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Hydroseral habitat requirement of the endangered Shining Ramshorn Snail Segmentina nitida

Hydroseral habitat requirement of the endangered Shining Ramshorn Snail Segmentina nitida Volume 4 † Number 2 † June 2011 10.1093/biohorizons/hzr019 ......................................................................................................................................................................................................................................... Research article Hydroseral habitat requirement of the endangered Shining Ramshorn Snail Segmentina nitida Ruth M.F. Clark* Canterbury Christ Church University, 38, Chestnut Drive, Sturry, Canterbury, Kent CT2 0NB, UK. * Corresponding author: Tel: þ44 7830537657. Email: rclark85@hotmail.co.uk Supervisor: Professor Georges B.J. Dussart, Biological Sciences, Canterbury Christ Church University, 38, Chestnut Drive, Sturry, Canterbury, Kent CT2 0NB, UK. ........................................................................................................................................................................................................................................ Before the 1950s, the Shining Ramshorn snail Segmentina nitida was widespread across marshes and drainage ditches in Britain, con- tinental Europe and Scandinavia. However, the population has declined rapidly and the IUCN Red Data list highlights the species as seriously vulnerable to extinction. It is now one of the six freshwater molluscan species protected under the UK Biodiversity Action Plan. Most previous research has focused on species decline and conservation issues. The aim of the research reported here was to clarify the habitat requirements of S. nitida in East Kent within the context of a seral classification. Six hydroseral stages were defined according to plant species composition. Segmentina nitida was limited uniquely to the Carex-Juncus-Eleocharis-Oenanthe community, a late seral stage in ditch succession, which confirms the work of other authors. A general linear statistical model applied to data from these sites suggested that (i) the total number of molluscs within each species varied across samples; (ii) the number of molluscs varied between samples with or without S. nitida; (iii) there was no variation in the total number of molluscs across the locations and (iv) there was no relationship between number of molluscs and sample site within location, implying some degree of connectivity between molluscan communities. Also a two-way ANOVA with Factor 1 as the number of mollusc and Factor 2 as the presence/absence of S. nitida showed a significant interaction effect. These observations are novel for these sites in East Kent and have implications for the ecology, life history strategy and conservation management of S. nitida. Key words: Segmentina nitida, wetlands, succession, mollusc. Submitted September 2010; accepted March 2011 ........................................................................................................................................................................................................................................ Introduction Ditches themselves are dynamic habitats in which the flora and fauna are a function of the seral stage. Ditches are tem- The Shining Ramshorn snail Segmentina nitida is listed as porary habitats, which will change by a process of ecological Endangered in the ICUN Red list based on pre1994 guide- succession. The classic hydrosere model of plant succession lines and is currently on the list of priority species set out from wet to dry land involves the infilling of a lake or in the UK Biodiversity Action Plan (BAP). It is one of the basin with sediment and detritus to form intermediate six freshwater molluscs covered by the BAP, invertebrates marsh, fen or bog communities, culminating in a mature comprising almost half the species on the list. Its population upland or forest ‘climax’; the latter is the definition given has declined sharply over the last 50 years (Fig. 1). Before the to a plant community, which appears to be in equilibrium 1950s, it was widespread across marshes and drainage with its surrounding environment, and where no further ditches in Britain, Europe, and Scandinavia. Today in major change is likely to occur. Several authors’ have pro- Britain, it is restricted to just a few sites including the posed pathways for this process. Tansley (1939) put Norfolk Broads, Pevensey Levels, Lewis Levels and East forward a sequence of four stages beginning with a floating Kent. The marshes and drainage ditches in which this aquatic community, to a reed swamp, followed by a fen or species can be found support a wide range of biodiversity. bog, and finishing with carr or climax forest. By contrast, They are therefore important environments that receive Goodwin (1956) proposed two models, one ending in strong emphasis in conservation legislation. ......................................................................................................................................................................................................................................... The Author 2011. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 158 Bioscience Horizons † Volume 4 † Number 2 † June 2011 Research article ......................................................................................................................................................................................................................................... Figure 1. UK distribution showing a decline in the population over the last century: (A) distribution in 1950 and (B) distribution in 2010. Each square represents 10 km (taken from the NBN Gateway, accessed 12 November 2010). The information used here was sourced through the NBN Gateway website and included the resources listed here. Chronological society of Great Britain & Ireland. ‘Mollusc (non-marine) data for Great Britain and Ireland’, Updated 10/05/2006. Natural England. ‘Invertebrate Site Register - England’, Updated 14/01/2010. Suffolk Biological Records Centre. ‘Suffolk Biological Records Centre (SBRC) dataset’, Updated 25/06/2010. Countryside Council for Wales. ‘Welsh Invertebrate Database (WID)’, Updated 23/10/ 2008. Pond Conservation. ‘National Pond Monitoring Network collated pond survey data for Great Britain 1972 to 2007’, Updated 18/06/2009. Staffordshire Ecological Record. ‘Mollusc records for specimens held at the Stoke-on-Trent Potteries Museum’, Updated 04/01/2002. Staffordshire Ecological Record. ‘Stoke-on-Trent Environmental Survey results (1982-1984)’, Updated 22/06/2010. Buckinghamshire and Milton Keynes Environmental Records Centre. ‘Molluscs in Buckinghamshire’, Updated 02/02/2010. Tullie House Museum. ‘Tullie House Museum Natural History Collections’, Updated 25/06/2010. Worcestershire Biological Records Centre. ‘WBRC Species data for Worcestershire collated by species group’, Updated 13/08/2010. West Wales Biodiversity Information Centre. ‘CCW Regional Data: all taxa (excluding sensitive species), West Wales’, Updated 18/03/2010. ,http:// data.nbn.org.uk/. Accessed 7 July 2008. The data providers and NBN Trust bear no responsibility for the further analysis or interpretation of this material, data and/or information. Crown Copyright. All rights reserved NERC 100017897 2004. climax forest, the other ending in raised bog. Despite the (affecting the fetch of the waves) and aspect. These factors popularity of the classic model, some questions have been are all strongly interlinked and difficult to consider individu- raised over the validity of the ‘climax’. The holistic ‘mono- ally. Changes occur both spatially and temporally as a result climax’ theory proposed by Clements (1916) defined the of these factors. The distinct seres of vegetation, reflecting climax as the type of vegetation that would occur in a the physio-chemical conditions of the water (zonation), given region if climate was the sole determining factor. In alter their position with the infilling of the water body (suc- Britain, the climax is said to be temperate deciduous forest. cession). This apparently simple process may be quite evident Gleason (1926) however, recognized the relative importance in some cases but in other circumstances, stages may not of the other factors besides climate. He proposed the reduc- occur one after the other and some may be absent. tionist ‘polyclimax’ theory in which vegetation is in equili- Succession differs from zonation in that changes occur over brium with its actual environment rather than the potential time rather than space, making the process difficult to environment. In this respect, an alternative ‘climax’ is the model. Some processes happen over long time periods and bog climax of Goodwin (1956). the equilibrium point is not always clear. On a broad scale, climate, geology and topography are the Several studies have indicated that S. nitida is found in 8,9 main determining factors affecting the pathways of succes- dense emergent vegetation. Ormerod (2009) explored the sion. These give rise to the distribution of the major possibility of S. nitida and two other endangered freshwater global biomes. At a more local level, both biotic and taxa as indicators of species richness (alpha diversity), com- abiotic factors depict a microclimate environment. Jeffries position (beta diversity) and conservation importance in 7 1 and Mills (1990) point these out to be form of the water associated wetlands. Although he found that other non- body (depth and slope), material (rock, sand and clay), size priority species within wetlands were just as important ......................................................................................................................................................................................................................................... 159 Research article Bioscience Horizons † Volume 4 † Number 2 † June 2011 ......................................................................................................................................................................................................................................... Table 1. Succession key outlining the characteristic plants of each indicators of these factors, conserving the specific resource seral stage requirements of other species increased the area of wetlands under conservation management, thereby maintaining their Serial stage Plant species ................................................................................................................ unique biodiversity and environmental quality. Watson and O: Open water Ormerod (2009) and Ormerod et al. (2003) both drew atten- 1: Submerged plants Potomogeton (pondweed) tion to the occurrence of S. nitida and other species in ditches with different vegetation structure and also discussed what Bryophytes (mosses) this meant for ditch management for this and other species. Elodea (waterweed) Thus, the general aim of this study was to clarify the Najas (water-nymph) habitat requirements of S. nitida in East Kent, according to Ceratophyllum (hornworts) a seral classification. The specific objectives were to Nitella (stone warts) confirm (i) that S. nitida could be associated with a particular 2: Submerged plants with floating Potomageton (pondweed) stage (or stages) of seral succession and to test the following leaves/floating plants Nuphar/Nymphaea/Nymphoides hypothesis; (ii) that the species richness of molluscs varied (water-lilly) across the samples; (iii) that the presence or absence of Polygonum (amphibious bistort) S. nitida may be related to the abundance of other molluscan Lemna (duckweed) species; (iv) that there was significant variation in number of Hydrocharis (frogbit) molluscan species across a range of locations; and (v) as a Ranunculus (water-crowfoots) test of connectivity between molluscan communities, that the number of molluscs varied across sample sites within par- 3: Emerged plants—swamp Glyceria (reed sweet grass) ticular locations. Each of (i)–(v) was tested via appropriate Juncus (rushes) null hypotheses. Iris (yellow iris) Typha (bulrush) Phragmites (common reed) Materials and methods Mentha (water mint) This investigation had three stages: (i) the classification of 4: Emerged plants—bog/marsh Oenanthe (water-dropworts) water bodies into successional stages, with characteristic Rumex (water dock) plant species defining each sere; (ii) the investigation of the Scrophularia (water figwort) association of S. nitida with a particular seral stage Carex (sedges) (‘known sites’); (iii) the use of seral stage to predict the pres- Apium (fools water-cress) ence of S. nitida in locations where its presence was pre- C: Climax viously unknown (‘predicted sites’). Sere classification Grove Ferry and Wincheap. At each site, over a period of Water bodies can be classified by a number of variables, 2 h, plants were identified to species using Spencer-Jones depending on the reason for classification. Variables could and Wade (1986). The seral succession of plant commu- include geographical position, water chemistry, depth, size, nities described in Jeffries and Mills was used to assign a human use and macrophyte composition. For this study, seral stage to each site (Table 1). Open water (O) defined macrophytes were used. Plants have different environmental the starting point of the succession process and the climax requirements that depict their distribution and they can (C) was considered to be the final equilibrium point. The therefore tell us a lot about the environment in which they seral succession is a dynamic continuum but for the purposes grow. In the past, they have been used to define the nutrient of this research, it was necessary to define intermediate stages status of lakes; thus Nygaard (1949) defined water as according to dominant plant species. Four stages were eutrophic or oligotrophic based on the composition of the chosen: submerged plants, submerged plants with floating algal community. Plants occur across the whole spectrum leaves, emerged plants: swamp and emerged plants: bog/ of aquatic habitats from waterlogged soils to permanently marsh. Erosion and sedimentation are the dominating flooded areas. The characteristics of a waterlogged environ- factors affecting the distribution of submerged plants, ment mean that adaptive modifications are required if whilst exposure to wind and waves are the dominant plants are to survive. The level of the water affects light factors affecting distribution of emerged plants. Swamps and pressure conditions as well as the concentrations of are inundated with water, even during the summer season, oxygen and nitrogen. and so tend to contain tall narrow leaved monocotyledons During the summer of 2009, 16 sites were visited around that allow little resistance to wind and waves, whilst Kent. These study sites comprised lakes and ditches spread marshes are not flooded during the summer though they across five locations: Westbere, Broad Oak, Stodmarsh, ......................................................................................................................................................................................................................................... 160 Bioscience Horizons † Volume 4 † Number 2 † June 2011 Research article ......................................................................................................................................................................................................................................... Figure 2. Examples of successional stages. (A) Stage 1, (B) Stage 2, (C) Stage 3 and (D) Stage 4. Table 2. GPS locations of ‘Known’ and ‘Predicted’ sites for S. nitid remain water logged, and thus contain more herbaceous plants along with the monocotyledons (Fig. 2). Known sites Predicted sites ................................................................................................................ Sampling for Segmentina nitida E624270 N161880 E615710 N159200 E624310 N161750 E615700 N159190 The preferred habitat environment of S. nitida was initially determined through the sampling of sites that were known E630950 N162580 E618330 N159870 to have supported it in the past. The most recent and compre- E631300 N162270 E618300 N159810 hensive survey for S. nitida was carried out by Killeen (1999) E631400 N162240 E619380 N160840 on behalf of English Nature and found S. nitida to be frequent E623010 N161650 E619960 N160630 or common at 104 sites. Sixteen of these sites spread over E622950 N161650 E619400 N160430 four locations; Preston Valley, Ash Level, Westmarsh and E622390 N161230 Stodmarsh (not in the NNR) were sampled. This survey did E624090 N162590 not include the sites that had been used to establish the seral stages described above. Randomly located (30 s) hand-net samples were taken at each and sorted for live S. nitida in investigate the following questions: whether (i) the total the field. Each site was assigned to the appropriate seral number of molluscs within each species varied across stage according to the succession key. The presence of other samples; (ii) the number of molluscs varied between freshwater molluscs was noted. samples with or without S. nitida; (iii) molluscan species On the basis of this information, a further nine sites (‘pre- richness varied across the locations; and (iv) there was a dicted’) were found which were in the appropriate seral stage relationship between number of molluscs and sample site for S. nitida, but where the presence of S. nitida had not been within location, implying the possibility of connectivity recorded in the past (Table 2). These sites were visited and between molluscan communities. sampled using the same technique. Other freshwater mol- luscs were also noted. Results Statistical methods Of the 19 sites classified into seral stages, a total of 9 were A general linear statistical model was applied to the mollus- found at Stage 1, 10 were found at Stage 2, 10 at Stage 3 can data from these sites. Null hypothesis were set up to and 9 were found at Stage 4. ......................................................................................................................................................................................................................................... 161 Research article Bioscience Horizons † Volume 4 † Number 2 † June 2011 ......................................................................................................................................................................................................................................... S. nitida was present in seven of the sixteen ‘known’ sites Ramshorn snail Planorbis (Bathyomphalus) contourtus (L.), sampled from the Killen 1999 survey (Table 2). These were the Whirlpool Ramshorn snail Planorbis (Anisus) vortex located between Stodmarsh (not in the NNR), Preston Valley (L.), the Great Ramshorn snail Planorbis corneus (L.), the and Ash level. On several occasions recent dredging had common Bithynia Bithynia tentaculata (L.), the bladder removed all vegetation and thus available habitat. On other snail Physa fontinalis (L.), the great pond snail Lymnaea occasions, although no specific chemical analysis was under- (Lymnaea) stagnalis (L.), the Horny Orb Mussel Sphaerium taken, it seemed that pollution had altered the water quality (S.) corneum (L.) and the Wandering Pond Snail Lymnaea and no living molluscs were found. Thus some sites were (Radix) peregra (Muller) forma ovata Draparnaud. excluded from the investigation. No S. nitida were found at Westmarsh, where they had been recorded by Killeen; at Discussion this location, ditches had been left to overgrow. In each of the seven cases where S. nitida was found, the habitat Using presence known from the literature, the sere that sup- was Stage 4 on the succession key, with dominant plant ports S. nitida was identified as Stage 4, thereby confirming 1,8,9 species such as Oenanthe (Water-dropworts), Carex the observations by other authors. This information (Sedges) and Apium (Fools Water-Cress). However, the dis- was then used to predict sites where it might be found. tinction was not always clear and in a few incidences, This prediction was correct for two out of nine sites Stage 3 indicator species such as Typha (Bulrush) and sampled. Due to time constraints, it was not possible to vali- Juncus (Rushes) occurred in some of the Stage 4 sites. date this process, though appropriate methods are available Of the nine sites sampled at Stage 4 of the succession, two which could be used in future work. A previous study on contained S. nitida. Both of these sites were located at dispersal and fragmentation by Niggebrugge et al. (2007) Westbere. Segmentina nitida wasnot presentinany of used 15 environmental variables to define habitat preferences the remaining Stage 4 sites located at the Canterbury of 20 gastropod species, including S. nitida. However, in this Environmental Education Centre, Stodmarsh and Grove Ferry. research, again due to time constrains, plant species compo- In order to investigate further the distribution of S. nitida in sition was solely used to indicate the preferred habitat of association with other molluscs, samples taken from eight S. nitida and therefore did not take into account other known sites and four predicted sites. Data from these environmental variables. samples were analysed using ANOVA tests carried out on In this study, S. nitida was found to be limited to the the number of molluscs per sample (log X þ 1). A general Carex-Juncus-Eleocharis-Oenanthe community, a late seral 10 i linear model (GLM) on number of molluscs in each species stage in ditch succession. A general linear statistical model showed a significant variation (F 5. 93, P, 0.001). applied to date from these sites suggested that (i) the total 8,107 This suggests that the total number of molluscs within each number of molluscs within each species varied across species varied across the samples. A GLM of number of mol- sample; (ii) the number of molluscs varied between samples luscs versus the presence or absence of S. nitida also showed a with or without S. nitida; (iii) there was no variation in the significant difference (F 10.12, P ¼ 0.002). This total number of molluscs across the locations and (iv) there 1,107 suggests that the number of molluscs varied between was no relationship between number of molluscs and samples with or without S. nitida. A GLM of molluscs sample site within location, implying some degree of connec- versus location showed no significant variation (F tivity between molluscan communities. Also (v), a two-way 5,107 1.53, P ¼ 0.188). This suggested that there was no variation ANOVA with Factor 1 as the number of mollusc and the in the total number of mollusc across the locations. In a presence/absence of S. nitida as Factor 2, showed a signifi- two-way analysis of variance (ANOVA), the interaction of cant interaction effect. Observations (i)–(v) are novel for species as Factor 1 and the presence or absence of S. nitida East Kent. As Niggerbrugge et al. (2007) point out there as Factor 2 showed a significant effect (F 2.71, P ¼ are other constraints to the population of S. nitida besides 8,107 0.010). This suggested that the number of mollusc within habitat loss due to eutrophication and management prac- each species varied according to the presence or absence of tices. Dispersal ability and habitat fragmentation as well as S. nitida. The interaction of both species and location now the life history strategy of this species are also important showed a significant effect (F 1.89, P ¼ 0.015), factors. These will now be examined in more detail, followed 40,107 which suggested that some species were more abundant in by the relationship of S. nitida with other mollusc species. some samples than others. A GLM number of molluscs and Life cycle and biology sample site within location (related to connectivity) showed no significant variation (F 2.60, P ¼ 0.079). This Organisms can exhibit several adaptations to the seasonal, 2,107 suggested that there was no relationship between number of temporary water bodies in which S. nitida is found. molluscs and sample site within location. Segmentina nitida, as with most other Planorbidae, can Other freshwater species which were identified included the survive a period of unfavourable conditions in a state of aes- Ramshorn snail Planorbis (P.) planorbis (L.), the Twisted tivation. Planorbidae are known to reach sexual maturity ......................................................................................................................................................................................................................................... 162 Bioscience Horizons † Volume 4 † Number 2 † June 2011 Research article ......................................................................................................................................................................................................................................... quickly but exhibit only one or two reproductive events per extinct. Thus, habitat fragmentation is another possible year. However, Ksia˛z˙kiewicz and Gołdyn (2008) found factor for its rarity. S. nitida to have three reproductive events starting at the Management practices beginning of April, beginning of May and the beginning of June. Each cycle lasted 4 weeks, with reproduction The characteristic drainage ditches of the British landscape ending in July as the water table became lower. Adults domi- were originally designed to divert water away from wetland nated the population at this point, whilst smaller individuals areas, maximizing agricultural land use. Today, conservation dominated the early spring. This enables those that do schemes are bringing water back in some areas. Despite this, survive through the winter or droughts to reproduce as poor ditch management and changes in water chemistry are soon as appropriate conditions arise. thought to be a major factor in S.nitida’s population Sampling for S. nitida took place in late April and early decline, not only reducing the possible habitat area but May 2010. According to Ksia˛z˙kiewicz and Goldyn (2008), also the possible habitat type. Lack of proper management this would be after the first reproductive cycle event of the practices leaves some ditches completely void of all veg- year. However, due to unpredictable weather variations, etation, whilst others dry up. Ormerod (pers comm) notes spring was unusually late in 2010 and there were still wide- that rotational ditch management interacts directly with spread frosts which might account for its absence from hydroseral development to reset succession to earlier samples at some sites. Due to time constraints, it was not stages. The few, small isolated places in which it could possible to postpone sampling. exist may then be affected by agricultural run-off to such an extent that the water quality is no longer suitable. The Dispersal and connectivity preference of S. nitida for shallow ditches with dense emer- Segmentina nitida belongs to the Pulmonata, a group of mol- gent vegetation means that careful management practices luscs which developed primitive lungs when, during their are required to maintain this specific stage of succession evolution, they ventured onto land. Many species in the which will, of its nature be quite temporary. Pulmonata have now returned to aquatic environments, but All stages of succession are unique habitats for different still retain structural reminiscences of this adaptation. species of plants and animals, and a proper management Despite the evolutionary success of the group as a whole, plan must ideally not only provide a variety of these stages, individual aquatic species remain vulnerable. Their ability but also be attuned to accommodate the local flora and to disperse and reach other suitable habitats across land is fauna of ecological importance. Thus, in this case, man- relatively limited. Isolated populations and fragmented agement should ideally consist of clearing in sections, allow- habitat make it difficult to colonize new environments, ing a range of habitats to be available at all times. In the case even if they have the ability to do so, as shown by the of S. nitida, where ditches are often used as drainage chan- number of suitable habitat sites located in this study. nels, light maintenance on an annual or biennial rotation, Changes in the way we use the land over the last century removing half the channel each year, is recommended. It is have led to wide-scale land-cover transformation. Not only also necessary to determine how S. nitida colonizes new within the UK but worldwide, demand for crops, minerals sites. The most likely contenders are carriage by water and wood as well as the building of infrastructure, such as flow, on the feet of birds or through anthropogenic activities. roads and railways, had resulted in patchy isolated fragments Segmentina nitida and other molluscs of natural landscapes. From 1860–1978 alone, over eight thousand square kilometre were converted to cropping The ANOVA tests produced a variety of results concerning worldwide, wetland itself accounting for 2.5% of this. the interaction of S. nitida and other mollusc species. In par- Habitat fragmentation poses a threat for many wildlife ticular, there was a variation in molluscan diversity accord- species, resulting in higher extinction rates and causing ing to the presence or absence of S. nitida. Ormerod et al. changes in community structures. The number of generalist (2009) found that sites containing S. nitida and two other species tends to rise, whilst the numbers of specialist BAP species held greater richness of gastropod species than species tends to fall. those that did not. This relationship of molluscan species Unless ditches are linked, the possibility of isolated popu- with sites in which S. nitida is present or absent might indi- lations getting to a new suitable habitat is slim. Connecting cate that similar factors that operate on S. nitida might also all suitable habitats is made difficult by land ownership, act on some but not on all the other species of mollusc. This land use and the requirements of other species. Ideally, loca- association might be mediated through some other factor of lized connectivity should be maintained so that stable popu- the environment (such as water chemistry) or biotic factors lations can exist in small areas. In this sense, the species may (such as predators). For example, Watson and Ormerod be nationally rare by area, but abundant in its own niche. If (2003) also found that water quality, vegetation and anthro- ditches or habitat areas are not connected then these isolated pogenic factors affected the distribution of S. nitida. It is also pockets may eventually die out and the species will go possible that S. nitida has a similar alimentation to certain ......................................................................................................................................................................................................................................... 163 Research article Bioscience Horizons † Volume 4 † Number 2 † June 2011 ......................................................................................................................................................................................................................................... other species. The latter could therefore act as indicators for and learning support staff, in particular John Hills and the potential of a site without S. nitida to support S. nitida. Lois Hodgson. This could be valuable information for conservation man- agement. In addition, although there was no variation in Author biography the total number of mollusc across the samples in a R.M.F.C. completed her degree in Ecology and Conservation one-way ANOVA, a two-way ANOVA revealed an inter- at Canterbury Christ Church University in 2010 as a mature action with species, the numbers between samples becoming student, having spent a few years out of education. Here she more varied. This again could also link relationships between found herself working on the Shining Ram’s-horn snail as molluscan species and highlight the presence of factors other part of her third year individual study under the supervision than plant distribution in determining habitat preferences. of Georges Dussart. She has greatly enjoyed working on this This investigation has highlighted the dynamic nature of endangered species and hopes to continue with the conserva- processes involved in plant succession. The large number of tion of this pretty little snail. variables that affect plant distribution makes modelling quite difficult. Thus, Stage 3 plants sometimes occurred in places where the soils were well drained and Stage 4 plants References sometimes occurred where the water level was high. 1. Ormerod SJ, Durance I, Terrier A, Swanson AM (2009) Priority wetland Monoculture stands of Phragmites and Glyceria occurred invertebrates as conservation surrogates. Conserv Biol 24: 573–582. often in both deep and shallow water levels. In this study, 2. The National Biodiversity Network (2010). http://data.nbn.org.uk (accessed S. nitida occurred most frequently where there was a rich November 2010). emergent fauna and at least 60 cm of water. 3. Painter D (1999) Macroinvertebrate distribution and the conservation value The habitat preferences of S. nitida would indicate veg- of aquatic Coleoptera, Mollusca and Odonata in the ditches of traditionally etation suited to the later stages of succession and ditch managed and grazing fen at Wicken Fen, UK. J Appl Ecol 36: 33–48. environments. This was indicated by is presence at nine 4. Tutin TG (1941) The hydrosere and current concepts of the climax. J Ecol 29: 268–279. such locations. Although further surveys of other sites exhi- 5. Tansley AG (1939) British ecology during the past Quarter-Century: the plant biting the same vegetation stage did not prove as fruitful as community and the ecosystem. J Ecol 27: 513–530. hoped, possible reasons for this have been examined. 6. Klinger LF (1996) The myth of the classic hydrosere model of bog succes- sion. Arctic Alpine Res 28: 1–9. Conclusion 7. Jeffries M, Mills D (1990) Freshwater Ecology: Principles and Applications. London: Belhaven Press. In relation to the ecology of S. nitida, this investigation has 8. Watson AM, Omerod SJ (2003) The distribution of three uncommon fresh- highlighted the importance of seral stage which in turn is water gastropods in the drainage ditches of British grazing marshes. Biol related to issues such as ditch management and habitat connec- Conserv 118: 455–466. tivity. Freshwater species can be indicators of species richness 9. Watson MA, Omerod SJ (2004) The microdistribution of three uncommon (alpha diversity), composition (beta diversity) and conserva- freshwater gastropods in the drainage ditches of British grazing marshes. Aquat Conserv 14: 221–236. tion importance in associated wetlands. Around 9% of all non- 10. Etherington JR (1983) Wetland Ecology. London: Edward Arnold. marine molluscs in Europe are thought to be threatened. 11. Spencer-Jones D, Wade M (1986) Aquatic Plants: A Guide to Recognition. Ormerod et al. (2009) noted that conserving the specific Hants: Borcombe Printers. resource requirements of the endangered species increased the 12. Killeen IJ (1999) A survey of the East Kent grazing marshes for the freshwater area of wetlands under conservation management and snail Segmentina nitida. English Nature Research Report 356. improved their unique biodiversity and environmental 13. Niggebrugge K, Durance I, Watson AM, Leuven RSEW, Ormerod SJ (2007) quality. This research is novel in that it indicates an association Applying landscape ecology to conservation biology: spatially explicit analy- between S. nitida and other molluscan species at these sites in sis reveals dispersal limits on threatened wetland gastropods. Biol Conserv East Kent, mediated through seral stage. Creating a workable 139: 286–296. management strategy for S. nitida might not only benefit this ` 14. Gołdyn R, Klimaszyk P, Kuczynska-Kippen N, Piotrowicz R (eds) (2008) The functioning and protection of water ecosystems. Poznan: Bonami Publishing species, but also associated species in this area. House. 15. Huggett RJ (1998) Fundamentals of Biogeography. London: Routledge. Acknowledgements 16. UK Biodiversity Action Plan (1995–1999). http://www.ukbap.org.uk/ UKPlans.aspx?ID=570 (accessed November 2010). Special thanks for the help and support of my family and 17. The Royal Society for the Protection of Birds (2010) http://www.rspb.org.uk/ friends, particularly Daniel for being my field companion. ourwork/policy/water/ (accessed November 2010). Thank you to Prof. G.B.J. Dussart who guided and super- 18. Wells SM, Chatfield JE (1995) Conservation priorities for European non- vised throughout the investigation. I would also like to marine Mollusca. In AC Van Bruggen, SM Wells, CM Kemperman, eds. thank Prof. S.J. Ormerod for his helpful reviewing and Biodiversity and Conservation of the Mollusca. Oegsteest-Leiden: Backhuys advice. And last but not least thank you to the technical Publishers, pp. 113–152. ........................................................................................................................................................................................................................................ ......................................................................................................................................................................................................................................... http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Bioscience Horizons Oxford University Press

Hydroseral habitat requirement of the endangered Shining Ramshorn Snail Segmentina nitida

Bioscience Horizons , Volume 4 (2) – Jun 1, 2011

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10.1093/biohorizons/hzr019
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Abstract

Volume 4 † Number 2 † June 2011 10.1093/biohorizons/hzr019 ......................................................................................................................................................................................................................................... Research article Hydroseral habitat requirement of the endangered Shining Ramshorn Snail Segmentina nitida Ruth M.F. Clark* Canterbury Christ Church University, 38, Chestnut Drive, Sturry, Canterbury, Kent CT2 0NB, UK. * Corresponding author: Tel: þ44 7830537657. Email: rclark85@hotmail.co.uk Supervisor: Professor Georges B.J. Dussart, Biological Sciences, Canterbury Christ Church University, 38, Chestnut Drive, Sturry, Canterbury, Kent CT2 0NB, UK. ........................................................................................................................................................................................................................................ Before the 1950s, the Shining Ramshorn snail Segmentina nitida was widespread across marshes and drainage ditches in Britain, con- tinental Europe and Scandinavia. However, the population has declined rapidly and the IUCN Red Data list highlights the species as seriously vulnerable to extinction. It is now one of the six freshwater molluscan species protected under the UK Biodiversity Action Plan. Most previous research has focused on species decline and conservation issues. The aim of the research reported here was to clarify the habitat requirements of S. nitida in East Kent within the context of a seral classification. Six hydroseral stages were defined according to plant species composition. Segmentina nitida was limited uniquely to the Carex-Juncus-Eleocharis-Oenanthe community, a late seral stage in ditch succession, which confirms the work of other authors. A general linear statistical model applied to data from these sites suggested that (i) the total number of molluscs within each species varied across samples; (ii) the number of molluscs varied between samples with or without S. nitida; (iii) there was no variation in the total number of molluscs across the locations and (iv) there was no relationship between number of molluscs and sample site within location, implying some degree of connectivity between molluscan communities. Also a two-way ANOVA with Factor 1 as the number of mollusc and Factor 2 as the presence/absence of S. nitida showed a significant interaction effect. These observations are novel for these sites in East Kent and have implications for the ecology, life history strategy and conservation management of S. nitida. Key words: Segmentina nitida, wetlands, succession, mollusc. Submitted September 2010; accepted March 2011 ........................................................................................................................................................................................................................................ Introduction Ditches themselves are dynamic habitats in which the flora and fauna are a function of the seral stage. Ditches are tem- The Shining Ramshorn snail Segmentina nitida is listed as porary habitats, which will change by a process of ecological Endangered in the ICUN Red list based on pre1994 guide- succession. The classic hydrosere model of plant succession lines and is currently on the list of priority species set out from wet to dry land involves the infilling of a lake or in the UK Biodiversity Action Plan (BAP). It is one of the basin with sediment and detritus to form intermediate six freshwater molluscs covered by the BAP, invertebrates marsh, fen or bog communities, culminating in a mature comprising almost half the species on the list. Its population upland or forest ‘climax’; the latter is the definition given has declined sharply over the last 50 years (Fig. 1). Before the to a plant community, which appears to be in equilibrium 1950s, it was widespread across marshes and drainage with its surrounding environment, and where no further ditches in Britain, Europe, and Scandinavia. Today in major change is likely to occur. Several authors’ have pro- Britain, it is restricted to just a few sites including the posed pathways for this process. Tansley (1939) put Norfolk Broads, Pevensey Levels, Lewis Levels and East forward a sequence of four stages beginning with a floating Kent. The marshes and drainage ditches in which this aquatic community, to a reed swamp, followed by a fen or species can be found support a wide range of biodiversity. bog, and finishing with carr or climax forest. By contrast, They are therefore important environments that receive Goodwin (1956) proposed two models, one ending in strong emphasis in conservation legislation. ......................................................................................................................................................................................................................................... The Author 2011. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 158 Bioscience Horizons † Volume 4 † Number 2 † June 2011 Research article ......................................................................................................................................................................................................................................... Figure 1. UK distribution showing a decline in the population over the last century: (A) distribution in 1950 and (B) distribution in 2010. Each square represents 10 km (taken from the NBN Gateway, accessed 12 November 2010). The information used here was sourced through the NBN Gateway website and included the resources listed here. Chronological society of Great Britain & Ireland. ‘Mollusc (non-marine) data for Great Britain and Ireland’, Updated 10/05/2006. Natural England. ‘Invertebrate Site Register - England’, Updated 14/01/2010. Suffolk Biological Records Centre. ‘Suffolk Biological Records Centre (SBRC) dataset’, Updated 25/06/2010. Countryside Council for Wales. ‘Welsh Invertebrate Database (WID)’, Updated 23/10/ 2008. Pond Conservation. ‘National Pond Monitoring Network collated pond survey data for Great Britain 1972 to 2007’, Updated 18/06/2009. Staffordshire Ecological Record. ‘Mollusc records for specimens held at the Stoke-on-Trent Potteries Museum’, Updated 04/01/2002. Staffordshire Ecological Record. ‘Stoke-on-Trent Environmental Survey results (1982-1984)’, Updated 22/06/2010. Buckinghamshire and Milton Keynes Environmental Records Centre. ‘Molluscs in Buckinghamshire’, Updated 02/02/2010. Tullie House Museum. ‘Tullie House Museum Natural History Collections’, Updated 25/06/2010. Worcestershire Biological Records Centre. ‘WBRC Species data for Worcestershire collated by species group’, Updated 13/08/2010. West Wales Biodiversity Information Centre. ‘CCW Regional Data: all taxa (excluding sensitive species), West Wales’, Updated 18/03/2010. ,http:// data.nbn.org.uk/. Accessed 7 July 2008. The data providers and NBN Trust bear no responsibility for the further analysis or interpretation of this material, data and/or information. Crown Copyright. All rights reserved NERC 100017897 2004. climax forest, the other ending in raised bog. Despite the (affecting the fetch of the waves) and aspect. These factors popularity of the classic model, some questions have been are all strongly interlinked and difficult to consider individu- raised over the validity of the ‘climax’. The holistic ‘mono- ally. Changes occur both spatially and temporally as a result climax’ theory proposed by Clements (1916) defined the of these factors. The distinct seres of vegetation, reflecting climax as the type of vegetation that would occur in a the physio-chemical conditions of the water (zonation), given region if climate was the sole determining factor. In alter their position with the infilling of the water body (suc- Britain, the climax is said to be temperate deciduous forest. cession). This apparently simple process may be quite evident Gleason (1926) however, recognized the relative importance in some cases but in other circumstances, stages may not of the other factors besides climate. He proposed the reduc- occur one after the other and some may be absent. tionist ‘polyclimax’ theory in which vegetation is in equili- Succession differs from zonation in that changes occur over brium with its actual environment rather than the potential time rather than space, making the process difficult to environment. In this respect, an alternative ‘climax’ is the model. Some processes happen over long time periods and bog climax of Goodwin (1956). the equilibrium point is not always clear. On a broad scale, climate, geology and topography are the Several studies have indicated that S. nitida is found in 8,9 main determining factors affecting the pathways of succes- dense emergent vegetation. Ormerod (2009) explored the sion. These give rise to the distribution of the major possibility of S. nitida and two other endangered freshwater global biomes. At a more local level, both biotic and taxa as indicators of species richness (alpha diversity), com- abiotic factors depict a microclimate environment. Jeffries position (beta diversity) and conservation importance in 7 1 and Mills (1990) point these out to be form of the water associated wetlands. Although he found that other non- body (depth and slope), material (rock, sand and clay), size priority species within wetlands were just as important ......................................................................................................................................................................................................................................... 159 Research article Bioscience Horizons † Volume 4 † Number 2 † June 2011 ......................................................................................................................................................................................................................................... Table 1. Succession key outlining the characteristic plants of each indicators of these factors, conserving the specific resource seral stage requirements of other species increased the area of wetlands under conservation management, thereby maintaining their Serial stage Plant species ................................................................................................................ unique biodiversity and environmental quality. Watson and O: Open water Ormerod (2009) and Ormerod et al. (2003) both drew atten- 1: Submerged plants Potomogeton (pondweed) tion to the occurrence of S. nitida and other species in ditches with different vegetation structure and also discussed what Bryophytes (mosses) this meant for ditch management for this and other species. Elodea (waterweed) Thus, the general aim of this study was to clarify the Najas (water-nymph) habitat requirements of S. nitida in East Kent, according to Ceratophyllum (hornworts) a seral classification. The specific objectives were to Nitella (stone warts) confirm (i) that S. nitida could be associated with a particular 2: Submerged plants with floating Potomageton (pondweed) stage (or stages) of seral succession and to test the following leaves/floating plants Nuphar/Nymphaea/Nymphoides hypothesis; (ii) that the species richness of molluscs varied (water-lilly) across the samples; (iii) that the presence or absence of Polygonum (amphibious bistort) S. nitida may be related to the abundance of other molluscan Lemna (duckweed) species; (iv) that there was significant variation in number of Hydrocharis (frogbit) molluscan species across a range of locations; and (v) as a Ranunculus (water-crowfoots) test of connectivity between molluscan communities, that the number of molluscs varied across sample sites within par- 3: Emerged plants—swamp Glyceria (reed sweet grass) ticular locations. Each of (i)–(v) was tested via appropriate Juncus (rushes) null hypotheses. Iris (yellow iris) Typha (bulrush) Phragmites (common reed) Materials and methods Mentha (water mint) This investigation had three stages: (i) the classification of 4: Emerged plants—bog/marsh Oenanthe (water-dropworts) water bodies into successional stages, with characteristic Rumex (water dock) plant species defining each sere; (ii) the investigation of the Scrophularia (water figwort) association of S. nitida with a particular seral stage Carex (sedges) (‘known sites’); (iii) the use of seral stage to predict the pres- Apium (fools water-cress) ence of S. nitida in locations where its presence was pre- C: Climax viously unknown (‘predicted sites’). Sere classification Grove Ferry and Wincheap. At each site, over a period of Water bodies can be classified by a number of variables, 2 h, plants were identified to species using Spencer-Jones depending on the reason for classification. Variables could and Wade (1986). The seral succession of plant commu- include geographical position, water chemistry, depth, size, nities described in Jeffries and Mills was used to assign a human use and macrophyte composition. For this study, seral stage to each site (Table 1). Open water (O) defined macrophytes were used. Plants have different environmental the starting point of the succession process and the climax requirements that depict their distribution and they can (C) was considered to be the final equilibrium point. The therefore tell us a lot about the environment in which they seral succession is a dynamic continuum but for the purposes grow. In the past, they have been used to define the nutrient of this research, it was necessary to define intermediate stages status of lakes; thus Nygaard (1949) defined water as according to dominant plant species. Four stages were eutrophic or oligotrophic based on the composition of the chosen: submerged plants, submerged plants with floating algal community. Plants occur across the whole spectrum leaves, emerged plants: swamp and emerged plants: bog/ of aquatic habitats from waterlogged soils to permanently marsh. Erosion and sedimentation are the dominating flooded areas. The characteristics of a waterlogged environ- factors affecting the distribution of submerged plants, ment mean that adaptive modifications are required if whilst exposure to wind and waves are the dominant plants are to survive. The level of the water affects light factors affecting distribution of emerged plants. Swamps and pressure conditions as well as the concentrations of are inundated with water, even during the summer season, oxygen and nitrogen. and so tend to contain tall narrow leaved monocotyledons During the summer of 2009, 16 sites were visited around that allow little resistance to wind and waves, whilst Kent. These study sites comprised lakes and ditches spread marshes are not flooded during the summer though they across five locations: Westbere, Broad Oak, Stodmarsh, ......................................................................................................................................................................................................................................... 160 Bioscience Horizons † Volume 4 † Number 2 † June 2011 Research article ......................................................................................................................................................................................................................................... Figure 2. Examples of successional stages. (A) Stage 1, (B) Stage 2, (C) Stage 3 and (D) Stage 4. Table 2. GPS locations of ‘Known’ and ‘Predicted’ sites for S. nitid remain water logged, and thus contain more herbaceous plants along with the monocotyledons (Fig. 2). Known sites Predicted sites ................................................................................................................ Sampling for Segmentina nitida E624270 N161880 E615710 N159200 E624310 N161750 E615700 N159190 The preferred habitat environment of S. nitida was initially determined through the sampling of sites that were known E630950 N162580 E618330 N159870 to have supported it in the past. The most recent and compre- E631300 N162270 E618300 N159810 hensive survey for S. nitida was carried out by Killeen (1999) E631400 N162240 E619380 N160840 on behalf of English Nature and found S. nitida to be frequent E623010 N161650 E619960 N160630 or common at 104 sites. Sixteen of these sites spread over E622950 N161650 E619400 N160430 four locations; Preston Valley, Ash Level, Westmarsh and E622390 N161230 Stodmarsh (not in the NNR) were sampled. This survey did E624090 N162590 not include the sites that had been used to establish the seral stages described above. Randomly located (30 s) hand-net samples were taken at each and sorted for live S. nitida in investigate the following questions: whether (i) the total the field. Each site was assigned to the appropriate seral number of molluscs within each species varied across stage according to the succession key. The presence of other samples; (ii) the number of molluscs varied between freshwater molluscs was noted. samples with or without S. nitida; (iii) molluscan species On the basis of this information, a further nine sites (‘pre- richness varied across the locations; and (iv) there was a dicted’) were found which were in the appropriate seral stage relationship between number of molluscs and sample site for S. nitida, but where the presence of S. nitida had not been within location, implying the possibility of connectivity recorded in the past (Table 2). These sites were visited and between molluscan communities. sampled using the same technique. Other freshwater mol- luscs were also noted. Results Statistical methods Of the 19 sites classified into seral stages, a total of 9 were A general linear statistical model was applied to the mollus- found at Stage 1, 10 were found at Stage 2, 10 at Stage 3 can data from these sites. Null hypothesis were set up to and 9 were found at Stage 4. ......................................................................................................................................................................................................................................... 161 Research article Bioscience Horizons † Volume 4 † Number 2 † June 2011 ......................................................................................................................................................................................................................................... S. nitida was present in seven of the sixteen ‘known’ sites Ramshorn snail Planorbis (Bathyomphalus) contourtus (L.), sampled from the Killen 1999 survey (Table 2). These were the Whirlpool Ramshorn snail Planorbis (Anisus) vortex located between Stodmarsh (not in the NNR), Preston Valley (L.), the Great Ramshorn snail Planorbis corneus (L.), the and Ash level. On several occasions recent dredging had common Bithynia Bithynia tentaculata (L.), the bladder removed all vegetation and thus available habitat. On other snail Physa fontinalis (L.), the great pond snail Lymnaea occasions, although no specific chemical analysis was under- (Lymnaea) stagnalis (L.), the Horny Orb Mussel Sphaerium taken, it seemed that pollution had altered the water quality (S.) corneum (L.) and the Wandering Pond Snail Lymnaea and no living molluscs were found. Thus some sites were (Radix) peregra (Muller) forma ovata Draparnaud. excluded from the investigation. No S. nitida were found at Westmarsh, where they had been recorded by Killeen; at Discussion this location, ditches had been left to overgrow. In each of the seven cases where S. nitida was found, the habitat Using presence known from the literature, the sere that sup- was Stage 4 on the succession key, with dominant plant ports S. nitida was identified as Stage 4, thereby confirming 1,8,9 species such as Oenanthe (Water-dropworts), Carex the observations by other authors. This information (Sedges) and Apium (Fools Water-Cress). However, the dis- was then used to predict sites where it might be found. tinction was not always clear and in a few incidences, This prediction was correct for two out of nine sites Stage 3 indicator species such as Typha (Bulrush) and sampled. Due to time constraints, it was not possible to vali- Juncus (Rushes) occurred in some of the Stage 4 sites. date this process, though appropriate methods are available Of the nine sites sampled at Stage 4 of the succession, two which could be used in future work. A previous study on contained S. nitida. Both of these sites were located at dispersal and fragmentation by Niggebrugge et al. (2007) Westbere. Segmentina nitida wasnot presentinany of used 15 environmental variables to define habitat preferences the remaining Stage 4 sites located at the Canterbury of 20 gastropod species, including S. nitida. However, in this Environmental Education Centre, Stodmarsh and Grove Ferry. research, again due to time constrains, plant species compo- In order to investigate further the distribution of S. nitida in sition was solely used to indicate the preferred habitat of association with other molluscs, samples taken from eight S. nitida and therefore did not take into account other known sites and four predicted sites. Data from these environmental variables. samples were analysed using ANOVA tests carried out on In this study, S. nitida was found to be limited to the the number of molluscs per sample (log X þ 1). A general Carex-Juncus-Eleocharis-Oenanthe community, a late seral 10 i linear model (GLM) on number of molluscs in each species stage in ditch succession. A general linear statistical model showed a significant variation (F 5. 93, P, 0.001). applied to date from these sites suggested that (i) the total 8,107 This suggests that the total number of molluscs within each number of molluscs within each species varied across species varied across the samples. A GLM of number of mol- sample; (ii) the number of molluscs varied between samples luscs versus the presence or absence of S. nitida also showed a with or without S. nitida; (iii) there was no variation in the significant difference (F 10.12, P ¼ 0.002). This total number of molluscs across the locations and (iv) there 1,107 suggests that the number of molluscs varied between was no relationship between number of molluscs and samples with or without S. nitida. A GLM of molluscs sample site within location, implying some degree of connec- versus location showed no significant variation (F tivity between molluscan communities. Also (v), a two-way 5,107 1.53, P ¼ 0.188). This suggested that there was no variation ANOVA with Factor 1 as the number of mollusc and the in the total number of mollusc across the locations. In a presence/absence of S. nitida as Factor 2, showed a signifi- two-way analysis of variance (ANOVA), the interaction of cant interaction effect. Observations (i)–(v) are novel for species as Factor 1 and the presence or absence of S. nitida East Kent. As Niggerbrugge et al. (2007) point out there as Factor 2 showed a significant effect (F 2.71, P ¼ are other constraints to the population of S. nitida besides 8,107 0.010). This suggested that the number of mollusc within habitat loss due to eutrophication and management prac- each species varied according to the presence or absence of tices. Dispersal ability and habitat fragmentation as well as S. nitida. The interaction of both species and location now the life history strategy of this species are also important showed a significant effect (F 1.89, P ¼ 0.015), factors. These will now be examined in more detail, followed 40,107 which suggested that some species were more abundant in by the relationship of S. nitida with other mollusc species. some samples than others. A GLM number of molluscs and Life cycle and biology sample site within location (related to connectivity) showed no significant variation (F 2.60, P ¼ 0.079). This Organisms can exhibit several adaptations to the seasonal, 2,107 suggested that there was no relationship between number of temporary water bodies in which S. nitida is found. molluscs and sample site within location. Segmentina nitida, as with most other Planorbidae, can Other freshwater species which were identified included the survive a period of unfavourable conditions in a state of aes- Ramshorn snail Planorbis (P.) planorbis (L.), the Twisted tivation. Planorbidae are known to reach sexual maturity ......................................................................................................................................................................................................................................... 162 Bioscience Horizons † Volume 4 † Number 2 † June 2011 Research article ......................................................................................................................................................................................................................................... quickly but exhibit only one or two reproductive events per extinct. Thus, habitat fragmentation is another possible year. However, Ksia˛z˙kiewicz and Gołdyn (2008) found factor for its rarity. S. nitida to have three reproductive events starting at the Management practices beginning of April, beginning of May and the beginning of June. Each cycle lasted 4 weeks, with reproduction The characteristic drainage ditches of the British landscape ending in July as the water table became lower. Adults domi- were originally designed to divert water away from wetland nated the population at this point, whilst smaller individuals areas, maximizing agricultural land use. Today, conservation dominated the early spring. This enables those that do schemes are bringing water back in some areas. Despite this, survive through the winter or droughts to reproduce as poor ditch management and changes in water chemistry are soon as appropriate conditions arise. thought to be a major factor in S.nitida’s population Sampling for S. nitida took place in late April and early decline, not only reducing the possible habitat area but May 2010. According to Ksia˛z˙kiewicz and Goldyn (2008), also the possible habitat type. Lack of proper management this would be after the first reproductive cycle event of the practices leaves some ditches completely void of all veg- year. However, due to unpredictable weather variations, etation, whilst others dry up. Ormerod (pers comm) notes spring was unusually late in 2010 and there were still wide- that rotational ditch management interacts directly with spread frosts which might account for its absence from hydroseral development to reset succession to earlier samples at some sites. Due to time constraints, it was not stages. The few, small isolated places in which it could possible to postpone sampling. exist may then be affected by agricultural run-off to such an extent that the water quality is no longer suitable. The Dispersal and connectivity preference of S. nitida for shallow ditches with dense emer- Segmentina nitida belongs to the Pulmonata, a group of mol- gent vegetation means that careful management practices luscs which developed primitive lungs when, during their are required to maintain this specific stage of succession evolution, they ventured onto land. Many species in the which will, of its nature be quite temporary. Pulmonata have now returned to aquatic environments, but All stages of succession are unique habitats for different still retain structural reminiscences of this adaptation. species of plants and animals, and a proper management Despite the evolutionary success of the group as a whole, plan must ideally not only provide a variety of these stages, individual aquatic species remain vulnerable. Their ability but also be attuned to accommodate the local flora and to disperse and reach other suitable habitats across land is fauna of ecological importance. Thus, in this case, man- relatively limited. Isolated populations and fragmented agement should ideally consist of clearing in sections, allow- habitat make it difficult to colonize new environments, ing a range of habitats to be available at all times. In the case even if they have the ability to do so, as shown by the of S. nitida, where ditches are often used as drainage chan- number of suitable habitat sites located in this study. nels, light maintenance on an annual or biennial rotation, Changes in the way we use the land over the last century removing half the channel each year, is recommended. It is have led to wide-scale land-cover transformation. Not only also necessary to determine how S. nitida colonizes new within the UK but worldwide, demand for crops, minerals sites. The most likely contenders are carriage by water and wood as well as the building of infrastructure, such as flow, on the feet of birds or through anthropogenic activities. roads and railways, had resulted in patchy isolated fragments Segmentina nitida and other molluscs of natural landscapes. From 1860–1978 alone, over eight thousand square kilometre were converted to cropping The ANOVA tests produced a variety of results concerning worldwide, wetland itself accounting for 2.5% of this. the interaction of S. nitida and other mollusc species. In par- Habitat fragmentation poses a threat for many wildlife ticular, there was a variation in molluscan diversity accord- species, resulting in higher extinction rates and causing ing to the presence or absence of S. nitida. Ormerod et al. changes in community structures. The number of generalist (2009) found that sites containing S. nitida and two other species tends to rise, whilst the numbers of specialist BAP species held greater richness of gastropod species than species tends to fall. those that did not. This relationship of molluscan species Unless ditches are linked, the possibility of isolated popu- with sites in which S. nitida is present or absent might indi- lations getting to a new suitable habitat is slim. Connecting cate that similar factors that operate on S. nitida might also all suitable habitats is made difficult by land ownership, act on some but not on all the other species of mollusc. This land use and the requirements of other species. Ideally, loca- association might be mediated through some other factor of lized connectivity should be maintained so that stable popu- the environment (such as water chemistry) or biotic factors lations can exist in small areas. In this sense, the species may (such as predators). For example, Watson and Ormerod be nationally rare by area, but abundant in its own niche. If (2003) also found that water quality, vegetation and anthro- ditches or habitat areas are not connected then these isolated pogenic factors affected the distribution of S. nitida. It is also pockets may eventually die out and the species will go possible that S. nitida has a similar alimentation to certain ......................................................................................................................................................................................................................................... 163 Research article Bioscience Horizons † Volume 4 † Number 2 † June 2011 ......................................................................................................................................................................................................................................... other species. The latter could therefore act as indicators for and learning support staff, in particular John Hills and the potential of a site without S. nitida to support S. nitida. Lois Hodgson. This could be valuable information for conservation man- agement. In addition, although there was no variation in Author biography the total number of mollusc across the samples in a R.M.F.C. completed her degree in Ecology and Conservation one-way ANOVA, a two-way ANOVA revealed an inter- at Canterbury Christ Church University in 2010 as a mature action with species, the numbers between samples becoming student, having spent a few years out of education. Here she more varied. This again could also link relationships between found herself working on the Shining Ram’s-horn snail as molluscan species and highlight the presence of factors other part of her third year individual study under the supervision than plant distribution in determining habitat preferences. of Georges Dussart. She has greatly enjoyed working on this This investigation has highlighted the dynamic nature of endangered species and hopes to continue with the conserva- processes involved in plant succession. The large number of tion of this pretty little snail. variables that affect plant distribution makes modelling quite difficult. Thus, Stage 3 plants sometimes occurred in places where the soils were well drained and Stage 4 plants References sometimes occurred where the water level was high. 1. Ormerod SJ, Durance I, Terrier A, Swanson AM (2009) Priority wetland Monoculture stands of Phragmites and Glyceria occurred invertebrates as conservation surrogates. Conserv Biol 24: 573–582. often in both deep and shallow water levels. In this study, 2. The National Biodiversity Network (2010). http://data.nbn.org.uk (accessed S. nitida occurred most frequently where there was a rich November 2010). emergent fauna and at least 60 cm of water. 3. Painter D (1999) Macroinvertebrate distribution and the conservation value The habitat preferences of S. nitida would indicate veg- of aquatic Coleoptera, Mollusca and Odonata in the ditches of traditionally etation suited to the later stages of succession and ditch managed and grazing fen at Wicken Fen, UK. J Appl Ecol 36: 33–48. environments. This was indicated by is presence at nine 4. Tutin TG (1941) The hydrosere and current concepts of the climax. J Ecol 29: 268–279. such locations. Although further surveys of other sites exhi- 5. Tansley AG (1939) British ecology during the past Quarter-Century: the plant biting the same vegetation stage did not prove as fruitful as community and the ecosystem. J Ecol 27: 513–530. hoped, possible reasons for this have been examined. 6. Klinger LF (1996) The myth of the classic hydrosere model of bog succes- sion. Arctic Alpine Res 28: 1–9. Conclusion 7. Jeffries M, Mills D (1990) Freshwater Ecology: Principles and Applications. London: Belhaven Press. In relation to the ecology of S. nitida, this investigation has 8. Watson AM, Omerod SJ (2003) The distribution of three uncommon fresh- highlighted the importance of seral stage which in turn is water gastropods in the drainage ditches of British grazing marshes. Biol related to issues such as ditch management and habitat connec- Conserv 118: 455–466. tivity. Freshwater species can be indicators of species richness 9. Watson MA, Omerod SJ (2004) The microdistribution of three uncommon (alpha diversity), composition (beta diversity) and conserva- freshwater gastropods in the drainage ditches of British grazing marshes. Aquat Conserv 14: 221–236. tion importance in associated wetlands. Around 9% of all non- 10. Etherington JR (1983) Wetland Ecology. London: Edward Arnold. marine molluscs in Europe are thought to be threatened. 11. Spencer-Jones D, Wade M (1986) Aquatic Plants: A Guide to Recognition. Ormerod et al. (2009) noted that conserving the specific Hants: Borcombe Printers. resource requirements of the endangered species increased the 12. Killeen IJ (1999) A survey of the East Kent grazing marshes for the freshwater area of wetlands under conservation management and snail Segmentina nitida. English Nature Research Report 356. improved their unique biodiversity and environmental 13. Niggebrugge K, Durance I, Watson AM, Leuven RSEW, Ormerod SJ (2007) quality. This research is novel in that it indicates an association Applying landscape ecology to conservation biology: spatially explicit analy- between S. nitida and other molluscan species at these sites in sis reveals dispersal limits on threatened wetland gastropods. Biol Conserv East Kent, mediated through seral stage. Creating a workable 139: 286–296. management strategy for S. nitida might not only benefit this ` 14. Gołdyn R, Klimaszyk P, Kuczynska-Kippen N, Piotrowicz R (eds) (2008) The functioning and protection of water ecosystems. Poznan: Bonami Publishing species, but also associated species in this area. House. 15. Huggett RJ (1998) Fundamentals of Biogeography. London: Routledge. Acknowledgements 16. UK Biodiversity Action Plan (1995–1999). http://www.ukbap.org.uk/ UKPlans.aspx?ID=570 (accessed November 2010). Special thanks for the help and support of my family and 17. The Royal Society for the Protection of Birds (2010) http://www.rspb.org.uk/ friends, particularly Daniel for being my field companion. ourwork/policy/water/ (accessed November 2010). Thank you to Prof. G.B.J. Dussart who guided and super- 18. Wells SM, Chatfield JE (1995) Conservation priorities for European non- vised throughout the investigation. I would also like to marine Mollusca. In AC Van Bruggen, SM Wells, CM Kemperman, eds. thank Prof. S.J. Ormerod for his helpful reviewing and Biodiversity and Conservation of the Mollusca. Oegsteest-Leiden: Backhuys advice. And last but not least thank you to the technical Publishers, pp. 113–152. ........................................................................................................................................................................................................................................ .........................................................................................................................................................................................................................................

Journal

Bioscience HorizonsOxford University Press

Published: Jun 1, 2011

Keywords: Segmentina nitida wetlands succession mollusc

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