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

I.
Deep Sea
• Life strongly influenced by environmental conditions
A.
Conditions
1.
Temperature
•
•
•
•
•
•
Cold – Typically -1 to 4 o C
Exceptions
Deep Mediterranean is ca.
13 o C
Red Sea can be 21.5 o C @ 2000 m depth
Weddell Sea can be -1.9 o C
Hydrothermal vent effluent can approach 400 o C
2.
Pressure
• Increases predictably by 1 atmosphere (14.7 psi) every 10 m
•
•
Mean depth of oceans – 3800 m = 5600 psi
Affects biological molecules – Membranes, enzymes
3.
Light
• Decreases with depth
•
•
Sunlight present in mesopelagic zone; absent below 1000 m
Affects development of eyes

I.
Deep Sea
A.
Conditions
4.
Dissolved Oxygen
• Near saturation and not limiting in most of the deep sea
• Exceptions: OMZ and certain enclosed basins (Santa
Barbara Basin, Cariaco Basin, Black Sea)
• OMZ and anoxic basins may act as barriers
5.
Substrate
• Exposed hard rock is uncommon
• Biogenic hard substrate may be important
• Sediment is common
• Continental margins – coarse terrigenous material
• Deep-sea floor – biogenic oozes, terrigenous clays
• 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 (O
2 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)

I.
Deep Sea
A.
Conditions
4.
Dissolved Oxygen
• Near saturation and not limiting in most of the deep sea
• Exceptions: OMZ and certain enclosed basins (Santa
Barbara Basin, Cariaco Basin, Black Sea)
• OMZ and anoxic basins may act as barriers
5.
Substrate
• Most of deep sea floor covered by sediments
• Margins – Coarse terrigenous sediments
• Basins – Biogenic oozes (>30% biogenic skeletal material) and terrigenous clays (depth related)
• Siliceous oozes – Diatoms (high latitudes) or radiolarians (tropics)
• Calcareous oozes – Foraminiferans (productive areas)
• Low organic content (typically <1%)
• Exposed hard substrate uncommon
• Rocks, manganese nodules, biogenic

I.
Deep Sea
A.
Conditions
6.
Currents
• 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
Typically last days to weeks
Tidal currents
Source of temporal and spatial variability
7.
Food Supply
• 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
8.
Trends
•
•
Gigantism – Ex: Xenophyophores, Amphipods, Isopods
Miniaturization – Ex: Ostracods, Tanaids, Harpacticoid Copepods

Philippine Trench
Hirondellea gigas – Scavenging Amphipods

I.
Deep Sea
A.
Conditions
6.
Currents
• 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
Typically last days to weeks
Tidal currents
Source of temporal and spatial variability
7.
Food Supply
• 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
8.
Trends
•
•
Gigantism – Ex: Xenophyophores, Amphipods, Isopods
Miniaturization – Ex: Ostracods, Tanaids, Harpacticoid Copepods

I.
Deep Sea
B.
Fauna
• Most animal phyla present
• Total faunal abundance decreases sharply with depth
• Pelagic community biomass at 4000 m values ca.
1% of surface
• Sinking food accumulates at interfaces ( surface) e.g.
sediment
• Pelagic biomass 10 mab double that at 200 mab
(Wishner)
• Changes in relative abundance of faunal taxa with depth
• Kurile-Kamchatka Trench - Sponges dominant component of benthic macro-/megafauna to 2000 m
• Holothuroids important below 2000 m and dominant below 8000 m
• Asteroids important to 7000 m and absent below that

I.
Deep Sea
B.
Fauna
• Trophic modes
• Detritivores and scavengers dominant
•
Good chemosensory capabilities
•
Distensible guts
• Predators relatively uncommon
• Opportunistic feeding strategies especially useful
•
Why?

http://news.bbc.co.uk/1/hi/sci/tech Dec 11 2006

I.
Deep Sea
B.
Fauna
• 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
Whale skull
• Sessile organisms may be attached to hard substrate of many types
– Exposed rock
– Manganese nodules or bits of geological material
– Biogenic hard substrate (sponges, shells, wood, bone)
• Occurrence limited by
– Available substrate
– Flux of POM (food)

Crinoids
Antipatharians
Gorgonians
Barnacle

Brachiopods
Bryozoan Stalked tunicate

I.
Deep Sea
C.
Diversity
• Through 1960s, deep sea perceived as highly uniform and consistent over time/space
• 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)
• 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
• Number of spp. within many taxa ( gastropods, polychaetes) tends to increase from surface to mid-slope depths ( ca.
decrease with increasing depth e.g.
bivalves,
2000 m) then

I.
Deep Sea
C.
Diversity
• Trend suggests low species diversity in deep sea
• Pattern could be artifact of reduced sampling effort with increasing depth
• 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?

I.
Deep Sea
C.
Diversity
• 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
• 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
• Samples: 798 species from 14 invertebrate phyla

I.
Deep Sea
C.
Diversity
• Rarefaction curves for most deep-sea habitats never approach an asymptote
• Expected number of species increasing at about
25 m -2
• Prediction: 5-10 million species in deep sea!!
• No single species >8% of community
• Similar to other deep-sea sites (except HEBBLE, where single species may be 50-64% of community)

I.
Deep Sea
C.
Diversity
1. Patterns
• Deep-sea species diversity differs among ocean basins
• 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)

I.
Deep Sea
C.
Diversity
2. Maintenance a) Equilibrium processes
• Ex: Resource partitioning, habitat partitioning
• Species that are well-adapted to a particular set of conditions co-exist at densities near carrying capacity of environment b) Disequilibrium processes
• Ex: Local disturbance
• 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
• Connell (1978) suggested that highest diversity maintained at intermediate levels of disturbance

(2 m tall)

Alvinella pompejana
& A. caudata
Fine-scale adaptation to thermal niches
Distribution patterns at the vents.
Black Smoker Warm vent
Bythograea thermydron
Cool vent
Cool vent
Riftia pachyptila
Deep Sea- Vent
H
2
S 0->1mM
Temp 2-400°C pH 8 -2.8
Calyptogena magnifica
Bathymodiolus thermophilus





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

Tolerance Adaptations : adapt to perturbation 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

• Reduced intensity of locomotory activity less reliance on visual predation = lower metabolic capacity.
• Reduced muscle protein levels = lower costs of maintenance metabolism & growth
• Lower O
2 consumption
• Reduced/Absent swim bladders; reduced calcification
• Migrators and Non-Migrators differ

:
• Adaptive Solutions: a cooperative venture between macroand ‘micro’molecules.



Proteins: amino acid substitutions
– Enhance flexibility
– Conserve Km (substrate binding) at habitat pressure
Osmolytes: protein-stabilizing solutes
Lipids & membranes: fluidity-effects
– Homeoviscous adaptation

More unsaturated acyl phospholipid chains

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

Shifts in acyl chain ‘saturation’ (double-bond content: =) saturated mono-unsaturated
Viscous poly-unsaturated
Fluid

Homeoviscous adaptation
Change lipid composition (saturation of fatty acid side chains, cholesterol)
Maintain stable fluidity at habitat conditions
Preserve membrane permeability and membrane enzyme function
A
B
C
A B C
Temperature (°C)
Pressure (atms)