Biomass and size structure of the scyphomedusa Aurelia aurita in the northwestern Black Sea during spring and summer |
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Authors: | Weisse Thomas; Gomoiu Marian-Traian |
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Institution: | 1 Max-Planck-Institute for Limnology, PO Box 165, D-24302 Plön, Germany and
2 National Institute of Marine Geology and GeoecologyGeoEcoMar, Constanta Branch, 300 Mamaia Blv., RO-8700 Constanta, Romania |
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Abstract: | The abundance, biomass and size structure of the scyphomedusa,Aurelia aurita, was measured during two research cruises tothe northwestern Black Sea (JulyAugust 1995 and AprilMay1997). Average biomass of Aurelia was relatively constant (132179g wwt m2) throughout the investigation period and similarto previous years. Abundance and biomass at individual stationsappeared to be unrelated to temperature and salinity when thelatter exceeded ~13. Biomass was low at coastal stations inthe plume of the Danube where depth was <20 m and salinitydropped to <11. The spring cruise (AprilMay) coincidedwith, or just followed the peak of strobilation. The summercruise (JulyAugust) took place near the beginning ofplanulae larvae release. The population size structure was dominatedby small individuals in spring, while large medusae prevailedmainly in late summer. Aurelia was, on average, larger at deepwater stations during summer, suggesting that per capita foodsupply was higher further offshore. The individual body massincreased from spring through summer. Accordingly, the volume(wet wt) to length (bell diameter) relation changed significantly.If all medusae measured throughout the seasons were pooled,volume (V, in cm3) was related to length (L, in cm) accordingto V = 0.08 L2.71, which is similar to measurements conductedin other coastal areas. In contrast to the common conjecture,we did not find inverse relations between biomasses of Aureliaand the combjelly Mnemiopsis leidyi. Preliminary feeding experimentsindicate that Aurelia may feed upon small Mnemiopsis. The significanceof indirect trophic relations and direct feeding interactionsamong the gelatinous zooplankton in the Black Sea has importantconsequences for the energy flow along the food web and, therefore,needs further study. |
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