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The effectiveness of different pond restoration techniques for aquatic invertebrates

Report on the Second Life for Ponds project at Hampton Nature Reserve in Peterborough, Cambridgeshire

March 2011

Funded by SITA Trust through its Enriching Nature Programme

The Froglife Trust 2A Flag Business Exchange Vicarage Farm Road Fengate Peterborough PE1 5TX 01733 558844 [email protected] Author

Peter Kirby

Acknowledgements

SITA Trust for funding through its Enriching Nature Programme. Hampton Nature Reserve Volunteers. Francesca Barker and Kathy Wormald (Froglife). Photos © Froglife.

froglife froglife froglife Contents

1. Introduction 5 1.1 Second Life for Ponds Project 5 1.2 Hampton Nature Reserve 5

2. Invertebrates on Hampton Nature Reserve 7

3. Survey Methods 10 3.1 Inventory survey methods 10 3.2 Quantitative sampling methods 11 3.3 Sample sorting and identification 12 3.4 Target groups 12 3.4.1 Nomenclature 13 3.4.2 Statuses 14 3.5 Timetable of work 15 3.6 Limitations of the sampling methodology 15

4. Results 16 4.1 Character of the pond fauna prior to management 16 4.2 Records after management 22 4.3 General observations and possible confounding factors in the aftermath of management 33 4.4 Conclusions and implications for management for invertebrates 35

5. Literature 37 4 1. Introduction

1.1 Second Life for Ponds Project Between 2008 and 2010 an evidence-based conservation project called Second Life for Ponds was conducted on Hampton Nature Reserve in order to halt and reverse the decline in abundance of bearded stonewort on the Reserve. At the same time, due to the high value of the ponds to other taxa, it was also vital to monitor the effects of these restoration techniques on the wider ecological community, including the aquatic invertebrates which are the subject of this report. (Other taxa included in the project included other aquatic plants and stoneworts, great crested newts and water voles.) Furthermore, the unique superabundance of ponds on the reserve presented the opportunity to conduct research into the effectiveness of a wider range of management techniques than would normally be feasible for achieving these goals.

The Second Life for Ponds Project was made possible through funding from SITA Trust through its Enriching Nature Programme.

The objectives for this project, as they related directly to aquatic invertebrates, were: 1. To monitor changes, either positive or negative, within aquatic invertebrates from management action to implement the restoration and creation of ponds for the recolonisation of bearded stonewort Chara canescens on Hampton Nature Reserve 2. To evaluate four different pond management techniques - new pond creation, complete mechanical restoration, partial mechanical restoration and partial manual restoration - against a control of non-intervention, in terms of their effects on aquatic invertebrates 3. To disseminate the results of the project and encourage land managers to use proven evidence-based conservation techniques on their sites

The Second Life for Ponds Project report included an abridged version of this report on the effectiveness of different pond restoration techniques for aquatic invertebrates. In order to assist in informing land managers’ decision-making throughout the wider conservation community, Froglife is making the entire report on aquatic invertebrates available through its website.

This report was written by Dr. Peter Kirby, the aquatic invertebrates specialist responsible for planning and conducting the survey and analysing the results from this aspect of the project.

The complete Second Life for Ponds Project report (The effectiveness and cost efficiency of different pond restoration techniques for bearded stonewort and other aquatic taxa) is also available from Froglife.

1.2 Hampton Nature Reserve Hampton Nature Reserve (Orton Pits SSSI/SAC) is located in south Peterborough (UK) and covers 126ha of what is known locally as ‘ridge and furrow’, a unique landscape consisting of a series of over 300 ponds and their corresponding spoil heaps, created as a by-product of clay extraction for brick making (centre point TL 163943). This reserve is now managed by Froglife in partnership with the landowner, O&H Hampton, and Natural England.

Many of the ponds in the complex qualify as Priority Ponds for invertebrates, and the whole site qualifies as a Flagship Ponds site, both under multiple criteria (Pond Conservation, 2009).

The photos on page 4 show some of the ponds on Hampton Nature Reserve.

5 The site also qualifies as a key reptile site under multiple criteria (Froglife, 1999), and hosts a variety of BAP priority mammal species including brown hare, harvest mouse, several species of bat as well as a large and widespread population of water voles.

However, the reserve is most famed for supporting the largest extant population of great crested newt Triturus cristatus in Great Britain and possibly in Europe, estimated as up to 30,000 adults. The site is designated as a Special Area of Conservation (SAC) due to the size of its great crested newt population and because of the diversity and abundance of its stoneworts, especially the critically endangered bearded stonewort.

6 2. Invertebrates on Hampton Nature Reserve

Brick pits in the Peterborough area support exceptional assemblages of aquatic invertebrates, in terms both of number of species and the representation of rarities. The most important water bodies are moderate to small ponds of no great depth, including very small shallow seasonal pools, though even the large lakes are not devoid of interest. Interest is taxonomically widespread, except that the ponds tend to be markedly poor in molluscs and leeches. Overwhelmingly the greatest interest lies in the water beetles. Hampton Nature Reserve is the richest single site for aquatic invertebrates in general and for water beetles in particular, with more than 120 species of water beetle recorded. The particularly high interest of the Reserve seems to stem largely from the number and variety of ponds rather than from any other characteristic particular to the site: almost all of the recorded species are known elsewhere in the area. Invertebrates associated with water margins and emergent vegetation perhaps have a better claim to unique character at Hampton, but this may in part result from under-recording elsewhere, since such groups are less easy to record, and less recorded, than aquatic species.

Only aquatic invertebrates have been examined in this study, and since there is no definition of ‘aquatic’ invertebrates which is both straightforward and useful, this requires a little more consideration. The groups recorded in practice can be seen from the list of target groups and from the species list. They essentially comprise groups which are routinely and consistently captured using a pond net or sieve, which are so captured in a reasonably easily identified stage, but excluding species living within the bottom sediment (except insofar as individuals in superficial loose sediments are inadvertently disturbed and captured). The latter exclusion is in part conventional: a large proportion of the sediment fauna is of larval stages of flies, especially, which often cannot be identified to a useful level of precision, and such species as can be identified add little to overall assessment for the expenditure of considerable effort. In the present study, an additional, and over-riding, consideration is that to take any useful sample of the sediment fauna would involve a level of disturbance that could significantly affect the process of plant colonisation. This restriction means that in all likelihood only a minority of pond-dependent species are considered: more species will almost always be associated with shallow sediments, water margins, and emergent and marginal vegetation. These missed groups are important, not only because they are numerous, but also since many rare species belonging to them are known from the site, and the impacts on them of the management undertaken in this project will be at least as great as that on the aquatic fauna. The aquatic fauna, as defined here, has the advantage that it can be readily, easily, thoroughly and consistently recorded.

There are records of aquatic invertebrates from many ponds at Orton Pit and from other brick pit sites in the Peterborough area. They have been made using a range of methodologies, at different times of year, and often for quite specific reasons. This variation slightly limits their comparative value, but to only a limited extent provided they were carried out at a good time of year and were reasonably thorough: only tightly prescribed methodology, such as timed samples or specified numbers of net sweeps, seriously inhibit comparisons. There are observations on ponds of various sizes, ages and succession stages, including records from very new ponds, some created in mitigation or compensation for development, others dug in existing conservation sites. These include some with repeat observations which record the development of the fauna, though few which have experienced a good, regular and prolonged sampling programme. It is clear, and unsurprising, that there is considerable variation in the amount of interest and the rate of development of interest in these ponds according to size, depth, situation, and degree of isolation from colonizing wetland vegetation, but a few generalizations are possible. - Provided they are isolated from sources of polluted water, such ponds invariably develop significant invertebrate interest.

7 - Though early colonists arrive rapidly after the creation of ponds, the progress of colonisation is slow. Isolated ponds to which no vegetation is deliberately introduced may have no more than a handful of established macroscopic invertebrate taxa in the first year. - Increase in invertebrate diversity is closely correlated with colonisation by vegetation and increasingly complex vegetation structure. The rate at which vegetation, and thus invertebrate diversity, develops varies considerably between ponds, but for a ‘typical’ new pond, of moderate size, simple outline, and containing permanent water in its deepest parts, an expectation of five years to the development of something approaching peak diversity is reasonable; it can be more, but is unlikely to exceed ten years. - Interest can remain high for a substantial time, especially if aided by considerable seasonal fluctuations in water level, local trampling or grazing of the margins or a deep central basin in which emergent vegetation cannot easily grow. - The richest ponds, with varied vegetation structure, contain a mix of invertebrates with very varied requirements: many early colonists, with a requirement for bare margins and open water, can remain for as long as suitable conditions exist over part of the margin, and can co-exist with species requiring dense vegetation, including dense beds of emergents. However, some pioneer species may be rapidly lost, perhaps more as a result of competition with later arrivals than because of the absolute unsuitability of conditions. - Serious decline in the pond invertebrate assemblage comes with shading, either by dense and continuous beds of emergent plants (especially reed) or marginal shrubs and trees, or with a build-up of organic material and anaerobic decay in the sediments: the two are often closely associated. Brick pit ponds tend to be slow to develop such conditions. This in part is the result of generally slow succession change, but also because several of the commoner emergent plants in brick pit ponds tend to produce fairly open-structured stands, often not very tall, which do not cast heavy shade. The build-up of organic sediments seems also to be unusually slow: a brick pit pond may contain large amounts of plant debris in the form of dead stems and leaves of emergent plants without a serious build-up of anaerobic conditions in the underlying sediments. Large seasonal fluctuations in water levels are probably an important factor in maintaining such conditions.

Substantial invertebrate assemblages often co-exist with large beds of stoneworts in brick pit ponds. Indeed, stoneworts provide a well-structured habitat for many invertebrates, and some feed partly or entirely on them. However, the most emphatically stonewort-dominated ponds are rather too open-structured to be at their peak for invertebrates. Indeed, it is temptingly possible to suggest that, as a rule of thumb, the point at which the increase in aquatic invertebrate interest begins to level off is the point at which stonewort interest is definitively past its best. Invertebrate interest may remain high long after stoneworts have been almost or entirely lost, and even after the aquatic fauna begins to decline, interest in the terrestrial and semi-terrestrial fauna may remain, or even increase. On a site which is important for both groups, the dove-tailing of their requirements is potentially therefore a matter for careful consideration. Both groups require, for the maintenance of a full assemblage of species, the maintenance or regular recreation of early succession stages, but the preferred balance of the various possible stages and structures, and the preferred methods to maintain them, may differ.

The experimental work at Hampton Nature Reserve is interesting for the information it will give on management for invertebrates not only in its own right, but in the wider context of brick pit ponds, because: - though there are records from a number of newly created ponds in the brick pits, they are few and from other places: more observations, especially if they can become the first in a long and continuous sequence, are beneficial; - complete clearance of existing ponds is almost unprecedented, and the only example with good observations of re-colonisation is compromised by road run-off;

8 - substantial clearance of existing ponds is relatively rare, and though such management exists, and the results are being monitored, the ponds are being brought back from a later stage of succession ; substantial or complete clearance of ponds which are currently of high wildlife interest is rarely contemplated.

Information which it will be particularly interesting to seek from the current project will be: - the scale of loss of existing interest from the managed ponds; - what, if any, pioneer and early succession species of invertebrates, especially species absent from the ponds prior to management, benefit from the clearances; - whether large-scale clearance is of greater benefit than smaller clearance either in general or to particular species; - the rate at which invertebrates colonise the new and completely cleared ponds (the colonisation of areas of partial clearance will inevitably be confused by strays from the unmanaged parts of the pond, and is likely to be relatively uninformative).

Within the time-scale of this project, it has been possible to examine only the early stages of colonisation, but these early observations should provide a good base on which to build.

9 3. Survey Methods

Samples to provide baseline data on the invertebrates of the ponds to be managed, and those selected as controls, were taken in October 2008. For each pond, an overall inventory of the fauna was made, and quantitative samples were taken from each of the marked five-metre stretches. Sampling of the five-metre stretches in experimental and control ponds was repeated in the spring, summer and autumn of 2009 and the spring of 2010. Inventory samples were taken from new and entirely mechanically cleared ponds in autumn 2009, but they included no species which were not also recorded in the five-metre stretches, so have not been separately reported.

3.1 Inventory survey methods No reasonable amount of sampling of any pond with a rich fauna will produce a complete species list. As a definable and reasonably achievable target for the preparation of an inventory for each pond, recording was as far as possible exhaustive for water beetles (i.e. recording continued until capture of new species has apparently ceased, and involved sampling of all habitat components within and at the margins of the pond) with all other readily identifiable invertebrates captured during the sampling also identified. The sampling method was as follows: - deeper water in each pond was sampled using a standard pond net of side twenty-four centimetres and mesh size one millimetre; - water margins and dense vegetation in shallow water were sampled using a plastic sieve of seventeen centimetres diameter, with a mesh size of two millimetres (giving holes of approximately one millimetre); - fine bare and thinly vegetated sediments were sampled using a small sieve, eight centimetres in diameter and with a mesh size of 0.5 millimetre; - representative bulk samples obtained by the larger pond net were examined in the net and large and obvious animals extracted immediately; - net samples from representative areas were spread on metal grids of mesh size 5 millimetres suspended over plastic trays, and active animals allowed to make their own way through the grid for a minimum of ten minutes; - material remaining in the sieve was then sorted for less active invertebrates, such as molluscs, and additional larger individuals unable to fit through the mesh of the grid; - representative portions of the material from both the larger net and the sieve were immersed in water to encourage activity in those taxa, such as caddisflies, which are infrequent in sieve-sorted samples.

Sampling was continued until new discoveries had apparently ceased. Large and very distinctive taxa were noted in the field. Other field-sorted animals were preserved in 70% iso-propanol for later examination. Material extracted via the sieve was preserved with formalin as a bulk sample for later sorting and identification.

No precise length of pond margin was used for sampling; sub-samples were taken from a number of points chosen both to reflect the character of the pond and to include the areas which seemed likely to hold the richest fauna. The marked experimental/control stretches were not included in the inventory sampling.

An estimate was made of the frequency of each recorded taxon in the sample from each pond. If only one or two individuals of a species were captured, the actual number was recorded. A three- point scale was used beyond this: occasional (3 - 10); frequent (11 - 100); common (more than one hundred). It would be useful in principle to add a further level of ‘abundant’ for particularly

10 numerous species, since the ‘common’ category includes a very wide range of frequencies, but estimating numbers in the hundreds in the field was found to be effectively impossible.

Estimates of numbers are inevitably somewhat approximate, especially at the borderline between ‘frequent’ and ‘common’. Potential difficulty is posed by groups whose members are not readily distinguishable in the field, and one or more species of which is common in the samples. As far as possible, this problem was addressed by noting the overall number of the group seen, and taking for identification a sufficiently large sample that all or most of the contained species would be likely to be included, and their relative proportions in the sample give a good idea of the number of each present in the catch as a whole. There were, in practice, not very many cases where this occurred. Almost certainly, the greatest source of error in estimating abundance at the lower levels of the scale is simply failing to notice some individuals of some species, and at the higher levels making poor estimates of numbers of individual taxa amongst the general mass of material; under- estimates of frequencies are likelier than over-estimates. The abundance codes are intended to give only a general impression of the relative frequency of the different species.

3.2 Quantitative sampling methods Samples were taken from the central three metres of each five-metre experimental stretch to avoid contamination from adjoining stretches. In the well-vegetated state of the ponds at the time of taking the first samples this was excessively precautionary, but in ponds with little or no vegetation after management, animals disturbed by sampling may easily and rapidly swim, or drift in an induced current, for distances of a metre or more.

The method for quantitative sampling was devised with several constraints and requirements in mind. The area for sampling was quite small; sampling frequency over the course of the project was quite high; samples removed should not be large enough to significantly deplete the invertebrate populations within the sample area; and it was important that invertebrate sampling did not cause disturbance sufficient to influence the course of vegetation colonisation. Vigorous or exhaustive sampling, as might be used in a one-off whole-pond sample, would be likely, in the early stages of colonisation, to significantly deplete the invertebrate populations, to damage colonising vegetation, or both. The selected method was intended to be reasonably unintensive, to gather a sample of adequate but not damaging size, and to be operable without wading into the water in the early stages of colonisation.

In each experimental stretch, a sample was taken using a standard pond net at three different depths, along lines parallel with the pond margin. The first was along the margin itself; the second at a depth equal to the breadth of the net frame; the third further from shore, but at a less precise depth, an inconsistency forced by variation in pond profile and vegetation. Where there was a distinct change in vegetation - typically, the cessation of a dense marginal fringe – the final sample was taken beyond the point of change; where there was no obvious change in the vegetation structure (especially R12 and R13 prior to management, where emergent reed spread over the entire pond) the sample was taken in deeper water at the limit of net reach (using a net and handle two metres in length) from the shore. Each three metre stretch was gone over three times: on the first pass, from right to left, the net was worked to disturb the vegetation and, where exposed, the surface of the mud; on the second and third, made from left to right and right to left respectively, the net was moved at a steadier rate over the same track. Where emergent vegetation was open or sparse, the entire three-metre stretch was sampled in three complete passes; where vegetation was very dense, and sampling slow, the sampling was done over shorter sub-stretches, with three passes over six successive half-metre samples in the densest areas. In shallow water, the net contacted the bed of the pond, but was not allowed to dig in. The net was emptied into a tray of water at the end of each three-metre transect. Large pieces of vegetation (especially long lengths of dead stems, but also large pieces of pondweed and stonewort) were removed to a separate tray

11 of water, rinsed thoroughly, brushed with a nylon-bristled paintbrush where there was a dense covering of material which might make rinsing alone inefficient in removing attached organisms, and discarded. Remaining material from each of the trays was then strained through a 0.5 mm. mesh sieve, and the sieve contents placed in a polythene bag. Material from the three transects in each experimental area was combined in a single bag, the sample preserved with formalin, labelled, and sealed.

A further minute was devoted to sampling with sieves in denser vegetation in each experimental stretch, searching for water beetles especially, but also bugs, which are liable to be under-recorded by standardised sampling with a large net. Collected material was placed on the 5mm metal grid and animals allowed to make their way through for several minutes, after which large and easily identified species were noted, and representatives of the remainder were removed, preserved in 70% iso-propanol in a tube, and sealed into the bag with the quantitative sample from the same stretch. This sampling was not wholly consistent in character between samples, and was consciously aimed to fill likely gaps in the species lists. Invertebrate species were recorded simply by presence. The invertebrates taken in this way are not strictly part of the quantitative sample, but provide further data for comparison of the overall fauna in the experimental and other parts of each pond, and potentially add to the overall inventory list for the pond, especially if any species occur in the experimental area but not in the remainder of the pond.

3.3 Sample sorting and identification Organisms for the inventory survey which were preserved in the field in iso-propanol, and which were kept in a single container for each pond, were emptied into a Petri dish and identified directly under a binocular microscope. Formalin-preserved bulk samples from inventory sampling were poured into a 0.5 mm mesh sieve and rinsed thoroughly in tap water, then immersed in water in an oval white ceramic dish for examination under a binocular microscope. As much material as possible was identified immediately; organisms requiring dissection or drying for certain identification were removed to Petri dishes and separately examined.

The contents of each bag of preserved material from quantitative sampling were drained through a 0.5mm. sieve, rinsed by repeated gentle immersion in tap water, then emptied into a white plastic tray of dimensions 340 x 250mm., and covered with water to an approximate depth of one centimetre. Sufficient material was placed in the tray to form a fairly continuous thin cover over the base. From one to three trayfuls were needed per sample, depending on the amount of fine vegetation and detritus. Each tray-full of material was examined first under a bright fluorescent lamp using a head-mounted magnifier of 1.5x magnification. All visible organisms were removed and placed into 70% iso-propanol in Petri dishes, in groups sorted as far as was possible at this magnification. After the first sorting, the sample was agitated and re-examined. After this low- power search, successive small amounts of the remaining material were poured into an oval white ceramic dish and examined under the low powers (10x) of a binocular microscope; any small organisms missed by the earlier search were removed and added to the sorted material. Sorted material in Petri dishes was then identified and counted.

3.4 Target groups The following invertebrate groups were identified if found: • Tricladida (flatworms) • Mollusca (water snails and mussels) • Hirudinea (leeches) • Larger Crustacea • Araneae

12 • Coleoptera (beetles) • Diptera (flies - to family or genus only, except for Cylindrotomidae, Dixidae, Stratiomyidae) • Ephemeroptera (mayflies) • Hemiptera (bugs) • Lepidoptera (moths) • Megaloptera (alder-flies) • Odonata (dragonflies) • Trichoptera (caddisflies). Note was also made of the presence of Oligochaeta and Hydracarina.

Some minor liberties have been taken in assigning individuals to taxon: - All Agrypnia have been assigned to varia, though some are sufficiently small for their identification to be ambiguous; A. pagetana has been recorded from Hampton Nature Reserve in the past, but all confidently identifiable individuals captured recently, and all those found during this sampling exercise, have been A. varia. - All Asellus have been assigned to A. aquaticus, though this means that a large proportion have been assigned on the basis of head pattern alone, and some very small ones with ambiguous head patterns have also been included; all Asellus certainly identified from Hampton Nature Reserve have been aquaticus. - Cloeon are most easily assigned to species on the form of the gills, which are easily lost. Most individuals seen retained at least one gill for confirmation. Prior to management, all Cloeon identified from gill form (and all loose gills seen) were dipterum, a finding repeated in well-vegetated ponds through several previous years of fieldwork on the site. Even somewhat ambiguous examples were therefore referred to dipterum in the tables. In managed ponds in subsequent years, C. simile has also been recorded. Labial palp structure and body pattern have been employed for identification for those individuals from which all gills were absent, and all specimens have by this means been assigned to one or the other taxon. - Counts of Enochrus coarctatus include females which are not strictly distinguishable from E. nigritus. E. nigritus has not so far been recorded from Hampton Nature Reserve, while E. coarctatus is frequent. E. nigritus could occur here: though typically a species of fens and drainage ditches, it has been recorded from secondary sites. However, referring the recorded females to E. coarctatus seems very likely to be correct.

There is an element of inconsistency in the listing in the liberties taken and the extent to which taxa have been combined. For example, the only Noterus ever recorded from Hampton Nature Reserve is clavicornis, so the larvae of this genus captured can be referred to this species with confidence; it is, however, of minor interest initially to separate records of larvae and adults, so the larvae are separately listed, and recorded as Noterus sp..

Some identifications which are currently only to genus level could be improved. Pisidium are potentially identifiable, but all those captured appear to be the same species, so there will be little practical gain. Chaoborus can be identified, but a proportion of the larvae seen ideally require slide mounting for confident identification; all identifications so far have been made using a binocular microscope. Two species, obscuripes and crystallinus, appear to be present. Identification of all specimens might require considerable effort for little return.

3.4.1 Nomenclature The following sources have been used as the basis for nomenclature in this report, though occasional changes subsequent to the listed works have been incorporated: Tricladida Reynoldson & Young, 2000 Mollusca Anderson, 2005 Hirudinea Elliott & Mann, 1979

13 Crustacea Gledhill et al., 1993 Araneae Harvey et al., 2002 Coleoptera Duff, 2008 Diptera Chandler, 1998 Ephemeroptera Macadam, 2001 Heteroptera Aukema & Rieger, 1995-2006 Lepidoptera Bradley, 1998 Megaloptera Plant, 1997 Odonata Merritt et al., 1997 Trichoptera Edington & Hildrew, 1995; Wallace et al., 1990.

3.4.2 Statuses Each species recorded by the survey has been assigned a status. These are, as far as possible, formal published statuses derived from the most recent relevant publications, mostly those of the Joint Nature Conservation Committee or its predecessor, the Nature Conservancy Council, as follows: Coleoptera Foster, 2010 Diptera Falk, 1991

Criteria for the selection of species in the insect Red Data Book (Shirt 1987) and most subsequent national reviews of individual invertebrate groups do not take into account the most recent changes in IUCN Red List categories and criteria. Amongst the groups of invertebrates of which species with formal conservation status have been recorded in this study, only water beetles have been assessed in a published document against the most recent IUCN criteria.

Only one national status from the older system has been used in this report: Nationally Scarce (N) For some less well-recorded groups and species, it has not been possible to determine which of the Nationally Scarce categories (A or B) is most appropriate for scarce species. These species have been assigned to an undivided Notable category.

Only three statuses from the newer IUCN guidelines have been used: Lower Risk. A taxon is Lower Risk where it has been evaluated, but does not satisfy the criteria for any of the categories Critically Endangered, Endangered or Vulnerable. Taxa included in the LR category can be separated into four subcategories, of which only two are relevant here: Near Threatened (NT). Taxa which do not qualify for Conservation Dependent, but which are close to qualifying for Vulnerable - in Britain, defined as occurring in 15 or fewer hectads but not CR, EN or VU. The absolute count of hectads is, in this review, considered subordinate to evidence of decline to an extent not qualifying the species for CR, EN or VU. Nationally Scarce (NS). Taxa which do not qualify for Conservation Dependent or Near Threatened - in Britain defined as species occurring in 16 to 100 hectads but not CR, EN or VU. This subcategory associates a level of threat with rarity status, whereas the previous National Scarcity listings were based solely on rarity. Those species, the populations of which occasionally occupy more than 100 hectads, can still be listed if it is thought that their baseline populations frequently fall below these thresholds, or if the habitats occupied are considered under threat.

The abbreviations given above are those used in all subsequent tables of records in this report.

14 3.5 Timetable of work The table below summarises the timetable of sampling.

Autumn 2008 10 October Samples from Clusters 1 & 2 11 October Samples from Cluster 3 Spring 2009 18 April Samples from Clusters 1 & 2 20 April Samples from Cluster 3 10 May Samples from Experimental Ponds Summer 2009 25 July Samples from Clusters 1 & 2 26 July Samples from Cluster 3 & Experimental Ponds Autumn 2009 29 October Samples from Clusters 1 & 2 (except 26a) 30 October Samples from Cluster 3, Experimental Ponds & 26a Spring 2010 10 April Samples from all ponds

3.6 Limitations of the sampling methodology The chief concern is that the samples are relatively small. They are necessarily so, because of the short stretches of margin used for recording and the needs to avoid both affecting the colonisation by vegetation, and removing any large proportion of the fauna. However, even before management many species were present in the samples only at low density. This is certainly and generally true of many water beetles.

It is apparent from the numbers captured that the inventory samples in this survey, though intended to be exhaustive, in fact were almost certainly not. As a result of the low density, the quantitative samples may contain a rather limited proportion of the pond’s fauna and very small numbers of the more important species.

15 4. Results

4.1 Character of the pond fauna prior to management Table 1 summarises invertebrate captures from each of the ponds prior to management. It gives the estimates of frequency from inventory sampling, but not the numbers from quantitative sampling. A plus in a cell indicates that a taxon was captured from the experimental/control stretches but not from the part of the pond used for general inventory surveying. A frequency placed in brackets indicates that the actual count for that taxon placed it in the next frequency category down, but that unidentifiable females were captured which probably belonged to that species, and which would raise the frequency if included in the count. The most recent published formal conservation status is given for those species possessing them, though these statuses are of limited practical value for current purposes, being in need of revision and not always reflecting the local frequency or interest of the species involved.

The recorded fauna has largely the features expected of ponds on Hampton Nature Reserve, characterised especially by an absence of leeches; a very restricted range and low density of gastropod molluscs; and a high diversity of water beetles and water bugs, with a good representation of local and rare species. Overall, they support somewhat more than 50% of the aquatic species in general, and of water beetles in particular, known from the reserve as a whole. Most of the recorded taxa were previously known from the site, but the soldierflies Odontomyia tigrina and Oxycera morrisii and the caddisfly Agraylea sexmaculata appear to be new. O. tigrina is easily overlooked, but is not a usual brick pit species; O. morrisii is interesting because, in view of the number captured, and the number of ponds occupied in 2008, it is surprising that it has not appeared in previous samples. The quality of the fauna in each of the ponds is sufficiently high to qualify it as a priority pond under the Habitat Action Plan for ponds, on grounds of both overall diversity and representation of scarce species.

Though the ponds are all broadly similar in general characteristics, there is considerable variation: 23 taxa were caught only once; 68 were found in less than half the samples; and only 25 in every sample (and this includes a number of taxa so common and widely distributed that almost any pond capable of supporting significant life would be expected to contain them). The richest pond supports almost 54% more recorded taxa than the poorest. The differences between ponds may be somewhat less than these figures suggest: in particular, the inventory samples are likely to miss some species which are present at low density; it is probably impossible to generate a complete list of invertebrates from any pond and leave that pond in an acceptable condition at the end of sampling.

Pond 29A has, for the site, an unusually high number of mollusc taxa recorded at moderate frequency. However, several species were represented only by depauperate individuals, and these appeared to be quite localised within the pond (most were not captured in the experimental stretches). It is tempting to think that this anomalous mollusc assemblage has been somehow introduced into a pond to which they are unsuited.

It is surprising to find that the richest fauna is recorded from pond R12, since this pond is sufficiently heavily invaded by reed that it would seem at first sight that the fauna should be in decline. There is an element of truth in this first impression, in that recorded interest was patchy, with species associated with open conditions largely restricted to small areas with lighter reed cover; a less rich fauna was recorded from the superficially similar R13, with more continuous and uniform reed cover. However, it is also the case that species characteristic of ponds with heavy build-up of organic debris (water beetles of the genus Cercyon, for example), were generally not recorded. Thus, none of the ponds prior to management supported anything which could be described as a late-succession fauna. Even the most heavily vegetated ponds were probably close to the mid-succession peak of their invertebrate diversity.

16 Table 1. Frequency of invertebrate species prior to management (p17 - 21). Note: Explanations of symbols are in the text.

Pond numbers No .of Taxon Status R6 R7 R12 R13 26A 27A 28A 29A 29B 29Cn 29Cm 29Cs finds MOLLUSCA Hydrobiidae Potamopygrus antipodarum + 1 2 Lymnaeidae Galba truncatula 1 1 Radix balthica o o f 2 o f 6 Physidae Physa fontinalis f 1 Planorbidae Gyraulus crista o f 2 Planorbis planorbis f 1 Sphaeriidae Musculium lacustre 1 1 Pisidium sp. f f f f f f f f o o o 12 OLIGOCHAETA + + + o 1 + + + + + + 12 CRUSTACEA Aselidae Asellus aquaticus c f c c c o c f c f c f 12 Crangonyctidae Crangonyx pseudogracilis c c c f c c c f f f o f 12 Gammoridae Gammarus pulex f f 1 3 ARANAE Cybaeidae Argyroneta aquatica f f f f f 2 f f f f f f 12 COLEOPTERA Dryopidae Dryops luridus (f) (f) o o (f) 1 o o (f) (o) + + 12 Dryops similaris NS 2 1 Dryops sp. female o o o o o + o o o o 2 + 12 Dytiscidae Agabus bipustulatus 2 + o 3 Agabus nebulosus 1 1 2 Agabus sturmii 2 + o 3 Colymbetes fuscus 1 1 2 Dytiscus dimidatus NT 1 1 Graptodytes granularis o o f f f f f o f o 1 2 12 Graptodytes pictus f o 2 2 f o f o o 9 Hydroglyphus geminus f f o + 1 + 6 Hydroporus angustatus 2 2 1 2 + 5 17 18

Hydroporus memnonius o o 2 Hydroporus palustris 1 + 2 Hydroporus planus o 2 + o 1 o 1 7 Hydroporus pubescens 2 + 2 Hydroporus tessellatus o 2 1 1 + 5 Hygrotus impressopunctatus o 1 f o 2 + 2 1 + 2 10 Hygrotus inaequalis o f o o o 2 f f f f o 11 Hyphydrus ovatus 1 o o + o + f f o o o + 12 Ilybius fuliginosis 1 1 Ilybius quadriguttatus + 2 o o o o 1 7 Laccophilus minutus o + 1 + 1 o 2 + 8 Liopterus haemorrhoidalis + + + 2 4 Porhydrus lineatus 2 1 o f f o 1 7 Rhantus grapii + + 2 o 1 o 6 Rhantus suturalis o o 1 + 4 Indet. larvae f o o o f o + f o f o 11 Errirhinidae Stenopelmus rufinasus 1 1 Gyrinidae Gyrinus marinus o 1 Gyrinus paykulli NS 1 + 2 Gyrinus substriatus + 1 Haliplidae Haliplus confinis 2 1 2 Haliplus immaculatus 2 1 + 3 Haliplus lineatocollis 1 + 1 o + 5 Haliplus obliquus o + 1 o o f f 7 Haliplus ruficollis f o o (f) o (o) 6 Haliplus sp. female 2 o o + o o o o o 9 Haliplus sp. larvae 2 + + 2 1 o + f o 9 Helophoridae Helophorus brevipalpis 1 1 Helophorus minutus + o + 1 o o + 7 Helophorus obscurus 1 1 Helophorus sp. female o 2 o 1 4 Hydraenidae Hydraena riparia o f + 1 1 + 6 19 Hydraena testacea o 1 o 2 2 5 Limnebius nitidus o 1 o 2 f o o f + 2 + 11 Limnebius papposus NT 1 + 1 2 2 + + o 8 Ochthebius minimus o o o o o f o o f o + + 12 Hydrochidae Hydrochus crenatus NT 1 + 1 1 1 o 6 Hydrochus ignicollis NT 1 1 + o 4 Hydrophilidae Anacaena bipustulata + o + 1 o + 6 Anacaena globulus + o f 1 4 Anacaena limbata f f f f f o o 2 f o + o 12 Anacaena lutescens + + o 3 Berosus affinis 1 + 1 3 Berosus luridus NT 1 f 1 3 Berosus sp. larva 1 1 Chaetarthria seminulum NS o o o 3 Coelostoma orbiculare 1 1 2 Cymbiodyta marginella 1 + 1 Enochrus coarctatus f o o o o o + + o + o 1 12 Enochrus halophilus NS 1 1 2 Enochrus testaceus o 2 1 o 2 + 2 2 2 o o 11 Helochares lividus o + o 1 o + 6 Hydrobius fuscipes 2 1 o 1 4 Laccobius bipunctatus f f o o f 1 o o + + o o 12 Laccobius colon 1 2 + o + + + 7 Laccobius minutus o o 2 3 Laccobius sinuatus + 1 + 3 Indet. larvae + + + + 4 Noteridae Noterus clavicornis o o f o f 1 + o o o o o 12 Noterus sp. larva + + + + 1 + + 7 Scirtidae Cyphon sp. larvae 2 o 2 3 DIPTERA Ceratopogonidae 1 1 2 Chaoboridae Chaoborus sp. f f + + + o + f f o + o 12 19 20

Chironomidae f o o f f f f o f o o + 12 Culicidae Coquilletidia richiardii 1 + 2 Cylindrotomidae Phalacrocera replicata N 1 o o 1 + 2 + + 2 9 Dixidae Dixella autumnalis f o o f f o o o o o o f 12 Limoniidae o o o o f o o + o + o o 12 Psychodidae 2 2 + + 4 Ptychopteridae Ptychoptera sp. 1 2 2 + o 1 2 7 Stratiomyidae Odontomyia tigrina N + 1 Oplodontha viridula 1 o o o o + o 1 2 o 1 1 12 Oxycera morrisii N + + o o + + 6 Oxycera trilineata + + + 3 Tabanidae Chrysops sp. 1 1 Tipulidae 1 1 EPHEMEROPTERA Baetidae Cloeon dipteron o o f c f o c f o f f f 12 Caenidae Caenis horaria o o 2 + 1 5 Caenis luctuosa o f o 1 f + f f f o f o 12 HEMIPTERA Corixidae Callicorixia praeusta + 1 Corixa panzeri o o + 3 Corixa punctata 2 o 2 1 4 Cymatia bonsdorffi + + + 3 Cymatia coleoptera o f f o 4 Hesperocorixa linnaei + o o o 2 o o f 1 o 1 11 Hesperocorixa moesta f f o o o + o f o f o f 12 Hesperocorixa sahlberfi o o + 3 Sigara distincta 1 1 Sigara dorsalis + 1 Sigara fossarum o 1 Gerridae Gerris lacustris + o o + o o + o + 9 Hebridae Hebrus ruficeps + o 2 21 Naucoridae Ilyocoris cimicoides 2 o o o 4 Nepidae Nepa cinerea o + o o 2 o 1 7 Notonectidae Notonecta glauca o o o o o + o o o 2 2 11 Notonecta obliqua o 1 1 o o o o + 8 Notonecta viridis 1 1 2 + 1 o 1 7 Pleidae Plea minutissima f o f o 1 o o o f o o 11 Veliidae Microvelia reticulata f f f o f f o o o o o o 12 LEPIDOPTERA Pyralidae Cataclysta lemnata + 1 MEGALOPTERA Sialidae Sialis lutaria f 2 1 o 1 o f f 1 o 2 11 ODONATA Aeshindae Aeshna sp. 1 o 2 Anax imperator o o o + o o o o f o 10 Brachytron pratense o 2 o o + 2 o 1 o + o 11 Coenagriidae Coenagrion sp. f f f f f o f f f o f f 12 Enallagma cyathigerum + 1 Ischnura elegans o o + o o o 6 Pyrrhosoma nymphula f f f f o o f o + 9 Indet. larvae f o f f + o f o o f + 11 Libellidae Libellula quadrimaculata o + + 1 o 1 1 7 Libellula sp. + + + 3 Sympetrum sp. o 1 + 1 + + + + + + 10 TRICHOPTERA Hydroptiliidae Agraylea sexmaculata + 1 Leptoceridae Athripsodes aterrimus 1 o 1 o + 1 + 1 + + o 11 Limnephilidae Limnephilus sp. larvae f f o + + f + o 2 f f 12 Phryganeidae Agrypnia varia f f o o 2 + o f f o f f 12 Polycentropidae Holocentropus dubius o o f o + + 1 2 1 + 10 Total of mutually exclusive taxa 131 77 65 80 61 57 52 62 70 74 66 62 62 Total N/RDB species 12 6 3 5 2 5 1 7 3 7 3 2 2 21 4.2 Records after management Table 2 provides a very simplified summary of invertebrate records. Each pond is treated as a single unit, with records from the three separately sampled sections amalgamated; and species are recorded by simple presence or absence, not by counts. The absence of numbers of individuals removes some of the most conspicuous post management changes, but these are for the most part unsurprising: numbers were very low in the immediate aftermath of management, and for most species remained so throughout the duration of the study; declines were most apparent in species with the highest counts beforehand; a few taxa, such as the mayfly Cloeon simile and the planktonic larvae of the phantom midge Chaoborus, have increased to substantial populations in at least some managed ponds and areas. However, the most numerous species, both before and after management, are generally unimportant from a conservation viewpoint, and changes generally merely confirm what is visually obvious. Many species, especially of water beetles, were caught only in small numbers even in ponds where there is little doubt that they are well- established residents. In general, it is more important that species are present in a pond than that their populations are high. There are unquestionably cases where the numbers would paint a more complete picture (the detritus-feeding Asellus aquaticus, for example, present in large numbers before management, was unsurprisingly almost absent from ponds following removal of detritus, even by the second year, but occasional individuals turned up).

Table 2 also sums records for all three ponds managed in any given way. This undoubtedly loses some significant information: the differences between ponds are sufficient that there can be little doubt that the only way fully to understand the data is to examine each pond entirely separately. This, however, would confuse any broad trends with a plethora of details. For current purposes, it is considered better to wilfully avoid the detail in the interests of developing a simple picture.

Two columns of figures are given for 2009 records: those from the autumn sampling period, and those for the year as a whole, summed over all three samples. The autumn sample is the only one which is directly comparable with the baseline survey in autumn 2009: the first sample in the spring after management recorded essentially the loss of the previous fauna and the first arrivals of strays and potential colonists, before most species would have been able to establish breeding populations; mid-summer samples of aquatic invertebrates tend to be incomplete and misleading for important major groups; and since a large proportion of aquatic invertebrates have a single generation per year, amalgamation into a single set of records makes logical sense. The amalgamated list should be a reasonably complete list of the species established in or regularly visiting the experimental stretches over the course of the year; the autumn sample is the one which should, logically, be the most appropriate for comparative purposes. It is unfortunate that only a spring sample is available for 2010. The timing of the sample matters less than in 2009: invertebrates have had time to colonise, and the ponds to settle; spring and autumn samples of aquatic invertebrates from ponds are almost interchangeable, and spring samples are, if anything, more reliable because, provided there has been reasonable winter rainfall, they are less influenced by drying out. However, in these early stages of colonisation, a further summer to establish breeding populations could have made a difference.

Table 2 gives formal statuses for all species that possess them. A second estimate of conservation significance has been made for all species, which takes into account their local status. This estimate has been made on a six-point scale, and is an informed subjective opinion rather than one based on defined criteria. Different opinions might produce somewhat different scores, but it is hoped that they would not be so different as to affect the broad thrust of the results obtained. By assigning a score to each point on the scale, it is possible to sum the individual scores to produce an overall interest score for each management group. Common and slightly local species are scored zero; scarcer species are scored from 1 (the least scarce) to 5 (the most scarce).

Three overall measures of the fauna are given for each pond group: the average number of taxa per pond; the number of species with formal conservation status recorded; and the summed

22 interest score. By scoring common species at zero, this scoring system divorces, to a reasonable extent, conservation interest deriving from scarcity from simple diversity.

As far as can be judged from these data, in 2008 prior to management the sample stretches of the ponds appear to have contained approximately 84% of the fauna of the entire pond as a whole and to be essentially typical of the whole.

Samples from 2009 and 2010 add 27 taxa which had unambiguously not been recorded in 2008 (ignoring larvae and nymphs not identifiable to species and which could belong to species previously recorded as adults, and species identified as adults which could be the same as larvae previously recorded only to genus). A few were probably present in 2008 but missed: the water beetle Enochrus quadripunctatus, the pondskater Gerris odontogaster, the damselfly Lestes sponsa, the water measurer Hydrometra stagnorum; some may be strays or adventives (a difficult set of species to identify with certainty, but including the water beetle Ilybius ater, a characteristic species of muddy habitats with abundant decaying vegetation, but here found as a single individual in a fully cleared pond, and the leech Theromyzon tessulatum, a parasite of waterfowl which is only ever recorded on this largely leech-free reserve as isolated, scattered individuals); a few species are ambiguous as to category. Some, however, are unambiguously new arrivals.

The distribution of species richness between control and experimental ponds follows a fairly clear, if sometimes approximate, pattern: the highest figures are for the control ponds, the next highest for the manually cleared ponds, then the partially mechanically cleared ponds, the wholly cleared ponds, and finally the new ponds. This is in stark reverse to the trend in Stonewort colonisation. Figures for interest scores and representation of species with formal conservation interest are less neat: the highest figures are again for the control ponds and the lowest for the new ponds, but differences between the different methods and amounts of clearance are less consistent. Figures for species richness and interest scores increased between 2009 and 2010 for the partially cleared ponds, but not for the completely cleared or newly dug ponds. It is a reasonable, but not provable, assumption that the higher values for richness and interest in the partly cleared ponds, especially in the first year, result in substantial measure from the straying and spreading of invertebrates from the unmanaged portions of the ponds to cleared areas, in which they might not be able to breed successfully. The difference between manually and mechanically cleared ponds may be explicable by the less thorough clearance of roots from the manually cleared ponds, leading to conditions which might more rapidly provide either suitable habitat for the establishment of breeding populations of a wider range of species, or simply conditions which encourage lingering or attempted breeding by un-established strays and wanderers. Increased diversity is expected with succession change in the managed areas and ponds: the evidence, so far as it can be safely interpreted over such a short period and such limited change, suggests that the rate of succession will be more rapid in the managed areas of the partly cleared ponds.

A complicating factor in this general and simple interpretation is that the results from control ponds show a marked decline in richness and interest scores between 2008 and 2009, partially recovering in 2010. This seems to be a genuine phenomenon, rather than merely an artefact of sampling, but results from changes in only two of the ponds. Pond 26A held its values well, while those of 6A and 29B changed substantially. In both cases, the difference in the character of the fauna was sufficient to be subjectively apparent even during sampling, and was seen in both spring and autumn samples. In R6, the declines in richness and quality were accompanied by a decline of 28% in the numbers of individual invertebrates captured in autumn samples, but in 29B the catch was larger in 2009 than in 2008. There are no immediately obvious reasons for the change. In the absence of changes to the ponds or their surroundings, it is usual and logical to look for reasons such as changes in the weather, but if the cause does lie here, it is not easy to see what aspect of the weather might have been responsible, and certainly impossible to prove that it was. The fact that the change was not equally felt in all ponds diminishes the chance that weather was the cause. Whatever the cause, the fact that changes of this scale can occur between successive years in unmanaged ponds emphasizes the need for caution in interpretation of changes in the experimental ponds.

23 24

Table 2. Taxon per pond according to sample date (p24 - 30) inv = inventory sample; exp = samples from experimental lengths Taxa not recorded during sampling in 2008 are highlighted in yellow.

Manual part Machine part Complete 08 Control New clearance clearance clearance Taxon

score inv exp 08 Full Sep 10 Full Sep 10 Full Sep 10 Full Sep 10 Full Sep 10 status Formal Interest 09 09 09 09 09 09 09 09 09 09 MOLLUSCA Hydrobiidae Potamopygrus antipodarum 0 2 1 Lymnaeidae Galba truncatula 0 1 1 Radix balthica 0 6 4 1 1 1 1 1 1 Physidae Physa fontinalis 0 1 1 1 Planorbidae Gyraulus crista 0 2 Planorbis planorbis 0 1 1 Sphaeriidae Musculium lacustre 0 1 1 1 1 1 Pisidium sp. 0 12 12 3 3 3 3 3 3 3 3 3 2 3 2 1 HIRUDINEA Glossiphoniidae Theromyzon tessulatum 0 1 1 1 1 OLIGOCHAETA 0 12 12 3 3 2 2 3 1 2 2 1 CRUSTACEA Aselidae Asellus aquaticus 0 12 12 3 3 3 3 3 2 2 3 3 2 3 2 2 1 Crangonyctidae Crangonyx pseudogracilis 0 12 12 3 3 3 3 3 3 3 3 3 3 3 3 3 2 2 1 Gammoridae Gammarus pulex 0 3 2 1 1 1 1 1 ARANAE Cybaeidae Argyroneta aquatica 1 12 10 3 3 3 3 3 3 3 3 2 1 3 1 2 1 COLEOPTERA Dryopidae Dryops luridus 0 12 12 3 3 2 3 3 1 2 1 1 2 3 2 1 1 1 Dryops similaris NS 4 1 1 1 1 Dryops sp. female 0 12 12 3 3 1 2 3 2 1 1 1 2 2 2 2 2 Dytiscidae Acilius sulcatus 1 1 1 Agabus bipustulatus 0 3 2 1 1 1 1 1 1 2 1 Agabus nebulosus 0 2 1 1 2 2 1 1 Agabus sturmii 0 3 3 1 1 1 Colymbetes fuscus 0 2 Dytiscus dimidatus NT 5 1 26

Dytiscus sp. larvae 0 2 2 2 Graptodytes granularis 2 12 11 3 3 1 1 2 1 1 2 1 1 Graptodytes pictus 0 9 9 2 3 1 3 3 3 2 3 2 3 2 1 1 Hydroglyphus geminus 1 6 6 1 1 2 2 1 2 2 1 1 1 1 3 1 1 Hydroporus angustatus 0 5 4 1 3 2 2 1 1 Hydroporus memnonius 0 2 1 1 Hydroporus palustris 0 2 1 Hydroporus planus 0 7 5 2 1 2 1 1 1 3 2 Hydroporus pubescens 0 2 1 Hydroporus tessellatus 0 5 3 1 Hygrotus confluens 1 2 1 1 1 1 3 2 3 2 3 2 2 Hygrotus impressopunctatus 0 10 8 3 3 3 2 1 Hygrotus inaequalis 0 11 11 3 3 3 2 3 2 3 3 2 3 2 1 1 1 Hyphydrus ovatus 0 12 10 2 2 1 3 3 3 3 2 2 2 3 3 1 Ilybius ater 0 1 Ilybius fuliginosis 0 1 Ilybius quadriguttatus 0 7 6 2 2 1 1 1 Laccophilus minutus 0 8 6 1 2 1 1 1 1 Liopterus haemorrhoidalis 0 4 4 1 3 3 1 Nebrioporus elegans 0 1 Porhydrus lineatus 1 7 6 1 2 1 2 1 1 2 1 1 Rhantus grapii 1 6 3 1 1 1 3 1 1 Rhantus suturalis 0 4 3 1 1 1 1 Scarodytes halensis NS 2 1 Indet. larvae 0 11 11 3 3 3 2 1 1 1 3 1 1 2 Errirhinidae Stenopelmus rufinasus 0 1 1 Gyrinidae Gyrinus marinus 0 1 1 1 Gyrinus paykulli NS 3 2 1 1 1 1 Gyrinus substriatus 0 1 1 1 3 2 2 2 1 3 1 3 1 Haliplidae Haliplus confinis 1 2 2 1 Haliplus flavicolis 1 1 Haliplus immaculatus 0 3 1 2 1 1 2 1 1 Haliplus lineatocollis 0 5 5 1 1 1 1 1 1 1 1 1 1 Haliplus mucronatus NS 4 1 1 1 2 2 1 25 26

Haliplus obliquus 2 7 5 2 1 3 3 2 2 1 3 1 2 Haliplus ruficollis 0 6 6 1 2 1 1 3 2 2 1 2 2 1 Haliplus sp. female 0 9 6 2 3 2 1 1 1 1 2 Haliplus sp. larvae 0 9 7 1 1 1 1 1 1 3 3 2 1 1 Helophoridae Helophorus aequalis 0 1 1 1 1 1 Helophorus brevipalpis 0 1 1 1 Helophorus grandis 0 1 2 Helophorus minutus 0 7 6 2 2 1 2 2 2 2 1 2 3 2 3 Helophorus obscurus 0 1 1 1 1 1 Helophorus sp. female 0 4 1 1 1 1 1 1 1 1 2 2 1 Hydraenidae Hydraena riparia 1 6 4 2 Hydraena testacea 1 5 4 2 Limnebius nitidus 2 11 10 3 3 2 2 2 1 3 1 1 1 1 1 Limnebius papposus NT 3 8 3 3 1 1 1 1 1 Ochthebius minimus 0 12 12 3 3 3 3 1 1 2 2 1 1 1 1 Octhebius pusillus NS 4 1 1 Hydrochidae Hydrochus crenatus NT 3 6 3 1 2 2 1 1 Hydrochus ignicollis NT 4 4 2 1 1 1 1 1 Hydrophilidae Anacaena bipustulata 1 6 6 2 1 2 1 1 1 Anacaena globulus 0 4 4 2 2 2 2 1 1 1 Anacaena limbata 0 12 12 2 3 3 3 3 2 3 2 1 1 1 2 1 2 Anacaena lutescens 0 3 3 1 1 Berosus affinis 1 3 2 1 3 2 1 3 3 2 3 2 1 2 2 2 Berosus luridus NT 3 3 2 1 2 2 2 2 1 1 1 Berosus signaticollis 1 1 1 Berosus sp. larva 0 1 1 1 2 1 1 1 1 2 1 3 1 1 1 2 Chaetarthria seminulum NS 3 3 1 1 Coelostoma orbiculare 1 2 2 1 1 1 Cymbiodyta marginella 1 1 1 1 2 2 1 1 Enochrus coarctatus 1 12 12 3 3 3 3 2 2 1 Enochrus halophilus NS 3 2 1 Enochrus quadripunctatus NS 3 1 Enochrus testaceus 0 11 7 1 2 2 2 1 1 1 1 Helochares lividus 0 6 5 3 1 1 1 1 28

Hydrobius fuscipes 0 4 2 1 2 1 3 1 1 1 Laccobius bipunctatus 0 12 12 3 3 3 3 3 2 3 2 1 2 2 1 2 3 Laccobius colon 1 7 4 1 3 1 3 1 3 1 1 1 Laccobius minutus 0 3 3 1 1 2 1 2 Laccobius sinuatus 1 3 3 1 1 2 1 3 2 2 2 2 1 2 1 1 Indet. larvae 0 4 3 1 1 2 1 1 Noteridae Noterus clavicornis 0 12 12 3 3 3 2 2 2 1 Noterus sp. larva 0 7 7 2 2 1 1 Peliobiidae Hygrobia hermanni 0 1 1 1 Scirtidae Cyphon sp. larvae 0 3 1 1 DIPTERA Ceratopogonidae 0 2 1 Chaoboridae Chaoborus sp. 0 12 12 3 3 3 3 3 3 3 3 3 2 3 3 3 3 2 2 Chironomidae 0 12 12 3 3 3 3 3 3 3 2 2 3 3 3 3 2 1 3 Culicidae Anopheles messae/atroparvus 0 1 Coquilletidia richiardii 0 2 2 Cylindrotomidae Phalacrocera replicata N 3 9 8 3 2 1 Dixidae Dixella autumnalis 0 12 11 3 2 2 1 Limoniidae 0 12 12 3 3 2 2 2 1 1 1 2 1 1 Psychodidae 0 4 3 1 1 1 1 1 Ptychopteridae Ptychoptera sp. 0 7 2 2 1 Stratiomyidae Odontomyia tigrina N 3 1 1 1 1 Oplodontha viridula 1 12 11 3 3 2 3 2 1 1 2 Oxycera morrisii N 2 6 6 2 2 1 2 1 1 1 1 Oxycera trilineata 1 3 3 2 1 1 2 Syrphidae 0 1 Tabanidae Chrysops sp. 0 1 1 1 1 1 1 1 1 1 1 Tipulidae 0 1 1 1 EPHEMEROPTERA Baetidae Cloeon dipteron 0 12 12 3 3 3 3 3 2 3 3 1 2 2 3 3 2 3 Cloeon simile 0 3 3 3 3 3 3 3 2 3 3 2 2 Procloeon bifidum 0 1 Caenidae Caenis horaria 0 5 4 1 1 1 2 2 1 1 Caenis luctuosa 0 12 8 3 3 3 3 3 3 2 3 3 1 3 2 3 1 1 1 27 28

HEMIPTERA Corixidae Callicorixia praeusta 0 1 1 Corixa panzeri 1 3 3 2 2 2 1 1 1 1 1 2 1 1 Corixa punctata 0 4 1 1 1 1 1 1 2 1 1 Corixa sp. nymph 0 Cymatia bonsdorffi 1 3 3 1 1 Cymatia coleoptera 1 4 4 1 1 2 1 2 1 1 Hesperocorixa linnaei 0 11 11 1 3 3 3 2 2 2 1 2 2 1 1 Hesperocorixa moesta 1 12 12 3 3 3 3 3 3 3 3 2 2 2 1 3 3 Hesperocorixa sahlberfi 0 3 3 Hesperocorixa sp. nymph 0 2 2 1 Sigara concinna 1 1 1 1 Sigara distincta 0 1 1 1 1 2 1 Sigara dorsalis 0 1 1 1 1 1 1 2 2 1 Sigara fossarum 0 1 3 1 2 2 2 2 2 1 2 Sigara lateralis 0 2 1 1 1 3 3 3 3 2 1 Sigara limitata 2 1 1 1 1 2 Sigara nigrolineata 0 1 1 2 2 2 Sigara sp. nymph 0 3 3 3 2 Gerridae Gerris lacustris 0 9 8 3 3 1 2 3 2 3 2 2 3 3 1 2 1 2 Gerris odontogaster 0 3 1 2 1 2 1 1 Gerris thoracicus 0 1 1 Gerris sp. nymph 0 3 1 2 1 1 1 Hebridae Hebrus ruficeps 2 2 2 1 1 1 Hydrometridae Hydrometra stagnorum 0 1 Naucoridae Ilyocoris cimicoides 0 4 3 1 1 1 1 Nepidae Nepa cinerea 0 7 6 3 3 3 2 1 Notonectidae Notonecta glauca 0 11 9 3 3 3 2 3 1 1 3 1 3 2 2 2 1 2 Notonecta obliqua 1 8 7 2 2 2 2 1 2 2 1 2 3 Notonecta viridis 1 7 3 1 1 1 1 1 1 2 1 2 1 Notonecta sp. nymph 0 3 2 2 2 1 1 Pleidae Plea minutissima 0 11 11 3 3 2 2 3 3 3 3 2 1 2 2 1 3 2 1 Veliidae Microvelia reticulata 0 12 12 3 3 1 1 2 2 1 LEPIDOPTERA Pyralidae Cataclysta lemnata 0 1 1 1 MEGALOPTERA Sialidae Sialis lutaria 0 11 7 2 3 2 1 2 2 1 3 1 1 1 1 1 ODONATA Aeshindae Aeshna sp. 0 2 1 1 1 1 1 1 2 1 Anax imperator 1 10 10 2 3 2 2 2 2 2 2 1 2 2 2 1 Brachytron pratense 1 11 8 3 3 2 3 1 1 1 Coenagriidae Coenagrion sp. 0 12 12 3 3 3 3 3 3 3 3 3 3 3 2 3 Enallagma cyathigerum 0 1 1 2 2 1 1 1 2 2 1 2 2 Ischnura elegans 0 6 2 3 3 3 3 3 2 3 2 2 2 2 2 2 2 2 Pyrrhosoma nymphula 0 9 8 1 1 2 3 3 2 1 1 Indet. larvae 0 11 11 3 3 3 3 3 3 3 3 2 3 3 2 3 2 1 1 Lesitdae Lestes sponsa 0 1 1 Libellidae Libellula depressa 1 1 Libellula quadrimaculata 1 7 4 1 3 1 3 2 1 2 2 2 2 2 1 Libellula sp. 0 3 3 1 3 3 1 2 2 1 3 3 3 3 2 1 1 1 Sympetrum striolatum 0 2 1 1 2 1 1 1 Sympetrum sp. 0 10 10 2 3 2 2 3 3 1 2 1 2 2 2 1 2 2 3 TRICHOPTERA Hydroptiliidae Agraylea sexmaculata 0 1 1 Leptoceridae Athripsodes aterrimus 0 11 10 3 3 3 2 3 3 3 2 2 2 2 2 1 1 1 Oecetis furva 0 1 1 2 1 1 Limnephilidae Limnephilus flavicornis 0 1 2 1 1 Limnephilus lunatus 0 1 1 1 2 Limnephilus marmoratus 0 2 3 1 2 3 1 Limnephilus sp. larvae 0 11 11 3 3 1 3 3 1 3 2 3 1 3 1 1 Phryganeidae Agrypnia varia 0 12 12 3 3 2 1 3 3 2 3 3 1 3 3 1 Polycentropidae Holocentropus dubius 0 10 9 1 2 2 1 2 2 1 3 3 1 3 3 1 1 Total of mutually exclusive taxa 158 131 118 84 100 70 77 94 68 73 69 49 69 76 50 49 52 37 39 Average taxa per pond 65.7 55.3 57.0 68.7 46.3 52.3 63.7 41.0 44.3 49.0 29.3 36.0 46.0 29.3 29.3 29.3 17.7 20.7 Total N/RDB species 16 12 7 6 8 4 8 5 1 3 3 1 4 5 4 3 1 0 0 Total interest score 72 54 46 53 32 45 39 23 35 30 14 30 35 30 26 14 9 9 29 It is possible to identify, with reasonable confidence, a set of species which are newly arrived as a result of management, or which have clearly benefited, as indicated by a disproportionate representation in managed areas. The following annotated list includes all these species, together with a small number for which the evidence of benefit is rather more ambiguous, but which are included for completeness.

Acilius sulcatus (Coleoptera, Dytiscidae) Evidence for benefit to this species is ambiguous: it was not recorded from any pond prior to management, but of the two records after management, one is from a control pond. This is an unusual water beetle in that it has planktonic larvae which require open water of at least moderate depth. The beetle is therefore most characteristic of ponds with partial cover of open-structured vegetation, and ponds in the early years after creation are often favoured. Conditions in the new and fully cleared ponds in particular may become more suitable after further plant growth.

Hydroglyphus geminus (Coleoptera, Dytiscidae) A characteristic species of the early stages of succession, sometimes forming large populations in shallow water over largely or entirely unvegetated beds, and in all sizes of water bodies. It is not, however, restricted to such early succession stages, and often persists at lower density for many years, provided the organic content of a pond does not become too great. It is a fairly frequent and widespread species on the reserve, and it was expected to be one which would benefit from the management. Its response so far has been less dramatic than might perhaps be expected.

Hygrotus confluens (Coleoptera, Dytiscidae) A very characteristic species of early succession, always associated with shallow water over unvegetated beds with low organic content, and sometimes forming large populations. It was not recorded from any ponds before management, but was frequent after, and had arrived by the time of the first post management visit in spring 2009. It has also been found in two of the control ponds, but it can be safely assumed that this is the result of strays: adults of this species are often found in unsuitable water bodies if they are within easy reach of breeding sites.

Nebrioporus elegans (Coleoptera, Dytiscidae) A characteristic species of bare-bedded water bodies, but more often a species of lakes and rivers with a gravelly substrate. It may benefit from the newly created open conditions, but it is not entirely clear from the single record and the non-ideal conditions how well-established it is or will become.

Scarodytes halensis (Coeloptera, Dytiscidae) A pioneer species and very rapid colonist, arriving rapidly, but rather unpredictably, in newly created or managed ponds and ditches. It is often found in water bodies completely devoid of macroscopic vegetation and with few other invertebrates, and can occur in unlikely water bodies, such as concrete and metal drinking troughs. Populations are often transient, not infrequently a single generation, and it is doubtful whether it is sensible to talk of this species having ‘sites’ in the sense that can be used of most species. It has been recorded only once from one pond, and it is not certain that the species managed even a single generation here.

Gyrinus substriatus (Coleoptera, Gyrinidae) A common species throughout the pit, but one which needs a reasonable area of open water surface and is therefore absent or scarce in heavily vegetated ponds and favoured by ponds in the early years after creation. The species is, however, sufficiently common in larger and deeper pools on the reserve that any increase in these experimental ponds is of no significance.

Haliplus flavicollis (Coleoptera, Haliplidae) There are too few records of this species to be sure it has benefited from the management, but it was not recorded from any ponds prior to management, or from control ponds afterwards, and is often associated with stonewort beds in open water.

30 Haliplus mucronatus (Coleoptera, Haliplidae) Members of the Haliplidae feed on algae, and H. mucronatus is usually, and probably invariably as a breeding species, associated with stoneworts. It is an efficient colonist of new sites, but is nonetheless considerably scarcer than the plants. It does not require large stands of the plants, and where there is extensive stonewort coverage often seems quite localised. Its preferred water bodies appear to be small, often seasonal water bodies, such as very shallow drains or vehicle ruts, but it appears fairly regularly in larger ponds.

Haliplus obliquus (Coleoptera, Haliplidae) Another stonewort-associated haliplid, but of far more frequent occurrence than H.mucronatus: it is an expected species wherever there is a substantial bed of stoneworts, and usually occurs throughout the bed, sometimes in substantial numbers.

Helophorus aequalis and H. grandis (Coleoptera, Helophoridae) These are common opportunists of small, often seasonal, water bodies and the margins of larger water bodies, especially where there is flooded grass such as Alopecurus. Both occur widely at Hampton Nature Reserve, not only in grassy seasonal pools but also in seasonal pools in vehicle ruts and along tracks. No conservation significance attaches to their occurrence in the newly created ponds.

Ochthebius pusillus (Coleoptera, Hydraenidae) A characteristic species of early succession, living on the surface of bare sediments in shallow unshaded water. It is well-known from Hampton Nature Reserve, and is a species expected to benefit from this management exercise. It has, in practice, been found only once. It is not clear whether this is because the newly created bare areas are less suitable for the beetle than they appear, or whether, as seems likelier at the moment, it takes rather longer for suitable conditions to develop. Certainly, previous records from the brick pits are from ponds which, though extensively bare-bedded, had been in existence for several years at least, and casual sampling of the marginal fringe of the newly created pond in R1 in the summer of 2010 found several, despite its absence from samples earlier in the year.

Berosus affinis (Coleoptera, Hydrophilidae) An efficient colonist, often developing large populations, and most often associated with shallow, unshaded water, partly vegetated or with very open-structured vegetation. This was a species expected to benefit from pond management, but it is quite widely distributed on the reserve where there are reasonably open conditions.

Berosus signaticollis (Coleoptera, Hydrophilidae) This species was recorded too rarely to be sure that it has benefited: it was not recorded from ponds prior to management, and occurs especially in partly-vegetated ponds with substantial areas of bare bed, so should be a beneficiary, but it has been recorded from more established ponds elsewhere on the reserve.

Laccobius sinuatus (Coleoptera, Hydrophilidae) A characteristic species of bare water margins on silt or clay, and an expected beneficiary of management. Extensive areas of bare fringe are not essential, however, and provided the organic content of the substrate is low, it can occur amongst tall marginal plants or trailing vegetation.

Hygrobia hermanni (Coleoptera, Peleobiidae) The few records of this species are from new, completely cleared and partially machine-cleared ponds. It is typically a species of ponds of moderate depth with a mix of open water and patches of vegetation, the latter usually reaching the surface. Vegetation can be almost continuous provided it is open-structured. It is a frequent species of recently created ponds, but ideally requires somewhat greater vegetation cover than the new and fully cleared ponds that had developed by the end of the project.

31 Cloeon simile (Ephemeroptera, Baetidae) Seemingly confined to the managed areas and new pools, but showing a very rapid increase and forming large populations on sparsely vegetated beds and amongst stoneworts; by far the most numerous of the ‘new’ species added since management. It was already known from the site, but seemingly very local within it. This is characteristically a species of more open conditions than C. dipterum, which is often abundant in well-vegetated ponds, and often found in deeper water.

Procloeon bifidum (Ephemeroptera, Baetidae) Recorded from only a single sample, but usually found in small numbers and possibly more widespread in cleared areas. It is typically a species associated with bare areas of bed, often where these form a mosaic with plants, and is more usually a species of rivers and lakes than of smaller ponds.

Sigara spp. (distincta, dorsalis, lateralis, fossarum, nigrolineata, concinna, limitata) (Hemiptera, Corixidae) All these species feed, entirely or in part, from bottom sediments and require at least a partly bare bed. Sigara distincta, dorsalis and fossarum are common species which often all coexist in lakes, large ponds and slow rivers where partly open conditions are permanently maintained. S. nigrolineata is also common, but tends to occur less predictably and in smaller numbers. S. concinna and S. lateralis are poor competitors but efficient dispersers, and are typically the first species to arrive. S. concinna is a rather scarce and often transient species, though occasionally it can build up large numbers in a short time. S. lateralis tends to decline more slowly as other species establish, and is far commoner generally because of high tolerance to organic enrichment. S. limitata is the scarcest species of the genus recorded. It has a wide but very local distribution, apparently needing silt or clay beds in small to medium-sized unshaded ponds with neutral to calcareous water. It is the dominant species in some special conditions - dew ponds on the chalk and stock-grazed field ponds on carboniferous limestone - but is more usually a minor component of a larger corixid assemblage. It has previously been recorded in part-vegetated, recently created ponds at King’s Dyke Pit, Whittlesey.

Gerris thoracicus (Hemiptera, Gerridae) A characteristic early colonist of new water bodies, and also found on brackish waters. On new ponds, it is especially found on completely open water surfaces, and is replaced by the commoner G. lacustris as vegetation cover and shelter increases.

Libellula depressa (Odonata, Libellulidae) A characteristic species of water bodies with extensively bare beds, where the larvae live on the surface of the sediment or amongst superficial loose material.

This gives a total of 27 species which have definitely or probably benefited to date from the management work (17% of the species recorded during the project), including three which are Nationally Scarce (almost 19% of the total recorded) and 20 which were not recorded from any of the ponds prior to management. However, they also include several very common species whose fate in individual ponds is of little concern, and others which, though of some interest, are widespread on the site and occur in more established ponds; and it needs to be borne in mind that all of the other previously recorded species have suffered or gone.

The table below lists those species benefiting from management and pond creation which have been assigned an interest score above zero, and lists the number of ponds in each management category from which they have been recorded.

32 Table 3. Species benefiting from different types of management

Number of ponds from which recorded Formal Interest Manual Machine Machine Species status score part- part- complete New clearance clearance clearance Acillus sulcatus 1 1 Hydroglyphus geminus 1 3 2 2 3 Hygrotus confluens 1 2 3 3 3 Scarodytes halensis NS 2 2 Haliplus flavicollis 1 1 Haliplus mucronatus NS 4 1 1 2 Haliplus obliquus 2 3 2 3 Ochthebius pusillus NS 4 1 Berosus affinis 1 3 3 3 2 Berosus signaticollis 1 1 1 Laccobius sinuatus 1 3 2 2 2 Sigara concinna 1 1 1 Sigara limitata 2 1 1 2 Libellula depressa 1 1 No. species 9 9 7 9 Total pond records 18 17 16 16

4.3 General observations and possible confounding factors in the aftermath of management New ponds and managed areas of previously existing ponds generally had little fauna on the spring visit, suggesting that management had been fairly efficient in wiping the slate clean, and that little had yet colonised. There was, however, considerable variation in detail between ponds.

Throughout the period of sampling, it was noticeable that the details of pond construction and minor habitat details had a significant effect on the recorded fauna. The scale at which such features had their effect varied: differences could be apparent over as little as a metre, or could differ between two ponds over the whole of the managed (or sampled) stretch. Judged subjectively, the most significant factors affecting invertebrate numbers and diversity in managed areas appear to be: • - The presence of unmanaged vegetation elsewhere in the pond; • - The speed of re-development of vegetation after management; • - The presence of drifted plant fragments along the marginal fringe; • - The angle of slope of the pond edge.

Besides these general features influencing invertebrate distribution, there were some pond- specific features which definitely, or possibly, affected the invertebrate fauna.

Brief notes were made of the state of the ponds at the time of survey. Characteristics which might affect the fauna colonising, or the fauna recorded, in a way significant for comparative purposes are briefly noted in the table below:

33 Table 4. Characteristics of surveyed ponds that might have influenced the occurrence and detectability of invertebrate species

Cluster Pond no. Management Characteristics 1 R6 Control R7 Partial manual Water level was dramatically lower in spring 2009, and had still clearance not fully recovered by spring 2010. This has greatly altered the character of the unmanaged parts of the pond, and means that the band of habitat sampled is rather different to that in other ponds. A repeat inventory survey of the unmanaged areas in autumn 2009 showed a decline of more than 30% in the species-richness of the samples from the baseline in 2008. R12 Partial mechanical The water level was low in July 2009, and very low in clearance October 2009, making sampling difficult and not necessarily representative. R13 Complete clearance An extensive root system remained despite clearance; July and October 2009 water levels were low. New Newly dug Variable in structure; the best areas of gently-sloping bed are not within the sample stretches. This pond is readily accessible and in a well-visited area, and trampling and disturbance at the margins appears to be having a significant impact. 2 26A Control A gelatinous coating over stems and submerged plants, very marked in 2009, is likely to have affected the fauna, and may have affected sampling. Any effect will have been more serious in summer, when the relatively uncoated marginal fringe was left exposed by falling water levels and the volume of gelatinous material appeared greater. Samples were considerably cleaner in spring 2010. 27A Complete clearance The pond edges tend to be very abrupt, steeply-sloping, and sometimes unstable, limiting the range of niches available for invertebrates. 28A Partial mechanical A partial marginal fringe remained after management; the pond clearance edge is generally abrupt. 29A Partial manual A well-developed, if narrow, marginal fringe remained after clearance management; the bed of the managed section appeared to have a fair content of organic material even quite close to the margin. 3 29B Control 29C(N) Partial manual Relatively well-structured for the 29C set, with an area of clearance gently-sloping edge at least seasonally flooded. 29C(M) Partial mechanical Abrupt-edged and falling quite steeply to fairly deep water, clearance limiting the range of niches for invertebrates. 29C(S) Complete clearance Very abrupt-edged and steeply-sloping to a considerable depth; very limited invertebrate niches. Exptl Exptl1 Newly dug Water level generally low in 2009. Exptl2 Newly dug Water level generally low in 2009.

There is considerable variation between ponds in the abundance and composition of the colonising fauna in the first two years since management. The most extreme edges are unlikely ever to develop high invertebrate interest, unless the angle slumps, or until aquatic vegetation becomes dense to the water surface, or a fringe of emergent vegetation develops.

34 4.4 Conclusions and implications for management for 4.4 Conclusions and implications for management for invertebrates Any conclusions relevant to management which are drawn from this study must be tentative, because it has been of short duration. Some of the ponds are at such an early stage of colonisation that at least one known species of early succession appears to have scarcely begun to colonise, and the rate of succession seems likely to remain slow. Continued study, especially of completely cleared and newly dug ponds, over a period of a decade or more is ideally needed. However, several relevant observations appear firmly based. -The invertebrate assemblages of the ponds prior to management were species-rich and included a substantial number of scarce species; by the end of the study, cleared areas and ponds were substantially less rich in species and in rarities. - Clearance of vegetation provides opportunity for a number of species of early succession stages and open conditions, including scarce species not present in more established ponds. - Early colonists arrive rapidly after pond management, but colonisation is generally slow. - There is rather little evidence that wholly cleared or new ponds support species which do not also colonise ponds with partial clearance, and vice versa - though there is scope for such evidence to be found in the future. - The rate of change amongst invertebrates appears greater in partially cleared ponds than in wholly cleared or newly dug ponds. - Cleared areas in partially cleared ponds may be prone to contamination by strays from the vegetated parts of the pond; it is not clear that this is in any way significant, but it is possible that such individuals provide unwanted competition for pioneer and early succession species, which include invertebrates which are known or suspected to be poor competitors.

Based on these observations, it would seem that the ideal management to maximize benefit to species occurring early in succession is to undertake complete clearance: this will prolong early stages of succession and remove any possibility of unwanted competition from species from unmanaged parts of the pond. There is potential benefit also to the later-colonising species if, as is to be expected, succession continues to be relatively slow, and it seems logical that occasional thorough clearance could more effectively and thoroughly prevent the build-up of decaying organic material in the bed than more piecemeal work. However, these advantages are, on current evidence, largely or entirely relative, rather than absolute. Partial clearance seems able to produce many of the same benefits, albeit probably not for so long; and the benefits from complete clearance must be balanced against the losses to existing interest.

A rotational pattern of thorough clearance of entire ponds can be contemplated only where there are sufficient ponds that such management can be carried out in confidence that no species will be lost from the site overall. At Hampton Nature Reserve there is the luxury that there are so many ponds, and invertebrate interest is sufficiently widespread amongst them, that rich invertebrate assemblages in individual ponds can be comfortably sacrificed without great qualms. Since the ponds are of recent origin, the species they contain must be at least moderately mobile, so that heavily managed ponds can be expected to recover their interest, or equivalent interest, in time if they are allowed to do so. In any isolated pond containing the level of invertebrate interest that the Hampton ponds had prior to management, or any pond in an old wetland or pond complex that might contain poorly mobile species, complete clearance would be unthinkable. If management is considered for invertebrates alone, the default recommendation would remain, as usual, management for steady state conditions if possible, or rotational partial clearance if not.

The position of new ponds in this is, based on the data from this project, a little ambiguous. Since all the ponds currently on the site were new once, and since new ponds created elsewhere in the brick pits, in quite a wide range of conditions, have never failed to produce good invertebrate assemblages unless there are obvious external causes why, there is no reason to expect that the assemblages produced here will not eventually also be good. However, the new ponds have not so

35 far performed as well as the completely cleared ponds. This may be simply because colonisation of new ponds, at least by specialist and uncommon species, is slower than for fully cleared ponds, but all the new ponds have been, within the duration of this project, somewhat different from the pre- management ponds. This is least true of the new pond in cluster 1: the difference here lies chiefly in its relative accessibility and proximity to a well-used walking route, which has led to considerable trampling of the margin. The two experimental ponds have been subject to extreme fluctuations in water level or complete drying, and took some time before they appeared properly pond-like to superficial view, rather than merely weedy wet depressions. These issues around individual ponds would also be likely to slow colonisation and the development of specialist faunas. The provisional assumption is that new ponds made on the site will be equivalent to completely cleared old ponds, and will develop invertebrate interest equivalent to that of existing ponds of similar size and profile on the site. This, however, is an assumption readily open to disproof by further recording.

The overall conclusion, then, is that complete clearance of ponds for the benefit of stoneworts at Hampton Nature Reserve is, in principle at least, acceptable from the point of view of conservation of the invertebrate fauna, and potentially brings significant benefits; that the large number and character of ponds at Hampton Nature Reserve enables a degree of flexibility in managing for different groups which might not be available in many sites; that newly dug ponds are tentatively assumed, though on little evidence from this project, to be able eventually to support similar levels of invertebrate interest to existing ponds on the site; and that longer-term observations are needed to flesh out and confirm all of these statements.

These brief statements leave many areas unconsidered. Two are especially worthy of consideration.

The recovery of lost interest and re-development of interest in thoroughly cleared ponds depends in part on their physical structure being similar before and after clearance. Despite selection of comparable ponds for study and standardisation of management at Hampton Nature Reserve, the individuality of character of the different ponds, was apparent from an early stage. Minor features such as small areas of shallows or exposed wet sediments make a considerable difference to habitat character. Some very abrupt and invertebrate-unfriendly edges in the managed ponds were forced into the design simply by available space and surrounding terrain, and at Hampton, where ponds are often tightly constrained by the ridge-and-furrow topography of the site, the tendency is likely to be for mechanical clearance to steepen the profiles. Details of design, location and the use made of ponds in the immediate aftermath of their creation are clearly indicated as factors worthy of further consideration.

There is substantial scope for consideration of different options for long-term management to favour both stoneworts and invertebrates. If rotational management involving whole-pond clearance were introduced, the length of the rotation would need careful consideration. From an invertebrate conservation point of view, the ponds cleared for this study were probably close to their richest point, and with management of plant growth might have been kept there for a long time. Many invertebrates would benefit from a long rotation, slowed as much as possible; most of the length of this rotation would be wasted time for some stoneworts, especially Chara canescens. There is, however, scope within the site for rotations of different lengths: maintaining ponds on a short rotation for stoneworts would still benefit early succession invertebrates, and would benefit the fauna as a whole provided other ponds were managed less frequently (and since there is no physical possibility, in terms of time, labour or access, of more than a small fraction of the ponds on the site being mechanically cleared on any sort of rotation, this is not a major issue). A management option which could not be investigated during this work, because of the absence of suitable ponds, is the partial clearance of ponds which are already at a quite early stage of succession, with a view to maintaining early succession stages indefinitely. This would certainly be appealing as a line of inquiry from an invertebrate conservation viewpoint. Early succession stages are valuable for many invertebrates whatever their history, but the best are ancient early succession stages, which have been present in one place for sufficiently long to accumulate a rich assemblage.

36 5. Literature

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