The Distribution and Habitat Preferences of Freshwater Sponges (Porifera) in Four Southern Lake Michigan Harbors

Article excerpt

ABSTRACT.-Three species of freshwater sponges (Porifera): Spongilla lacustris (Linneaus), Eunapius fragilis (Leidy) and Ephydatia muelleri (Lieberkuhn) were identified in four southern Lake Michigan harbors: Belmont (IL), East Chicago (IN), Michigan City (IN) and St. Joseph (MI). Samples were collected from artificial substrates and are the first report of sponges in three of the harbors. Sponge cover on revetment walls, stone rip-rap and wood pier posts ranged up to 13% of the available surface area, whereas no sponges were growing on the soft silt bottom. Eunapius fragilis appeared to be the most common species. An angle-- density relationship was observed for sponges growing on the stone rip-rap in Michigan City and East Chicago; as the orientation of the attachment substrate changed from horizontal to vertical, the density of sponges increased.

INTRODUCTION

The distribution and taxonomy of freshwater sponges (Porifera: Spongillidae) in North America has not received widespread attention, although some notable works exist for regions surrounding the Great Lakes (Potts, 1887; Smith, 1921; Old, 1931;Jewell, 1935; Neidhoefer, 1940; Ricciardi and Reiswig, 1993; Lauer and Spacie, 1996). In northern Wisconsin 10 species of sponges were found in 103 of the 127 lakes and 15 of the 17 streams examined (Jewell 1935). Old (1931) found twelve sponge species among the 84 lakes, 42 streams and 19 ponds he surveyed in Michigan. Ricciardi and Reiswig (1993) examined over 1500 specimens from five provinces in eastern Canada and demonstrated that sponges were more ubiquitous than previously indicated. They found fifteen different species and suggested that additional taxa could be identified in this geographical region with further study. Bailey et al. (1995) showed sponges were common at 36 of 50 stations throughout four Great Lakes (Ontario, Erie, Huron and Superior) but failed to identify them beyond class. Sponges may be more common than the available scientific literature indicates and the absence or limited ranges of some species may not reflect their true zoogeographical distribution, but rather a lack of observation (Frost, 1991). Only limited information exists describing sponge distribution and abundance for Lake Michigan (Early et al., 1996; Lauer and Spacie, 1996; Early and Glonek, 1999), despite the vast amount of scientific information that has been gathered on this lake.

Acknowledgments.-The authors wish to acknowledge the Illinois-Indiana Sea Grant program and Sigma Xi for financial assistance to one author (TEL).

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