Biodiversity and Biogeography of Hydrothermal Vent Species Thirty Years of Discovery and Investigations

This article has been published inOceanography , Volume 20, Number 1, a quarterly journal of The Oceanography Soci- S P E C I A L I ss U E F E AT U R E ety. Copyright 2007 by The Oceanography Society. All rights reserved. Permission is granted to copy this article for use in teaching and research. Republication, systemmatic reproduction, or collective redistirbution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of The Oceanography Society. Send all correspondence to: [email protected] or Th e Oceanography Society, PO Box 1931, Rockville, MD 20849-1931, USA. Biodiversity and Biogeography of Hydrothermal Vent Species Thirty Years of Discovery and Investigations B Y EvA R AMIREZ- L LO D RA, On the Seaoor, Dierent Species T IMOTH Y M . S H A N K , A nd Thrive in Dierent Regions C HRI S TO P H E R R . G E R M A N Soon after animal communities were discovered around seafl oor hydrothermal vents in 1977, scientists found that vents in various regions are populated by distinct animal species. Scien- Shallow Atlantic vents (800-1700-meter depths) tists have been sorting clues to explain how support dense clusters of mussels The discovery of hydrothermal vents and the unique, often endem- seafl oor populations are related and how on black smoker chimneys. they evolved and diverged over Earth’s • ic fauna that inhabit them represents one of the most extraordinary history. Scientists today recognize dis- scientific discoveries of the latter twentieth century. Not surprising- tinct assemblages of animal species in six major seafl oor regions (colored ly, after just 30 years of study of these remarkable—and extremely dots) along the system of volcanic remote—systems, advances in understanding the animals and mi- mountains and deep-sea trenches that form the borders of Earth’s crobial communities living around hydrothermal vents seem to tectonic plates. But unexplored Deep Atlantic vent communities (2500-3650-me- occur with every fresh expedition to the seafloor. On average, two ocean regions remain critical ter depths) are dominated by missing pieces for assembling swarms of shrimp called Rimica- new species are described each month—a rate of discovery that has the full evolutionary puzzle. •ris exoculata. been sustained over the past 25–30 years (Van Dover et al., 2002; Fisher et al., this issue). Furthermore, the physical, geological, and geochemical features of each part of the ridge system and its asso- ciated hydrothermal-vent structures appear to dictate which nov- el biological species can live where. Only 10 percent of the ridge Central Indian vent com- Northeast Pacifi c vent munities are populated by system has been explored for hydrothermal activity to date (Baker communities are domi- Western Pacifi c-type fauna, but and German, 2004), yet we find different diversity patterns in that nated by “bushes” of skinny tube- also have North Atlantic-type worms called Ridgea piscesae. •shrimp species. small fraction. While it is well known that species composition var- • ies along discrete segments of the global ridge system, this “bio- geographic puzzle” has more pieces missing than pieces in place (Figure 1, Table 1). In this paper, we start with a general picture of the global ridge Western Pacifi c vent com- Eastern Pacifi c vent com- system and hydrothermal environments, then continue with a de- munities are dominated by munities are dominated barnacles and limpets, as well as by tall, fat tubeworms called scription of known biodiversity—including physiological adapta- •hairy gastropods, shown above. E. Paul Oberlander •Riftia pachyptila. tions—and species distribution, which leads into a discussion of the factors that might drive observed biogeography patterns. We Challenger Deep New Zealand Chile Rise Southern Ocean South Atlantic Caribbean Arctic Ocean Unusual life forms may have This region has a full spectrum of This region has a variety of The Drake Passage may act as a Powerful currents and huge In this region, methane seeping The Arctic Ocean has never conclude with a look toward the future, describing the main efforts evolved under conditions of habitats supporting seafl oor life chemosynthetic habitats and key link or bottleneck for larval seafl oor chasms (fracture zones) from the seafl oor also supports had deep connections with Missing extreme pressure in this 11,000- (hydrothermal vents, cold seeps, geological features in close prox- dispersal between the Atlantic may act as barriers blocking the animal communities. Did other major oceans. It may being made to fill the gaps in our knowledge of vent biogeography. Pieces meter-deep trench, the deepest whale carcasses, and wood from imity. How do seafl oor popula- and Pacifi c. Whale carcasses and dispersal of vent larvae and dis- animals migrate between “cold harbor fundamentally part of the world’s oceans. shipwrecks and trees) in close tions diverge or converge at this shipwrecks (such as Shackleton’s connecting vent populations in seeps” and nearby hot vents over different vent animals that proximity. How have species triple junction on the “highway” Endurance) may offer refuges or the North and South Atlantic. evolutionary history? evolved in isolation over the evolved in these diverse settings? of mid-ocean ridges? stepping-stones between vents. past 25 million years. 30 Oceanography Vol. 20, No. 1 Figure 1. Schematic illustration of the global mid-ocean ridge system. Scientists today recognize distinct assemblages of animal species in six major seafloor regions (colored dots) along the system of volcanic mountains and deep-sea trenches that form the borders of Earth’s tectonic plates. However, unexplored ocean regions remain critical missing pieces for assembling the full evolutionary puzzle. From Shank (2004) On the Seaoor, Dierent Species Thrive in Dierent Regions Soon after animal communities were discovered around seafl oor hydrothermal vents in 1977, scientists found that vents in various regions are populated by distinct animal species. Scien- Shallow Atlantic vents (800-1700-meter depths) tists have been sorting clues to explain how support dense clusters of mussels seafl oor populations are related and how on black smoker chimneys. they evolved and diverged over Earth’s • history. Scientists today recognize distinct assemblages of animal species in six major seafl oor regions (colored dots) along the system of volcanic mountains and deep-sea trenches that form the borders of Earth’s tectonic plates. But unexplored Deep Atlantic vent communities (2500-3650-me- ocean regions remain critical ter depths) are dominated by missing pieces for assembling swarms of shrimp called Rimica- the full evolutionary puzzle. •ris exoculata. Central Indian vent com- Northeast Pacifi c vent munities are populated by communities are domi- Western Pacifi c-type fauna, but nated by “bushes” of skinny tube- also have North Atlantic-type •worms called Ridgea piscesae. •shrimp species. Western Pacifi c vent com- Eastern Pacifi c vent communities are dominated by munities are dominated barnacles and limpets, as well as by tall, fat tubeworms called •hairy gastropods, shown above. E. Paul Oberlander •Riftia pachyptila. Challenger Deep New Zealand Chile Rise Southern Ocean South Atlantic Caribbean Arctic Ocean Unusual life forms may have This region has a full spectrum of This region has a variety of The Drake Passage may act as a Powerful currents and huge In this region, methane seeping The Arctic Ocean has never evolved under conditions of habitats supporting seafl oor life chemosynthetic habitats and key link or bottleneck for larval seafl oor chasms (fracture zones) from the seafl oor also supports had deep connections with Missing extreme pressure in this 11,000- (hydrothermal vents, cold seeps, geological features in close prox- dispersal between the Atlantic may act as barriers blocking the animal communities. Did other major oceans. It may Pieces meter-deep trench, the deepest whale carcasses, and wood from imity. How do seafl oor popula- and Pacifi c. Whale carcasses and dispersal of vent larvae and dis- animals migrate between “cold harbor fundamentally part of the world’s oceans. shipwrecks and trees) in close tions diverge or converge at this shipwrecks (such as Shackleton’s connecting vent populations in seeps” and nearby hot vents over different vent animals that proximity. How have species triple junction on the “highway” Endurance) may offer refuges or the North and South Atlantic. evolutionary history? evolved in isolation over the evolved in these diverse settings? of mid-ocean ridges? stepping-stones between vents. past 25 million years. Oceanography March 2007 31 AbIOTIC SETUP OF THE Spreading rates for mid-ocean of the largest and longest-lived hydro- VENT HABITAT: PHysICAL, ridges—the speed at which two tec- thermal vents discovered thus far occur GEOLOGICAL, And tonic plates are being pulled apart from along the slow-spreading Mid-Atlantic GEOCHEMICAL PROPERTIES each other—vary across the whole sys- Ridge. In contrast, fast-spreading cen- Today, satellite technology provides a tem. Ridges can be classified accord- ters exhibit shallow and narrow (order clear visualization of the globe-encircling ing to their spreading rates into ultra- of tens of meters) summit calderas mid-ocean ridge. It is here, at seafloor- slow spreading (< 20 mm yr-1) such where hydrothermal plumes are not spreading centers, that lava wells up from as the Arctic Gakkel Ridge (see Snow constrained. Along the fastest sections Earth’s interior to generate fresh oce- and Edmonds, this issue), slow spread- of the East Pacific Rise, vent sites are so anic crust (see Langmuir and Forsyth, ing (20–50 mm yr-1) such as the Mid- geographically close that they can form this issue). While a small proportion Atlantic Ridge, intermediate spreading a continuum along the ridge axis. These of these volcanic systems are found in (50–90 mm yr-1) such as the Central topographic and physical characteristics back-arc basins close to subduction Indian Ridge, and fast (90–130 mm yr-1) have the potential to affect the patterns zones (see Martinez et al., this issue), the to superfast (130–170 mm yr-1) spread- of faunal distribution (see below).

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