engleski

Growth and longevity of the "living fossil" Congeria kusceri (Bivalvia: Dreissenidae) from the subterranean Dinaric karst of Croatia

The present study analysed growth and longevity of the endemic and endangered cave dwelling bivalve Congeria kusceri from the pit Jama u Predolcu, Croatia. A water temperature of 13-14ºC has been identified as the lower limit for both the initiation and cessation of shell growth and reproductive maturity of C. kusceri. Obtained hydrological data also indicated that enhanced calcium uptake by C. kusceri during its summer growth and reproductive phases coincided with a decrease in alkalinity of the pit water. Results of the marginal increment analysis showed that growth lines are formed annually, during the period when water temperature begins to increase, that is, from May to June. An analysis of shell growth rings in C. kusceri has identified an impressive longevity of 53 years. Calculations of growth rate suggested maximum theoretical shell lengths (L∞) of 16.7 mm for males and 18.7 mm for females and a growth constant of 0.04 year-1 for both sexes. Congeria kusceri can, however, grow to a shell length of >24 mm, suggesting that longevity could be greater than that identified in this study. Among the Dreissenidae, C. kusceri is the only species that displays extreme longevity, presumably because of its subterranean habitat and adaptations that uniquely fit it and recently identified congeners for such a troglodytic life style. This study of Congeria kusceri provides insights into a unique life history trait that facilitated occupation 5 million years ago of the subterranean environment of Croatia’s and the region’s Dinaric karst. In evolutionary terms, the species has survived occupation of underground karstic waters by reducing the effects and consequences of physiological ageing thereby nullifying reproductive senescence. The conservation of the unique Dinaric karst species and the rich diversity of habitats they occupy are essential and should be a matter of national as well as international priority.

bivalve ; age ; growth rings

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