Life on the edge: hydrogen sulfide and the fish communities of a Mexican cave and surrounding waters

Abstract

Most eucaryotic organisms classified as living in an extreme habitat are invertebrates. Here we report of a fish living in a Mexican cave (Cueva del Azufre) that is rich in highly toxic H(2)S. We compared the water chemistry and fish communities of the cave and several nearby surface streams. Our study revealed high concentrations of H(2)S in the cave and its outflow (El Azufre). The concentrations of H(2)S reach more than 300 muM inside the cave, which are acutely toxic for most fishes. In both sulfidic habitats, the diversity of fishes was heavily reduced, and Poecilia mexicana was the dominant species indicating that the presence of H(2)S has an all-or-none effect, permitting only few species to survive in sulfidic habitats. Compared to habitats without H(2)S, P. mexicana from the cave and the outflow have a significantly lower body condition. Although there are microhabitats with varying concentrations of H(2)S within the cave, we could not find a higher fish density in areas with lower concentrations of H(2)S. We discuss that P. mexicana is one of the few extremophile vertebrates. Our study supports the idea that extreme habitats lead to an impoverished species diversity.

Reduction of Energetic Demands through Modification of Body Size and Routine Metabolic Rates in Extremophile Fish

“…To compare size distributions in the four habitat types, we assembled data from previous studies (Tobler 2008;Tobler et al 2006Tobler et al , 2008aTobler et al , 2008bTobler et al , 2008c as well as several unpublished projects. In all cases, fish were collected using seines (4 m long, 4 mm mesh width), sexed, and weighed (blotted wet weight to the closest 0.01 g).…”

“…Fish were tested at 207, 257, or 307C, to test for potential population differences in the temperature dependence of metabolic rates. The four habitat types investigated here vary in both mean temperatures and temperature variability (with extreme environments typically exhibiting higher averages and lower variability), and the chosen temperatures reflect the range that P. mexicana typically encounter in natural habitats (Tobler et al 2006(Tobler et al , 2008a.…”

“…Accordingly, some organisms adapted to sulfidic environments have been documented to increase energy consumption in the presence of H 2 S (Gorodezky and Childress 1994;Schneider 1996). Clearly, exposure to extreme environmental conditions impacts organismal energy budgets through reduced energy availability, reduced ability for energy acquisition, and/or increased organismal maintenance costs, which is reflected in P. mexicana from both sulfidic and cave environments consistently having a lower body condition than fish from nonsulfidic surface habitats (assessed through abdominal distension [Plath et al 2005], body fat content [Tobler 2008], and mass-length relationships [Tobler et al 2006]). Consequently, adaptation to these environments should be linked to energy metabolism, and we hypothesized that extremophile populations should be selected for reductions in overall energy demand.…”

Patterns of Macroinvertebrate and Fish Diversity in Freshwater Sulphide Springs

“…While records for the macroinvertebrate fauna in surface sulphide springs remain fragmentary, it is important to note that such springs are also present in a variety of subterranean habitats, including the Movile Cave (Romania) [93], Frasassi Cave and Grotta de Fiume Coperto (Italy) [103,104], Villa Luz Cave (Mexico) [105,106], Lower Kane Cave (Wyoming) [107], and the Edwards Aquifer (Texas) [108]. The faunal communities of these subterranean aquatic habitats with elevated H 2 S concentrations have recently been reviewed by Summers Engel [109].…”

Hydrogen sulfide, bacteria, and fish: a unique, subterranean food chain

“…The sulfidic surface and cave streams are characterized by dissolved H 2 S concentrations of up to 300 lmol/L and low concentrations of dissolved oxygen (Hose et al 2000, Tobler et al 2006, Plath et al 2010. The non-sulfidic surface and cave streams have H 2 S concentrations below the detection threshold and dissolved oxygen concentrations of up to 4.3 mg/L (Tobler et al 2006, Plath et al 2010). In the surface stream habitats, samples were collected along approximately 50 m of stream, which included both riffle and pool habitats.…”