A Study of Predation Rates of Leeches on Tubificid Worms Under Laboratory Conditions

The objective of this study was to establish the rate at which predatory leeches consume tubificid worms, at worm population densities simulating those of Cleveland Harbor. Two common species of leeches from Lake Erie were studied, Helobdella stagnalis and Erpobdella punctata. A mixed population of tubificids, mostly Limnodrilus hojfmeisteri, Limnodrilus cervix and Peloscolex multisetosus were used for prey. The mean consumption rate for Helobdella stagnalis was 0.57 tubificids/leech/day. The mean consumption rate of Erpobdella punctata was 1.78 tubificids/leech/day. Previous studies of the benthos of the Cleveland Harbor reported 11 Helobdella stagnalis per square meter of bottom area. Using this number, specimens of Helobdella stagnalis were estimated to consume 6.27 tubificids per square meter of bottom area per day at 23.5° C. OHIO J. SCI. 76(4): 164, 1976 Predation or consuming other organisms is one of several means by which organisms interact to transmit energy. An unstudied, but possibly important, link in the Lake Erie food web is the relationship between tubificid worms and various species of predatory leeches. Very few studies concerning the environment and the behavior of various species of leeches have been done. Brinkhurst and Jamieson (1971), in referring to polluted lakes and streams, suggest that predatory leeches may be "the key to the relatively small numbers of tubificids present at ony one time." A more specific study on the biology of the leech Erpobdella punctata states that the leech "was often observed eating various types of meat and live individuals of several small species of earthworms" (Sawyer, 1970). The objective of this study was to establish the actual rates at which predator}' leeches consume tubificid worms at worm population densities simulating those of Cleveland Harbor. Estimations of energy flux rates for specific steps in the food web can be based on studies such as this. The results of this study may also aid in determining whether or not tubificids may be significant in coniManuscript received April 21, 1975 and in revised form April 14, 1970 (#75-24). centrating toxic elements in the sediments into the food web. METHODS AND MATERIALS Bottom samples containing benthos were collected from Station 4 (Rolan, 1973) at the east end of Cleveland Harbor, using a ponar grab. The mud samples were stored in large aquaria and the tubificids were removed as needed. A U.S. No. 30 sieve was used to separate the benthos from the mud. Cultures of tubificids and leeches were maintained throughout the study. Bacteria were isolated from the mud and mass cultured on nutrient agar. A quantity of mud was autoclaved to kill any tubificid cocoons, which might hatch during the test period and distort the results. The mud was then innoculated with the bacteria previously cultured in order to restore the food supply for the tubificids. A recent study by Rolan (1973) on the benthos of Cleveland Harbor determined that there were approximately 28,000 tubificids per square meter, or 2.8 per square centimeter, in the area from which the samples were obtained. This population density was selected for the experimental chambers. Beakers of 250 ml (bottom surface area, 33.2 sq cm) were used as test containers, each contained 4 cm of mud and about 4 cm of water at room temperature (23.5°C). To each test container, 100 tubificids and one leech were added. When sorting the tubificids for each test container, great care was taken in choosing medium size tubificids (4O-(5O mm in length) in order to avoid large tubificids which might slow consumption rates or small tubificids which could easily be missed when recounting. To determine natural death rate or loss from handling, controls were established with 100 tubificids but no leeches. The