FRESHWATER INVERTEBRATE RECORDER’S ANNUAL REPORT 2005/06

FRESHWATER INVERTEBRATES

61

FRESHWATER INVERTEBRATE RECORDER’S ANNUAL REPORT 2005/06 ADRIAN CHALKLEY This report covers the period from January 2005 to July 2006 and whilst previous reports from me have bemoaned the lack of records from other recorders I must start by saying that I have had more sent in this year than at any time in the past, please keep them coming, common species or rare, all are welcomed. My thanks to not only those people mentioned below but to all who sent in records this year.

Starting with Cladocera or Water Fleas, the following species have been generally found to be common in last 12 months: Bosmina longirostris, Eurycercus lamellatus, Chydorus sphaericus and C. ovatus, Daphnia longispina and D. obtusa, Scapholeberis mucronata and of course Simoncephalus vetulus though S. expinosus seems less often found than in previous years.

The Great Silver Water Beetle Hydrophilus piceus was of course a major find during this period and Jim Askins and Stuart Warrington did great work at Orford Ness recording this, our largest water beetle, not once but several times as reported elsewhere in SNS publications (White Admiral 60 and 63). Whilst thinking of the aquatic Coleoptera I must mention Suffolk Wildlife Trust’s Ponds Project and John Baker, from whom several interesting records of many orders have come. These include the beetles Ochthebius marinus (Nat. Notable B), Ochthebius minimus, Donacia marginata (Local).

As mentioned elsewhere in this volume mayflies have been a success story this year with Paraleptophlebia werneri at Elmsett being the most important find alongside Habrophlebia fusca in the same stream. Baetis vernus, Caenis luctuosa, Centroptilum luteolum and C. pennulatum were recorded from new sites in the west of the county on the Rivers Brett and Box whilst Caenis horaria and C. luctuosa were found together at Lound lakes. This last site should also be mentioned for the molluscs Painter’s mussel Unio pictorum and Duck mussel Anodonta anatina. I am sure this site will provide more interesting aquatic records in the future.

Heteroptera or Water Bugs are usually a conspicuous feature in the pond net and Plea minutissima, Nepa cinerea, Ranatra linearis, Ilyocoris cimicoides and Hydrometra stagnorum were the subject of many records sent to me, thankfully they continue to be very widespread in the county and easily identified. Not quite so common is Cymatia coleoptrata which was found by Paul Lee’s Field Studies Council students at Flatford Mill along with several other species. Paul himself got 2005 off to a good start by recording Gerris gibbifer on his garden pond back in April. Paul was pleased to have the second county record for the species which was followed by a third from Stuart Warrington at Dunwich Heath in May. At the same site Geof Nobes found both Microvelia pygmaea and Microvelia reticulata, both good records of very small species which are easy to overlook. Also of note was the sighting by Dr Barry Meatyard (admittedly in Norfolk) of Ranatra linearis swimming in the sea. He sent this in prompted by several pieces about the Water Stick Insect

Trans. Suffolk Nat. Soc. 42 (2006)

62

Suffolk Natural History, Vol. 42

which have appeared in White Admiral over the years. His observations (White Admiral 61) went on to feature in the Heteroptera Recording Scheme newsletter. Finally I found Sigara stagnalis at Lound Lakes which is a bit of a puzzle. This species is associated with brackish pools and ditches by the sea, and whilst Lound is not far from the coast it provides drinking water for Great Yarmouth and is in no way saline. Perhaps it had strayed in, certainly no juveniles were found with it, although (Huxley, 2003) suggests nutrient enrichment from waterbirds may influence the water chemistry to allow S. stagnalis to survive at the few definite inland sites.

One or two interesting caddis flies have been found including Notidobia ciliaris in the River Box for the first time in 10 years. Elsewhere Goera pilosa remains a common but fascinating caddis worth seeing for its beautifully constructed stone built case which almost always seems to include small fragments of brick! Whilst on the subject of the Trichoptera it is worth noting that Agraylea multipunctata, one of the purse-cased Caddis, continues to turn up more frequently in kick samples and Hydroptila species were also fairly common during the last season in the west of the county although at present the Hydroptilids still cannot be identified reliably to species level from larvae.

References Huxley, T. (2003). Provisional atlas of the British aquatic bugs (Hemiptera, Heteroptera). Centre for Ecology and Hydrology. Huntingdon Paraleptophlebia werneri (Ulmer) (Ephemeroptera: Leptophlebiidae), an unexpected addition to the Suffolk List On the 26 April 2006, whilst surveying farm ponds at Elmsett I noticed the sort of farm ditch that often contains little of interest for the freshwater entomologist. Steep sided, overgrown and mostly overhung with a mixture of nettles, bramble and hawthorn. Where the water was even visible it was shallow and muddy bottomed, with abundant grass and emerging water mint Mentha aquatica, though a slight flow was visible it was the sort of stream that would clearly soon dry up in summer.

Very little life was immediately visible, just some water slaters, small ramshorn snails and a few mayfly larvae. These were obviously poor swimmers, moving with a laboured motion and an exaggerated swaying of the abdomen resulting in only slow progress across the collecting dish. Under the microscope they keyed out to be Paraleptophlebia werneri, a new record for Suffolk. Comments in the FBA key (Elliot, Humpesch & Macan, 1988) suggested that little is known about the species and a glance at Bratton (1990) confirmed its national rarity. Craig Macadam at the Ephemeroptera Recording Scheme confirmed the identification from a voucher specimen.

It transpires that P. werneri has only been recorded from eight 10 km squares in Britain, the Elmsett site providing a ninth. It is listed by Bratton (1990) as potential RDB3 status and has recently been put forward as a priority species as part of the BAP review process. Elsewhere populations occur in calcareous streams with abundant vegetation, these are often

Trans. Suffolk Nat. Soc. 42 (2006)

FRESHWATER INVERTEBRATES

63

‘winterbornes’ i.e. streams which tend to dry up in the summer months.

Although chalk does occur sporadically in the underlying clay at Elmsett the stream there is not calcareous, though it has plenty of vegetation where overhanging plants permit, and probably has little summer flow. According to Elliot & Humpesch (1983) P. werneri is a ‘collector-gatherer’ meaning it burrows in the mud and feeds by gathering fine organic detritus from the sediment. It probably is univoltine (having one generation per year) and most likely overwinters in the egg stage, though much of this is guesswork based on central European studies and pointing the way to further observation at Elmsett.

As Craig Macadam and the Ephemeroptera Recording Scheme had never seen adults of the species weather conditions were monitored awaiting possible hatching of the larvae. By good fortune adults were taken and a male (Plate 6b), a female (Plate 6a) and a male sub-imago (Plate 6d) were photographed for both the county and national recording schemes. For the general reader it is worth noting here that the Ephemeroptera are unique amongst winged insects in having two adult stages, larvae (Plate 6e) first hatching into a non breeding subimago or winged adult. The subimago then moults again, usually within 24 hours if air temperature is sufficient, into the fully formed adult or imago. Facts contradict the popular view that mayflies only live for a day for although adults do not feed and some only live for an hour or two, some ovoviviparous species may live for up to fourteen days before laying several thousand eggs per female. Fishermen often call the subimago the dun and the imago the spinner.

Further studies of the stream at Elmsett have shown that it first flows across an open arable field before traversing the side of a copse and hedgerow, where it becomes very overgrown. P.werneri was only found in this second part of the stream which has an area of uncultivated grassland on the opposite bank. The stream later flows across a meadow and is less overshaded, P.werneri is replaced in this section by Hadrophlebia fusca, a more common mayfly from the same family.

Further studies and monitoring of the population are planned to establish: a. If there are further sites in the vicinity supporting P. werneri. b. Possible ecological threats to the population, particularly upstream of the favoured habitat. c. More data on the life cycle of P. werneri, which is imperfectly known.

Threats to the population of this rare mayfly may occur from: d. Any gross alteration to the vegetation structure such as weed cutting. e. Unsympathetic bank work such as dredging, bridge construction or bank stabilisation. f. Water quality issues, spray drift into the upstream section being the most likely source.

For this reason it may be hoped that DEFRA funding may be granted to establish a suitable and sympathetic management regime.

Trans. Suffolk Nat. Soc. 42 (2006)

64

Suffolk Natural History, Vol. 42

Acknowledgements My thanks to Juliet Hawkins for suggesting the site and facilitating access, to James Buckle for permission to survey on his land and to Craig Macadam of the Ephemeroptera Recording Scheme for help and advice.

References Bratton, J. H. (1990). A Review of the Scarcer Ephemeroptera and Plecoptera of Great Britain. Research & Survey in Nature Conservation No. 29, Joint Nature Conservation Committee, Peterborough.

Elliott, J. M. & Humpesch, U. H. (1983). A Key to the Adults of the British Ephemeroptera. Freshwater Biological Association Scientific Publication No. 47.

Elliott, J. M., Humpesch, U. H. & Macan, T. T. (1988). Larvae of the British Ephemeroptera. Freshwater Biological Association Scientific Publication No. 49.

Adrian Chalkley Freshwater Invertebrate Recorder 37 Brook Hall Road Boxford Sudbury Suffolk CO10 5HS

Trans. Suffolk Nat. Soc. 42 (2006)

a

b

c

C

d

Plate 6: Photos of the mayfly Paraleptophlebia werneri found during April 2006 in a stream (farm ditch) at Elmsett, Suffolk TM039484. a: Adult female, b: Adult Male, c: wing, d: Subimago male, e: Larva. (p. 63)

A. Chalkley

e