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The occurrence of Hydra circumcinta (Schultze, 1914) (Hydrozoa: Hydridae) in a well in the Dorset Chalk, UK

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Lee Knight Tim Johns British Hypogean Crustacea Recording Scheme Environment Agency UK

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The user has requested enhancement of the downloaded file. CAVE AND KARST SCIENCE, Vol.39, No.2, 2012 © British Cave Research Association 2012 Transactions of the British Cave Research Association ISSN 1356-191X

The occurrence of Hydra circumcincta (Schulze, 1914) (Hydrozoa: Hydridae) in a well in the Dorset Chalk, UK.

Lee R F D KNIGHT 1, 2 and Tim JOHNS 3

1 No.1 The Linhay, North Kenwood Farm, Oxton, Nr. Kenton, Devon, EX68EX, UK. 2 Hypogean Crustacea Recording Scheme e-mail: www.freshwaterlife.org/hcrs

3 The Environment Agency, Red Kite House, Howbery Park, Wallingford, Oxfordshire, OX10 8BD, UK. e-mail: [email protected]

Abstract:This report details the first record of a Hydra species, Hydra circumcincta, from British groundwater. Ten polyps of the species were recorded from a well in the Dorset Chalk, while sampling for groundwater fauna as part of the Groundwater Animals–UK project. The Hydrozoa is a group rarely recorded from groundwater habitats with only one stygobitic species known to science. International records of Hydrozoa are discussed and several possible colonization pathways into the well are hypothesized.

Received: 04 May 2012; Accepted: 14 July 2012.

The class Hydrozoa (within the phylum Cnidaria) is a group of predatory Swellings in the body wall develop into either a simple ovary or testes. animals which can be either solitary or colonial. They are related to the The testes release free-swimming gametes into the water, and these jellyfish, corals and seas anemones and along with these groups form an can fertilize the egg in the ovary of another individual. The fertilized important component of the marine biota. Although most Hydrozoa are eggs secrete a tough outer coating, and, as the adult dies, these resting marine, a few genera live in freshwater. Most species include a polypoid eggs fall to the bottom of the lake or pond to await better conditions, and medusoid stage in their life cycle, although a number of species whereupon they hatch into nymph hydras. have only one or the other. The polypoid stage consists of sessile polyps, Four species of Hydra have been recorded from the British Isles. which may be solitary or colonial soft-bodied contractile animals, with a tubular body, the lower end of which forms an attachment disc and the Hydra viridissima (Pallas, 1766) is common in small waterbodies such upper end of which is ringed with feeder tentacles. The medusoid stage as duck ponds and ditches. (Schuchert, 2010). It is known as the ‘green resembles the classic ‘jellyfish form’ and when present within the life hydra’, due to the symbiotic green algae (zoochlorellae) commonly found cycle represents the sexually-reproductive phase. in its structure, and was formerly placed in its own genus Chlorohydra. In British freshwaters Hydrozoa are represented by three families: Hydra oligactis (Pallas, 1766) is a fairly large (extended polyp length Olindiidae, Clavidae and Hydridae. The Olindiidae is represented 10 to 30mm) species with very long tentacles (longer than the body), by a single species of freshwater jellyfish Craspedacusta sowerbyi found on stones in streams and lakes (Schuchert, 2010). Hydra vulgaris (Lankester, 1880). This tiny introduced species has been found in aquaria (Pallas, 1766) is a small (extended polyp: 3–6mm up to 10mm) brown- and hot-house ponds and occasionally in lakes, reservoirs and canals. to ochre-coloured species found throughout Europe (Schuchert, 2010). The Clavidae is also represented by a single species Cordylophora Hydra circumcincta (Schulze, 1914) is another small species (extended lacustris (Pallas, 1766), which forms branching shrub-like colonies 5 polyp: 5 to 15mm) that is much rarer than the other species listed above to 6cm tall, each polyp borne at the end of a slender stalk covered by and has a pale (whitish to pale brown-grey, in some cases red due to a tube of chitinous material. It is found attached to aquatic plants, tree pigments taken up in food) colouration. It is found throughout northern roots and similar substrata in fresh or slightly brackish water in the Europe and is rather photophobic, occurring on stones and leaves in lower reaches of rivers, canals and in the Norfolk Broads. The family shallow waters (Schuchert, 2010). Hydridae consists of the freshwater hydras, common animals found Records of Hydrozoa are rare from subterranean waters. Hydra in almost any permanent body of water; attached to aquatic plants, vulgaris, H. oligactis and H. viridissima have been found in interstitial sunken wood, rocks and stones and may also be found hanging from habitats in large rivers in Slovenia, Croatia, Germany, Romania and France (Zagmajster et al., 2011). Additionally, Chappuis (1922) recorded the surface film. Hydras have slender bodies and about four to eight Hydra viridissima from a single well near Basel in Switzerland. There contractile tentacles, arranged in a single ring, that capture small prey are records from the first half of the 20th century for Hydridae from such as Copepoda and Cladocera. Hydras do not possess a medusoid caves in Germany, the Czech Republic, Austria, Mexico and Florida stage within their life cycle. When food is plentiful hydras reproduce (USA) and in recent years they have also been recorded from a cave asexually by budding (small polyps budding on the side of their parent in Australia, two caves in West Virginia (USA), a second cave in and breaking off when mature). When conditions are harsh, often Mexico and two additional caves in Slovenia (Zagmajster et al., 2011). before winter or in poor feeding conditions, sexual reproduction occurs. The majority of the records listed in Zagmajster et al. (2011) are of

63 Hydra sp., although Cordylophora lacustris is listed from Little River The Hydra specimens were later identified as Hydra circumcincta Spring in Florida and Hydra viridissima was identified from Semriach (Fig.2) by Peter Schuchert of the Muséum d’Histoire Naturelle, Lurhöle in Austria. They also mention records from the literature of Geneva, the first record of Hydrozoa from groundwater in the UK. Hydra vulgaris, H. oligactis and H. viridissima from caves and a mine, Peter Schuchert stated that “it is somewhat surprising to find it in a although these are not included in the list provided in an otherwise deep well, but as long as there is prey, they will survive.” Hydras feed comprehensive table in the paper. The records also include Velkovrhia on any small animal that blunders into their tentacles and which can enigmatica (Matjašič & Sket, 1971) (Family Bougainvilliidae), the be subdued by their stinging cells (Fitter and Manuel, 1995). Thus it is only species of hydrozoan considered to be stygobitic. This species was likely that they would be feeding on the cyclopoid copepods present in first described from Planinska jama cave in southwest Slovenia and has the well water but the pathway the species used to colonize the well is since been recorded from three additional caves in the Dinarides in the unknown. The well itself was disused, although the remains of a pump countries of Slovenia, Croatia and Bosnia-Herzegovina (Zagmajster et were still in place on the surface and the top of the shaft was only open al., 2011). to the surface via two small slots either side of the pump equipment. Overall, records of Hydra species are rare in Britain, despite the genus The top of the water column was measured at 13.74m below ground being widespread and common in most bodies of unpolluted freshwater level (61.67m above Ordnance Datum). (including rivers, streams, ponds and lakes). This is due primarily to The nearest surface watercourse, the upper reaches of a tributary of the fact that the group is often overlooked and also to difficulties in the River Allen (at an elevation of 70m above ordnance datum), lies identifying most of the species accurately within the genus, which approximately 500m to the southwest of Dean Farm. This tributary relies on the examination of intact nematocysts (Schuchert, 2010). rises to the west of Minchington at Minchington Farm (elevation Consequently many records are not identified further than family or 74m), approximately 900m to the west of Dean Farm. A collection genus. On the National Biodiversity Network (NBN) web portal (www. of wells in the small village of Farnham, a few hundred metres to the nbn.org) there is only a single record for Hydra circumcincta, from the northwest of this source intercept the groundwater flow that surfaces as moat at Cardiff Castle. None of the previously known British records of Hydrozoa are from groundwater sites. the tributary’s headwaters. The next nearest watercourses are a second While carrying out sampling as part of the ‘Groundwater Animals- tributary of the Allen that rises at the village of Chettle, approximately UK’ project, a collaborative study into the distribution of groundwater 1.6km to the southwest (elevation 70m) and the source of the River fauna in Britain, the authors collected ten Hydra polyps from a disused Allen at Monkton Up Wimborne, about 2km to the southeast of Dean deep well at Dean Farm, Minchington, (NGR: ST 9785 1518) to the Farm, which rises at a height of 56m above Ordnance Datum. northeast of Blandford Forum (Dorset) on 01 October 2009. The well was The hydrogeological map of the area (Institute of Geological excavated in rocks of the Seaford Chalk Formation, and the specimens Sciences and Wessex Water Authority, 1979) and the local topography were collected using a modified funnel-shaped plankton net (63 micron (indicating the direction of several dry and active valleys in the mesh), fitted with a screw-on filter and a lead weight suspended beneath. surrounding landscape) suggest that general groundwater flow is from The net was lowered to the base of the well on the end of a cable, the the northwest to the southeast, draining off the ridge of Cranborne substrate at the bottom of the well was agitated with the weight and the Chase. Thus, groundwater intercepted by the well at Dean Farm flows net was then drawn up through the water column; a procedure that was in a parallel valley to that in which the Minchington tributary is located, repeated three times. A range of groundwater chemical parameters were with the two valleys separated by a ridge of higher ground (see Fig.1). measured, the most pertinent being: pH: 8.08; conductivity: 580μS/ However, the higher elevation of the upper reaches of the Minchington cm; dissolved oxygen: 98%; and temperature: 13.06°C. Other fauna Farm tributary, in comparison to the groundwater level within the well collected during the sampling included: 56 Cyclopoida, 2 Collembola, at Dean Farm, suggests that it could be possible for some subterranean 1 Acari, 3 Oligochaeta and 4 Niphargus kochianus kochianus (Bate, flow to occur towards the east, perhaps via a fracture network providing 1859) (a stygobitic amphipod) (Johns and Dunscombe, 2011). a preferential pathway.

Figure 1: Hydrogeological map of the local area, showing the geology, groundwater flow pathways in the Dean Farm and Minchington valleys (shown by black arrows) and the predominant direction of groundwater flow in the area (shown by the larger white arrow). Note that the contour pattern is sketched for illustrative purposes only and might not be accurate locally. (Figure reproduced using data from: Institute of Geological Sciences and Wessex Water Authority, 1979.)

64 Hydra circumcincta from the Minchington stream could have entered Acknowledgements the groundwater via the hyporheic zone and conceivably travelled along The authors thank Peter Schuchert for identification of the specimens, for some fracture networks within the Chalk to Dean Farm. However, this would helpful comments and for permission to reproduce the figure from Tardent et seem to be against the prevailing direction of groundwater flow and, al. (1968). The ‘Groundwater Animals-UK’ project was funded by the Esmée given the relatively sedentary nature of this species, seems unlikely. Fairbairn Foundation and was a collaborative project involving Roehampton An alternative colonization pathway could be via a more local, former University, the British Geological Survey, University of Loughborough, the surface water body. Fig.1 illustrates that Dean Farm is located half way Freshwater Biological Association, University of Plymouth, the Environment down a dry valley, where the Chalk is overlain by Quaternary fluvial Agency and the Hypogean Crustacea Recording Scheme. The authors also thank sands and gravels, suggesting an historic river channel, although no Paul Wood (Loughborough University) and Lou Maurice (British Geological Survey) for their useful comments on an earlier draft of the Report. permanent surface waterbodies are evident. The nearest watercourse up hydraulic gradient of the valley is approximately 8km to the north on References the opposite side of the Cranborne Chase ridge and hence hydraulically Chappuis, P A, 1922. Die Fauna der unterirdischen Gewasser von Basel. Archiv separate. It is possible that during high groundwater events springs für Hydrobiologie, Bd.XIV, Stuttgart. Fitter, R and Manuel, R, 1995. Collins Photo Guide: Lakes, Rivers, Streams and may issue from the Chalk at the valley head, giving rise to ephemeral Ponds of Britain and North-West Europe. [Hong Kong: Harper Collins.] surface water bodies where a population of Hydra could exist. In such Institute of Geological Sciences and Wessex Water Authority, 1979. circumstances, the hyporheic zone associated with such a water body Hydrogeological map of the Chalk and associated minor aquifers of Wessex. could have provided refugia and connection to the groundwater for the Johns, T and Dunscombe, M, 2011. The Groundwater Animals Project: an Hydra, as the surface water receded. The use of the hyporheic zone investigation into the diversity and distribution of groundwater fauna in as a refuge during times of flood or drought is well documented (e.g., England. Unpublished report to the Esmée Fairbairn Foundation. Report Wood et al., 2010 and the ‘hyporheic refuge hypothesis’ of Williams available at: http://www.freshwaterlife.org/hcrs/links/contentParagraph/07/ and Hynes, 1974) and so, theoretically, the Hydra could have entered document/GWAnimalsProjectReport.pdf the groundwater via this pathway. Finally, the Hydra could simply have Schuchert, P, 2010. The European athecate hydroids and their medusae (Hydrozoa, Cnidaria): Capitata Part 2. Revue Suisse de Zoologie, Vol.117(3), been present in a small, temporary, surface pool in the yard of the farm 337–555. and were either washed directly into the well, via the small openings at Tardent, P, Leuter, R and Frie, E, 1968. Untersuchungen zur taxonome von the top of the shaft, or were washed down into the underlying superficial Hydra circumcincta Schulze 1914, Hydra stellata Schulze 1914 und Hydra deposits from where they then penetrated the groundwater. However, ovata Boecker 1920. Revue Suisse de Zoologie, Vol.75(49), 983–998. although Hydra can survive in ephemeral waterbodies, they are usually Williams, D D and Hynes, H B N, 1974. Occurrence of benthos deep in the recorded from permanent aquatic habitats; the conditions in the farm substratum of a stream. Freshwater Biology, Vol.4, 233–255. yard suggested that any ephemeral pools that form are likely to exist Wood, P J, Boulton, A J, Little, S and Stubbington, R, 2010. Is the hyporheic for only a short duration and are not likely to support a population, and zone a refugium for aquatic macroinvertebrates during severe low flow the same is likely to apply to any temporary streams that might form in conditions? Fundamentals of Applied Limnology, Archiv für Hydrobiologie, Vol.176(4), 377–390. the dry valley, although this cannot be entirely ruled out without further Zagmajster, M, Porter, M L and Fong, D W, 2011. Freshwater hydrozoans in studies. caves with report on new records. Speleobiology Notes, 3, 4–10. We have no evidence to support any of the above colonization theories for Hydra circumcincta. The possibility of passive migration in groundwater flow through conduits in the Chalk from the Minchington stream to the well would present the most likely option, despite the fact that this would appear to be against the general direction of groundwater flow in the area. Without further investigation the colonization pathway of Hydra circumcincta, into the groundwater at Dean Farm is currently unresolved. Zagmajster et al. (2011) suggest that “the occurrence of hydrozoans in caves may be more common than currently known.” This might be true of cavernicolous waters, where small organisms such as Hydrozoa may well be overlooked. However, the ‘Groundwater Animals-UK’ project involved the sampling of 198 sites (164 wells and boreholes and 34 springs) across Dorset and Devon and the samples from these sites were analysed in detail by washing through fine-mesh sieves and picking out specimens from tiny portions of each sample placed in a petri dish and sorted beneath a binocular microscope (Johns and Dunscombe, 2011). Hydrozoa were not recorded in any of the other samples. Similarly the first author has sampled numerous groundwater sites (wells, boreholes, springs and streams and pools in caves and mines) across the UK and Ireland over many years and has previously failed to find Hydrozoa in any of the samples. Staff at the British Geological Survey have also been carrying out detailed invertebrate sampling of boreholes across the UK and have not found Hydrozoa; neither have any other researchers who have worked on the groundwater fauna of the UK in the past. There are no records of Hydrozoa on the Hazelton Database of biological records maintained by Graham Proudlove, the BCRA Biological Recorder. This would suggest that, in the UK at least, the occurrence of Hydrozoa in groundwaters is extremely rare, although this could be partly due to the group being overlooked. Hydroid polyps commonly contract when preserved or removed from water and could possibly have been overlooked in samples in the past. If the specimens reported did enter the well via the groundwater and were not flushed in from the surface, then this recent record, in a deep Chalk well, relatively remote from existing surface watercourses, adds further interest both in terms of the habitat Hydra circumcincta is able to occupy and the subterranean transport pathways by which it may be able to disperse. Additional hydrogeological assessment of the area may help provide supporting evidence for its colonization pathway. In particular repeat sampling at the Dean Farm site and also of a second well at the nearby Dean Cross Farm (up hydraulic gradient from Dean Farm) would be of benefit, as well as sampling in the Minchington stream to identify nearby surface populations of the species. Figure 2: Illustration of Hydra circumcincta (after Tardent et al, 1968).

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