Temporal Community Structure and Biodiversity of Malacofauna from an Urban New Jersey Pond

Robert S. Prezant and Eric J. Chapman

Passaic River Institute, Montclair State University, Montclair, NJ 07043, phone 973-655-5108, fax 973-655-4390,

prezantr@mail.montclair.edu and chapmane@mail.montclair.edu

http://www.csam.montclair.edu/biology/bioweb/robert_prezant,_ph.d._profe.html

Urban waterways are often subject to intense environmental pressures from road and storm-water run-off, erosion, trash dumping, high organic loads, sewer overflow, and community over-use. Barbour’s Pond, a 55,000 m² pond on Garrett Mountain and within the Passaic River watershed, is located in Passaic County, northern New Jersey, one of the densest urban regions in the United States. Despite its small size and the surrounding urban sprawl, this pond, in a heavily used public park, holds 18 species of molluscs, the most abundant being the gastropods Amnicola limosa, Helisoma anceps, and Physa acuta and the small bivalves Pisidium casertanum and Pisidium henslowanum. The pond has diverse habitats that range from very soft muds, to small Typha marshes, to steep granite rock fronts. Monthly samples from the eastern side of the pond from March 2004 through March 2005 found the highest diversity in shallow waters in March and December 2004 and January 2005. Total molluscan abundance was greatest in July and November 2004, possibly reflecting young adults from late spring and autumn population expansions. May 2004 showed the lowest diversity and abundance. There is a strong correlation between frequency of occurrence and relative abundance. Using Bray-Curtis Similarity Indices, we determined small groupings of temporal communities (see below). The two species of Pisidium were always found together and usually in the presence of Amnicola limosa. These three taxa were found with Physa acuta about 90% of the time and all four with Helisoma anceps and Goniobasis virginica over 80% of the time. Amnicola limosa was found in every month except May 2004; Helisoma anceps every month except February 2005. These temporal communities could be correlated with specific environmental changes currently being examined.