Aquatic Microannelids (Oligochaeta and Aphanoneura) of Underground Waters of Southeastern New York

Abstract

We investigated the distribution of aquatic oligochaetes and Aeolosoma in the hyporheic zone and other underground habitats in southeastern New York. Twenty-four species of oligochaetes were found, exclusive of the Enchytraeidae, which could not be identified to species. Two of the species, Rhyacodrilus cf. subterraneus and Chaetogaster cf. krasnopolskiae, are reported for the first time from North America. Most of the oligochaetes found in underground waters are widespread in surface waters as well. Annual cycles of abundance and reproductive activity of five abundant taxa are described; these cycles are similar to those of the oligochaetes from lakes and streams. INTRODUCTION The underground waters of North America remain largely unexplored biologically, despite the economic importance of groundwaters, the ecologically significant connections between groundand surface waters (e.g, Hynes, 1983) and the demonstration by European zoologists that underground waters contain rich and often distinctive faunas (Delamare Deboutteville, 1960; Botosaneanu, 1986). Notable exceptions include ecological and evolutionary studies of the macroscopic animals of caves (Culver, 1982; Barr and Holsinger, 1985), investigations into the systematics of some of the larger invertebrates (e.g, Holsinger, 1978; Herschler and Longley, 1986) and an increasing body of ecological works on the hyporheic macrobenthos of streams (Williams, 1984). Reported here are some of the results of a survey of the invertebrate fauna of the shallow groundwaters of southeastern New York. The goals were to describe the composition of the invertebrate communities, the natural history of their dominant members and to make comparisons with invertebrate communities of groundand surface waters elsewhere. Because of technical difficulties in sampling the fauna of underground waters, this study was limited to shallow groundwaters and zones of contact between underground and surface waters, such as gravel bars associated with streams, seeps and springs, rather than deep groundwater. STUDY AREA Most samples came from Dutchess or Ulster counties in southeastern New York. Single sites in nearby Litchfield Counsy, Connecticut, and in Columbia County, New York, were visited. Most of the area is underlain by shales of Ordovician age. Consequently, most surface waters in the region are hard (pH = ca. 8; Ca44 = 0.5 to 1 meq/ liter) and fertile. There are a few outcrops of limestone and, in Ulster County, a large exposure of a hard Silurian quartzite conglomerate that forms the Shawangunk Mountains. Waters on the Shawangunks are soft and acid (pH = 4 to 6; Ca44 = 0.02 to 0.2 meq/liter), in marked contrast to surrounding areas. The entire study area was glaciated. Most samples were taken from gravel bars along or beneath streams (the hyporheic zone, habitat type Li of Botosaneanu, 1986). These sites are fed largely by stream water, because the water temperature in such sites was typically only 1-3 C cooler than stream water during the summer and 1-2 C warmer than stream water during the winter. However, many of these sites receive lateral seepage from nearby slopes as well. Other samples were taken from seeps (habitat N, the hypotelminthorheic, of Botosa'Present address: 65 Linnmoore Street, Hartford, Connecticut 06114.