Analysis of the ecology of Anchialine Caves using carbon and nitrogen stable isotopes

Abstract

Carbon and nitrogen stable isotopes were used to investigate the biogeochemical and ecological processes that govern anchialine cave ecosystems in the Yucatan Peninsula, Quintana Roo, Mexico. Anchialine caves are subterranean passages that are partially or totally submerged by stratified fresh and marine waters and are prominent geological features found along many tropical karstic and volcanic coastlines (Iliffe 1992a). Previous biological research on anchialine caves has been limited to taxonomic and biogeographic investigations on the troglobitic (cave limited) fauna, but fundamental questions regarding organic carbon and nitrogen cycling in these systems remain unexplored. This thesis represents the first detailed ecological investigation of an anchialine ecosystem. Stable carbon and nitrogen isotopes were used to discriminate food sources in these caves and to trace their utilization by the troglobites. The isotope data suggest the cave ecosystem is supported by two allochthonous organic sources and possibly one chemoautolithotrophic source. The allochthonous sources are the open water cenotes and the overlying jungle soil, while environmental and stable isotope data imply that nitrification is the chemoautolithotrophic contributor. Conceptual models for carbon and nitrogen cycling among the biotic and abiotic components of the ecosystem were constructed from the data. Suspension feeding troglobitic fauna occupying the same niche exhibited selective and species specific feeding behavior and are herein classified according to feeding type. This evidence for niche partitioning is the first reported for any cave community. the lines of evidence for the 13carbon data, 15 nitrogen data and morphological analysis all converge to the same conclusions. These ideas offer a new paradigm for understanding how this ecosystem operates both locally and throughout the Caribbean region. This understanding may prove fundamental to protecting this sensitive and economically significant resource as development in the Yucatan Peninsula and Caribbean continue.