engleski

Influence of isolation and peculiar eclological properties on biodiversity: meio- and nematofauna from the marine lake Mir (Dugi otok island, Adriatic Sea)

Salt lake Mir is landlocked marine environment, situated on the southern edge of Dugi otok island, connected with the surrounding coastal waters by a system of subterranean fissures in the karstic rock substratum. Due to its isolated position, low depth, reduced water dynamics and lack of fresh-water tributaries the lake represents peculiar biotop with considerable temperature amplitude and high salinity. In order to assess the influence of isolation and specific ecological properties on biodiversity, meio- and nematofauna assemblages were studied in six sediment samples ranging from coarse sand rich in biolithic elements (site LM 1) to fine muddy sand (site LM 6), collected in subtidal zone at 1 m depth. At all six sites similar patterns in both meio- and nematofauna assemblages structure were found. Meiofauna involved 13 higher taxa, characterized with moderate high overall densities (DLM1=747, DLM2=920, DLM3=911, DLM4=1054, DLM5=1147, DLM1=898, ind./10 cm-2), dominance of Copepoda (DCo= 52-72 %), subdominant position of Nematoda (DNe= 14-33 %), and notable share of other meiobenthic taxa (DVaria= 13-16%). These findings are in accordance with results obtained world-wide for shallow sandy detritic bottoms, suggesting that meiofauna, but not nematofauna community structure is rather influenced by sediment type, than by peculiar environmental features. Taxonomic composition of nematofauna was rather uniform, poor in terms of species richness (10-15 species per site) and species diversity (H'= 1.93-2.65 bits/ind). In all, 18 free-living nematode species, comprised in 16 genera and 9 families were recorded. At all sites nematofauna characterized by dominance of two families (Comesomatidae and Xyalidae), outstanding position of 1 or 2 species per site, and predominance of Paracomesoma sp. (DLM1=41%, DLM2=54%, DLM3=67%, DLM4=41%, DLM5=49%, DLM1=52% ind./10 cm-2). These results substantially differs from data reported for shallow sandy bottoms, and were considered to be a biotop specific. Unusual finding of dense population of Paracomesoma sp. was interesting from several reasons. Up to date seven Paracomesoma species were described ; they usually occur in low numbers in muddy sediment, and substantially differ from specimens we collected in most of differential characters. In all appearance, the species predominated in marine lake Mir might be a new species to science, and it will be proposed in a subsequent paper. This finding, together with peculiarity and pronounced similarity in nematofauna assemblages structure pointed out a distinctive community pattern that could be linked with specific properties of the area investigated. Preliminary results suggested that both, spatial isolation and restrictive environmental conditions play an important role in formation of distinctive nematofauna community inhabiting shallow sandy bottom of the salt lake Mir. For final assessment of nematofauna diversity, the study on spatial and temporal variability along a depth and sediment gradients is needed.

marine lake; isolation; meiofauna; nematodes; Adriatic Sea

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