Comparative shell morphology of the zebra mussel, Dreissena polymorpha in the Drava River (Croatia)

Abstract

We examined the shell morphometrics of the zebra mussel (Dreissena poly-morpha) collected from the system of the Dubrava hydro-electric power plant on the Drava river (Croatia). Study sites had different sediment types, depth, and physical and chemical conditions. Site 1 was the shallow of the Drava river, while sites 2 and 3 were located in the artificial Dubrava lake at depths of 3 and 8 m, respectively. A total of 1,200 zebra mussels were collected. The following morphological variables were examined: shell length (SL), shell width (SW), shell height (SH) and shell mass (SM). In addition three dif-ferent ratios were defined: SW/SL, SH/SL and SW/SH. Analysis of variance (ANOVA) and Duncan multiple comparison test were applied to test the dif-ferences of the ratios among the three sites and to determine which of them was significantly different from the others. The analysis showed that the ratios SW/SL and SW/SH differ significantly between all three sites (P < 0.0001), while the ratio SH/SL did not differ between sites. The log-transformed vari-ables were further analysed using principal component analysis. ANOVA and Duncan test were applied to the resulting principal components to test for differences in component scores among the three sites. The analysis sepa-rated the riverine and the lake populations of mussels into two morphological groupings, indicating that considerable phenotypic plasticity exists among the populations of the zebra mussel.