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Limnomysis benedeni Czerniavski (Crustacea, Mysidae) - A New Species in the Fauna of Croatia

Limnomysis benedeni (Czerniavsky, 1882) (Mysidacea) was recorded for the first time in Croatia in the summer of 2004. The species was found in Kopački rit, Nature park which is a floodplain of the Danube River, located in the north-eastern part of Croatia, and is on RAMSAR list of weetlands of international importance. Sampling was conducted weekly during July, August and September in Lake Sakadaš, which is the deepest water depression in the rit (depth 10 to 11.5 m during high water levels). Specimens of L. benedeni, with other invertebrate groups, were found in stands of Myriophyllum spicatum (L.) and Ceratophyllum demersum (L.), both submerged macrophytes with dissected leaves. Water depth, transparency or Secchi depth, water temperature, and dissolved oxygen (by WTW Multi 340i/set) were measured in situ. Results given by analysis of the total chlorophyll-a, phosphorus and transparency, indicated eutrophy to hypereutrophy what corresponds with earlyer data on water quality of Lake Sakadaš. In the laboratory, samples from the field were put into plastic trays with tap water, and the remaining material and fauna were sieved through a 60 µ m mesh screen, transferred to plastic bottles, and preserved in a solution containing 96% ethanol, distilled water, 4% formaldehyde, and glycerine with an addition of Rose Bengal. Invertebrates were counted and isolated under a stereozoom-microscope Olympus SZX9. A total of 24 invertebrate groups were recorded with a dominance of Chironomidae larvae, Rotifera, Oligochaeta, and Crustacea (Cladocera and Copepoda). The total of five specimens of L. benedeni were found ; four specimens within the stands of C. demersum and one specimen within the stand of M. spicatum. Is it just a random finding of few individuals or it is a part of a larger population we can not state for sure. However, some authors state C. demersum and M. spicatum as repellent species for Mysidae, so we can assume that there is a larger population of L. benedeni within the stands of other macrophytes in the lake, which are less dense and have a higher concentration of dissolved oxygen what is the preferred habitat for this species. Since L. benedeni is recorded in the Danube River, the Main-Danube Canal and in the Rhine basin, we presume that this “ southern corridor” is the pathway by which L. benedeni came to Kopački rit. From environmental monitoring data of Kopački rit, no important effect from the presence of this species has been recorded yet. However, according to its biological attributes, especially a short life span and generation time, protection of its juveniles, non-specific food preference, and suspension feeding, L. benedeni is characterized as a successful Ponto-Caspian invader, so monitoring of this species, not only in Kopački rit, but in all in Croatian inland waters, is important.

Mysidacea ; Kopački rit ; Ponto-Caspian invader

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