Transcript ENVI 21 Life in the Ocean

Why should we bother to study deep-sea biology?
“..we know more about the
moon’s behind than the
ocean’s bottom…”
Dr. Cindy Lee Van Dover
New Yorker classic
Most of “biology” (~80%) takes place in the deep sea:
The deep sea is the most common habitat in the biosphere!
Average depth = 3,800 m
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Deep Sea
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A.
Life strongly influenced by environmental conditions
Conditions
1.
Temperature
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2.
Cold – Typically -1 to 4 oC
Exceptions
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Deep Mediterranean is ca. 13 oC
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Red Sea can be 21.5 oC @ 2000 m depth
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Weddell Sea can be -1.9 oC
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Hydrothermal vent effluent can approach 400 oC
Pressure
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3.
Increases predictably by 1 atmosphere (14.7 psi) every 10 m
Mean depth of oceans – 3800 m = 5600 psi
Affects biological molecules – Membranes, enzymes
Light
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Decreases with depth
Sunlight present in mesopelagic zone; absent below 1000 m
Affects development of eyes
I.
Deep Sea
A.
Conditions
4.
Dissolved Oxygen
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5.
Near saturation and not limiting in most of the deep sea
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Exceptions: OMZ and certain enclosed basins (Santa
Barbara Basin, Cariaco Basin, Black Sea)
OMZ and anoxic basins may act as barriers
Substrate
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Exposed hard rock is uncommon
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Biogenic hard substrate may be important
Sediment is common
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Continental margins – coarse terrigenous material
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Deep-sea floor – biogenic oozes, terrigenous clays
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Deep-sea sediments typically very low in organic carbon
– 0.5% beneath productive areas and <0.1% beneath
oligotrophic waters
Oxygen Minimum Zone (OMZ)
Oxygen Minimum Zone (OMZ)
How do OMZ species adapt to low levels of oxygen?
•Metabolic rate (O2 consumption) declines
•Gill ventilation rates increase
•Hemoglobin binds oxygen at lower saturation
•Gene expression: enzyme isoforms for anaerobiosis
•Some may be food-deprived
Oxygen Minimum Zone (OMZ)
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Deep Sea
A.
4.
5.
Conditions
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Dissolved Oxygen
Near saturation and not limiting in most of the deep sea
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Exceptions: OMZ and certain enclosed basins (Santa
Barbara Basin, Cariaco Basin, Black Sea)
OMZ and anoxic basins may act as barriers
Substrate
Most of deep sea floor covered by sediments
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Margins – Coarse terrigenous sediments
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Basins – Biogenic oozes (>30% biogenic skeletal
material) and terrigenous clays (depth related)
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Siliceous oozes – Diatoms (high latitudes) or
radiolarians (tropics)
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Calcareous oozes – Foraminiferans (productive areas)
Low organic content (typically <1%)
Exposed hard substrate uncommon
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Rocks, manganese nodules, biogenic
I.
Deep Sea
A.
Conditions
6.
Currents
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7.
Generally slow – Mean speeds typically <5 cm s-1, with peaks less
than 20 cm s-1 in most areas
Periodically, certain areas experience benthic storms
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Typically last days to weeks
Tidal currents
Source of temporal and spatial variability
Food Supply
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8.
Variable in time and space
Seasonal variation
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Seasonality in productivity, migration patterns, storms, etc.
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May produce seasonal patterns in biological processes (Ex:
behavior, feeding, metabolism, reproduction, recruitment)
Episodic large inputs may introduce variability on other time and
space scales
Trends
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Gigantism – Ex: Xenophyophores, Amphipods, Isopods
Miniaturization – Ex: Ostracods, Tanaids, Harpacticoid Copepods
Philippine Trench
Hirondellea gigas – Scavenging Amphipods
I.
Deep Sea
A.
Conditions
6.
Currents
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7.
Generally slow – Mean speeds typically <5 cm s-1, with peaks less
than 20 cm s-1 in most areas
Periodically, certain areas experience benthic storms
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Typically last days to weeks
Tidal currents
Source of temporal and spatial variability
Food Supply
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8.
Variable in time and space
Seasonal variation
•
Seasonality in productivity, migration patterns, storms, etc.
•
May produce seasonal patterns in biological processes (Ex:
behavior, feeding, metabolism, reproduction, recruitment)
Episodic large inputs may introduce variability on other time and
space scales
Trends
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Gigantism – Ex: Xenophyophores, Amphipods, Isopods
Miniaturization – Ex: Ostracods, Tanaids, Harpacticoid Copepods
I.
Deep Sea
B.
Fauna
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Most animal phyla present
Total faunal abundance decreases sharply with depth
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Pelagic community biomass at 4000 m ca. 1% of surface
values
Sinking food accumulates at interfaces (e.g. sediment
surface)
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Pelagic biomass 10 mab double that at 200 mab
(Wishner)
Changes in relative abundance of faunal taxa with depth
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Kurile-Kamchatka Trench - Sponges dominant
component of benthic macro-/megafauna to 2000 m
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Holothuroids important below 2000 m and dominant
below 8000 m
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Asteroids important to 7000 m and absent below that
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Deep Sea
B.
Fauna
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Trophic modes
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Detritivores and scavengers dominant
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Good chemosensory capabilities
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Distensible guts
Predators relatively uncommon
Opportunistic feeding strategies especially useful
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Why?
Scavengers converge on a food fall
2000m deep off coast of Mexico
http://news.bbc.co.uk/1/hi/sci/tech Dec 11 2006
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Deep Sea
B.
Fauna
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Fishes relatively scarce and modified to various
degrees, compared to shallow living relatives
Typically have reduced or large eyes, watery
tissues, low muscle protein content, reduced
skeletons, oil-filled swim bladders, body forms
not designed for rapid swimming
Most important mobile scavengers in deep sea,
along with amphipods & isopods
Many apparently find food using olfaction
Some sit-and-wait predators (e.g. Bathypterois)
Some nomadic foragers (e.g. Coryphaenoides)
Coryphaenoides
Bathypterois
Lycodes
I.
Deep Sea
B.
Fauna
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Whale skull
Sessile organisms may be attached to hard
substrate of many types
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Exposed rock
Manganese nodules or bits of geological material
Biogenic hard substrate (sponges, shells, wood, bone)
Occurrence limited by
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Available substrate
Flux of POM (food)
Crinoids
Antipatharians
Gorgonians
Barnacle
Brachiopods
Bryozoan
Stalked tunicate
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Deep Sea
C.
Diversity
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Through 1960s, deep sea perceived as highly
uniform and consistent over time/space
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Prevailing ecological theory predicted that spatial and
temporal uniformity plus sparse, low-grade food
resources should lead to an equilibrium condition with
a few competitively dominant species
Mid-1960s: epibenthic sled developed and
deployed by Howard Sanders and Bob Hessler
(WHOI)
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Covered much smaller area than conventional deepsea bottom trawl but sampled upper few cm of
sediments and retained organisms in a fine-meshed
sampling bag
Samples effectively ended notion of low diversity in
deep sea
I.
Deep Sea
C.
Diversity
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Number of spp. within many taxa (e.g. bivalves,
gastropods, polychaetes) tends to increase from
surface to mid-slope depths (ca. 2000 m) then
decrease with increasing depth
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Deep Sea
C.
Diversity
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Trend suggests low species diversity in deep sea
Pattern could be artifact of reduced sampling
effort with increasing depth
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How do we know if we’ve sampled enough area
and organisms to generate a meaningful picture
of the actual diversity of the deep-sea benthic
community?
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Deep Sea
C.
Diversity
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Rarefaction curves for most deep-sea habitats
never approach an asymptote
Largest quantitative data set to date for deepsea macro- and meiofauna was obtained during
early 1980s from Atlantic slope off US
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554 box cores (30 x 30 cm) from depths to 3000 m
Over 1600 species identified
Factoring out depth, 233 cores taken at 2100 m depth
along 176-km long transect
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Samples: 798 species from 14 invertebrate phyla
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Deep Sea
C.
Diversity
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Rarefaction curves for most deep-sea habitats
never approach an asymptote
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Expected number of species increasing at about
25 m-2
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Prediction: 5-10 million species in deep sea!!
No single species >8% of community
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Similar to other deep-sea sites (except HEBBLE, where
single species may be 50-64% of community)
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Deep Sea
C.
Diversity
1.
Patterns
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Deep-sea species diversity differs among ocean basins
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Differences may be related to oxygen content,
nutritional input, geological history, etc.
High species diversity may be due to
1) Processes that establish diversity (speciation)
2) Process that maintain diversity (extinction)
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Deep Sea
C.
Diversity
2.
Maintenance
a)
Equilibrium processes
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Ex: Resource partitioning, habitat partitioning
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Species that are well-adapted to a particular set of
conditions co-exist at densities near carrying
capacity of environment
b) Disequilibrium processes
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Ex: Local disturbance
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Patchy habitat supports many populations at early
growth stages, hence at relatively low densities
(not near carrying capacity), reducing competitive
exclusion as an important structuring mechanism
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Connell (1978) suggested that highest diversity
maintained at intermediate levels of disturbance
Hydrothermal Vents
Hydrothermal Vent fluids:
Acidic (pH 2.8), Hydrogen Sulfide >1mM
Temperature up to 400°C
Chemosynthetic Food Web:
Sulfide Oxidizing Bacteria
Riftia pachyptila (2 m tall)
Fine-scale adaptation to thermal niches
Distribution patterns at the vents.
Black Smoker
Warm vent
Alvinella pompejana
& A. caudata
Bythograea
thermydron
Cool vent
Deep Sea- Vent
H2S 0->1mM
Temp 2-400°C
pH
8 -2.8
Calyptogena magnifica
Cool vent
Riftia
pachyptila
Bathymodiolus
thermophilus
Vents are short-lived.
Seamounts have higher biomass
and different communities
Seamount
Food Webs
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Vertical migrators move to
regions with more food
Swept over seamounts by
currents
Trapped on top at dawn
Abundance of predators high,
musculature robust, but SLOW
growth
What types of adaptations are needed
to support life at depth?
• Tolerance Adaptations: adapt to perturbation
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from abiotic conditions, e.g., hydrostatic
pressure and temperature
Capacity Adaptations: adjust rates of life in
accord with the abiotic and biotic conditions
‘Rate of living’ falls for visual predators, but not
for gelatinous ‘float and wait’ predators.
For review, see: Childress, J.J. (1995). Trends Ecol. Evol. 10: 30-36
“Float-and-wait” feeding may become
more important than intense predation
with reduced visual predation
Capacity Adaptations: conclusions
•Reduced intensity of locomotory activity
less reliance on visual predation = lower
metabolic capacity.
•Reduced muscle protein levels = lower costs of
maintenance metabolism & growth
•Lower O2 consumption
•Reduced/Absent swim bladders; reduced
calcification
•Migrators and Non-Migrators differ
Tolerance Adaptations:
Pressure & Temperature
• Adaptive Solutions: a cooperative venture between macroand ‘micro’molecules.
 Proteins: amino acid substitutions
– Enhance flexibility
– Conserve Km (substrate binding) at habitat pressure
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Osmolytes: protein-stabilizing solutes
Lipids & membranes: fluidity-effects
– Homeoviscous adaptation
 More unsaturated acyl phospholipid chains
Gas-filled spaces—obvious problems
V = nRT/P
PRESSURE EFFECTS IN THE LIQUID PHASE—
PROTEIN conformational changes a problem!
•Movement during substrate binding/release
•Subunit polymerization
Lactate Dehydrogenase (LDH)
Pyruvate + NADH + H+  lactate + NAD+
Pressure inhibits membrane-spanning proteins:
resistance to conformational change.
Membrane-spanning protein
Conformational change
Low resistance—high activity
High resistance--inhibition
Homeoviscous Adaptation
Shifts in acyl chain ‘saturation’ (double-bond content: =)
saturated
mono-unsaturated
Viscous
poly-unsaturated
Fluid
Homeoviscous adaptation
Viscosity
Change lipid composition (saturation of fatty acid
side chains, cholesterol)
Maintain stable fluidity at habitat conditions
Preserve membrane permeability and membrane
enzyme function
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B
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C
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Temperature (°C)
Pressure (atms)