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The Occurrence of Hydra Circumcincta (Schulze, 1914) (Hydrozoa: Hydridae) in a Well in the Dorset Chalk, UK

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The Occurrence of Hydra Circumcincta (Schulze, 1914) (Hydrozoa: Hydridae) in a Well in the Dorset Chalk, UK See discussions, stats, and author profiles for this publication at: https://www.researchgate.net/publication/266182826 The occurrence of Hydra circumcinta (Schultze, 1914) (Hydrozoa: Hydridae) in a well in the Dorset Chalk, UK Article in Cave and Karst Science · August 2012 CITATIONS READS 2 320 2 authors: Lee Knight Tim Johns British Hypogean Crustacea Recording Scheme Environment Agency UK 25 PUBLICATIONS 246 CITATIONS 28 PUBLICATIONS 123 CITATIONS SEE PROFILE SEE PROFILE Some of the authors of this publication are also working on these related projects: Invasive shrimps View project Groundwater Animals View project All content following this page was uploaded by Tim Johns on 11 February 2015. 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.
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