Baker Et Al. 2010
Total Page：16
File Type：pdf, Size：1020Kb
Chapter 9 Biogeography, Ecology, and Vulnerability of Chemosynthetic Ecosystems in the Deep Sea Maria C. Baker1, Eva Z. Ramirez-Llodra2, Paul A. Tyler1, Christopher R. German3, Antje Boetius4, Erik E. Cordes5, Nicole Dubilier4, Charles R. Fisher6, Lisa A. Levin7, Anna Metaxas8, Ashley A. Rowden9, Ricardo S. Santos10, Tim M. Shank3, Cindy L. Van Dover11, Craig M. Young12, Anders Warén13 1School of Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton, UK 2Institut de Ciències del Mar, Barcelona, Spain 3Woods Hole Oceanographic Institution, Woods Hole, Massachusetts, USA 4Max Planck Institute for Microbiology, Bremen, Germany 5Department of Biology, Temple University, Philadelphia, Pennsylvania, USA 6Muller Laboratory, Pennsylvania State University, Pennsylvania, USA 7Integrative Oceanography Division, Scripps Institution of Oceanography, La Jolla, California, USA 8Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada 9National Institute of Water and Atmospheric Research, Wellington, New Zealand 10Department of Oceanography and Fisheries, University of the Azores, Horta, Portugal 11Nicholas School of the Environment and Earth Sciences, Duke University Marine Laboratory, Beaufort, North Carolina, USA 12Oregon Institute of Marine Biology, Charleston, Oregon, USA 13Department of Invertebrate Zoology, Swedish Museum of Natural History, Stockholm, Sweden phylogeographic relationships among different chemosyn- 9.1 Life Based on Energy of thetic habitats, evidence of conduits and barriers to gene the Deep flow among those habitats, and environmental factors that control diversity and distribution of chemosynthetically driven fauna. Investigations of chemosynthetic environ- 9.1.1 A spectacular discovery ments in the deep sea span just three decades, owing to This chapter is based upon research and findings relating their relatively recent discovery. Despite the excitement of to the Census of Marine Life ChEss project, which addresses many discoveries in the deep ocean since the early nine- the biogeography of deep-water chemosynthetically driven teenth century, nothing could have prepared the scientific ecosystems (www.noc.soton.ac.uk/chess). This project has community for the discovery made in the late 1970s, which been motivated largely by scientific questions concerning would challenge some fundamental principles of our under- standing of life on Earth. Deep hot water venting was observed for the first time in 1977 on the Galápagos Rift, Life in the World’s Oceans, edited by Alasdair D. McIntyre in the eastern Pacific. To the astonishment of the deep-sea © 2010 by Blackwell Publishing Ltd. explorers of the time, a prolific community of bizarre L 161 McIntyre—Life in the World’s Oceans c09.indd 161 6/21/2010 8:44:52 PM 162 Part II Oceans Present – Geographic Realms animals were seen to be living in close proximity to these ecosystems, where abundances and biomass of fauna are vents (Corliss et al. 1979). Giant tubeworms and huge much greater than on the surrounding deep-sea floor. white clams were among the inhabitants, forming oases of Eight years after the discovery of hydrothermal vent life in the otherwise apparently uninhabited deep seafloor communities, the first cold seep communities were described (Figs. 9.1A, B, and C). Most of the creatures first observed in the Gulf of Mexico (Paull et al. 1984). Cold seeps occur on vents were totally new to science, and it was a complete in both passive and active (subduction) margins. Seep habi- mystery as to what these animals were using for an energy tats are characterized by upward flux of cold fluids enriched source in the absence of sunlight and in the presence of in methane and often also other hydrocarbons, as well as toxic levels of hydrogen sulfide and heavy metals. a high concentration of sulfide in the sediments (Sibuet & Olu 1998; Levin 2005). The first observations of seep com- munities showed a fauna and trophic ecology similar to that 9.1.2 Chemosynthetic of hydrothermal vents at higher taxonomical levels (Figs. ecosystems: where energy from 9.1D and E), but with dissimilarities in terms of species and the deep seabed is the source of life community structure. The energetic input to chemosynthetic ecosystems in the Until the discovery of hydrothermal vents, benthic deep-sea deep sea can also derive from photosynthesis as in the case ecosystems were assumed to be entirely heterotrophic, com- of large organic falls to the seafloor, including kelp, wood, pletely dependent on the input of sedimented organic matter large fish, or whales. After a serendipitous discovery of a produced in the euphotic surface layers from photosynthesis whale fall in 1989, the first links between vents, seeps, and (Gage 2003) and, in the absence of sunlight, completely the reducing ecosystems at large organic falls were made devoid of any in situ primary productivity. The deep sea is, (Smith & Baco 2003). Bones of whales consist of up to 60% in general, a food-poor environment with low secondary lipids that, when degraded by microbes, produce reduced productivity and biomass. In 1890, Sergei Nikolaevich chemical compounds similar to those emanating from vents Vinogradskii proposed a novel life process called chemosyn- and seeps (Fig. 9.1F) (Treude et al. 2009). Another deep- thesis, which showed that some microbes have the ability to water reducing environment is created where oxygen mini- live solely on inorganic chemicals. Almost 90 years later the mum zones (OMZs, with oxygen concentrations below discovery of hydrothermal vents provided stunning new 0.5 ml l−1 or 22 µM) intercept continental margins, occur- insight into the extent to which microbial primary produc- ring mainly beneath regions of intensive upwelling (Helly & tivity by chemosynthesis can maintain biomass-rich meta- Levin 2004) (Figs. 9.1G and H). Only in the second half of zoan communities with complex trophic structure in an the twentieth century was it understood that OMZs support otherwise food-poor deep sea (Jannasch & Mottl 1985). extensive autotrophic bacterial mats (Gallardo 1963, 1977; Hydrothermal vents are found on mid-ocean ridges and in Sanders 1969; Fossing et al. 1995; Gallardo & Espinoza back arc basins where deep-water volcanic chains form new 2007) and, in some instances, fauna with a trophic ecology ocean floor (reviewed by Van Dover 2000; Tunnicliffeet al. similar to that of vents and seeps (reviewed in Levin 2003). 2003). The super-heated fluid (up to 407 °C) emanating from vents is charged with metals and sulfur. Microbes in these habitats obtain energy from the oxidation of hydro- 9.1.3 Adaptations to an gen, hydrogen sulfide, or methane from the vent fluid. The “extreme” environment microbes can be found either suspended in the water column or forming mats on different substrata, populating seafloor Steep gradients of temperature and chemistry combined sediments and ocean crust, or living in symbiosis with with a high disturbance regime, caused by waxing and several major animal taxa (Dubilier et al. 2008; Petersen & waning of fluid flow and other processes during the life cycle Dubilier 2009). By microbial mediation, the rich source of of a hydrothermal vent, result in low diversity communities chemical energy supplied from the deep ocean interior with only a few mega- and macrofauna species dominating through vents allows the development of densely populated any given habitat (Van Dover & Trask 2001; Turnipseed Fig. 9.1 Hydrothermal vent (A, B, and C), cold seep (D and E), whale fall (F), and OMZ communities (G and H). (A) Zoarcid fish over a Riftia pachyptila tubeworm community in EPR vents; (B) Bathymodiolus mussel community in EPR vents (© Stephen Low Productions, Woods Hole Oceanographic Institution, E. Kristof, the National Geographic Society, and R. A. Lutz, Rutgers University). (C) Dense aggregations of the MAR vent shrimp Rimicaris exoculata (© Missao Sehama, 2002 (funded by FCT, PDCTM 1999/MAR/15281), photographs made by VICTOR6000/IFREMER). (D) Lamellibrachia tubeworms from the Gulf of Mexico cold seeps (© Charles Fisher, Penn State University). (E) Bathymodiolus mussel bed by a brine pool in the Gulf of Mexico cold seeps (© Stéphane Hourdez, Penn State University/Station Biologique de Roscoff). (F) Skeleton of a whale fall covered by bacteria (© Craig Smith, University of Hawaii). (G) Ophiuroids on an OMZ in the Indian margin (© Hiroshi Kitazato, JAMSTEC, and NIOO). (H) Galatheid crabs on an OMZ on the upper slopes of Volcano 7, off Acapulco, Mexico (©Lisa Levin, Scripps Institution of Oceanography). L McIntyre—Life in the World’s Oceans c09.indd 162 6/21/2010 8:44:52 PM Chapter 9 Biogeography, Ecology, and Vulnerability of Chemosynthetic Ecosystems in the Deep Sea 163 (A) (B) (C) (D) (E) (F) (G) (H) L McIntyre—Life in the World’s Oceans c09.indd 163 6/21/2010 8:44:58 PM 164 Part II Oceans Present – Geographic Realms et al. 2003; Dreyer et al. 2005). The proportion of extremely genus Bathymodiolus generally widespread at vents and rare species (fewer than five individuals in pooled samples seeps but largely absent from seeps and vents in the north- containing tens of thousands of individuals from the same eastern Pacific Ocean? In 2002, at the onset of the ChEss vent habitat) is typically high, in the order of 50% of the project, biological investigations of known vent sites pro- entire species list for a given quantitative sampling effort vided enough data to describe six biogeographic provinces (C.L. Van Dover, unpublished observation). for vent species (Van Dover et al. 2002) and identified Deep-water chemosynthetic habitats have also been several gaps that needed to be closed to complete the “bio- shown to have a high degree of species endemicity in each geographical puzzle of seafloor life” (Shank 2004) (Fig. 9.2). habitat: 70% in vents (Tunnicliffe et al. 1998; Desbruyères In contrast, cold seep and whale fall communities appear to et al. 2006a), about 40% in seeps both for mega epifauna share many of the key taxa across all oceans. The ChEss (Bergquist et al.