Feeding spectra of bivalve mollusks Unio and Dreissena from Kanevskoe Reservoir, Ukraine: are they food competitors or not?
One of the most abundant freshwater invaders is Dreissena polymorpha which provide wide-ranging direct and indirect impacts on the invaded ecosystems. A particularly notable impact on benthic communities is the extinction of native mollusks of the order Unionida. However, the settlement of D. polymorpha on unionid's shells in Kanevskoe Reservoir did not increase native unionid mortality. Since the reason for the successful coexistence of native unionids and invading dreissenids in Kanevskoe
... ds in Kanevskoe Reservoir is unknown, we hypothesized that these mollusks have different feeding spectra. To evaluate this hypothesis, we compared feeding spectra of the mollusks using a fatty acid (FA) marker analysis. Results: Significant differences in the number and percentages of FAs were found among the mollusks and their food sources, seston, and sediments. Analyses of FA trophic markers in mollusk tissues showed that U. tumidus and Dreissena species mainly consumed algae (greens, diatoms, and dinoflagellates), cyanobacteria, and detritus particles enriched with bacteria. According to the multivariate statistical analysis, the mollusks had different feeding spectra: Dreissena species fed on planktonic sources, while U. tumidus mostly consumed food sources of benthic origin, mainly detritus. In addition, U. tumidus and Dreissena species differed in percentages of long-chain polyunsaturated FAs of n-3 and n-6 families and specific FAs which they could synthesize (20:1n-13 and 22:3 Δ7,13,16). Conclusions: U. tumidus and Dreissena species obviously obtained foods of different qualities. Dreissena consumed plankton species, i.e., more-valuable food, while U. tumidus fed on detritus and phytobenthic species which were of a lower food quality in terms of levels of physiologically important eicosapentaenoic and docosahexaenoic fatty acids. We concluded that the different feeding spectra of mollusks and adaptations of U. tumidus, the synthesis of specific FAs, might be the basis for the successful coexistence of native species and invaders for a long time.