DIET NICHE RELATIONSHIPS AMONG EARLY-LIFE STAGES OF FISH IN GERMAN ESTUARIES

Diet composition, selectivity, food niche width and food niche overlap of early life stages of fishes were studied in the Barther Bodden sys tem and in the Weser arid Elbe estuaries during spring and summer from 1987 to 1991 and from 1993 to 1994. Larvae of perch (Perca fluviatili s) and roach (Rutilus rutilus) dominated in the Barther Bodden. Herrin g (Clupea harengus) and perch were the dominant species in the Barther Strom. Smelt (Osmerus eperlanus) was the most common species in the E lbe estuary. Sprat (Sprattus sprattus) was of most importance in the W eser estuary. The dominant prey of fish larvae were copepodids, naupli i and eggs of Eurytemora affinis. The highest food niche width was obs erved for nine-spined stickleback (Pungitius pungitius), ruffe (Gymnoc ephalus cernuus), three-spined stickleback (Gasterosteus aculeatus) an d perch in the Barther Bodden. Negative selectivity indices indicated that populations of rotifers were scarcely influenced by predation by fish larvae. In contrast, E. affinis was preferred by early life stage s of fish. Positive relationships were estimated between maximum prey lengths and predator lengths of different fish species. Key species wi th regard to niche overlap were nine-spined stickleback, roach, three- spined stickleback and perch in the Barther Bodden, perch and herring in the Barther Strom, herring and three-spined stickleback in the Elbe estuary, and sprat and common goby (Pomatoschistus microps) in the We ser estuary. High geographical overlap between fish species occurred i n the Elbe estuary and Barther Bodden, whereas high diet overlap was e stimated for both the Weser estuary and Barther Strom.