AN ISOTOPIC EXAMINATION OF CAVE, SPRING AND EPIGEAN TROPHIC STRUCTURES IN MAMMOTH CAVE NATIONAL PARK Name: Zacchaeus Greg Compson Date: October 15, 2004 Pages: 56 Directed by: Philip Lienesch, Doug McElroy, Michael Stokes and Richard Bowker Department of Biology Western Kentucky University Abstract High-water events in the Green River result in flow-reversals which flush native and introduced fishes into Mammoth Cave, posing threats to indigenous cave fauna. However, little is known about the trophic interactions between cave and epigean aquatic systems or their connectivity via natural springs. The purpose of this study was to use stable isotopes of C and N to describe and compare the trophic structure of epigean, spring and cave aquatic systems within Mammoth Cave National Park. Fourteen sites were sampled from fall 2002 to fall 2003; four in the Green River (epigean), four in spring-heads, and three inside Mammoth Cave. Two a priori hypotheses were tested: fish and invertebrates living in spring heads should express delta 13C values intermediate to those of organisms in cave and epigean aquatic systems and overall trophic levels in cave and spring samples should be compressed, showing lower delta15N values compared to epigean sites. Though cave and spring systems were dominated by allochthonous leaf litter, characteristic of headwater streams, the epigean system was also largely dependent on detrital inputs. Primary differences in delta13C were seen at higher trophic levels, particularly in top consumers such as Lepomis species, where delta13C values decreased from epigean to spring to cave habitats. Though all three habitats supported a similar number of trophic levels (N: 5), the trophic structure was compressed in cave and spring compared to epigean habitats. This trend, however, was obfuscated by delta15N values of accidental species in caves, which tended to be enriched, even when compared to epigean signals. This was attributed to either trophic enrichment from yolk sacs or starvation and subsequent self-processing. Overall, spring trophic structure was found to be intermediate to cave and epigean trophic structures in terms of delta13C values of upper-level fish consumers, but spring trophic structure was more similar to the cave trophic structure in terms of delta15N values, excluding cave accidentals.

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