Population and Reproductive Dynamics of Nais communis (Oligochaeta: Naididae) from a Wisconsin Limnocrene

Abstract

Population and reproductive dynamics of Nais communis were studied from August 1982 to November 1983 in an Ozaukee Co., Wisconsin, limnocrene. Population density was significantly (P 0.05) correlation of percentage of worms undergoing paratomy to environmental physico-chemical parameters and worm density. Mean aSD doubling time for the field population of N. communis was 13.57 4 13.00 days. INTRODUCTION Naidid oligochaetes are primarily freshwater organisms, although a few species can be found in brackish waters (Brinkhurst and Jamieson, 1971). Large seasonal fluctuations in density have been observed for many naidid species from a variety of habitats (e.g., Dyga and Lubyanov, 1980; Frenzel, 1981, 1983; Learner et al., 1978; Loden, 1981; McElhone, 1978). Often, a complete absence of naidids is noted during certain months (e.g., Frenzel, 1981, 1983; Learner et al., 1978; Loden, 1981). Reproduction in the Naididae is generally asexual by paratomy or fragmentation. Asexual reproduction is observed throughout the majority of the life cycle in most species (Frenzel, 1983; Learner et al., 1978; Loden, 1981; McElhone, 1978; Pfannkuche, 1979, 1981). Sexual reproduction in naidids usually takes place during a particular time of the year and can be short-lived (Frenzel, 1983; Hiltunen, 1967; Poddubnaya, 1968). The purpose of this study was to examine the population and reproductive dynamics of Nais communis Piguet from a Wisconsin limnocrene, a spring discharging into a small basin which overflows into a stream channel. Furthermore, several abiotic and biotic parameters were correlated in an attempt to characterize and quantify the intrinsic and extrinsic factors regulating N. communis population and reproductive parameters. MATERIALS AND METHODS The study site was located between 43?20' and 42?25'N, 87057'30 and 88?30E in the township of Saukville, Ozaukee Co. (Ti iN, R2 1 E), Wisconsin. The limnocrene was roughly circular with a diam of approximately 5 m and a maximum depth of approximately 1.5 m. Physico-chemical parameters of the study site were measured immediately prior to collection of oligochaetes using APHA (1976) methods. Organic content of the substratum was estimated based on volatile matter. Four samples were collected from September 1982-September 1983 at 4-month intervals. Six replicates were measured in each collection by placing substratum in a crucible, drying at 100 C and weighing. These samples were then ashed in a muffle furnace at 600 C, cooled and weighed. The difference between dry weight and ashed weight was volatile matter (Lind, 1979). Naidid oligochaetes were sampled monthly from August 1982-April 1983 and twice monthly from May 1983-November 1983. Naidids were found only among the large floating mats of Spirogyra (Chlorophyta) which covered most of the limnocrene. Spirogyra was present during all months except February and March; hence, naidids were not