Food Limitation in Lake-Dwelling Leeches: Field Experiments

The leeches, Erpobdella octoculata, Glossiphonia complanata and Helobdella stagnalis, and their prey were manipulated inside experimental enclosures, matched by controls, erected on the stony shore of an eutrophic, English lake. Five separate manipulations were performed: the addition of tubificid oligochaetes, the addition of snails, the increase in numbers of G. complanata and H. stagnalis, the increase in numbers of E. octoculata, and the reduction in numbers of all three leech species. All invertebrates were sampled, using trays buried in the substratum, in early March, prior to leech reproduction, in July and in late October/early November when breeding had ceased. Leech manipulations were executed immediately after the first sampling of invertebrates, when food addition, at fortnightly intervals, also commenced