Methane- and dissolved organic carbon-fueled microbial loop supports a tropical subterranean estuary ecosystem.

Subterranean estuaries extend inland into density-stratified coastal carbonate aquifers containing a surprising diversity of endemic animals (mostly crustaceans) within a highly oligotrophic habitat. How complex ecosystems (termed anchialine) thrive in this globally distributed, cryptic environment is poorly understood. Here, we demonstrate that a microbial loop shuttles methane and dissolved organic carbon (DOC) to higher trophic levels of the anchialine food web in the Yucatan Peninsula (Mexico). Methane and DOC production and consumption within the coastal groundwater correspond with a microbial community capable of methanotrophy, heterotrophy, and chemoautotrophy, based on characterization by 16S rRNA gene amplicon sequencing and respiratory quinone composition. Fatty acid and bulk stable carbon isotope values of cave-adapted shrimp suggest that carbon from methanotrophic bacteria comprises 21% of their diet, on average. These findings reveal a heretofore unrecognized subterranean methane sink and contribute to our understanding of the carbon cycle and ecosystem function of karst subterranean estuaries.

Marine lava cave fauna: composition, biogeography, and origins.

An assemblage of endemic cavernicolous marine invertebrates, including taxa found on both sides of the Atlantic Ocean of great phylogenetic age or with affinities to deep sea organisms, inhabits the Jameos del Agua cave, a sea waterflooded Holocene lava tube cave on Lanzarote in the Canary Islands. This marine cave contains both relicts from Tethyan times, such as an apparently new crustacean family belonging to what had been the monotypic class Remipedia, and relicts of groups that are now common only in the deep sea as well as species that occur outside the cave.

Specific glycine uptake by identified neurons of Aplysia californica. II. Biochemistry.

Glycine is taken up twice as rapidly by neurons R3-R14 as by other identified neurons in the Aplysia parietovisceral ganglion. Earlier studies had shown that R3-R14 have much higher glycine concentrations than other Aplysia neurons. Most of the glycine taken up by R3-R14 was biochemically untransformed for at least 1 h following its uptake. Glycine is actively transported into into R3-R14 and other Aplysia neurons by carrier-mediated processes. Glycine uptake by R3-R14 was markedly reduced in the absence of Na+ and in the presence of Hg2+, while these treatments had little effect on glycine uptake by other Aplysia neurons. There appears to be a special glycine uptake system present in R3-R14 and a general glycine uptake system common to all Aplysia neurons. The elevated glycine concentrations and special glycine uptake associated with R3-R14 may indicate that glycine is utilized as a neurotransmitter by those neurons.