so that they often dry out in summer.

Pannel Valley is a small marsh whose management has been altered to encourage wetland birds. Three fields remain as cattle-grazed pasture and the rest, that make up about two-thirds of the whole site, are grazed very lightly and have raised water levels leading to a large area of swamp. New scrapes and ponds have been dug. Most of the original ditches remain but some have become subsumed into the scrapes or swamp.

The survey was undertaken to establish the invertebrate interest on the sites and to provide advice that would retain or enhance the fauna. Aquatic invertebrates and those dependent upon the water-margin were targeted. Methods

Sampling Aquatic invertebrates were sampled using the method described in Drake et al. (2010). It involved bank-side sorting of the catch and sampling, standardised by searching for a set time. A representative length of ditch was selected, usually about half-way between intersections. The sample was taken using a pond-net. The aim was to collect from as many micro-habitats a possible, so netting was not formally structured but continued until either the range of microhabitats had been sampled well or the net was about one-third full of debris and plants (which is as much material as can be inspected in the time available). Some time was spent trampling vegetation in the shallow margins, thus forming a pool that could be netted, as most invertebrates can be found here; this was also effective for collecting wetland beetles and bugs living at the margin. The material was inspected on a white polythene sheet for about 7-8 minutes. Species that could be identified reliably in the field were noted a field form and a sample of most other taxa was collected into 70% alcohol. This was repeated four times, giving a total of 30 minutes searching. Searched debris and plants were put into a bucket and, at the end of the search period, was washed and most of the material removed by hand or tipped away gently to leave a heavy residue containing molluscs. This was tipped into a white tray, in which the molluscs were conspicuous.

A few minutes were spent directly searching the margins for wetland beetles and bugs which were added to the aquatic sample.

A few key environmental variables were collected, including physical dimension, plant cover and conductivity. A full list of the variables is given in Appendices 3 and 4.

Ten ditches were sampled on each site, those at East Guldeford on 18 June 2010 and at Pannel Valley on 19 June. The character of the Pannel Valley sampling points varied with the different management. Three were in traditional cattle-grazed pasture (ditches 8-10), one was next to sheep-grazed pasture (ditch 5), and the rest were in the raised-water area where their margins tended to be close to the land level, resulting in broad swampy margins. One scrape with a broad shallow margin was sampled (3).

Analysis Rarity statuses were obtained from the biological recording database ‘Recorder’ and updates in recent reviews (Daguet et al. 2008; Foster 2010). Recorder statuses were based on the JNCC system, whereas those for recently reviewed groups are based on the IUCN system. This results in a confusing mix of statuses, codes, definitions and criteria. I have used the term ‘Scarce’ as a synonym for ‘Notable’ in the JNCC system but have used the suffix ‘Na’

2 for the more restricted of the scarce species, although this distinction is not retained in the latest IUCN-based reviews. Appendix 5 gives definitions. Dragonflies were reviewed only to Red Data level using IUCN criteria; the authors did not include the British status of nationally scarce, although the opportunity to apply this is allowed in IUCN rules, as was done for water beetles. In this report, dragonflies with JNCC scarce status have been noted although it is not clear whether they still retain this status.

A simple scoring system that captures the rarity value of a sample of invertebrates has been in use for many years. It is the average of scores allocated to each species in a sample or site, where the individual scores reflect a species’ rarity. There are several variations of this Species Conservation Score (SCS) but the method used here was based on the method described in Drake et al. (2010). In this version, the species’ scores are allocated on a linear scale from 1 (common) to 5 (rarest), rather than the often-used geometric scale, as it was found to give smaller variance when means were calculated (i.e. was more discriminating when sites were compared). The sum of the scores is divided by the number of species to give the average. By taking the average, some account is taken of sampling effort so that, provided enough species are included (at least five), scores can be compared between sites sampled by different surveyors.

A score for brackishness was the sum of scores (not averaged per species) a species tolerance or requirement for saline conditions, and these were 1 for species most often found in brackish conditions and 2 for obligate halophils.

Species richness and SCS can be put into context by comparing with values for ditches sampled nationally (Drake et al., 2010). Freshwater and brackish ditches were treated separately in that study because brackish ditches support fewer species, notably molluscs. Brackish ditches were defined as having a conductivity greater than 2000μS cm-1. The number of all species is lower in brackish ditches but the number of beetles remains the same (although comprising different suites of species).

Figure 1. East Guldeford sampling points (X).

Figure 2. Pannel Valley sampling points.

Results and recommendations

East Guldeford

Species richness A total of 100 distinct aquatic taxa were recorded, excluding taxa that possibly duplicated named species (Appendix 1). Another 44 wetland or terrestrial species were recorded, which were mostly beetles. While the distinction between these two groups is often blurred, it has been retained to allow comparison with other ditch surveys which were restricted to the traditionally accepted aquatic groups.

The aquatic species were mainly beetles (56 species), bugs (13 distinct taxa) and molluscs (10 species). The remaining 24 taxa were in many groups. Vertebrates found were the two common sticklebacks and the tadpoles of frogs, which were almost certainly marsh frog Pelophylax ridibundus, and immature newts, which were likely to have been smooth newts Lissotriton vulgaris.

There were between 34 and 51 aquatic taxa in each sample (Table 1). Comparison with the national values of species-richness was complicated by the closeness of the conductivity of most ditches to the brackishness threshold of 2000μS cm-1. For total species, the national median and interquartile range is 47 (40-53) for freshwater and 39 (29-46) for brackish water. The East Guldeford ditches could be viewed as either rather average examples of freshwater ditches or quite good examples of brackish ditches. This may be resolved by noting that molluscs were indeed uncommon at East Guldeford, almost certainly as a direct result of their intolerance of saline conditions, and that the numbers of water beetles was always above the median and often in the top quartile of the national values of 19 (14-25). Brian Banks obtained readings that were higher than those given here in late July when some ditches were close to drying out.

Rare species Eighteen nationally rare or scarce aquatic species were found and another 11 ‘terrestrial’ species that live at the margins (Table 2). Nearly all were beetles which will be discussed after dispensing with the few members of other groups first.

The large rare soldierfly Odontomyia ornata may be regarded as one of the flagship species of grazing marshes as it occurs frequently in marsh ditches but is very scarce in other habitats. It was clearly well established at East Guldeford, and has been recorded at several other grazing marshes in Walland Marsh. The other two soldierflies, O. tigrina and Stratiomys singularior, were similarly widespread at East Guldeford, but it is doubtful that they deserve the status of ‘scarce’. The tiny skater Hebrus pusillus was ubiquitous here.

A single individual of medicinal leech Hirudo medicinalis was seen, and this was not unusual as it is well known from Walland to Dungeness. There are recent records of it from grazing marsh ditches in the Walland area.

Five Near Threatened and eight Scarce water beetles were found, and one Scirtidae (Scirtes orbicularis) which was assessed as a water beetle in the recent review (Foster, 2010) but is not usually treated as such despite having completely aquatic larvae. Some of the beetles were widespread and a few were represented by many individuals. The scarce or near

5 threatened Hydrophilidae crawling water beetles were among the most frequent, and included the Great Silver water beetle Hydrophilus piceus. Records of this species were boosted by the ease with which its larvae and egg case can be recognised, and such records accounted for most at East Guldeford. This is the largest British water beetle. One of the tiniest, Chaetarthria simillima, was more frequent than normally encountered in ditch systems, and this was thought to be a result of the shallow margins where spike-rush Eleocharis was prevalent. The two very similar species Hydrochus elongatus (in four ditches) and H. ignicollis (in five ditches) were found together only once, but this is not an error in identification since both sexes can be reliably separated. While H. elongatus is found in a variety of habitats with shallow water, H. ignicollis is reputed to be confined to shallow pools in ancient fenland, but clearly this is an over-simplification unless old grazing marshes are included within the scope of ancient fenland. The minute Aulacochthebius exaratus deserves a mention as it has a small range that historically extended from Hampshire to Suffolk, but here it was at the southern extremity of an apparently retracting range that now extends only from East Sussex to south Essex. The occurrence of both species of Hydrovatus in the same marsh was of interest as H. cuspidatus was added to the British list only in 2006 when recognised at Cheyne Court, a few kilometres north of East Guldeford. The remaining scarce water beetles are well known as grazing marsh species.

A large number of species of the ‘aquatic’ Bagous weevils were found. The larvae of many of them feed on submerged plants or the underwater parts of wetland plants. Most species in the genus are rare in Britain, so it was surprising to find several species in one small area. The host plants for these species are known although often based on continental records: B. tubulus on Glyceria spp. and Alopecurus aequalis (not recorded in the Walland or Romney marsh area (Perring & Walters 1990)), B. limosus on Potamogeton spp., B. subcarinatus on Ceratophyllum submersum, B. longitarsis on Myriophyllum spp., B. glabrirostris on various aquatic plants including Ceratophyllum submersum and Stratiotes aloides. Of these plants, Ceratophyllum submersum, Myriophyllum spicatum, Potamogeton pectinatus and P. crispus have been recorded at East Guldeford (Brian Banks, pers. comm.). The other scarce wetland weevil was Thyrogenes scirrhosus which associated with Sparganium, and was among much more numerous T. nereis which is associated with spike rush Eleocharis.

The rare ground beetle Badister collaris has a very restricted range centred on Walland and Romney areas, where it has been recorded from the margins of water-filled sand and gravel pits, ponds and marshes (Luff, 1998). One of the two records at East Guldeford was based on a female (which cannot be identified to species) but was superficially identical to the male from another ditch.

The remaining wetland beetles have been recorded from grazing marshes previously. The rove beetle Paederus fuscipes appears to be particularly widespread on marshes, and the tiny Stenus fornicatus is also frequent on southern marshes. The distribution of Scirtes orbicularis, whose larvae are completely aquatic, shows a strong correlation with English and Welsh grazing marshes and may be partly dependent upon them, like Hydrophilus.

The Species Quality Scores (SCS) ranged from 1.65 to 1.84. These may be compared with the national median and interquartile range of 1.39 (1.31-1.48) for freshwater ditches and 1.50 (1.41-1.62) for brackish water ditches. Whichever national value is used, all the East Guldeford ditches were well into the top quartile and are therefore exceptional.

The brackishness score for the ditches was small as only four species were involved: the common ‘shrimp’ Gammarus duebeni and the uncommon water beetles Graptodytes bilineatus, Coelambus parallellogrammus and Ochthebius viridis. The score was only poorly correlated with the conductivities so was not helpful in identifying ditches with a better developed brackish-water fauna.

Relating the numbers of species or the SCS to conditions in the ditches was only partly successful. A few ditches were exceptional in having high numbers of species and SCS. These were ditches 543 and 548 which run along the north-east boundary, with either hay or arable on the opposite bank. The vegetation structure was more varied than in many other ditches, and included less grassy mat (Agrostis) than on many ditches. They appeared to have been cleaned out more recently and were among the deeper ditches. However, many other ditches at a later successional stage were almost as rich as this boundary ditch 543 – 548. At the poorest end of the rather narrow spectrum were three ditches (542, 549 and 560) that were almost completely covered by a grassy mat of Agrostis which almost excluded submerged plants and left only very small patches of open water. They were among the shallowest ditches and had no measurable silt on their bottoms, suggesting that they dry up (which results in the silt oxidising away). The scarcity of molluscs in these few ditches also suggested that they dried up.

Comparison with other sites in Walland Marsh The results for East Guldeford are compared with those from a survey of the aquatic fauna of four SSSI marshes undertaken for English Nature (Drake, 2005). Ten ditches were sampled using the same method as used in the present survey. This comparison is limited to just the Species Conservation Score which was re-calculated using the same species scores as here, since those used in the 2005 report were based on different values.

East Guldeford had the highest median score and its lowest score (the minimum) was higher than the median of these other sites (Table 3). This was unexpectedly better and probably reflected the lack of effort to keep water levels high, which is an aim on SSSI marshes since this benefits other interests such as the aquatic plants, and the slightly brackish water. Both these features lead to an increase in uncommon water beetles which tend to dominate the SCS scores.

Management Aquatic assemblages in ditch systems are influenced mainly by salinity and the mix of wetland vegetation (which is dependent on grazing and the stage of the ditch clearance cycle). In comparison with freshwater ditches, brackish ditches tend to support fewer species, except for water beetles and crustaceans, but have greater concentrations of uncommon species. Maintaining the range of salinities on a site should therefore lead to fresher ditches with high species-richness but perhaps fewer rarities, and more brackish ditches with high numbers of rarities. East Guldeford ditches had a range of conductivities that spanned the freshwater-brackish water transition and this was probably one of the reasons for the site’s great interest. It is recommended that the existing hydrological regime is not changed as importing water from main drains such as the Guldeford Sewer could reduce the salinity range, reducing the attractiveness of the site for brackish water species.

The changing composition of the fauna with the aging of ditches is the reason for recommending that a wide range of ditch plant communities should be retained within a site, rather than cleaning out a large number at one time. Only in particularly ‘old’ shallow

7 ditches does the interest drop, although there is some evidence that these may be good for wetland species that require damp conditions. The shallowest ditches at East Guldeford appeared to agree with this generalisation, in being less interesting in several ways than the bulk of ditches that were at a slightly earlier successional stage. Although only one uncommon species was found only in these three ditches (the ground beetle Badister collaris), it may be prudent to retain part of their late-stage character and not deepen their entire length. For instance, several small ‘pools’ could be dug along their length so there are pockets of more permanent water. Such pools were dug in a drought summer at the Inner Thames Marshes SSSI before RSPB bought the site, and sampling showed that they acted as refuges in otherwise dry ditches.

The ground beetle Badister collaris may prefer very late-stage conditions since my other Romney Marsh record, from Cheyne Court, was from a reed-choked ditch with very little water. As this was one of the rarest species found at East Guldeford, its preferences may take priority over those requiring more permanent water which is relatively more abundant on the site. There is little information on its habitat preferences but it does appear to need water margins. Whether these have to be permanent or merely seasonally wet is not known.

Two features, the gently sloping margins and the fringe of spike-rush Eleocharis, were thought to be particularly important in leading to the high richness of these ditches.

Many ditches had gently sloping margins at and just under the water’s surface. Few of the East Guldeford ditches were steep-sided in this crucial under-water edge (ditch 539 along the track was steep-sided). There is no need to alter the present profiles unless water levels are raised, which could move the water’s edge from the present gently sloping profile near the ditches’ bottom to the steepest part of the slope half-way up. If water levels are to be raised, then it may be worth widening parts of some ditches to ensure a gentle slope. An underwater shelf provides an alternative to a gentle slope, such as that found at ditch 541; whether made deliberately, by cattle, or accidentally, this was a good example. Shelves risk becoming stranded when water levels fall, as was seen in parts of ditch 548 (which otherwise had an excellent shallow margin).

Ditch 551 had a moderately steep margin which could be improved by allowing heavy trampling or by re-profiling by machine, but it also has a good population of marsh mallow Althea officinalis on which marsh mallow moth Hydraecia officinalis subsp hucherardii feeds, so this margin will need to be kept untouched. East Guldeford is one of a handful of sites where the moth now lives.

Almost all ditches had a fringe of Eleocharis spike-rush and other low plants such as tufted water forget-me-not Myosotis laxa living at the edge in very shallow water. This was always a highly productive zone to sample, and it is probably rich because the vegetation casts little shade so that the water can become warm and growth of algae and other micro-organisms is rapid, leading to a productive food-chain with many predatory water beetles at its top. In comparison, the dense Agrostis mats produced rather small numbers of animals, and although the grass was not tall its dense structure probably had the effect of shading-out micro- organisms and insulating the water from sunlight.

Gentle trampling and grazing by sheep may be the origin of the Eleocharis zone. If so, then the currently relaxed grazing regime may lead to increased shading by taller plants such as Juncus or Bolboschoenus which are unimportant at the moment. However, a possible benefit

8 of relaxed grazing is an increase in the flowering of wetland plants, particularly those with short corollas, such as the water dropworts Oenanthe, used by the aquatic soldierflies and hoverflies.

Although several ditches have features that indicate that they dry out, and are consequently of less interest than some others, there is enough evidence that drying-out for short periods is not a problem for most aquatic species, for example Collinson et al. (1995) found that there was no difference in the species-richness or species rarity scores of permanent and semi- permanent ponds (that dry up for a short period). True temporary ponds that dry out for longer periods also can have a similar range of species to permanent ponds, but with additional species not found in the permanent ponds (Nicolet et al., 2004). There seems little need to ensure that all ditches at East Guldeford are permanently wet, especially as water from outside the site may have more nutrients or lower saline content, either of which could lead to deterioration in the current interesting fauna.

The ditch along the far west end of the track was not sampled but was the only example with dense reed. This is not a scarce vegetation type in Walland Marsh and usually supports only a moderate fauna and few specialists; the whirligig Gyrinus paykulli is one of the few species found more often in this type than elsewhere. Because of its value to small birds, there may be no need to restore this ditch unless the relaxed grazing regime results in reed starting to take a hold in more ditches.

Table 1. Number of taxa and Species Conservation Score at East Guldeford.

Ditch number 539 540 541 542 543 548 549 551 560 563 Total taxa aquatics 39 37 46 46 51 50 34 50 35 46 wetland 9 9 16 14 11 15 11 11 12 10 water beetles 23 24 25 24 32 31 20 32 21 29 Rare & Scarce aquatics 13 12 13 9 16 12 9 16 10 13 wetland 2 1 2 3 3 3 0 2 2 1 SCS 1.78 1.82 1.70 1.65 1.87 1.65 1.79 1.84 1.77 1.80 Brackishness score 3 3 2 2 2 1 3 3 1 1

Table 2. Nationally rare and scarce species at East Guldeford.

Order / Family Species Status Ditch number 539 540 541 542 543 548 549 551 560 563 TERRESTRIAL COLEOPTERA Carabidae Badister collaris pRDB1 + + Curculionidae Bagous longitarsis pRDB1 + + + + Bagous glabrirostris Scarce + + Bagous limosus Scarce + Bagous puncticollis RDB1 + + Bagous subcarinatus Scarce Na + + + + Bagous tubulus RDB2 + + Thryogenes scirrhosus Scarce + Scirtidae Scirtes orbicularis NS + Staphylinidae Paederus fuscipes Scarce + + Stenus fornicatus Scarce + AQUATIC COLEOPTERA Dytiscidae Graptodytes bilineatus NS + + + + + Hydrovatus (females) NS + + + Hydrovatus clypealis NS + + + Hydrovatus cuspidatus NS + Hygrotus parallellogrammus NS + Haliplidae Peltodytes caesus NS + Hydraenidae Aulacochthebius exaratus NT + + Ochthebius viridis NS + + + Hydrochidae Hydrochus elongatus NT + + + + Hydrochus ignicollis NT + + + + + Hydrophilidae Chaetarthria simillima NS + + + + + + + Hydrophilus piceus NT + + + + + + Limnoxenus niger NT + + + + + + + + + + Noteridae Noterus crassicornis NS + + + + + + + DIPTERA Stratiomyidae Odontomyia ornata RDB2 + + + + + Odontomyia tigrina Scarce + + + + Stratiomys singularior Scarce + + + + + HEMIPTERA Hebridae Hebrus pusillus Scarce + + + + + + + + + HIRUDINEA Hirudinidae Hirudo medicinalis RDB3 + Total terrestrial 3 1 2 3 3 3 0 4 2 1 Total aquatic 13 12 13 9 16 12 9 16 10 13

Table 3. Species Conservation Score at five Walland Marsh sites.

Site median (min-max) East Guldeford 1.79 (1.65-1.87) Broomhill 1.60 (1.37-1.73) Cheyne 1.63 (1.44-1.85) Fairfield 1.45 (1.33-1.74) Snargate 1.61 (1.38-1.89)

Pannel Valley

Species richness A total of 108 distinct aquatic taxa were recorded. Thirty-six wetland species were recorded, just half of which were beetles, and a few terrestrial species associated with grassland (Table 4). Ten-spined stickleback was found at one ditch only. The aquatic species were mainly beetles (41 species), bugs (20 species) and molluscs (14 species). The nine species of caddis included three identified from adults only, and several of the records were also from adults. The remaining 21 taxa were from a number of groups.

The number of aquatic species per sample was lower than or occasionally just about the same as the national median for freshwater ditches (median and interquartile range of 47 (40-53)), and several fell into the bottom quartile. The fauna of these ditches was therefore rather poor for freshwater grazing marsh. The number of beetles was similarly low compared to the national values of 19 (16-23), although the molluscs were not quite to low compared to the national values for freshwater ditches of 10 (7-13). Few terrestrial species were found at the margins but there was no obvious reason why this was so.

Rare species Six scarce or threatened aquatic species and eight wetland species were found (Table 5). Five of the aquatic species were also found at East Guldeford so are not discussed in detail here, except to point out that three of them were moderately widespread here as at East Guldeford (Hydrochus ignicollis, Hydrophilus piceus, Limnoxenus niger). The additional aquatic species was the Hairy Dragonfly Brachytron pratense, which is a frequent species in ditch systems. It is now very widespread in lowland south-east England and probably no longer deserves ‘scarce’ status.

Of the wetland species, the ground beetles Demetrias imperialis and Odacantha melanura are often associated with reeds. Odacantha melanura is sparsely distributed in coastal marshes of southern England and south Wales and inland at fens in East Anglia. Demetrias imperialis used to have a similar very restricted distribution but has become widespread in south-east England in the last 30 years. Bembidion clarkii and Tachys bistriatus live at still-water margins. Bembidion clarkii and is widely distributed in England but T. bistriatus is much more restricted, and found mainly along the southern coastal counties of England. The reed beetle Donacia thalassina is found widely in Britain, and are associated with several common marginal or emergent monocotyledons. Larvae of the weevil Bagous lutulentus feed within the stems of the horsetail Equisetum fluviatile.

The Species Conservation Scores for the aquatic species in sites 1-7 in the raised-water area were within or close to the interquartile range of national values for freshwater ditches (1.31- 1.48). The three ditches in cattle-grazed pasture (8-10) were well into the top quartile. All these values were higher than expected given the few nationally scarce species, and may be the result of the low species-richness (the SCS is the sum of score divided by the total species, so a poor ditch with a smattering of uncommon species can have the same SCS as a good ditch that has a very large number of species).

The ditches had conductivities in the range 390-580μS cm-1 which was particularly low for coastal marsh ditches but similar to those in river valley marshes. The inflow from the southwest corner of the site (ditch 4) supported the running-water shrimp Gammarus pulex

(which had ‘escaped’ into the neighbouring but unconnected ditch 5) and more caddisflies than normally found in still-water ditch systems. There were no species characteristic of brackish water.

The fauna of one scrape that was sampled (3) was similar to most of the ditches in the raised- water part of the site. The shallow water over an almost flat clay bottom nearly free of vegetation encouraged corixid water boatmen that were scarce in the deep ditches. The scrape’s assemblage was otherwise indistinguishable from that of the ditches.

Management The interest was low for a coastal marsh on the south coast. Much of the lack of interest could be attributed to the vegetation structure, profile of the ditches and the very fresh nature of the water. All the ditches (but not the scrape) had steep margins just below water level, usually about 60º but almost vertical in those of the cattle-grazed pasture. They were also deep; six were at least 1m deep. Steeps sides and deep water gives little opportunity for marginal vegetation to develop or for a mat to spread out from the shore. Most ditches had had an open, featureless character, dominated by completely open water surfaces, no mats of vegetation, little submerged vegetation and only sparse fringes of emergents. As invertebrates need plenty of vegetation in which to live and hide, it was unsurprising that the samples were rather poor.

Ditches in the raised-water area had dense marginal fringes of tall rush and horsetail which often overhung the water’s edge, leading to cool shaded conditions. The slightly better fauna of the grazed pasture may be partly attributed to having less dense fringes and to a narrow shelf developing in places as a result of trampling and grazing.

This cannot account for the near absence of invertebrates in the swampy margins that were sampled intensively in the expectation that they would form a refuge. It could only be speculated why invertebrates were so scarce in the swamp zone, and the most likely reason was that the vegetation was sufficiently dense that it maintained rather shady and cool conditions.

The single biggest action that would improve the site for invertebrates, notably insects, would be giving the banks a much more gentle slope just at and below water level. This would allow a wider fringe of emergents and mat-forming plants to grow. In the absence of grazing, a wide shallow margins would not be so over-hung by tall rush, which discourages invertebrates. As the ditches are deep and the water levels high, spoil taken from the banks may be dumped back into the ditch, provided their drainage function is unimportant.

Maintaining the open character of vegetation fringes may require grazing higher than the current intensity in the raised-water area.

Clearly water levels are as high as practicable and desirable so there is nothing more to do except not change levels too wildly, since not all aquatic species can migrate quickly back- and-forth across swampy ground in an effort to regain the permanent ditch.

Table 4. Number of taxa and Species Conservation Score at Pannel Valley.

Ditch number 1 2 3 4 5 6 7 8 9 10 Total taxa aquatic 42 38 46 48 40 31 36 48 45 41 wetland 15 7 10 7 9 2 3 9 7 10 aquatic beetles 18 9 21 15 14 11 13 19 18 22 aquatic molluscs 7 8 8 10 8 10 8 8 10 9 Rare & Scarce aquatic 3 2 2 2 1 0 0 3 2 3 wetland & terrestrial 4 1 3 1 1 0 0 1 1 2 SCS 1.44 1.29 1.40 1.39 1.31 1.46 1.41 1.65 1.62 1.82

Table 5. Nationally rare and scarce species at Pannel Valley.

Order / Family Species Status Ditch number Total 1 2 3 4 5 6 7 8 9 10 TERRESTRIAL COLEOPTERA Carabidae Bembidion clarkii scarce + 1 Demetrias imperialis scarce + 1 Odacantha melanura scarce + + + 3 Tachys bistriatus scarce + 1 Chrysomelidae Donacia thalassina scarce + + + 3 Curculionidae Bagous lutulentus scarce + 1 Bagous puncticollis RDB1 + + 2 Staphylinidae Stenus fornicatus scarce + 1 AQUATIC COLEOPTERA Haliplidae Peltodytes caesus NS + + + + 4 Hydrochidae Hydrochus ignicollis NT + + 2 Hydrophilus piceus NT + + + 3 Limnoxenus niger NT + + + + + + 6 DIPTERA Stratiomyidae Odontomyia tigrina scarce + + 2 ODONTATA Aeshnidae Brachytron pratense scarce + 1

References

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Drake, M., Palmer, M., Stewart, N. & Kindemba, V. 2010. The ecological status of ditch systems. Report to Buglife - the Invertebrate Conservation Trust, Peterborough.

Foster, G.N. 2010. A review of the scarce and threatened Coleoptera of Great Britain. Part (3): Water beetles of Great Britain. Species Status 1. Joint Nature Conservation Committee, Peterborough.

Luff, M.L. 1998. Provisional atlas of the ground beetles (Coleoptera, Carabidae) of Britain. Biological Records Centre, CEH, Huntingdon.

Nicolet, P. Biggs, J., Fox, G., Hodson, M. J., Reynolds, C., Whitfield, M. & Williams, P. 2004. The wetland plant and macroinvertebrate assemblages of temporary pools in England and Wales. Biological Conservation 120: 265-282.

Perring, F.H. & Walters, S.M. 1990. Atlas of the British Flora. Botanical Society of the British Isles. Botanical Society of the British Isles.

Acknowledgements I thank Brian Banks for arranging the project, and Peter Hodge for checking my identification of weevils.

Appendix 1. Raw data for East Guldeford. Values are the number of specimens identified or estimated in the field.

Order Family Species 539 540 541 542 543 548 549 551 560 563 Wetland and terrestrial species Coleoptera Cantharidae Cantharis cryptica 1 1 1 1 Cantharis lateralis 1 Carabidae Badister collaris 2 1 Bembidion articulatum 1 Bembidion assimile 13 Chrysomelidae Chaetocnema confusa 1 1 1 1 Phaedon cochleariae 1 1 2 2 Prasocuris phellandrii 1 Coccinellidae Anisosticta novemdecimpunctata 1 1 1 1 Coccidula rufa 1 1 1 1 1 3 1 Tytthaspis sedecimpunctata 1 1 1 Curculionidae Bagous longitarsis 1 1 2 7 Bagous glabrirostris 2 2 Bagous limosus 1 Bagous puncticollis 10 7 Bagous subcarinatus 1 6 1 1 Bagous tubulus 3 1 Hypera pollux 1 1 2 1 1 Poophagus sisymbrii 1 Tanysphyrus lemnae 5 2 11 16 20 7 5 9 24 4 Thryogenes nereis 15 8 4 13 11 14 13 12 7 Thryogenes scirrhosus 1 Scirtidae Cyphon laevipennis 1 Scirtes orbicularis 1 Scirtidae 1 2 4 1 2 Staphylinidae Paederus fuscipes 3 1 Paederus riparius 1 Stenus binotatus 1 Stenus boops 1 1 1 5 1 Stenus cicindeloides 1 4 1 2 1 3 5 Stenus formicetorum 4 Stenus fornicatus 1 Stenus incrassatus 1 1 Stenus latifrons 1 1 Diptera Ephydridae Notiphila dorsata 1 Parydra fossarum 1 Pelina similis 1 1 1 2 1 2 Psilopa nigritella 1 Scatella stagnalis 1 Hemiptera Cicadellidae Macrosteles viridigriseus 1 Streptanus sordidus 1 1 Mollusca Succineidae Oxyloma elegans 1 1 1 1 1 1 Aquatic species Coleoptera Dryopidae Dryops luridus 2 6 7 2 2 3 3 5 1 Dytiscidae Agabus bipustulatus 2 1 3 3 6 1 1 6 Agabus sturmii 2 Dytiscus 1 1 1 1 1

Order Family Species 539 540 541 542 543 548 549 551 560 563 Graptodytes bilineatus 1 1 1 7 4 Graptodytes pictus 1 1 Hydroporus angustatus 1 1 1 Hydroporus erythrocephalus 1 1 6 Hydroporus palustris 5 1 5 22 19 5 2 2 5 Hydroporus planus 1 Hydroporus pubescens 22 1 Hydrovatus 1 1 1 Hydrovatus clypealis 5 1 2 Hydrovatus cuspidatus 1 Hygrotus impressopunctatus 1 Hygrotus inaequalis 2 1 1 1 1 1 Hygrotus parallellogrammus 2 Hyphydrus ovatus 1 Ilybius ater 1 2 5 4 3 Ilybius quadriguttatus 1 Laccophilus minutus 1 1 1 Liopterus haemorrhoidalis 1 1 Porhydrus lineatus 1 1 Gyrinidae Gyrinus marinus 1 Gyrinus substriatus 1 7 13 1 Haliplidae Haliplus 1 1 3 6 1 Haliplus immaculatus 2 Haliplus lineatocollis 3 1 5 1 3 Haliplus ruficollis 1 1 2 Peltodytes caesus 1 Helophoridae Helophorus aequalis 1 Helophorus brevipalpis 1 3 3 4 1 1 5 Helophorus minutus 1 Hydraenidae Aulacochthebius exaratus 1 1 Hydraena testacea 1 1 3 Limnebius nitidus 1 1 5 8 Ochthebius minimus 1 2 1 2 4 1 12 Ochthebius viridis 1 1 2 Hydrochidae Hydrochus elongatus 1 1 1 1 Hydrochus ignicollis 6 2 1 4 2 Hydrophilidae Anacaena bipustulata 8 8 7 1 5 20 4 3 Anacaena globulus 18 Anacaena limbata 1 2 6 13 5 1 5 3 12 Cercyon marinus 5 Cercyon sternalis 44 2 3 20 17 3 13 30 18 1 Cercyon ustulatus 2 1 5 2 2 2 1 Chaetarthria simillima 4 3 30 4 4 5 8 Coelostoma orbiculare 5 1 30 6 5 30 4 7 1 Cymbiodyta marginellus 5 3 5 5 5 1 7 5 17 6 Enochrus coarctatus 4 1 1 5 6 1 2 1 7 Enochrus testaceus 1 12 Helochares lividus 3 5 7 5 10 4 5 2 4 Hydrobius fuscipes 1 1 1 1 1 5 3 1 Hydrophilus piceus 1 2 1 1 1 2 Laccobius bipunctatus 12 1 1 6 Limnoxenus niger 6 4 2 2 1 10 2 5 2 3 Noteridae Noterus clavicornis 6 2 4 2 4 3 2 7 4 12

Order Family Species 539 540 541 542 543 548 549 551 560 563 Noterus crassicornis 1 1 1 4 1 2 1 Diptera Culicidae Anopheles maculipennis agg. 1 1 1 1 1 1 1 Ptychopteridae Ptychoptera contaminata 1 1 Stratiomyidae Odontomyia ornata 1 1 1 1 1 Odontomyia tigrina 1 1 1 2 Oplodontha viridula 2 3 30 5 3 2 6 1 1 Oxycera trilineata 2 Stratiomys singularior 3 2 2 1 1 Ephemeroptera Caenidae Caenis robusta 3 Hemiptera Corixidae Corixa 1 30 100 1 1 1 Corixa panzeri 1 Corixa punctata 1 2 1 Corixidae 30 100 1 Hesperocorixa linnaei 1 1 Hesperocorixa sahlbergi 4 4 5 2 Gerridae Gerris 1 Hebridae Hebrus pusillus 18 2 5 4 2 3 2 9 1 Hebrus ruficeps 12 3 3 Naucoridae Ilyocoris cimicoides 1 30 30 1 1 30 1 1 Nepidae Nepa cinerea 1 1 Ranatra linearis 1 Notonectidae Notonecta 30 1 1 1 1 30 1 1 Pleidae Plea minutissima 1 100 1 1 30 Veliidae Microvelia reticulata 1 1 2 1 1 Neuroptera Sialidae Sialis lutaria 1 Odonata Aeshnidae Aeshna 2 Lestidae Lestes sponsa 1 2 Libellulidae Sympetrum 2 3 2 2 4 2 1 30 Trichoptera Leptoceridae Athripsodes aterrimus 2 Oecetis furva 1 1 Amphipoda Crangonycitidae Crangonyx pseudogracilis 2 1 1 3 100 1 2 1 Gammaridae Gammarus duebeni 4 100 3 5 1 3 Isopoda Asellidae Asellus aquaticus 4 7 100 2 30 1 7 6 Asellus meridianus 1 4 Mollusca Bithyniidae Bithynia leachii 1 1 1 1 Lymnaeidae Lymnaea stagnalis 1 1 1 1 Radix balthica 1 1 100 100 1 100 1 1 1 Planorbidae Bathyomphalus contortus 100 Gyraulus crista 1 1 Hippeutis complanatus 1 Planorbis carinatus 2 Planorbis planorbis 1 100 30 100 1 100 1 100 1 30 Sphaeriidae Musculium lacustre 1 Valvatidae Valvata piscinalis 1 1 100 Hirundinea Hirudinidae Haemopis sanguisuga 1 1 1 1 Hirudo medicinalis 1 Tricladida Dugesiidae Dugesia 1 Anura Ranidae Pelophylax ridibundus 30 30 Thoracostei Gasterosteidae Gasterosteus aculeatus 1 1 1 1 1 Pungitius pungitius 1 1 1 1 Urodela Salamandridae Lissotriton vulgaris 30 1

Appendix 2. Raw data for Pannel Valley.

Order Family Species 1 2 3 4 5 6 7 8 9 10 Wetland and terrestrial species Coleoptera Cantharidae Cantharis cryptica 1 1 Cantharis livida 1 Carabidae Bembidion assimile 2 Bembidion clarkii 1 Demetrias imperialis 1 Odacantha melanura 1 1 1 Tachys bistriatus 1 Chrysomelidae Chaetocnema confusa 1 Donacia thalassina 2 1 1 Donacia vulgaris 1 1 Galerucella nymphaeae 1 Prasocuris phellandrii 1 Hippuriphila modeeri 1 Anisosticta Coccinellidae novemdecimpunctata 1 1 Coccidula rufa 1 1 1 2 1 1 1 Coccidula scutellata 2 1 Curculionidae Bagous lutulentus 2 Bagous puncticollis 2 1 Thryogenes nereis 1 5 1 1 Scirtidae Scirtidae 1 2 1 3 Staphylinidae Paederus riparius 1 1 2 Stenus binotatus 1 Stenus cicindeloides 3 1 Stenus fornicatus 1 Diptera Empididae Hilara pseudocornicula 1 1 Ephydridae Notiphila dorsata 1 1 1 1 Notiphila graecula 1 Notiphila riparia 1 1 1 Lonchopteridae Lonchoptera lutea 1 Opomyzidae Opomyza germinationis 1 1 Rhagionidae Chrysopilus cristatus 1 Sciomyzidae Limnia unguicornis 1 Sepsidae Sepsis flavimana 1 Hemiptera Cicadellidae Arthaldeus pascuellus 1 1 Cicadula quadrinotata 1 Delphacidae Javesella dubia 1 Saldidae Chartoscirta cincta 1 Isopoda Armadillidiidae Armadillidium nasatum 1 1 Armadillidium vulgare 1 1 Ligiidae Ligidium hypnorum 1 Philosciidae Philoscia muscorum 1 Mollusca Succineidae Oxyloma elegans 1 1 1 1 Aquatic species Coleoptera Dryopidae Dryops luridus 2 1 2 Dytiscidae Agabus bipustulatus 3 8 1 2 Agabus sturmii 1 Dytiscus 1 1

Order Family Species 1 2 3 4 5 6 7 8 9 10 Hygrotus impressopunctatus 1 Hygrotus inaequalis 2 Hyphydrus ovatus 1 1 2 1 2 30 Ilybius ater 1 2 1 1 1 Ilybius quadriguttatus 2 Laccophilus hyalinus 9 30 30 30 3 30 4 2 30 Laccophilus minutus 30 30 30 3 1 1 Liopterus haemorrhoidalis 2 1 Gyrinidae Gyrinus 1 1 1 Gyrinus marinus 2 30 10 5 Haliplidae Haliplus fluviatilis 1 Haliplus ruficollis 3 2 1 4 2 1 2 17 2 Peltodytes caesus 1 4 1 1 Helophoridae Helophorus aequalis 2 2 Helophorus brevipalpis 3 2 3 2 17 4 5 5 28 Helophorus minutus 1 2 1 2 Helophorus obscurus 1 Hydraenidae Hydraena riparia 1 Hydraena testacea 3 3 1 3 3 3 2 Ochthebius dilatatus 1 1 Hydrochidae Hydrochus ignicollis 1 3 Hydrophilidae Anacaena bipustulata 1 1 1 4 4 14 Anacaena globulus 1 1 Anacaena limbata 100 10 2 4 12 14 6 22 Berosus affinis 2 Berosus signaticollis 1 Cercyon convexiusculus 1 Cercyon sternalis 1 1 1 Coelostoma orbiculare 4 1 1 1 Cymbiodyta marginellus 4 1 1 Enochrus coarctatus 3 4 Enochrus testaceus 1 1 2 Helochares lividus 2 8 1 4 4 Hydrophilus piceus 1 1 1 Laccobius bipunctatus 4 1 5 1 1 4 6 11 Laccobius colon 1 1 2 1 Limnoxenus niger 1 1 6 1 3 1 Noteridae Noterus clavicornis 10 2 30 3 1 2 2 5 10 6 Diptera Chaoboridae Chaoborus 1 1 Anopheles maculipennis Culicidae agg. 6 Dixidae Dixella attica/autumnalis 1 1 1 1 Ptychopteridae Ptychoptera contaminata 1 Stratiomyidae Odontomyia tigrina 1 1 Oplodontha viridula 1 2 2 3 1 Ephemeroptera Caenidae Caenis robusta 1 1 2 Hemiptera Corixidae Callicorixa praeusta 1 1 Corixa 1 1 1 Cymatia coleoptrata 1 Hesperocorixa linnaei 1 1 1 Paracorixa concinna 3

Order Family Species 1 2 3 4 5 6 7 8 9 10 Sigara distincta 1 2 Sigara dorsalis 2 1 Sigara falleni 16 Sigara fossarum 8 2 2 Sigara nigrolineata 2 Gerridae Gerris 1 Gerris lacustris 4 Gerris odontogaster 2 2 1 2 1 2 2 1 Gerris thoracicus 1 Hydrometridae Hydrometra stagnorum 1 1 Naucoridae Ilyocoris cimicoides 30 30 30 1 1 1 30 30 30 Nepidae Nepa cinerea 1 Ranatra linearis 1 1 1 1 Notonectidae Notonecta 1 1 1 30 30 1 30 30 1 30 Pleidae Plea minutissima 30 100 1 1 1 1 1 30 1 30 Veliidae Microvelia reticulata 1 1 1 4 2 2 Neuroptera Sialidae Sialis lutaria 1 2 1 1 1 Odonata Aeshnidae Aeshna 4 2 1 30 2 4 2 1 Brachytron pratense 1 Coenagriidae Ischnura elegans 30 4 1 30 30 3 30 5 4 Coenagrionidae Coenagrion 1 1 Lestidae Lestes sponsa 2 Libellulidae Sympetrum 1 Trichoptera Leptoceridae Athripsodes aterrimus 1 1 Oecetis furva 1 2 1 Oecetis lacustris 1 1 Triaenodes bicolor 1 1 Limnephilidae Limnephilus lunatus 1 1 Phryganeidae Agrypnia pagetana 3 1 4 Polycentropodidae Holocentropus dubius 1 Holocentropus picicornis 4 1 Psychomyiidae Lype 1 Amphipoda Crangonycitidae Crangonyx pseudogracilis 30 100 100 30 30 30 4 100 30 30 Gammaridae Gammarus pulex 2 1 Isopoda Asellidae Asellus aquaticus 100 5 3 30 1 100 30 30 3 30 Mollusca Bithyniidae Bithynia leachii 30 1 1 2 1 3 1 1 Bithynia tentaculata 1 1 1 1 30 30 2 1 1 1 Lymnaeidae Lymnaea palustris 2 2 1 2 2 2 1 1 Lymnaea stagnalis 1 30 1 1 1 1 Radix balthica 1 1 1 1 1 1 Physidae Physa fontinalis 1 1 100 1 1 2 3 1 Planorbidae Anisus vortex 30 30 1 Gyraulus albus 1 2 1 9 1 Hippeutis complanatus 1 1 Planorbis planorbis 1 30 2 2 1 2 1 1 1 Sphaeriidae Musculium lacustre 1 2 2 1 3 1 Pisidium 1 2 1 1 2 1 1 Sphaerium corneum 2 1 3 1 2 Valvatidae Valvata piscinalis 1 1 1 Hirudinea Erpobdellidae Erpobdella octoculata 1 Erpobdellidae 1 1 Glossiphoniidae Helobdella stagnalis 1 1

Order Family Species 1 2 3 4 5 6 7 8 9 10 Theromyzon tessulatum 1 1 1 1 1 1 1 Thoracostei Gasterosteidae Pungitius pungitius 1

Appendix 3. Environmental variables at East Guldeford. sample 539 540 541 542 543 548 549 551 560 563

grid

959210

TQ955206 TQ954208 TQ955202 TQ953210 TQ957212 TQ TQ956209 TQ957207 TQ959206 TQ963207 landuse semi-improved 1 1 1 1 1 1 1 1 arable [1] [1] [1] [1] track [1] sheep 1 last clean (years ago) 4 -10 4 -10 4-10 2 -3 >10 4 -10 >10 4-10 grazing (0-3 scale) 0 0 0 0 0 0 0 0 0 0 poaching 0 0 0 0 0 0 0 0 0 0 block formation 0 0 0 0 0 0 0 0 0 0 shelf formation 0 1 0 0 0 1 0 0 0 0 tangledness 2 2 3 2 3 2 2 2 2 3 grassy margin 1 1 3 3 1 1 3 2 3 1 overhanging veg. 0 0 1 1 0 1 0 0 1 2 width of water (m) 2.5 5 3 3 4 3 2 2.5 2 2 top of bank (m) 5 7.5 7.5 7.5 7.5 7.5 7.5 5 7.5 7.5 freeboard (cm) 100 70 100 130 120 150 120 130 170 180 depth (cm) 55 70 50 40 50 60 40 50 30 40 silt depth (cm) 5 5 0 0 5 20 0 0 0 0 conductivity μS cm-1 1960 1920 1380 1060 1890 2000 1950 2000 1790 1290 slope A (º) 30 55 55 55 30 55 55 55 55 30 slope B (º) 55 55 55 55 30 55 30 55 55 55 profile at water edge (º) 90 10 10 10 30 30 10 30 10 60 open water (DAFOR) 3 5 2 2 4 4 3 3 2 3 floating Lemna 0 0 0 1 0 0 0 0 0 0 floating plants 1 0 0 0 0 0 0 1 0 0 floating algae 4 2 1 1 2 2 2 1 2 3 submerged plants 3 4 4 1 3 3 1 2 2 3 submerged algae 3 3 1 1 2 1 2 1 2 3 emergents 5 3 4 3 4 4 2 4 2 5 mat 1 4 5 2 2 5 3 5 0 litter 1 1 2 2 1 1 2 2 emergents in channel (%) 90 5 95 95 80 30 95 80 100 80

Appendix 4. Environmental variables at Pannel Valley. sample 1 2 3 4 5 6 7 8 9 10

grid TQ893148 TQ892147 TQ892145 TQ892145 TQ893144 TQ894145 TQ893146 TQ894150 TQ894152 TQ894154 landuse semi-improved 1 [1] 1 1 1 track 1 rank grass 1 1 1 1 1 1 swamp [1] 1 [1] cattle [1] ? 1 1 1 sheep [1] ? last clean (years ago) 2-3 2-3 4-10 4-10 4-10 2-3 grazing (0-3 scale) 0 0 0 0 0 0 0 3 3 3 poaching 0 0 0 0 0 0 0 2 3 1 block formation 0 0 0 0 0 0 0 2 1 0 shelf formation 0 0 0 0 0 0 0 0 2 0 tangledness 1 1 2 1 1 1 1 1 1 2 grassy margin 0 0 1 0 0 0 0 1 0 1 overhanging veg. 1 1 1 2 2 3 3 1 1 0 width of water (m) 5 5 pond 5 3.5 4 4 3 5 top of bank (m) 7.5 5 5 5 5 5 7.5 7.5 freeboard (cm) 40 10 0 20 50 10 50 100 50 depth (cm) 150 150 70 40 100 120 150 70 100 silt depth (cm) 10 15 10 15 conductivity μS cm-1 390 420 440 390 580 430 400 400 490 slope A (º) 30 55 55 55 70 15 15 55 15 slope B (º) 30 55 55 55 70 15 15 55 55 profile at water edge (º) 60 60 10 60 60 60 90 60 90 90 open water (DAFOR) 5 5 5 5 5 5 5 5 5 5 floating Lemna 0 0 0 0 0 0 0 0 0 0 floating plants 1 0 0 1 0 0 0 1 1 1 floating algae 0 0 0 0 0 0 0 0 4 1 submerged plants 1 0 0 1 3 3 5 1 1 3 submerged algae 0 0 0 0 0 0 0 0 2 1 emergents 3 3 4 3 4 3 3 3 3 1 mat 0 0 0 0 0 0 0 0 0 0 litter 1 1 0 2 4 4 3 0 2 1 emergents in channel (%) 2 2 2 60 5 2 2 5 2

Appendix 5. Status definitions

JNCC Invertebrate Status Categories

Red Data Book Category 1. RDB1 - Endangered Species in danger of extinction and whose survival is unlikely if the causal factors continue operating and whose numbers have been reduced to a critical level or whose habitats have dramatically reduced.

Red Data Book Category 2. RDB2 - Vulnerable Species likely to move into the Endangered category in the near future if the causal factors continue operating. Includes species of which most or all of the populations are declining throughout their range and those in vulnerable habitats.

Red Data Book Category 3. RDB3 - Rare Species with small populations that are not at present Endangered or Vulnerable, but are at risk. They are estimated to exist in only fifteen or fewer 10 km squares, and are usually localised within restricted geographical areas or habitats or are thinly scattered over a more extensive range.

Red Data Book Category I. RDBI - Indeterminate Species considered to be Endangered, Vulnerable or Rare, but where there is not enough information to say which of the three categories (RDB1 to 3) is appropriate.

Red Data Book Category K. RDBK - Insufficiently Known Species that are suspected, but not definitely known, to belong to any of the above categories, because of lack of information. They include species recently discovered or recognised in Britain, in poorly recorded or taxonomically difficult or unstable groups, inhabiting inaccessible or infrequently sampled but widespread habitats or of questionable native status.

Provisional Red Data Book pRDB The prefix "p" before any Red Data Book category indicates a provisional grading.

Nationally Scarce (Notable) Category A - Na Species which do not fall within RDB categories but which are uncommon and thought to occur in 30 or fewer 10 km squares of the National Grid or, for less well recorded groups, within seven or fewer Vice Counties.

Nationally Scarce (Notable) Category B - Nb Species which do not fall within RDB categories but which are uncommon and thought to occur in between 31 and 100 10 km squares of the National Grid or, for less well recorded groups, within between eight and twenty Vice Counties.

Nationally Scarce (Notable) Definition. Species which are estimated to occur in 16 to 100 10km squares in Great Britain. The subdividing of this category into Nationally Scarce A and Nationally Scarce B has not been attempted for some species because of either the degree of recording that has been carried out in the group to which the species belongs, or because there is some other reason why it is not sensible to be so exact.

Definitions of lUCN threat categories (IUCN 1994)

EXTINCT (EX). A taxon is Extinct when there is no reasonable doubt that the last individual has died.

EXTINCT IN THE WILD (EW). A taxon is Extinct in the wild when it is known to survive only in cultivation, in captivity or as a naturalised population (or populations) well outside the past range. A taxon is presumed extinct in the wild when exhaustive surveys in known and/or expected habitat, at appropriate times (diurnal, seasonal, annual) throughout its range have failed to record an individual. Surveys should be over a time frame appropriate to the taxon's life cycle and life form.

CRITICALLY ENDANGERED (CR). A taxon is Critically Endangered when it is facing an extremely high risk of extinction in the wild in the immediate future, as detailed by any of the criteria A to E.

ENDANGERED (EN). A taxon is Endangered when it is not Critically Endangered but is facing a very high risk of extinction in the wild in the near future, as defined by any of the criteria A to E.

VULNERABLE (VU). A taxon is Vulnerable when it is not Critically Endangered or endangered but is facing a high risk of extinction in the wild in the medium term future, as defined by any of the criteria A to D.

LOWER RISK (LR). A taxon is Lower Risk when it has been evaluated but does not satisfy the criteria for any of the categories Critically Endangered, Endangered or Vulnerable. Taxa included in the Lower Risk category can be separated into three sub-categories:

• Conservation Dependent (CD). Taxa which are the focus of a continuing taxon-specific or habitat-specific conservation programme targeted towards the taxon in question, the cessation of which would result in the taxon qualifying for one of the threatened categories above within a period of five years. • Near Threatened (NT). Taxa which do not qualify for Lower Risk (Conservation Dependent), but which are close to qualifying for Vulnerable; occurring in 15 or fewer hectads. • Nationally Scarce (NS). Taxa occurring in 16-100 hectads, but which are not Threatened, Lower Risk (near threatened) or Lower Risk (conservation dependent). • Least Concern (LC). Taxa which do not qualify for Lower Risk (Conservation Dependent) or Lower Risk (Near Threatened).

DATA DEFICIENT (DD). A taxon is Data Deficient when there is inadequate information to make a direct or indirect assessment of its risk of extinction based on its distribution and/or population status. A taxon in this category may be well studied, and its biology well known, but appropriate data on abundance and/or distribution are lacking. Data Deficient is therefore not a category of threat or Lower Risk. Listing of taxa in this category indicates that more information is required and acknowledges the possibility that future research will show that a threatened category is appropriate.

NOT EVALUATED (NE). A taxon is Not Evaluated when it has not been assessed against the criteria.

Summary of the thresholds for the IUCN Criteria

Criterion Main thresholds Critically Endangered Endangered Vulnerable A. Rapid decline >80% over 10 years or 3 >50% over 10 years or 3 >20% over 10 years or 3 generations in past or future generations in past or generations in past or future future B. Small range – extent of occurrence extent of occurrence extent of occurrence fragmented, declining or <100km2 or area of <5000km2 or area of <20,000km2 or area of fluctuating occupancy <10km2 (<1 x occupancy <500km2 (<5 x occupancy <2000km2 (<20 x 10km2) 10km2) 10km2) C small population and <250 mature individuals, <2500 mature individuals, <10,000 mature individuals, declining population declining population declining population declining D1 Very small population <50 mature individuals <250 mature individuals <1000 mature individuals D2 Very small range <100km2 or <5 locations E. Probability of >50% within 10 years >20% within 20 years >10% within 100 years extinction