JMBA2 - Biodiversity RecordsPublished on-line

The occurrence of the freshwater crab Potamon fluviatile (Decapoda: Brachyura) in Corfu

Peter G Sutton2 Fir Tree Close, Flitwick, Bedfordshire MK45 1NZ, UK. E-mail: petersutton@freeuk.com

Potamon fluviatile is one of four freshwater crabs to be found in the Balkan Peninsula. It was previously recorded from a north-western locality in Corfu during 1977. This paper reports a second site for this species, in the southern half of the island, and discusses the general prognosis for the continued presence of this and other freshwater crabs in habitats across their natural range in the Mediterranean region.

INTroDUCTIoNPotamon fluviatile (Herbst, 1785) is one of four species of freshwater crab (all Potamon species) to

be found in the Balkan Peninsula (Brandis et al., 2000). Maurakis et al. (2004) have recently reviewed its status in Greece, where they found this species to be ‘widely distributed in mainland Greece south and west of the Axios river in the Macedonian prefecture.’ An accompanying distribution map indicated that there was a single record for Corfu, and further investigation revealed that this related to specimens currently held in the Vienna Natural History Museum (P.J. Hogarth, personal communication) the details of which are provided: ‘one female specimen, carapace length 36 mm, from Mesaria, and 2 juveniles, location NE Kapsocholades, Corfu’, with identifications confirmed by Malicky in 1977 (Pretzmann, 1980). Both locations are adjacent at a locality in the north-western part of the island, in the catchment area of the Melissoúdi river which meets the coast at Sidari. These records are described as ‘Erstnachweis fur Korfu’ implying that there are no earlier records for this species. Potamon fluviatile has been recorded from two other Ionian islands: Lefkas (at Neo Vasiliki) and Kefalonia (at Neo Charaktion, Kulurata and Pastra) (Pretzmann, 1980).

In addition to Greece, the global distribution of P. fluviatile includes: Italy, Sicily, Malta, and the Dalmatian and Albanian regions of the Balkan Peninsula (Charmantier, 1992). Maurakis et al. (2004) have attributed Bulgarian records of this species (Bechev, 2000) to Potamon ibericum, which replaces P. fluviatile in north-eastern Greece.

HABITAT AND LIFE HISToryPotamon fluviatile spends its life in freshwater lakes, rivers and streams and does not require a

saline environment for successful reproduction. In common with some crayfishes, this species does not complete an external larval stage and the large eggs laid by the female in late summer produce juveniles which resemble smaller versions of the adults, which have been known to attain carapace widths of up to 185 mm (Maurakis and Grimes, unpublished). The adults, which have nocturnal habits, leave the water to search for food on land when conditions are sufficiently humid, and will burrow deeply to prevent desiccation when conditions are unfavourable. They are omnivorous and are known to feed on a wide variety of animal and plant material, including worms, insects, shrimps, small fish and amphibians, algae and mosses (Gherardi et al., 1987, 1988).

results from a study of a variety of lotic stream factors (stream order, width and depth, pH, water temperature, and distance from river mouth) by Maurakis et al. (2004) suggested that water temperature played a key role in dictating the limits of the observed distribution of Potamon species in Greece.

oCCUrrENCE oF PotAMon fluviAtile IN CorFUIn addition to the records described above, Potamon fluviatile (Figure 1) was discovered at a

second locality in Corfu close to the southern tip of the island. During a survey of the herpetofauna of Corfu, a small stream which leaves the island at Cape Koundouris was investigated along its upper reaches between Kavos and Spartera. Two large adult crabs were observed in a small dammed area which produced a pool approximately 0.5 m deep and 1.5 m radius. The pool was rich in aquatic life including dragonfly and other insect larvae, several adult newts (triturus vulgaris ssp. graeca), small frogs and freshwater shrimps. The adults were present in the margins of the pool and there was no evidence of burrowing activity above or below the waterline, with the exception of smaller burrows in adjacent waterlogged silty soil which were found to be made by the adults and nymphs

P.G. Sutton the freshwater crab Potamon fluviatile in Corfu

JMBA2 - Biodiversity RecordsPublished on-line

2

of mole crickets Gryllotalpa sp. The crabs were photographed at the site (Figure 1) and subsequently identified by E.G. Maurakis as P. fluviatile.

Regarding the possibility of finding P. fluviatile elsewhere on the island, it is interesting to note that a recent survey of otters in Corfu, which were detected at 19 sites across the island, showed no evidence of freshwater crab predation (ruiz-olmo, 2006). The diet of otters feeding in freshwater environments was found to include cyprinid fish, frogs, small mammals, insects, and reptiles including lizards and dice snake natrix tesselata. otters whose habitats included coastal lagoons were found to prey on decapods, but these were species typical of saline environments.

THE FUTUrEAll four of the Potamon species found in Greece are under threat from a variety of factors. The

freshwater habitats that they occupy are vulnerable to pollution which appears to be an increasing problem across the region. In Corfu, confirming the author’s observations, Ruiz-Olmo (2006) noted that, ‘rubbish was present to a high degree in most of the rivers, including the high mountain streams’, and also noted that chemicals and pesticides (the use of which merited the provision of warning signs for the public) were contributing to this problem.

Many of the problems which face organisms living in freshwater environments in Corfu are mirrored across the region, and include: the degradation and loss of freshwater habitats through excessive water abstraction (Bobori et al., 2001; Hadjibiros et al., 1998), the corresponding threat of desertification (Yassoglou and Kosmas, 2000), disturbance and habitat destruction through building development (ruiz-olmo, 2006), the increasing desiccation of sites in response to climate change (Maurakis and Grimes, unpublished), and ultimately, the inappropriate management of aquatic resources through lack of strategic planning, including unsustainable agricultural practices which have led to the loss of the majority (75%) of Greek wetlands since 1900 (oECD, 2000). In the light of this, it is unsurprising that the Potamon species facing the brunt of these changes will increasingly disappear from habitats as they become unsuitable. A measure of how quickly this can take place is provided by Gherardi et al. (1988), who have documented the rapid decline of this species from the Granchio river system in Italy. Elsewhere across their range, many formerly healthy populations of Potamon species are known to have been lost.

Maurakis and Grimes (unpublished) have recently highlighted the habitat protection needs of all four Potamon species, and suggested the implementation of a plan of action to address the problems described above. This, together with recognition of the fact that Potamon species should be used as indicators of the health of the freshwater environments in which they are found, may pave the way to halting the decline of these remarkable and increasingly threatened crabs.

Figure 1. Freshwater crab Potamon fluviatile.

the freshwater crab Potamon fluviatile in Corfu P.G. Sutton

JMBA2 - Biodiversity RecordsPublished on-line

3

Sincere thanks to Eugene Maurakis and Peter Hogarth for kind provision of information regarding the current status of Potamon species in Greece, and Ken Lambert for invaluable assistance with fieldwork.

rEFErENCESBechev, D.N., 2000. New localities of Potamon fluviatilis (Herbst) (Crustacea: Decapoda) in Bulgaria. travaux

Scientifiques de l’ Universite de Plovdiv Animalia, 36, 95–96.Bobori, D., Economidis, P.S. & Maurakis, E.G., 2001. Freshwater fish habitat science and management in Greece.

Journal of Aquatic Ecosystem Health and Management, 4, 381–391.Brandis, D., Storch, V. & Türkay, M., 2000. Taxonomy and zoogeography of the freshwater crabs of Europe, North

Africa and the Middle-East. Senckenbergiana Biologica, 80, 5–56.Charmantier, G., 1992. occurrence of fresh-water crabs, genus Potamon, in southern France. Journal of Crustacean

Biology, 12, 620–626.Gherardi F., Guidi S. & Vannini, M., 1987. Behavioural ecology of the freshwater crab, Potamon fluviatile. Preliminary

observation. Investigación Pesquera, 51, 389–402.Gherardi, F., Micheli, F., Monaci, F. & Tarducci, F., 1988. Note sulla biologia ed ecologia del Granchio di fiume,

Potamon fluviatile. Bollettino del Museo di Storia naturale della lunigiana, 6–7, 169–174.Hadjibiros, K., Economidis, P.S. & Koussouris, T., 1998. The ecological condition of major Greek rivers and lakes

in relation to environmental pressures. In Proceedings of the 4th EuroAqua Technical Review: Let the fish speak: the quality of aquatic ecosystems as an indicator of sustainable water management, 1997, October 23–24. (ed. J.A. Van de Kraats), pp. 103–123. Lelystad.

Herbst, J.F.W., 1785. Versuch einer Naturgeschichte der Krabben und Krebse, nebst einer systematischen Beschreibung ihrer verschiedenen Arten. Zürich: Johann Casper Fuessly, 1, 183–206, pls X-XIII. [For dates of publication see rathbun, 1897:157.]

Maurakis, E.G., Grimes, D.V., McGovern, L. & Hogarth, P.J., 2004. The occurrence of Potamon species (Decapoda, Brachyura) relative to lotic stream factors in Greece. Biologia Bratislava, 59, 173–179.

oECD. 2000. Environmental Performance Reviews: Greece. Athens: Greek Ministry of Environment and Public Works.

Pretzmann, G., 1980. Potamiden aus Griechenland (leg. Malicky, leg. Preztmann). Annalen des naturhistorischen Museums in Wien, 83, 667–672.

ruiz-olmo, J., 2006. The otter (lutra lutra L.) on Corfu Island (Greece): situation in 2006. iuCn otter Specialist. Group Bulletin, 23, 17–25.

yassoglou, N.J. & Kosmas, C., 2000. Desertification in Mediterranean Europe. A case in Greece. rALA report No. 200, pp. 27–33.

Submitted 15 May 2008. Accepted 3 June 2008.