Document: JAN-3-84-11

Applications of stable isotopes for understanding anthropogenic effects of aquatic food webs in Cuatro Cienegas, Mexico.

MARKS, J.* ¹, B.HUNGATE ¹ and D.HENDRICKSON ²

Northern Arizona University, Flagstaff, AZ 86011 USA ¹
University of Texas, USA ²

Abstract:
Cuatro Cienegas, a protected area in northern Mexico has over 200 freshwater habitats that host an unusual number of endemic fish and snails. The two major threats to the native species are water extraction and invading species. We used stable isotopes o to compare food web structure in pristine versus disturbed habitats with particular focus on Cichlasoma minckleyi, an endemic cichlid, which is widespread in the basin and has a trophic polymorphisim. The two common morphs, (detritivore and molluscivore), differ in pharyngeal tooth morphology. Diet studies suggest strong overlap between the morphs. We used stable isotopes to test whether the morphs have different diets. Stable isotopes offer two advantages over diet studies by allowing for large non-destructive samples and providing a temporally integrated assessment of diet. We collected fish from eight habitats and determined their morphology using an otoscope and took a small fin clipping for isotope analysis. Morphs differed in d¹³C, indicating that they have different food sources, but did not differ in d¹⁵N, suggesting that they occupy similar trophic positions. Hemichromis sp. an invading cichlid had similar d¹⁵N values as C. minckleyi but differed in d¹³C. Differences in isotope values among sites did not correlate with the Hemichromis invasion. Analysis of museum specimens of an endemic pupfish show reductions in d¹⁵N in disturbed but not pristine habitats.

Keywords: freshwater food webs, conservation, stable isotopes

This abstract is being presented at: 9:00 AM in session:
Oral Session #55: Invertebrates in Streams: Foodwebs.