A comparative survey of the Erpobdella octoculata (L.) populations in the Afon Crafnant, N. Wales, above and below an input of zinc from mine-waste

Abstract

The life-cycle, growth, and reproductive success of a stream-dwelling Erpobdella octoculata (L.) were studied over a 19-month period at two sites, one above and one below an input of zinc pollution from mine-waste. Samples were collected monthly using quadrats. The blotted wet weight of all leeches was measured. An histological technique was employed to determine sexual maturity. Reproductive success was measured by estimating the numbers of cocoons and number of eggs per cocoon at each site. A wet ashing technique, followed by analysis using flame atomic absorption spectrometry, was used to determine the extent of bioaccumulation of zinc. ‘Total’ zinc and other metals in the waters were similarly analysed.

Differences were found between the populations at the two sites. The life-history of the Erpobdella above the contamination was comparable to that found for other stream-dwelling populations previously studied. Observed differences in densities of leeches between sites in the present and in previous studies by other workers may be due to recorded differences in the abundance of available food. At the polluted site, there was evidence that (a) there was a delay in cocoon deposition and hence hatching of young, (b) the adult leeches produced more misshapened and empty cocoons, (c) no relationship existed between the area of cocoons with eggs and number of eggs present, and (d) the proportion of young to adult leech was smaller at the polluted site. At the polluted site, higher levels of zinc were recorded in the tissues of Erpobdella and there was some evidence for the active intake of zinc by the leech.