A Serological Study of Prey Selection by Helobdella stagnalis (Hirudinoidea)

Abstract

The feeding of H. stagnalis in the field was investigated using specific rabbit antisera against Chironomidae, Copepoda/Cladocera, Oligochaeta, Amphipoda and Gastropoda. Prey utilization was similar in all 3 field sites, with Chironomidae and Oligochaeta most heavily utilized, Amphipoda and Gastropoda moderately utilized and Copepoda/Cladocera slightly utilized. On any given sampling date all weight classes of H. stagnalis showed the same relative frequency of prey utilization. Prey utilization differed between months with the Chironomidae most heavily utilized in April, and Oligochaeta most heavily utilized in May and June. During other parts of the year there are no significant differences in the pattern of prey utilization. Feeding activity was highest in the spring and summer and lowest in the fall and winter. Annually the 0.0-7.9 mg weight range utilized the Oligochaeta most heavily followed by the Chironomidae. The contribution of the Copepoda/Cladocera to the overall diet was approximately equal to the contribution of the Amphipoda and Gastropoda. The 8.0-20 + mg weight range utilized the Chironomidae most heavily followed by the Oligochaeta. The Copepoda/Cladocera were an insignificant contributor to the overall diet. Food niche overlap values indicated that the weight classes segregated into 2 main groups with a high degree of overlap between the 0.0-7.9 mg weight classes and between the 8.0-20 + mg weight classes. Intra-specific differences in resource utilization may be accounted for in inter-specific overlap comparisons.