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__________________________________________________________________________________________________________ THE AQUATIC BEETLES (COL., DYTISCIDAE, GYRINIDAE, HELOPHORIDAE, HYDRAENIDAE etc.) OF THÁSOS
Eretes stictus (c) B.Dupont Although the mountains provide Thásos with an abundant water supply throughout the year, in the summer months this is largely held within the limestone aquifers and visible water bodies are extremely scarce. In fact the small reservoir, Fragma Marion, in the valley at Maries is the only significant area of open water that is readily accessible in the summer, with all of the major rivers usually drying up at lower levels by the end of May. Aquatic invertebrates of all kinds, therefore, are very limited on the island and this no doubt extends to water beetles as it does to dragonflies and freshwater molluscs. However, as with many other invertebrate species, water beetles are capable of occupying very small pockets of habitat or of living amongst swamp vegetation where there may be no apparent open water. Such situations do occur on Thásos in the form of shallow coastal pools behind the beaches at Cap Prinos and Potos, of tiny mountain runnels on the slopes of Ipsarion, of dense reedbeds at Skala Prinos and on the outskirts of Thassos Town, of small waterfalls in the Kastro valley, etc. Few of these localities, including Fragma Marion, have been surveyed for their water beetle fauna - or at least records of those surveys have not been published - so there is plenty of opportunity to add to knowledge of the island's biodiversity. Karnozickij (1959) managed to record 31 water beetle species in October 1942 and April-May 1943 (mainly the former), but these were mostly from around coastal towns and villages in the north of the island and they are characterised by a non-specialist fauna that was probably found mainly in seasonal lowland pools. Karnozickij's specimens need to be checked in light of subsequent taxonomic advances and may not all be correct. The only other published records of water beetles from Thásos derive from the studies of M.A. Jäch on various genera of hydraenids. From material collected by H. Malicky in October 1980 from a "notably small and cold stream" at Prinos, Jäch described Hydraena elisabethae as new to science (Jäch 1992; Audisio et al 1996) and from specimens taken by Malicky in thin films of water on coastal cliffs at Kinira in 1979 and 1980 he described Ochthebius anaxagoras new to science (Jäch 1999). Jäch visited Thásos in September 1991, finding H. elisabethae in a "little spring (ca. 40 m long), above the village of Potamia" and O. anaxagoras in the type locality at Kinira. During that visit he also found specimens of Limnebius nitigeus at Megalos Prinos and Potamia (Jäch 1993). All three are extremely restricted geographically and H. elisabethae is known only from Thásos. I have not targeted water beetles during my surveys on the island but have collected material opportunistically while looking for invertebrates in wetland habitats. The seventeen species I have recorded have mainly been found in shallow pools in olive groves on the outskirts of Thassos Town in May 1993, from a small montane stream on Profitis Ilias in May 1997, from the sandy margin of the stream at Skala Potamias in May 1999 and from pools in the dried up stream bed of the wooded gorge at Megalo Kazaviti in June 2005. Nine of these species are newly recorded for Thasos (asterisked in the Checklist below). A teneral male specimen of Eretes griseus collected at light in Thassos Town in September 1995 is apparently the first confirmed example of this species in Greece (Foster & Taylor 2006), although Karnozickij (1959) reported E. sticticus (Linnaeus, 1767) from Rahoni in October 1942. Miller (2002) recognised that griseus is a species in its own right, not a synonym of sticticus, and that griseus is the commoner species in Europe, hence the Rahoni record needs to be confirmed. I am grateful to Prof. Garth Foster for identifying all of the water beetle specimens I have collected on Thásos. Combining these records gives a total of 43 water beetle species recorded so far from Thásos. Csabai et al (2017) report on detailed water beetle surveys of Rhodes, Crete and Corfu and reviewing previous studies they report island totals as 48, 79 and 112, respectively. These three larger islands will presumably have a much greater variety of wetlands and water bodies than Thásos, capable of supporting a wider range of species, as does Chios where Foster & Taylor (2006) record 31 species of Hydradephaga in the families Gyrinidae, Haliplidae, Noteridae & Dytiscidae: the equivalent from Thásos is 21 species. The water beetle fauna of Thásos is presumably less diverse than these examples, but it is also quite likely that targeted survey effort in sites such as the Skala Potamias marshes or the valley fen at the south-eastern corner of Thassos Town could add considerably to our knowledge of the island's water beetle fauna. A Spring visit to the Dipotamos river would surely find additional species and there must be plenty left to discover in the mountain streams draining off Ipsarion around Kastro.
CHECKLIST DRYOPIDAE
Dryops subincanus (Kuwert, 1890) * DYTISCIDAE
Agabus affinis (Paykull, 1798)
Eretes griseus (Fabricius, 1781) ELMIDAE
Elmis aenea (Müller, P.W.J., 1806) GEORISSIDAE
Georissus crenulatus (Rossi, 1794) * GYRINIDAE
Gyrinus dejeani Brullé, 1832 * HYDRAENIDAE
Hydraena elisabethae Jach, 1992
Limnebius nitigeus d'Orchymont, 1945 HYDROPHILIDAE
Berosus luridus (Linnaeus, 1761)
REFERENCES
Audisio, P., de Biase, A. & Jäch, M.A. 1996. Greek species of the genus Hydraena (Subgenus Haenydra Rey) (Coleoptera, Hydraenidae). Aquatic Insects, 18: 65-90. Csabai, Z., Lőkkös, A., Pap, Zs. & Móra, A. 2017. Aquatic beetle fauna of Greek holiday islands (Rhodes, Crete and Corfu) (Coleoptera: Hydradephaga, Hydrophiloidea, Hydraenidae). Spixiana, 40:41-60. Foster, G.N. & Taylor, M.J. 2006. The Hydradephaga of Chios, Greece (Coleoptera Gyrinidae, Haliplidae, Noteridae, Dytiscidae). Memorie Soc. entomol. ital., 85: 75-84. Jäch, M.A. 1992. New and little known Palearctic species of the genus Hydraena (s.l.) Kugelann (Coleoptera: Hydraenidae). Koleopterologische Rundschau, 62: 77-125. Jäch, M.A. 1993. Taxonomic revision of the Palearctic species of the genus Limnebius Leach, 1815 (Coleoptera: Hydraenidae). Koleopterologische Rundschau, 63: 99–187. Jäch, M.A. 1999. Revision of the Palearctic species of the genus Ochthebius Leach. 16. Additional notes on the metallescens group (Coleoptera: Hydraenidae). Koleopterologische Rundschau, 69: 83-98. Karnozickij, N. 1959. Materialien zur Koleopteren-Fauna der Agäischen Küste und Insel Thasos. Izv. zool. Inst. Sof., 8: 237-253. Miller, K.B. 2002. Revision of the genus Eretes Laporte, 1833 (Coleoptera: Dytiscidae). Aquatic Insects, 24: 247-272.
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