A stable isotope study of organic cycling and the ecology of an anchialine cave ecosystem

Stable carbon and nltrogen isotope data, complen~ented wlth other geochemical parameters, were used to Identify the sources of organic mattrr that support the food web of an anchialine cave ecosystem In the northeastern Yucatan Peninsula, Mexlco. A n c h ~a l ~n e caves, coinmon along tropical kal-st~c and volcan~c coastlines, are completely or partially Inundated by highly stratified layers of fresh and marine waters. Stable isotope data from the cave fauna, the particulate organlc matter (POM) from the cenote pool and from the cave, the forest soil and the cave sedlmcnts ~ndicated that at least 3 soul-ces of nutritive organics could support the anchialine food web. Thcsr sources were. (1) soil from the overlying forest; (2) freshwater algae from adjoining open water pools; and (3) chernoautotrophic nitrifying bactei-la living in the cave. Production of nitrate a n d a tlccrcasc in O2 along the halocline provided geochemlcal evidence of nitrification. Stable nitrogen isotope datd defined 2 to 2.5 trophic levels In the food web. Furthermore, it was found that troglobitic (cave-limited) species res~ding In the water column a r e cilpable of preferentially feeding on specific organic reservoirs. This study presents the first extensive description of the ecological and biogeochemical relationships of the anchialine cave ecosystem.