Spicule records of <Emphasis Type="Italic">Ephydatia fluviatilis</Emphasis> as a proxy for hydrological and environmental changes in the shallow Lake Trasimeno (Umbria,Italy) |
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Authors: | Elda Gaino Francesca Scoccia Silvana Piersanti Manuela Rebora Luca Giorgio Bellucci Alessandro Ludovisi |
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Institution: | 1.Dipartimento di Biologia Cellulare e Ambientale,Università degli Studi di Perugia,Perugia,Italy;2.Istituto di Scienze Marine, U.O.S. di Bologna, CNR,Bologna,Italy |
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Abstract: | This research shows the results of an analysis of siliceous spicules found in sediment cores collected in Lake Trasimeno (Umbria,
Italy), a shallow lake that experienced an important water level lowering during the last century. A morphological analysis
of sedimentary sponge records revealed that the spicules accumulated in the lake sediments over the last 150 years are attributable
to Ephydatia fluviatilis, the only sponge species found in the lake in recent years. The stratigraphic analysis of the cores showed that the abundance
and size of the sponge spicules (megascleres) have remarkably decreased, suggesting that a significant depletion of the sponge
fauna occurred, particularly during the first half of the twentieth century. A correlation analysis has identified morpho-hydrological
and related variables (the theoretical fraction of lake surface subjected to resuspension and the amount of total suspended
solids) as the most significant factors explaining the change in density of sponge spicules. Two ecological explanations of
the sponge decline are proposed, based on the sensitivity of the sponge both to the availability of suitable hard substrata
for colonization, and to the amount of wind-resuspended solids. One-ended sigmoid response curves were obtained by regression
and corresponding transfer functions were derived, which allow the mean water depth of the lake and total suspended solids
to be inferred from spicule density records. The results support the use of sponge spicules as a paleohydrological and paleoecological
proxy, application of which appears particularly promising for shallow-water systems. |
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