Katherine A. Roach

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

Photoautotrophs are generally considered to be the base of food webs, and habitats that lack light, such as caves, frequently rely on surface-derived carbon. Here we show, based on analysis of gut contents and stable isotope ratios of tissues (13C:12C and 15N:14N), that sulfur-oxidizing bacteria are directly consumed and assimilated by the fish Poecilia mexicana in a sulfide-rich cave stream in Tabasco state, Mexico. Our results provide evidence of a vertebrate deriving most of its organic carbon and nitrogen from in situ chemoautotrophic production, and reveals the importance of alternative energy production sources supporting animals in extreme environments.

Diel Turnover of Assemblages of Fish and Shrimp on Sandbanks in a Temperate Floodplain River

Abstract Seven sandbanks in the main channel of the Brazos River, Texas, were sampled a total of 35 times during both day (1800–1900 hours) and night (2200–2300 hours) in June and July 2008 to examine the diel turnover of fish assemblages. Day samples had an average of 10.1 species, whereas night samples had an average of 12.9 species. Average abundance (catch per unit effort, here defined as the number of individuals per 10-m seine haul) for day samples was 41.5, compared with 80.5 for night samples. Species richness and abundance were significantly greater on sandbanks at night. Additionally, nonmetric multidimensional scaling analysis and cluster analysis indicated consistent differences in assemblage structure between day and night samples. Most of the diel change in assemblage structure was due to ictalurids and palaemonids (freshwater decapod crustaceans) that were only common on sandbanks nocturnally. Catastomids, clupeids, cyprinids, and poeciliids were present on sandbanks both diurnally and noct...

Autochthony in Karst Spring Food Webs

Trophic dynamics and the relative importance of allochthonous versus autochthonous production in supporting invertebrate consumers have been studied from headwaters to large rivers but rarely in springs. Our goals were to examine spatial and temporal invertebrate feeding pathways in three U.S. karst springs differing in canopy coverage and type (coniferous, open, or deciduous). Based on current food web models for headwaters, we initially hypothesized that: (a) overall biomass production would primarily depend on allochthonous carbon; (b) terrestrial carbon would be most important following leaf litter input; and (c) autochthonous carbon would be responsible for most of the biomass production in open canopy areas. To test these predictions, we analyzed trophic pathways using carbon and nitrogen stable isotopes, biomass measurements, and stoichiometric analyses. Contrary to our initial hypotheses, the proportional contribution of autochthonous carbon to consumer biomass exceeded that of allochthonous in each spring along temporal and spatial scales. Autochthony increased spatially along the gradient between spring sources and lower springbrook reaches and was highest in the open canopy spring. Allochthony increased slightly during the winter following litter fall. Despite the reported importance of periphyton to zoobenthic consumers, macroinvertebrate biomass was primarily supported by moss and water cress in these springs.

Population Structure, Habitat Use, and Diet of Giant Waterbugs in a Sulfidic Cave

Abstract In the southern Mexican Cueva del Azufre, a cave ecosystem with high concentrations of toxic hydrogen sulfide, one species of hemipteran (Belostoma cf. bakeri) has adopted a unique ecological function in that it acts as one of the top predators in the subterranean food web, preying on the abundant cavefish Poecilia mexicana. To date, several aspects of this predator-prey interaction have been explored, but basic questions related to the ecology of the waterbugs remained unstudied. We tested whether there is evidence for reproduction of waterbugs within the cave, which would indicate a self-sustaining population. Furthermore, we investigated the habitat affinities of different size-classes of waterbugs. We infer that waterbugs reproduce inside the cave despite the toxic properties of the water, as evidenced by the presence of nymphs of all sizes and males carrying developing zygotes. We also found size-dependent differences in use of habitat, and particularly small nymphs occupy different microhabitats than larger individuals. Adult waterbugs and large nymphs were most common at sites with cavefish. Small nymphs were rare at these locations, possibly to avoid cannibalism or exploit different resources in other locations. Furthermore, stable-isotope-analysis indicated that waterbugs likely derive their carbon from a combination of fish, dipteran larvae, and chemoautotropic bacteria.

Texas water wars: how politics and scientific uncertainty influence environmental flow decision-making in the Lone Star state

In 2007, Texas passed Senate Bill (SB) 3 mandating formation of science and stakeholder committees to make recommendations on the environmental flows (e-flows) needed to maintain the ecological integrity of river basins through a collaborative process designed to achieve consensus. The Texas Commission on Environmental Quality (TCEQ), the state agency that issues water rights permits, was to promulgate these recommendations and develop e-flow rules. For the first two basins to complete the SB3 process, the Sabine and Neches Basins and Sabine Lake Bay and the Trinity and San Jacinto Basins and Galveston Bay, final e-flow rules did not mimic a natural flow regime, rather, only subsistence flows, one level of base flows, and low flow pulses at a limited number of sites were adopted. In this article, I describe why the SB3 process was derailed for these basins. Science and stakeholder committees were skewed with more members representing short-term economic than ecological and recreational interests in freshwater. Many individuals on the science and stakeholder committees worked for river authorities, semiautonomous state agencies that receive the majority of their funding from surface water sales, and consulting firms that regularly contract with the river authorities. Water rights holders were from the outset distrustful of the SB3 process. There was a high degree of uncertainty associated with e-flow science, and adaptive management was used as justification for making low e-flow recommendations. In the end, TCEQ set environmental flow rules at levels lower than those recommended for protection of environmental benefits by the science teams.

Response of the fish assemblage to a saltwater barrier and paper mill effluent in the Lower Neches River (Texas) during drought

ABSTRACT In 2011, Texas experienced record heat and drought that escalated concerns about environmental flows for rivers. In response to these worries, fishes and water quality were sampled in the Lower Neches River, Texas, from May-August 2012 during continued drought. Potential effects of hydrology on environmental parameters and assemblages of small (seine samples) and large (gillnet samples) fishes were evaluated at multiple locations. Approximately 1 km downstream from the saltwater barrier, paper mill effluent discharges into the river. Salinity was higher and dissolved oxygen lower below the saltwater barrier during low-flow intervals. Fish species richness in seine samples, was higher when the barrier was open, and species richness for both gear types was lowest at sites closest to the paper mill effluent discharge. Overall, species richness was higher at sites below the barrier, with more estuarine and marine species present. When the barrier was closed, richness and abundance of sensitive freshwater species were lower below the barrier. Closure of the barrier during drought results in accumulation of dissolved organic compounds from paper mill effluent and lower dissolved oxygen in the reach below the barrier. To sustain biodiversity in the system, subsistence flows must pass across the saltwater barrier during droughts.