Seamount and Meso Bathypelagic Ecosystems Tony Koslow Primary readings Chapters 3 6 The Silent Deep The deep pelagic realm lecture outline Overview the largest habitat on Earth Physical characteristics light food pressure History of mid water science Deepwater pelagic fauna morphology Biochemical physiological adaptations Deep scattering layers vertical migrations Bioluminescence Lilliputian or giant fauna Diversity patterns in the pelagos The deep pelagos as a habitat The largest habitat on Earth Ocean volume 11 x volume of the land above sea level and it is all habitable 90 of the ocean volume is deeper than 200 m It is below the euphotic zone 1 Io In clearest oceanic water k light extinction coefficient 0 053 Light at 200 m 0 002 Io Humans perceive light to 600 m mid water fish to 1000 m No light penetrates 1200 m Pressure 1 atm 10 m 1 atm 1 kg cm 1 At 1000 m pressure 100 kg cm 1 Food availability in deep water Approximately exponential decline in zooplankton biomass with depth B1000 0 1 B0 B2000 0 1 B1000 Data Vinogradov 1968 Deep sea environments The discovery of deep pelagic faunas There is every reason to believe that the fauna of deep water is confined principally to two belts one at and near the surface and the other on and near the bottom leaving an intermediate zone in which larger animals vertebrate and invertebrate are nearly or entirely absent C W Thomson Leader Challenger expedition 1872 76 In the open sea even when close to the land the surface pelagic fauna does not descend far beyond a depth of 200 fathoms and there is not an intermediate pelagic fauna living between that depth and the bottom Alexander Agassiz 1892 following Albatross expedition off Ecuador Galapagos Confirmation of existence of midwater fauna followed Carl Chun s use of opening closing nets Valdivia expedition 1898 99 100 midwater tows to depths of 5000 m History of mid water science 2 Discovery of the deep scattering layer The recent discovery that a living cloud of some unknown creatures is spread over much of the ocean at a depth of several hundred fathoms below the surface is the most exciting thing that has been learned about the ocean for many years Rachel Carson 1951 The Sea Around Us 100 200 depth m 300 400 500 600 700 0 3 0 0 0 9 0 0 1 5 0 0 2 1 0 0 0 3 0 0 0 9 0 0 tim e P D T Discovery followed from widespread use of echo sounders during WWII The daily vertical migration of 100s of millions of tons of animals on the order of 10 000 body lengths is the greatest animal migration on Earth Zooplankton krill cm scale migrate a few hundred meters fish on scale of 10 cm migrate 100s 1000 m History of mid water science 3 the role of gelatinous zooplankton Praya dubia Courtesy S Haddock MBARI Praya dubia 30 50 m long siphonophore one of the largest animals on Earth The discovery that such giant siphonophores are dominant mesopelagic predators followed from advances in midwater ROVs and photography in 1980 90s Sampling observational technology played a key role throughout the development of midwater science Deepwater pelagic fauna morphology Murray Hjort 1912 the Lilliputian fauna Cyclothone spp most abundant vertebrate typical adults 2 5 5 cm TL Myctophids most diverse midwater fish family typically to 15 cm Or gigantism Giant squid Architeuthis colossal squid Mesonychoteuthis hamiltoni 10 12 m Giant siphonophores e g Praya dubia 30 50 m Football sized larvacean Bathochordaeus 35 cm mysid Gnathophausia Refuge from predation Energetic advantage of large gelatinous organisms in food poor environments with dilute organic C able to search filter large volumes with minimal energetic cost Fish morphological adaptations Typically dark above with photophores below for countershading to match downwelling light upward directed predators e g hatchetfish Shallow mesopelagic zone to 600 m fishes often silvery sided reflective on sides to blend in e g hatchet fish Eyes often enlarged in mesopelagic reduced in bathypelagic zones Enlarged jaws distensible stomachs to maximize prey size infrequent feeding Use of lures ambush predation flabby eel like body plans not adapted Myctophid Diaphus effulgens for speed Cyclothone Hatchetfish Argyropelecus affinis Viperfish Chauliodus Angler fish prey Biochemical physiological adaptations Increased water content decreased lipid protein related to minimum depth of occurrence typically 70 water near surface 8090 at 1000 m Childress Nygaard 1973 Decreased metabolism with min depth of occurrence Torres et al 1979 Related to low light or low food availability Reduced metabolism only in visually orienting inverts Low metabolism leads to higher growth efficiency for non migrators vs migrators despite low food resources Bioluminescence Bioluminescence almost universal among mesopelagic fauna Diverse uses Communication for mating To startle predators or serve as a decoy eg squid bioluminescent ink Lure Countershading intensity can be a variable function of downwelling light Searchlight e g Malacosteus invisible red spotlight to prey on red prawns Diversity patterns The mesopelagic fauna consists of out of date forms of life which can no longer compete with the vigorous shore dwelling rades and are therefore compelled to retreat to the deep sea AS Woodward 1898 1250 fish species living beyond the continental shelf 250 epipelagic mostly sharks scombroids tunas mackerels and flying fishes 850 mesopelagic fishes mostly myctophids hatchet fishes Sternoptychidae bristle mouths Gonostomatidae and predatory viperfihses Chauliodus and dragon fishes 150 bathypelagic species mostly angler fishes and gulper eels Seamounts and deepwater coral reefs What are seamounts where are they Physical circulation around seamounts Hubbs 1959 sets the stage for seamount research Benthic invertebrate and fish communities typical of seamount coldwater coral habitats Productivity Diversity Biogeography Endemism Seamounts Seamounts submerged volcanoes First sampled by Challenger expedition but not recognized until after invention of the echo sounder 1919 Present estimates 30 000 50 000 1000 m in Pacific 600 000 1 5 million of all sizes DK Smith 1991 Mostly in Pacific Physical circulation Currents waves tides interact with topography Seamounts can amplify currents 10 fold set up seamount trapped waves eddies e g Taylor columns extending 100s of meters above seamount and generating up downwelling Function of seamount height radius current speed Potential for some retention enhanced productivity Can winnow