AN AQUATIC INVERTEBRATE SURVEY OF THE HEN REEDBEDS

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AN AQUATIC INVERTEBRATE SURVEY OF THE HEN REEDBEDS ADRIAN CHALKLEY Introduction The Hen Reedbeds were created in 1999 for Suffolk Wildlife Trust to provide new breeding habitat for bittern and other wildlife as a response to perceived future problems for coastal wetlands caused by climate change. Lying beside the tidal River Wang, the 57 hectares of Hen Reedbeds have been designated as SSSI, NNR, RAMSAR, and Natura 2000 primarily due to the importance of the habitat for birdlife. With its mosaic of reedbeds, fens, dykes and pools it also provides extensive habitat for fish and aquatic invertebrates to support the bird populations. Whilst ongoing monitoring of the avian fauna has taken place since the creation of the reserve and the Environment Agency conducted a fishery survey in 2008; this survey provides a first opportunity to assess the freshwater invertebrate community supported by the Hen Reedbeds. The survey was conducted for the Suffolk Wildlife Trust and the RSPB with funding from Touching the Tide and the Heritage Lottery Fund. The Hen Reedbeds are divided in two by the A1095 road, running from the A12 to Southwold, with Wang Marsh to the west of the road and Wolsey Marsh to the east. Sampling of aquatic invertebrates was carried out on 7 September 2012 at four sample sites, two in each marsh.

Summary Simple water chemistry measurements showed that across both sites the waters are base-rich with pH values ranging between 7∙8 and 8∙7. Water temperatures on a very sunny day varied from 15∙1oC in shaded water to 24∙5oC in shallow water in full sun. Conductivity measurements referenced to 25oC showed that: Wang Marsh sites were freshwater, with measurements of 430 & 662 micro Siemens / metre Wolsey Marsh sites were brackish with readings of 2340 & 2760 micro Siemens / metre The survey followed the methodology laid out in the ISIS handbook produced by Natural England. A total of 76 species of aquatic invertebrates from 44 different families were caught and identified. The survey showed this site to have a rich beetle and bug fauna with 21 & 19 species respectively.

Several of the invertebrate species are characteristic of mineral marsh, permanent wet mire or brackish marsh / ditches. Specific habitat requirements are generally well provided for by the existing site management although consideration for the needs of Silver Water Beetle larvae should be taken into account during future clearance work.

After identification calculation of Biological Monitoring Working Party scores and Average Score Per Taxon showed that for aquatic invertebrates: Water quality in Wang Marsh was very good Water quality in Wolsey Marsh was good

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Analysis of the species forming the aquatic invertebrate community at the Hen Reedbeds was carried out using the Community Conservation Index developed by the Environment Agency. This indicates that: Wang Marsh has very high conservation value and is potentially of national significance, which underlines the existing statutory site protection.

The aquatic invertebrate community supports several rarities, including species of national importance (e.g. taxa included in the British RDBs). It is a community of very high taxon richness.

Wolsey Marsh has high conservation value. The aquatic invertebrate community supports several uncommon species, some of which may be nationally rare. It is a community of high taxon richness.

General Survey and Site Details The Four Sample Sites Sampling was carried out on 7 September 2012. Sample site 1 In Wang Marsh was an older, mature dyke and site 2 had been relatively recently restored. In the Wolsey Marsh sample site 3 is close to the A1095 and was covered in very dense reeds with extensive wet margins to the dykes. These margins were covered with up to 30 cm of water filled with reeds and reed debris.

Site 4 was located at the opposite side of the marsh in front of the bird hide.

This had fairly deep, reed-margined ditches to either side, with an area of large shallow scrapes in between the ditches. The shallow scrapes provide open water and from the hide give good views of feeding birds; they were full of hornwort, Ceratophyllum demersum. They also contained the warmest water on the site on a very hot, sunny day. The locations of these four areas are shown on the maps in Figs 1 & 2.

Weather Conditions The weather on 7 September was hot and sunny with only occasional cloud.

Table 1. Water Characteristics Sample Site 1 Sample Site 2 Sample Site 3 Sample Site 4 TM4686377115 TM4693077144 TM4716176978 TM4761876643 pH Conductivity1 µS / m (25oC) Temperature o C

8∙3

8∙7

8∙6

7∙8

430

662

2340

2760

17∙7

16∙2 (shady ditches) 24∙5 (shallow scrape in full sun)

15∙1

1

16∙6

Conductivity measured in micro Siemens per metre referenced to a standard temperature of 25oC

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Measurements on site with a freshly calibrated digital meter showed the water to be base-rich with relatively high pH. The conductivity readings show sites 1 & 2 in Wang Marsh to be fresh water and sites 3 & 4 in Wolsey Marsh to be marginally brackish. Typically, micro Siemen values under 1,000 are considered freshwater and those between 1,000 and 10,000 are brackish.

Whether the amount of salinity is great enough or persistent enough to influence the invertebrate community to any great extent is a difficult question. The most diverse and ecologically rich areas sampled were both in the freshwater area of Wang Marsh although the increased conductivity of Wolsey Marsh provides for the specialised habitat preferences for certain corixid bugs (see discussion).

Methodology After discussion with the warden Alan Miller, the methodology chosen was that specified for still waters by Natural England in their ISIS2 survey tool. Stillwater faunas are usually dominated by adult beetles, bugs and molluscs, for which this method produces high yields. It was felt that this methodology would be not only the most appropriate for the site, but would be easily repeatable for future surveys.

The only slight deviation from the ISIS method was that, whenever open water was sampled, the water surface was first observed to establish the presence of surface dwelling invertebrates such as Pondskaters or Whirligigs.

These have a habit of escaping out to open water as soon as the net enters the water; therefore, when present they were caught prior to the ISIS methodology being employed. This methodology may be summarised thus:

 The sampling method standardises effort by bank-sorting three qualitative hauls for 10 minutes each, giving 30 minutes of sorting.  The emphasis is on free-style netting of features (microhabitats) that are likely to be the most productive. Effort is deliberately not divided in proportion to the extent of features since species are not distributed in this fashion.  The net used was the standard FBA design with a rectangular frame 25 cm wide and 22 cm long, the net bag 30 cm deep with a 1 mm mesh.  While standing in or at the water margin, the vegetation was netted using short jabbing thrusts in any dense emergent and raft-forming plants, and using occasional longer strokes into submerged plants and over bare substrate in deeper water.  This method was repeated along the bank as netting proceeded, selecting patches of vegetation that exhibited the greatest small-scale mosaic structure since these patches yield more specimens.  Netting ended when the net began to fill to the point that it became more difficult to push, usually after about one to three minutes when it was usually about a third to a half full of plant material. When duckweed or similar small plants were abundant, the net would fill within seconds, so some careful manipulation was needed to slow the rate that it was caught while probing for more productive structures beneath.

2

ISIS is a computer application developed by Natural England for the recognition and scoring of invertebrate assemblage types.

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Figure 1. Wang Marsh

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Figure 2. Wolsey Marsh

AN AQUATIC INVERTEBRATE SURVEY OF THE HEN REEDBEDS

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 Bottom sediment was avoided since it clogs the net and contains almost no species that contribute to the analysis, though ‘grazing’ strokes across the sediment top were used to ‘put up’ invertebrates such as beetles and bugs which were then caught in the net.  Once the net was full a digital timer was used to time the 10 minutes sorting time as the sample was tipped onto a white polythene sheet and spread out quickly into a thin layer.  Fast-crawling beetles, bugs and dragonfly larvae were collected or identified (if recognisable) before they escaped during the spreading-out process.  Many invertebrates, such as flatworms and leeches react badly to the alcohol used as a sample preservative, others such as Water Scorpion or Stick Insect are instantly identifiable. During sorting these were placed in a bucket of water. They were then identified, noted and returned alive to the water.  The white sheet was then scanned for other animals as they recovered from their shock. After a few minutes, the debris was turned over and poked about, when more animals were usually found.  A pool of water forms in the centre of the sheet which allows weakly swimming animals a refuge and to be seen, these were collected towards the end of each 10 minute time period.  Fine flexible forceps were used for picking up animals; a tea strainer and white plastic spoon were used to ‘net’ animals in the pool in the middle of the sheet. However, a wet finger was often the best tool to pick up really small beetles and bugs. All were immediately put into a wide mouthed bottle containing 70 % alcohol.  During the last two minutes of the search some of the debris was put into a white tray with 1–2 cm depth of water. Feeble animals which swim free were collected.  Lastly, all plant material was tipped into a bucket of water, larger pieces and most of the water was removed. The heavy residue was tipped into the white tray with about 1 cm of water. Then by tipping the contents to and fro, the molluscs left stranded in a pile were collected.  At each sample site this operation was repeated twice more at bank sections about 25 m apart.

This protocol results in one tube of animals per sample site, which was then identified back in the laboratory. As no large amounts of debris or plant material are collected, the identification process is much easier and needs no pre-sorting which is very time consuming and costly.

Survey Results Table 2 contains data on all 84 invertebrates found in the survey, together with the sample sites where they were found. Any amphibians which were caught are also included in the table for completeness.

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Species

Authority

Description

Branchiura ~ Fish Lice (Do not count towards BMWP or CCI scores) 4 Argulidae Argulus foliaceus Linnaeus, 1758 Cladocera ~ Water Fleas (Do not count towards BMWP or CCI scores) 5 Daphniidae Simocephalus exspinosus (Koch, 1841) 6 Daphniidae Simocephalus vetulus (Koch, 1841) Coleoptera ~ Water Beetles 7 Dytiscidae Agabus bipustulatus (Linnaeus, 1767) 8 Dytiscidae Copelatus haemorrhoidalis (Fabricius, 1787) 9 Dytiscidae Dytiscus marginalis Linnaeus, 1758 10 Dytiscidae Dytiscus semisulcatus O.F. Müller, 1776 11 Dytiscidae Hydroporus gyllenhalii Schiødte, 1841 12 Dytiscidae Hygrotus inaequalis (Fabricius, 1777) 13 Dytiscidae Hyphydrus ovatus (Linnaeus, 1761) 14 Dytiscidae Laccophilus minutus (Linnaeus, 1758) 15 Dytiscidae Rhantus frontalis (Marsham, 1802)

Common Common V Common Frequent V Common Occasional Common Common Common Common Notable b

A Water Flea A Water Flea A Diving Beetle A Lesser Diving Beetle A Great Diving Beetle A Great Diving Beetle A Lesser Diving Beetle A Lesser Diving Beetle A Lesser Diving Beetle A Lesser Diving Beetle A Diving Beetle

2

3

3 4

4

3 4

3 1 2 3 4 2 1 2 3 4

1 1 1

1 2

1

1 2

Locally common Locally common

Frequent

1 2

Sites

Common

Status

The common fish louse

Amphibia~ Amphibians (Do not count towards BMWP or CCI scores) 1 Salamandridae Lissotriton vulgaris (Linnaeus, 1758) Smooth Newt Efts (tadpoles) Amphipoda ~ freshwater shrimps or scuds 2 Crangonyctidae Crangonyx pseudogracilis Bousfield, 1958 An American Freshwater Shrimp 3 Gammaridae Gammarus zaddachi Sexton, 1912 A Freshwater Shrimp

Family

Table 2: Full Species List AN AQUATIC INVERTEBRATE SURVEY OF THE HEN REEDBEDS

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Family

Species

Authority

Description

16 Dytiscidae Rhantus suturalis (Macleay, 1825) A Diving Beetle 17 Gyrinidae Gyrinus caspius Ménétriés, 1832 The Caspian Whirligig 18 Haliplidae Haliplus lineatocollis (Marsham, 1802) A crawling water beetle 19 Haliplidae Haliplus ruficollis (DeGeer, 1774) A crawling water beetle 20 Helophoridae Helophorus flavipes Fabricius, 1792 A Mud Beetle 21 Hydrophilidae Anacaena limbata (Fabricius, 1792) A Water Scavenger Beetle 22 Hydrophilidae Enochrus testaceus (Fabricius, 1801) A Water Scavenger Beetle 23 Hydrophilidae Helochares lividus (Forster, 1771) A water scavenger beetle 24 Hydrophilidae Hydrobius fuscipes (Linnaeus, 1758) A Water Scavenger Beetle 25 Hydrophilidae Hydrophilus piceus (Linnaeus, 1758) A Water Scavenger beetle 26 Hydrophilidae Laccobius bipunctatus (Fabricius, 1775) A Water Scavenger Beetle 27 Noteridae Noterus clavicornis (DeGeer, 1774) A Burrowing Diving Beetle Collembola ~ Springtails (Do not count towards BMWP or CCI scores) 28 Sminthurididae Sminthurides aquaticus (Bourlet, 1843) A surface dwelling springtail Decapoda ~ Crabs, Prawns and Shrimps 29 Palaemonidae Palaemonetes varians (Leach, 1817) A Brackish Water Shrimp Diptera ~ true flies, not identified to species (therefore do not count towards BMWP or CCI scores) 30 Ceratopogonidae Ceratopogonidae sp.

Biting Midge larvae / pupae 31 Chironomidae Chironomidae sp.

Non biting midge larvae 32 Culicinae Culex sp.

Mosquito larvae / pupae 33 Dixidae Dixidae sp.

Non Biting Midge pupae Ephemeroptera ~ Mayflies or Up-winged flies 34 Baetidae Cloeon dipterum (Linnaeus, 1761) The Pond Olive 35 Caenidae Caenis horaria (Linnaeus, 1758) White Midge

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Common

V Common 1 2 3 Common 1 2

4 1 2 3 4 1 2 3 4 1 2 4

4

4

4

1 2 3 4

4

Common

Sites 1 2 3 3 1 1 2 1 2 1 2 2 1 2 1 2 3 1 2 3

Notable b Frequent V Common V Common Common V Common Frequent Notable b V Common RDB 3 V Common Common

Status

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Family

Species

47 48 49 50 51 52 53 54

Gerridae Hydrometridae Naucoridae Nepidae Nepidae Notonectidae Pleidae Veliidae

Gerris thoracicus Hydrometra stagnorum Ilyocoris cimicoides Nepa cinerea Ranatra linearis Notonecta glauca Plea minutissima Microvelia reticulata

Hemiptera ~ Aquatic bugs 36 Corixidae Callicorixa praeusta 37 Corixidae Hesperocorixa linnaei 38 Corixidae Hesperocorixa sahlbergi 39 Corixidae Paracorixa concinna 40 Corixidae Sigara dorsalis 41 Corixidae Sigara falleni 42 Corixidae Sigara lateralis 43 Corixidae Sigara limitata 44 Corixidae Sigara stagnalis 45 Gerridae Gerris lacustris 46 Gerridae Gerris odontogaster (Fieber, 1848) (Fieber, 1848) (Fieber, 1848) (Fieber, 1848) (Leach, 1817) (Fieber, 1848) (Leach, 1817) (Fieber, 1848) (Leach, 1817) (Linnaeus, 1758) (Zetterstedt, 1828) Schummel, 1832 (Linnaeus, 1758) (Linnaeus, 1758) Linnaeus, 1758 (Linnaeus, 1758) Linnaeus, 1758 Leach, 1817 (Burmeister, 1835)

Authority

A Pond Skater The Water Measurer Greater Saucer Bug Water Scorpion Water Stick Insect Common Water Boatman A Lesser Water Boatman A Lesser Water Cricket

A Lesser Water Boatman A Lesser Water Boatman A Lesser Water Boatman A Lesser Water Boatman A Lesser Water Boatman A Lesser Water Boatman A Lesser Water Boatman A Lesser Water Boatman A Lesser Water Boatman The Common Pond Skater The Toothed Pond Skater

Description

Occasional V Common Occasional Frequent Local V Common Occasional Local

Frequent Occasional Common Local V Common V Common Common Local Local V Common Common

Status

4 2 3 1 2 3 4 1 2 2 4 1 2 3 1 1 2

4 1 2 3 4 3 4 1 2 3 4 1 4 1 1 1 4

Sites

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Trans. Suffolk Nat. Soc. 49 (2013) Various mite species, adults & larvae

A Leech of aquatic invertebrates A Leech of molluscs, worms, insect larvae A Leech of aquatic invertebrates The Duck Leech The Fish Leech

Description

66 67

Bithyniidae Hydrobiidae

Bithynia tentaculata (Linnaeus, 1758) Potamopyrgus antipodarum (J. E.Gray, 1843)

Common Bithynia Jenkins’ Spire Shell

Isopoda ~ Water Slaters or Hog Lice 61 Asellidae Asellus aquaticus (Linnaeus, 1758) A water Slater or Hog Louse Lepidoptera ~ Moths (with aquatic stages) (Do not count towards BMWP or CCI scores) 62 Crambidae Cataclysta lemnata (Linnaeus, 1758) Small China-mark moth caterpillar Mollusca …. Bivalvia ~ Bivalves (Mussels & Cockles) 63 Pisidiidae Pisidiidae sp.

Pea Shell Mussels 64 Sphaeriidae Musculium lacustre (Müller, 1774) Lake or Capped Orb Mussel (Cockle) 65 Sphaeriidae Sphaerium corneum (Linnaeus, 1758) Horny Orb Mussel (Cockle)

(O.F.Müller, 1774) (Linnaeus, 1761)

(Linnaeus, 1758)

Helobdella stagnalis

Glossiphoniidae

57

58 Glossiphoniidae Theromyzon tessulatum 59 Piscicolidae Piscicola geometra Hydracarina ~ Water Mites 60 Hydrachnellae Mites

(Linnaeus, 1758)

Glossiphonia complanata

Glossiphoniidae

56

Authority (Linnaeus, 1758)

Species

Erpobdella octoculata

Family

Hirudinea ~ Leeches 55 Erpobdellidae

Sites

2 3

1 2

V Common 1 2 V Common

V Common 1 2

4

4

1 2 3 4

1 2 3 4

1 2 3 4 3 4

1 Occasional 1

Common

Common Common

V Common 1 2

V Common

V Common 1 2

Status

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Family

Species

Authority

Limnephilidae Limnephilidae

83 84

(Fabricius, 1787) Curtis, 1834

Limnephilus flavicornis Limnephilus marmoratus

(Schmidt, 1861)

(Curtis, 1834)

Triaenodes bicolor

Tricladida ~ Free Living Flatworms 85 Dugesiidae Dugesia lugubris

Leptoceridae

82

Mollusca …. Gastropoda ~ Univalve Snails 68 Lymnaeidae Lymnaea fusca (C. Pfeiffer, 1821) 69 Lymnaeidae Lymnaea stagnalis (Linnaeus, 1758) 70 Lymnaeidae Radix balthica (Linnaeus, 1758) 71 Physidae Physa fontinalis (Linnaeus, 1758) 72 Physidae Physella gyrina (Say, 1821) 73 Planorbidae Anisus vortex (Linnaeus, 1758) 74 Planorbidae Bathyomphalus contortus (Linnaeus, 1758) 75 Planorbidae Hippeutis complanatus (Linnaeus, 1758) 76 Planorbidae Planorbis carinatus (O.F. Müller, 1774) Odonata ~ Dragonflies & Damselflies (larvae or exuviae) 77 Coenagrionidae Ischnura elegans Vander Linden,1820 78 Coenagrionidae Pyrrhosoma nymphula (Sulzer, 1776) 79 Libellulidae Libellula depressa Linnaeus, 1758 80 Libellulidae Libellula quadrimaculata Linnaeus, 1758 Trichoptera ~ Caddis or Sedge Flies 81 Leptoceridae Mystacides longicornis (Linnaeus, 1758)

A Freshwater Triclad or Flatworm Total records for each site

Common

Common Common

Common

Common

A cased caddis ‘The Grouse Wing’ A cased caddis ‘The Bicolour Sedge’ A cased caddis A cased caddis ‘The Cinnamon Sedge’

4

4

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57 51 32 36

1 2 3 4

1 2 1 2

1 2

2

V Common 1 2 Frequent 1 Common 1 2 Common 2

The Blue-tailed Damselfly The Large Red Damselfly The Broad-bodied Chaser The Four-spotted Chaser

3 1 2 3 1 2 3 4 4 4 1 2 1 2 1 3 1 2 3

Sites

Common V Common V Common V Common Occasional V Common Common Frequent V Common

Status

Marsh Snail Great Pond Snail Wandering Snail Fountain Moss Bladder Snail Large Bladder Snail Whirlpool Ramshorn Contorted Ramshorn Flat Ramshorn Keeled Ramshorn

Description

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Discussion The ecology, status and distribution of any rare or scarce species found during the survey, from a national and / or county perspective. Status values are those used for the calculation of CCI (Chadd & Extence, 2004), see Survey Analysis page 70.

Freshwater Beetles: Coleoptera Hydrophilus piceus – A Water Scavenger beetle – RDB3 (Plate 9) H. piceus in Britain is largely confined to drains in coastal levels especially those choked with vegetation such as ivy-leaved duckweed (Lemna trisulca) and fringed by common reed (Phragmites australis). H. piceus breeds in summer with larvae reported from mid-May to the beginning of August. The larvae feed on water snails leaving characteristic bite marks on empty shells.

Surveys in the Somerset Levels have found that adults occur mainly in rhynes that have been recently cleared, whereas larvae occur in ditches thickly choked with vegetation. Adults may also be caught in light traps.

From 1980 onwards, H. piceus has been recorded from 50 hectads in England and Wales. It appears to have contracted in range in that there are no modern records for the English Midlands, the Cambridgeshire Fens, Glamorgan and the immediate vicinity of London, there have however been several recent records in Suffolk and it should therefore be regarded as an important county species.

Management Loss of traditional grazing fen may result in loss of this species, particularly if drains are destroyed or become overgrown. Conditions favouring an abundance of large molluscs are essential for breeding by this species; piecemeal clearance of drains using hand shovels is therefore better than large scale clearance using heavy plant in that larger invertebrates can escape. Ensuring that sections of ditches are maintained such that they can be thickly colonised by vegetation and duckweeds will aid larval development.

Helochares lividus – A greenish brown water scavenger beetle – Nb Helochares lividus has been recorded from 174 ten kilometre squares from 1990 onwards and it was found in five samples of the British Countryside Survey in 1990. These data indicate the need for this species to lose its Nationally Scarce status (Foster, 2000). In Suffolk, it has been recorded from eleven sites since 2000 to my knowledge.

Rhantus frontalis – A Diving Beetle – Nb Rhantus frontalis has been recorded from 45 hectads in England and five in Scotland since 1950, the equivalent values since 1990 being 18 and zero. The disappearance of this species from Wales and northern England has resulted in a disjunct distribution, in Scotland from Lanarkshire to Fife, and then in East Anglia, the Thames estuary and at scattered sites in southern England west to the Somerset Levels. Loss of temporary, exposed habitats would

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result in loss of this species. Creation of new temporary ponds would be beneficial for this species. Many Essex and Kent Marshes SSSI support this species, which also occurs in protected parts of the Somerset Levels, in Wretham Heath and Thompson Common wildlife reserves of the Norfolk Wildlife Trust, as well as in Broadland.

In my Suffolk database I have three records between 1899 and 1904.

There is then a considerable gap to the first modern record in 2003, Hen Reedbeds is only the 3rd site it has been recorded at since then.

Rhantus suturalis – A Diving Beetle – Nb Rhantus suturalis occurs in exposed lowland ponds and ditches amongst vegetation. It is unusual among Rhantus spp. in that it overwinters as adults in the water rather than away from it. This species is often attracted to light at night and readily takes to flight.

R. suturalis has been recorded from 136 ten kilometre squares in England and four in Wales since 1950. It has been recorded from 89 English and two Welsh hectads since 1990. Many isolated records, including two for the only Scottish site, probably represent the full extent of the range of this dispersive species. Although not particularly under threat, the creation of new ponds will be beneficial to this species, it is not confined to primary fen conditions.

This is the 12th site added to my Suffolk database since 2000 for R. suturalis.

Freshwater Bugs: Heteroptera

Gerris thoracicus – A Pond Skater – Occasional (Plate 10) The distribution of Gerris thoracicus in Suffolk shows the majority of records to be brackish waters near the coast with a few records further inland. This seems to largely echo the national distribution. It is a pond skater which occurs in fresh waters, but shows a preference for higher conductivities and shallow, often muddy-bottomed waters. It is therefore no surprise that the scrapes in front of the bird hide had a large population and there were also several individuals noticeable in the water-filled tyre tracks leading down to site 4. Of the three species of pond skater at the site, G. thoracicus can be easily identified as the pronotum is reddish / brown–yellow whereas the other two species both have a black pronotum. Although very common at this site, there are records from less than 20 other sites in Suffolk.

Hesperocorixa linnaei – A Lesser Water Boatman – Occasional Records for this corixid are densest in a broad swathe running from Kent up through East Anglia across Derbyshire towards Lancashire. Elsewhere, the distribution appears sparse and scattered. In Suffolk, H. linnaei does not appear to be as common as the related species H. sahlbergi, which is found across the county in most suitable habitats. Both occur in all conductivities with a preference for base-rich, well vegetated waters containing substantial amounts of organic matter in the substratum. Therefore, it is perhaps surprising that at Hen Reedbeds, H. linnaei seems to be the dominant species with H. sahlbergi only found at sample site 3.

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Ilyocoris cimicoides – Greater Saucer Bug – Occasional Found in base-rich, still waters which are normally muddy-bottomed and usually amongst dense vegetation. I. cimicoides is often found either in very large numbers or not at all. It is often found in one location, but not in a neighbouring waterbody. It has been postulated that populations are self limiting due to poor dispersal caused by reduced wing musculature in a high proportion of adults. At Hen Reedbeds, I. cimicoides occurs in high numbers right across the site and clearly the current reedbed management suits this species. In Suffolk, it has been recorded from 34 out of over 750 surveyed sites.

Microvelia reticulata – A Lesser Water Cricket – Local This surface dwelling bug is abundant at Hen Reedbeds but, being less than 1∙5 mm long, is certainly rarely seen. It is found in many types of still water but always amongst emergent, marginal vegetation as here. It is not surprising that it occurs here in such large numbers given the amount of suitable habitat that has been created. Due to its tiny size the species is probably under recorded though clearly widespread and more often recorded in the south and east of Britain.

A related, but much rarer, species Microvelia pygmaea was not recorded here, but there are some records for this species from sites very close by.

Both species do occur together at sites elsewhere in East Anglia and it will be important to search also for M. pygmaea in any future surveys.

Paracorixa concinna – A Lesser Water Boatman – Local Widely distributed throughout Britain, P. concinna is most frequent in the south but is rarely common. A mobile species, it tends towards small transitory populations, possibly because of competition with other corixids.

However, it does favour open waters of moderate size with high conductivity and is known to breed in saline waters. This explains its presence at site 4 and the shallow, warm and weed filled scrapes provide an ideal habitat that seems as perfectly maintained for P. concinna as it is for birds and birders watching from the hide! The higher conductivity at this end of the site suits P. concinna as it may deter over competition by other corixids. The Suffolk database only contains only six other sites where P. concinna has been found since the year 2000.

Plea minutissima – A Lesser Waterboatman – Occasional Another tiny water bug (2–3 mm); Plea minutissima was found in small numbers amongst submerged water weeds which are its usual habitat.

P. minutissima is most common in the south east of Britain, but is widespread over most of the country except for Scotland. A very distinctive predator, it is usually found amongst dense weeds and swims upside down like the backswimmers Notonecta spp. In Suffolk, it is widespread but has been recorded in less than 10% of sites in the county database and is probably under-represented in the database.

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Ranatra linearis – Water Stick Insect – Local Not found in large numbers during the survey the habitat at this site is however typical for R. linearis being an open site with large amounts of emergent vegetation. The small numbers found could perhaps indicate low numbers spread thinly. However, experience suggests that the edges of the reeds where the water depth drops away may be a better area to search for this species. However, for that type of survey a boat will probably be needed.

In Britain, Ranatra is predominantly a species of the south-east but even so in Suffolk it is only recorded from 30 out of over 750 surveyed sites. I am sure that it is very much under-recorded and being unmistakably easy to recognise this is a species that would repay more interest from the general naturalist.

Sigara limitata – A Lesser Water Boatman – Local A difficult species to quantify. Although widely distributed in Britain, and more frequent in the south and east, there are only records from 79 ten km squares in the provisional atlas of British aquatic bugs (Huxley, 2003). Records come from habitats as diverse as moorland ponds and chalk streams, so it can hardly be described as fussy! As for the Suffolk database, the Hen Reedbeds are only the 7th site added since 2000 and none of the other sites are in reedbeds so habitat preferences and management considerations remain to be resolved.

Sigara stagnalis – A Lesser Water Boatman – Local This species usually prefers higher conductivity waters and so brackish pools and ditches by the sea are typical habitats; often associated with the prawn Palaemonetes varians. There are also records from inland locations which are not brackish but which may have altered chemistry due to enrichment from external sources. Although here it was only found at sample site 1, it seems probable that it will occur in low numbers across the whole site. In Suffolk, there are other records from locations close to the Hen Reedbeds but in all there are only 16 records between 1954 and the present day, this is therefore an important county record and it should be looked for again in future surveys.

Freshwater Snails: Mollusca Physella gyrina – Large Bladder Snail – Occasional Two of the water snail species recorded at Hen Reedbeds were sinistral or left handed; that is when held with the spire pointing upward the body opening is on the left. Of those two species, Physa fontinalis is the smallest and Physella gyrina is much larger. P. gyrina is originally a species of standing and slowly running waters in North America, where it is abundant. It apparently escaped in Great Britain and Ireland from aquaria into canals and similar habitats. It has been spreading since the 1990s, but there are as yet few records in Suffolk. It is also highly tolerant of salt and can survive even in coastal pools close to or in saltmarshes so the brackish waters at Hen Reedbeds pose no problems for it.

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Interpretation of CCI score6

CCI Score Number of species contributing to CCI score 43

CCI indicates that this is a site supporting several rarities, including species of national importance (e.g. taxa included in the British RDBs) and / or a community of very high taxon richness.

The site has very high conservation value. It is potentially of national significance and may merit statutory protection.

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CCI indicates that this is a site supporting several rarities, including species of national importance (e.g. taxa included in the British RDBs) and / or a community of very high taxon richness.

The site has very high conservation value. It is potentially of national significance and may merit statutory protection.

Very good water quality

Very good water quality

22∙79

25

27

22∙71

123 4∙92

Sample Site 2 TM4693077144

131 4∙85

Sample Site 1 TM4686377115

Analysis Results

BMWP score ASPT Number of families contributing to BMWP / ASPT Water Quality

Table 3

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6

17∙89 27 CCI indicates that this is a site supporting several uncommon species, at least one of which may be nationally rare and / or a community of high taxon richness.

The site has high conservation value.

26

CCI indicates that this is a site supporting several uncommon species, at least one of which may be nationally rare and / or a community of high taxon richness.

The site has high conservation value.

Good water quality

Good water quality

16∙15

20

17

The interpretation of each CCI score is extracted from Chad &Extence, (2004).

CCI Score Number of species contributing to CCI score Interpretation of CCI score6

91 4∙55

Sample Site 4 TM4761876643

73 4∙29

Sample Site 3 TM4716176978

Analysis Results Continued

BMWP score ASPT Number of families contributing to BMWP / ASPT Water Quality

Table 3

AN AQUATIC INVERTEBRATE SURVEY OF THE HEN REEDBEDS

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Survey Analysis Biomonitoring3 Analysis For each of the four sample sites three standard measurements or metrics 4 have been calculated, these are:

 The Biological Monitoring Working Party Score (BMWP Score)  The Average Score Per Taxon5 ASPT)  The Community Conservation Index (CCI) Interpretation of the calculations A full explanation of these three methods is given in Appendix 1, but in order to interpret the results in the table below the following may be a useful summary.

BMWP is a measure of the water conditions, of oxygenation and cleanliness. As a guide the following may be used: Score <25 = poor water conditions, 26–50 = moderate, 51–100 = good, 101–150 = very good, more than 150 = exceptional.

ASPT is based on the BMWP score and so also measures water quality. It is useful in showing year to year changes and trends in the invertebrate population supported by the water body. Being an average score, the higher its value the more ecologically valuable the population should be.

Any value greater than 4 generally indicates good water quality, but productive water bodies with large and varied populations will usually have an ASPT value between 4∙5 and 5∙0.

CCI is based on the rarity of the individual invertebrates living in the water.

It gives a numerical value to the conservation importance of the aquatic community. The higher the CCI value the greater the conservation interest.

CCI values can range from less than five for a site with little or no conservation value to a score greater than 20 for sites with very high conservation interest. This latter CCI value often indicates a site that is of national importance and of potential SSSI status.

3

Biomonitoring an evaluation of the condition of a water body using biological surveys and other direct measurements of the resident flora and fauna in surface waters.

4 Metric a quantifiable attribute of an aquatic community that is ecologically relevant and responds predictably.

5 Taxon A taxon is a single animal group, e.g. Pond skaters, Water Boatmen, Diving Beetles or Whirligig beetles.

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References Data in the discussion is taken from the database of the Freshwater Invertebrate Survey of Suffolk and also from: Buckle, P. Dec 23, (2011). Identification of Freshwater and Brackish-water Snails of Britain and Ireland. The Conchological Society of Great Britain and Ireland. Retrieved 29 September, 2012. from http:// www.conchsoc.org/aids_to_id/fwidbase.php Chadd, R. & Extence, C. (2004). The conservation of freshwater macroinvertebrate populations: a community-based classification scheme. Aquatic Conserv: Mar. Freshw. Ecosyst. 14: 597–624.

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

Foster, G. N. & Friday, L. E. (2011). Keys to adults of the Water Beetles of Britain and Ireland (Part 1). Royal Entomological Society, Shrewsbury.

Huxley, T. (2003). Provisional Atlas of the British Aquatic Bugs (Hemiptera, Heteroptera). Biological Records Centre, Huntingdon.

Savage, A. A. (1989). Adults of the British Aquatic Hemiptera Heteroptera. A key with ecological notes. Freshwater Biological Association. Scientific Publication 50. Ambleside.

Information on the CCI analysis method may be found in: Chadd, R. & Extence, C. (2004). The conservation of freshwater macroinvertebrate populations: a community-based classification scheme.

Aquatic Conservation: Marine & Freshwater Ecosystems 14: 597–624.

Adrian Chalkley, Freshwater Invertebrate Recorder 37 Brook Hall Road Boxford Suffolk CO10 5HS APPENDIX 1 A further explanation of the analysis methods BMWP – The Biological Monitoring Working Party Score system was set up by the Department of the Environment, originally to recommend a biological classification system for use in national river pollution surveys. It was finalised in the 1980’s and was revised in the mid 1990’s. In this system 82 different groups of animals are given scores that represent their tolerance to poor site conditions. Animals needing good conditions are given a high score and those that do not are given a low score. If there are many groups present that are intolerant to poor water then the site score is high and its biological condition tends to be good. This system is widely used in many European countries and has come to be used in Lentic ecosystems (still waters) although originally designed for Lotic or flowing water systems.

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ASPT – The Average Score Per Taxon is derived from the BMWP Score and is simply the average score, and therefore the average tolerance to poor conditions of all the animal groups present in the survey results. ASPT can be useful in comparing year on year results. A Taxon is a single animal group, such as Pond skaters or Water Boatmen, Diving Beetles or Whirligig beetles.

Both BMWP and ASPT were developed to reflect water cleanliness & oxygenation levels. However, water quality is not necessarily correlated intimately with importance for wildlife conservation. Each family present in a water body adds to the score but neither the number of members of that family nor the rarity of the species within the family is taken into account.

CCI – The Community Conservation Index is a monitoring system developed in the late 1980s by the old National Rivers Authority and subsequently used by the Environment Agency. It is a way of using species data from a freshwater site in order to classify its invertebrate community. Basically, it assigns a score to each species based on the status of that species both in the country as a whole and also in the local region. The result is a simple index, which aims to summarise the conservation value of the whole aquatic invertebrate community, as opposed to individual species. Rarity of species is a cornerstone of this system. Whilst BMWP and ASPT reflect only the number of different scoring groups of animals CCI reflects the species richness and rarity of the invertebrate community. CCI scores can range from 0 to >40, but a guide for interpretation of scores is as follows: CCI score < 5∙0 – Low conservation value.

Sites supporting only common species and/or a community of low taxon richness. >5∙0 to 10∙0 – Moderate conservation value.

Sites supporting at least one species of restricted distribution and / or a community of moderate taxon richness. >10∙0 to 15∙0 Fairly high conservation value.

Sites supporting at least one uncommon species, or several species of restricted distribution and / or a community of high taxon richness. >15∙0 to 20∙0 High conservation value.

Sites supporting several uncommon species, at least one of which may be nationally rare and / or a community of high taxon richness.

CCI score above 20∙0 Very high conservation value.

Sites supporting several rarities, including species of national importance, or at least one extreme rarity and / or a community of very high taxon richness.

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A. Chalkley A. Chalkley

Plate 9: Hydrophilus piceus â&#x20AC;&#x201C; a Water Scavenger beetle largely confined to drains in coastal levels; found at Hen Reedbeds in 2012. (p. 64).

Plate 10: Gerris thoracicus â&#x20AC;&#x201C; a Pond Skater found in good numbers at Hen Reedbeds in 2012. (p 65).

A. Chalkley A. Chalkley

Plate 11: Ventral view of Argulus foliaceus â&#x20AC;&#x201D; the common Fish Louse, found frequently at Hen Reedbeds in 2012. (p. 59).

Plate 12: Female Dytiscus marginalis â&#x20AC;&#x201D; a Great Diving Beetle found in good numbers at Hen Reedbeds in 2012. (p. 59).