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

Abstract

ABSTRACT. 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.

Foraminifera and testate amoebae (thecamoebians) in an anchialine cave: Surface distributions from Aktun Ha (Carwash) cave system, Mexico

“…A lack of soil-derived testate amoebae (e.g., Trigonopyxis), the rose Bengal staining of all FA fauna, and the additional taxa present in the cave that are not living in the open-water cenote (e.g., Difflugia) provide supporting evidence for a cave-based provenance of the FA. The dominance of C. aculeata indicates a saline-stressed testate amoeba community, which is consistent with testate amoebae communities found in other oligohaline environments (van Hengstum et al 2008 Pohlman et al 1997;Perry et al 2003).…”

“…These organisms have not yet been systematically examined in phreatic cave systems, with only a brief mention of foraminifera in preliminary test samples from marine phreatic caves (Javaux and Scott 2003). Previous geobiologic research in phreatic caves generally focuses on prokaryotic ecology and food webs of larger taxa (Sarbu et al 1996;Pohlman et al 1997). This study presents the first documentation of testate amoebae and foraminifera from the anchialine cave Aktun Ha (Carwash), Quintana Roo, Mexico (Fig.…”

“…Sangamon interglacial (MIS 5e) foraminifera: Stable isotopes from foraminiferan shells indicate that they were secreted in marine-derived waters, as the d 13 C (25.5%) and d 18 O (22.7%) are more consistent with saline water below modern haloclines on the Yucatan Peninsula (d 13 C DIC 5 23%; Pohlman et al 1997;Reinhardt et al 2003). This observation is expected, as foraminifera colonize marine environments and the halocline geochemically isolates the freshwater lens (precipitation derived) from the intruding marine water (ocean derived; Smart et al 2006).…”

Terrestrial filamentous fungi from Gruta do Catão (São Desidério, Bahia, Northeastern Brazil) show high levels of cellulose degradation

“…Some studies that assessed organic matter decomposition in aquatic and marine sediments in caves showed high microbial activity in the early stages of decomposition that correlated with increased microbial respiration (Fishez, 1991;Galas et al, 1996). Other researchers emphasized the importance of the microbial community as key organisms at the base of the subterranean environment food web and in decomposition processes (Pohlman et al, 1997;Graening and Brown, 2003). However, few researchers have studied the involvement of cellulolytic microorganisms in the decomposition process in cave environments (Semikolennykh et al, 1975;KoilRaj et al, 2012).…”

Dissecting the microbial food web: structure and function in the absence of autotrophs

“…In this cave lagoon, higher levels of ETS activity and bacterial abundance occur despite the lower TOC concentrations. Chemoautotrophy could also be due to filamentous sulfur bacteria, as suggested for other anchihaline cave systems (Pohlman et al 1997); however, this has not been tested in the present study and requires further investigation.…”