Chemical speciation drives hydrothermal vent ecology

The physiology and biochemistry of many taxa inhabiting deep-sea hydrotherm al vents have been elucidated(1-4); however, the physicochemical factors co ntrolling the distribution of these organisms at a given vent site remain a n enigma after 20 years of research(5-11). The chemical speciation of parti cular elements has been suggested as key to controlling biological communit y structure in these extreme aquatic environments(7,11,12). Implementation of electrochemical technology(13,14) has allowed us to make in situ measure ments of chemical speciation at vents located at the East Pacific Rise (9 d egrees 50' N) and on a scale relevant to the biology. Here we report that s ignificant differences in oxygen, iron and sulphur speciation strongly corr elate with the distribution of specific taxa in different microhabitats. In higher temperature (>30 degreesC) microhabitats, the appreciable formation of soluble iron-sulphide molecular clusters markedly reduces the availabil ity of free H2S/ HS- to vent (micro)organisms, thus controlling the availab le habitat.