Diverse styles of submarine venting on the ultraslow spreading Mid-Cayman Rise.

Thirty years after the first discovery of high-temperature submarine venting, the vast majority of the global mid-ocean ridge remains unexplored for hydrothermal activity. Of particular interest are the world's ultraslow spreading ridges that were the last to be demonstrated to host high-temperature venting but may host systems particularly relevant to prebiotic chemistry and the origins of life. Here we report evidence for previously unknown, diverse, and very deep hydrothermal vents along the approximately 110 km long, ultraslow spreading Mid-Cayman Rise (MCR). Our data indicate that the MCR hosts at least three discrete hydrothermal sites, each representing a different type of water-rock interaction, including both mafic and ultramafic systems and, at approximately 5,000 m, the deepest known hydrothermal vent. Although submarine hydrothermal circulation, in which seawater percolates through and reacts with host lithologies, occurs on all mid-ocean ridges, the diversity of vent types identified here and their relative geographic isolation make the MCR unique in the oceans. These new sites offer prospects for an expanded range of vent-fluid compositions, varieties of abiotic organic chemical synthesis and extremophile microorganisms, and unparalleled faunal biodiversity--all in close proximity.

Oxidative iron species and ocean challenges: a perspective.

The idea of using oxidative iron (Fe(6+)) to manage fouling and potentially invasive and pathogenic species in ballast water has merit and is attractive when viewed in the broadest context. Ferrate (Fe(6+)) has potential in ballast water management because it reduces a complex global problem to a single issue, viz.how to dispose of the waste which is predominantly Fe(3+). Waste iron disposal must be considered carefully because iron limits photosynthesis in oligotrophic oceans, alters physiological processes in bacteria and animals, produces reactive oxygen species, causes nitrosative stress and increased availability enhances the virulence of pathogenic bacteria. The case is made that the oxidative iron waste should be recycled rather than discharged into the ocean.

Evolution and biogeography of deep-sea vent and seep invertebrates.

Deep-sea hydrothermal vents and cold seeps are submarine springs where nutrient-rich fluids emanate from the sea floor. Vent and seep ecosystems occur in a variety of geological settings throughout the global ocean and support food webs based on chemoautotrophic primary production. Most vent and seep invertebrates arrive at suitable habitats as larvae dispersed by deep-ocean currents. The recent evolution of many vent and seep invertebrate species (<100 million years ago) suggests that Cenozoic tectonic history and oceanic circulation patterns have been important in defining contemporary biogeographic patterns.

Biogeography and ecological setting of Indian Ocean hydrothermal vents.

Within the endemic invertebrate faunas of hydrothermal vents, five biogeographic provinces are recognized. Invertebrates at two Indian Ocean vent fields (Kairei and Edmond) belong to a sixth province, despite ecological settings and invertebrate-bacterial symbioses similar to those of both western Pacific and Atlantic vents. Most organisms found at these Indian Ocean vent fields have evolutionary affinities with western Pacific vent faunas, but a shrimp that ecologically dominates Indian Ocean vents closely resembles its Mid-Atlantic counterpart. These findings contribute to a global assessment of the biogeography of chemosynthetic faunas and indicate that the Indian Ocean vent community follows asymmetric assembly rules biased toward Pacific evolutionary alliances.

Bacterial photosynthesis in surface waters of the open ocean.

The oxidation of the global ocean by cyanobacterial oxygenic photosynthesis, about 2,100 Myr ago, is presumed to have limited anoxygenic bacterial photosynthesis to oceanic regions that are both anoxic and illuminated. The discovery of oxygen-requiring photosynthetic bacteria about 20 years ago changed this notion, indicating that anoxygenic bacterial photosynthesis could persist under oxidizing conditions. However, the distribution of aerobic photosynthetic bacteria in the world oceans, their photosynthetic competence and their relationship to oxygenic photoautotrophs on global scales are unknown. Here we report the first biophysical evidence demonstrating that aerobic bacterial photosynthesis is widespread in tropical surface waters of the eastern Pacific Ocean and in temperate coastal waters of the northwestern Atlantic. Our results indicate that these organisms account for 2-5% of the photosynthetic electron transport in the upper ocean.

Sulfide as a Chemical Stimulus for Deep-Sea Hydrothermal Vent Shrimp.

Organisms dependent on deep-sea hydrothermal vents for their existence face extinction when their vents expire, unless they can establish populations on neighboring vents or on new vent sites. Propagules, including larvae and motile adults, are readily dispersed broadly by seafloor currents, but how they recognize active hydrothermal sites is problematical. Compelling evidence that vent organisms can find and colonize hydrothermal sites has been provided by a series of observations on the East Pacific Rise (1). New hydrothermal vents created there following a volcanic eruption on the seafloor in March 1991 were colonized by sessile invertebrates in less than one year. On the Mid-Atlantic Ridge, shrimp that normally cluster on sulfide surfaces have been observed to swim directly back to the surfaces when displaced from them. How do vent animals locate new or existing vents? Passive transport by currents (2) or active swimming without guidance by some physical cue is not likely to result in success (3). Chemicals present in hydrothermal fluids have been proposed as attractants. We provide the first evidence of a chemosensory response in a vent invertebrate to sulfides, which are prevalent in vent fluids and provide the energy,for chemosynthetic primary production at vents.

In Situ Spawning of Hydrothermal Vent Tubeworms (Riftia pachyptila).

Riftia pachyptila, the giant vestimentiferan tubeworm, dominates the biomass of many hydrothermal vent sites in the Gulf of California (Guaymas Basin) and on the East Pacific Rise and Galapagos Spreading Center (1). The worms typically occur in large clumps or thickets as mixed populations of males andfemales. On a dive series made by the submersible Alvin in the vicinity of 9{deg}50'N on the East Pacific Rise, I observed spawning tubeworms while I was sampling associated fauna. This note presents a brief account of the spawning activity.

Biogeography of hydrothermal vent communities along seafloor spreading centers.

Compared to terrestrial and shallow-water habitats, deep-sea hydrothermal vents are unique environments characterized by their local insularity, global distribution, individual ephemerality, collective geological longevity, geochemical homogeneity, and their physical and energetic isolation from the catastrophic events implicated in the extinction and speciation of terrestrial and shallow-water forms. Development of vent communities has thus occurred in novel biogeographical contexts that challenge our ability to understand evolutionary processes in the deep sea. Recent field work by French, Canadian, German, Japanese and American scientists has revealed intriguing patterns in the taxonomic composition and distribution of vent organisms at geographically disjunct study sites.

A novel eye in 'eyeless' shrimp from hydrothermal vents of the Mid-Atlantic Ridge.

Rimicaris exoculata is a shrimp that swarms over high-temperature (350 degrees C) sulphide chimneys at Mid-Atlantic Ridge hydrothermal fields (3,600 m). This shrimp lacks an externally differentiated eye, having instead a pair of large organs within the cephalothorax immediately beneath the dorsal surface of the transparent carapace, connected by large nerve tracts to the supraesophageal ganglion. These organs contain a visual pigment with an absorption spectrum characteristic of rhodopsin. Ultrastructural evidence for degraded rhabdomeral material suggests the presence of photoreceptors. No image-forming optics are associated with the organs. We interpret these organs as being eyes adapted for detection of low-level illumination and suggest that they evolved in response to a source of radiation associated with the environment of hydrothermal vents.