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.I. Deep SeaDeep Sea

• Life strongly influenced by environmental conditionsLife strongly influenced by environmental conditionsA.A. ConditionsConditions

1.1. TemperatureTemperature• Cold – Typically -1 to 4 Cold – Typically -1 to 4 ooCC• ExceptionsExceptions

• Deep Mediterranean is Deep Mediterranean is ca.ca. 13 13 ooCC• Red Sea can be 21.5 Red Sea can be 21.5 ooC @ 2000 m depthC @ 2000 m depth• Weddell Sea can be -1.9 Weddell Sea can be -1.9 ooCC• Hydrothermal vent effluent can approach 400 Hydrothermal vent effluent can approach 400 ooCC

2.2. PressurePressure• Increases predictably by 1 atmosphere (14.7 psi) every 10 Increases predictably by 1 atmosphere (14.7 psi) every 10

mm• Mean depth of oceans – 3800 m = 5600 psiMean depth of oceans – 3800 m = 5600 psi• Affects biological molecules – Membranes, enzymesAffects biological molecules – Membranes, enzymes

3.3. LightLight• Decreases with depthDecreases with depth• Sunlight present in mesopelagic zone; absent below 1000 mSunlight present in mesopelagic zone; absent below 1000 m• Affects development of eyesAffects development of eyes

I.I. Deep SeaDeep Sea

A.A. ConditionsConditions4.4. Dissolved OxygenDissolved Oxygen

• Near saturation and not limiting in most of the deep seaNear saturation and not limiting in most of the deep sea• Exceptions:Exceptions: OMZ and certain enclosed basins OMZ and certain enclosed basins

(Santa Barbara Basin, Cariaco Basin, Black Sea)(Santa Barbara Basin, Cariaco Basin, Black Sea)• OMZ and anoxic basins may act as barriersOMZ and anoxic basins may act as barriers

5.5. SubstrateSubstrate• Exposed hard rock is uncommonExposed hard rock is uncommon

• Biogenic hard substrate may be importantBiogenic hard substrate may be important• Sediment is commonSediment is common

• Continental margins – coarse terrigenous materialContinental margins – coarse terrigenous material• Deep-sea floor – biogenic oozes, terrigenous claysDeep-sea floor – biogenic oozes, terrigenous clays• Deep-sea sediments typically very low in organic Deep-sea sediments typically very low in organic

carbon – 0.5% beneath productive areas and carbon – 0.5% beneath productive areas and <0.1% beneath oligotrophic waters<0.1% beneath oligotrophic waters

Oxygen Minimum Zone (OMZ)Oxygen Minimum Zone (OMZ)

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)Oxygen Minimum Zone (OMZ)

I.I. Deep SeaDeep Sea

A.A. ConditionsConditions4.4. Dissolved OxygenDissolved Oxygen

• Near saturation and not limiting in most of the deep Near saturation and not limiting in most of the deep seasea

• Exceptions:Exceptions: OMZ and certain enclosed basins OMZ and certain enclosed basins (Santa Barbara Basin, Cariaco Basin, Black Sea)(Santa Barbara Basin, Cariaco Basin, Black Sea)

• OMZ and anoxic basins may act as barriersOMZ and anoxic basins may act as barriers5.5. SubstrateSubstrate

• Most of deep sea floor covered by sedimentsMost of deep sea floor covered by sediments• Margins – Coarse terrigenous sedimentsMargins – Coarse terrigenous sediments• Basins – Biogenic oozes (>30% biogenic skeletal Basins – Biogenic oozes (>30% biogenic skeletal

material) and terrigenous clays (depth related)material) and terrigenous clays (depth related)• Siliceous oozes – Diatoms (high latitudes) or Siliceous oozes – Diatoms (high latitudes) or

radiolarians (tropics)radiolarians (tropics)• Calcareous oozes – Foraminiferans (productive Calcareous oozes – Foraminiferans (productive

areas)areas)• Low organic content (typically <1%)Low organic content (typically <1%)• Exposed hard substrate uncommonExposed hard substrate uncommon

• Rocks, manganese nodules, biogenicRocks, manganese nodules, biogenic

I.I. Deep SeaDeep Sea

A.A. ConditionsConditions6.6. CurrentsCurrents

• 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 weeksTypically last days to weeks

• Tidal currentsTidal currents• Source of temporal and spatial variabilitySource of temporal and spatial variability

7.7. Food SupplyFood Supply• Variable in time and spaceVariable in time and space• Seasonal variationSeasonal variation

• Seasonality in productivity, migration patterns, storms, Seasonality in productivity, migration patterns, storms, etc.etc.

• May produce seasonal patterns in biological processes (May produce seasonal patterns in biological processes (Ex:Ex: behavior, feeding, metabolism, reproduction, recruitment)

• Episodic large inputs may introduce variability on other time Episodic large inputs may introduce variability on other time and space scalesand space scales

8.8. TrendsTrends• Gigantism – Ex: Xenophyophores, Amphipods, IsopodsGigantism – Ex: Xenophyophores, Amphipods, Isopods• Miniaturization – Ex: Ostracods, Tanaids, Harpacticoid Miniaturization – Ex: Ostracods, Tanaids, Harpacticoid

CopepodsCopepods

Philippine TrenchHirondellea gigas – Scavenging Amphipods

I.I. Deep SeaDeep Sea

A.A. ConditionsConditions6.6. CurrentsCurrents

• 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 weeksTypically last days to weeks

• Tidal currentsTidal currents• Source of temporal and spatial variabilitySource of temporal and spatial variability

7.7. Food SupplyFood Supply• Variable in time and spaceVariable in time and space• Seasonal variationSeasonal variation

• Seasonality in productivity, migration patterns, storms, Seasonality in productivity, migration patterns, storms, etc.etc.

• May produce seasonal patterns in biological processes (May produce seasonal patterns in biological processes (Ex:Ex: behavior, feeding, metabolism, reproduction, recruitment)

• Episodic large inputs may introduce variability on other time Episodic large inputs may introduce variability on other time and space scalesand space scales

8.8. TrendsTrends• Gigantism – Gigantism – Ex:Ex: Xenophyophores, Amphipods, Isopods Xenophyophores, Amphipods, Isopods• Miniaturization – Miniaturization – Ex:Ex: Ostracods, Tanaids, Harpacticoid Ostracods, Tanaids, Harpacticoid

CopepodsCopepods

I.I. Deep SeaDeep Sea

B.B. FaunaFauna• Most animal phyla present• Total faunal abundance decreases sharply with depth

• PPelagic community biomass at 4000 m ca. 1% of surface values

• Sinking food accumulates at interfaces (e.g. sediment surface)

• 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 thatAsteroids important to 7000 m and absent below that

I.I. Deep SeaDeep Sea

B.B. FaunaFauna• Trophic modes

• Detritivores and scavengers dominantDetritivores and scavengers dominant• Good chemosensory capabilities• Distensible guts

• Predators relatively uncommon• Opportunistic feeding strategies especially

useful• Why?

Scavengers converge on a food Scavengers converge on a food fall 2000m deep off coast of fall 2000m deep off coast of MexicoMexico

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

I.I. Deep SeaDeep Sea

B.B. FaunaFauna• Fishes relatively scarce and modified to Fishes relatively scarce and modified to

various degrees, compared to shallow living various degrees, compared to shallow living relativesrelatives

• Typically have reduced or large eyes, watery Typically have reduced or large eyes, watery tissues, low muscle protein content, reduced tissues, low muscle protein content, reduced skeletons, oil-filled swim bladders, body forms skeletons, oil-filled swim bladders, body forms not designed for rapid swimmingnot designed for rapid swimming

• Most important mobile scavengers in deep Most important mobile scavengers in deep sea, along with amphipods & isopodssea, along with amphipods & isopods

• Many apparently find food using olfactionMany apparently find food using olfaction• Some sit-and-wait predators (Some sit-and-wait predators (e.g.e.g.

BathypteroisBathypterois))• Some nomadic foragers (Some nomadic foragers (e.g.e.g.

CoryphaenoidesCoryphaenoides))

Bathypterois

Lycodes

Coryphaenoides

I.I. Deep SeaDeep Sea

B.B. FaunaFauna• 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)

Whale skull

Crinoids Gorgonians

Antipatharians Barnacle

Stalked tunicateBryozoan

Brachiopods

I.I. Deep SeaDeep Sea

C.C. DiversityDiversity• Through 1960s, deep sea perceived as

highly uniform and consistent over time/space

• Prevailing ecological theory predicted 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 deep-sea 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.I. Deep SeaDeep SeaC.C. DiversityDiversity

• 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

I.I. Deep SeaDeep Sea

C.C. DiversityDiversity• 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.I. Deep SeaDeep Sea

C.C. DiversityDiversity• Rarefaction curves for most deep-sea

habitats never approach an asymptote• Largest quantitative data set to date for

deep-sea 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.I. Deep SeaDeep Sea

C.C. DiversityDiversity• 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.I. Deep SeaDeep Sea

C.C. DiversityDiversity1. 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 to1) Processes that establish diversity

(speciation)2) Process that maintain diversity (extinction)

I.I. Deep SeaDeep Sea

C.C. DiversityDiversity2. 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

Hydrothermal VentsHydrothermal Vents

Hydrothermal Vent fluids: Acidic (pH 2.8), Hydrogen Sulfide >1mMTemperature up to 400°C

Chemosynthetic Food Web: Sulfide Oxidizing Bacteria

Riftia pachyptila (2 m tall)

Cool vent

Fine-scale adaptation to thermal Fine-scale adaptation to thermal nichesniches Distribution patterns at the vents. Distribution patterns at the vents.Black Smoker

Calyptogena magnifica

Riftia pachyptila

Alvinella pompejana & A. caudata

Warm vent

Bythograea thermydron

Bathymodiolusthermophilus

Cool vent

Deep Sea- VentH2S 0->1mMTemp 2-400°CpH 8 -2.8

Vents are short-lived.Vents are short-lived.

Seamounts have higher Seamounts have higher biomass and different biomass and different communitiescommunities

Seamount Seamount Food WebsFood Webs Vertical migrators move to Vertical migrators move to

regions with more foodregions with more food Swept over seamounts by Swept over seamounts by

currents currents Trapped on top at dawnTrapped on top at dawn Abundance of predators Abundance of predators

high, musculature robust, high, musculature robust, but SLOW growthbut SLOW growth

What types of adaptations are What types of adaptations are needed to support life at depth?needed to support life at depth?

• Tolerance AdaptationsTolerance Adaptations: adapt to : adapt to perturbation from abiotic conditionsperturbation from abiotic conditions, e.g., , e.g., hydrostatic pressure and temperaturehydrostatic pressure and temperature

• Capacity AdaptationsCapacity Adaptations: adjust : adjust rates of rates of lifelife in accord with the abiotic and biotic in accord with the abiotic and biotic conditionsconditions

‘‘Rate of living’ falls for visual predators, but Rate of living’ falls for visual predators, but notnotfor gelatinous ‘float and wait’ predators.for gelatinous ‘float and wait’ predators.

For review, see: Childress, J.J. (1995). Trends Ecol. Evol. 10: 30-36

““Float-and-wait” feeding may Float-and-wait” feeding may become more important than become more important than intense predation with reduced intense predation with reduced visual predationvisual predation

•Reduced intensity of locomotory activityReduced intensity of locomotory activity less reliance on visual predation = lower metabolic capacity.•Reduced muscle protein levelsReduced muscle protein levels = lower costs of maintenance metabolism & growth

•Lower OLower O22 consumption consumption

•Reduced/Absent swim bladders; reduced Reduced/Absent swim bladders; reduced calcificationcalcification•Migrators and Non-Migrators differMigrators and Non-Migrators differ

Capacity Adaptations: conclusions

Tolerance AdaptationsTolerance Adaptations:: Pressure & TemperaturePressure & Temperature

• Adaptive SolutionsAdaptive Solutions: : a cooperative venture between a cooperative venture between macro- and ‘micro’molecules.macro- and ‘micro’molecules.

ProteinsProteins: : amino acid substitutionsamino acid substitutions– Enhance flexibilityEnhance flexibility– Conserve Km (substrate binding) at habitat pressureConserve Km (substrate binding) at habitat pressure

OsmolytesOsmolytes: : protein-stabilizing solutesprotein-stabilizing solutes Lipids & membranesLipids & membranes: : fluidity-effectsfluidity-effects

– Homeoviscous adaptationHomeoviscous adaptation More unsaturated acyl phospholipid chainsMore unsaturated acyl phospholipid chains

Gas-filled spaces—obvious Gas-filled spaces—obvious problemsproblemsV = nRT/PV = nRT/P

PRESSURE EFFECTS IN THE LIQUID PHASE—PROTEIN conformational changes a problem!PROTEIN conformational changes a problem!

•Movement during substrate binding/releaseMovement during substrate binding/release•Subunit polymerizationSubunit polymerization

Lactate Dehydrogenase (LDH)Lactate Dehydrogenase (LDH)Pyruvate + NADH + H+ lactate + NAD+

Pressure inhibits membrane-spanning Pressure inhibits membrane-spanning proteins:proteins:resistance to conformational change.resistance to conformational change.

Membrane-spanning protein

Conformational change

LowLow resistance—high activity resistance—high activity HighHigh resistance--inhibition resistance--inhibition

Homeoviscous AdaptationHomeoviscous Adaptation

Shifts in acyl chain ‘saturation’ (double-bond Shifts in acyl chain ‘saturation’ (double-bond content: =) content: =)

saturated mono-unsaturated poly-unsaturated

Viscous Fluid

Homeoviscous adaptationHomeoviscous adaptation

Change lipid composition (saturation of fatty Change lipid composition (saturation of fatty acid side chains, cholesterol)acid side chains, cholesterol)

Maintain stable fluidity at habitat conditionsMaintain stable fluidity at habitat conditionsPreserve membrane permeability and Preserve membrane permeability and

membrane enzyme function membrane enzyme function

Temperature (°C)

Vis

cosi

ty AB

C

A B C

Pressure (atms)