Deep Ocean

  • Created by: rosieevie
  • Created on: 25-05-17 17:55

Technology to Investigate Deep-Sea Ecology

Determine location on Earth surface

Measure envrionmental parameters

Recover biological samples

Observe deep sea and inhabitants directly 

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Milestones in Deep-Sea Ecology

1818 - John Ross finds Echinodermata phylum member on sounding line ~1400m

1872-1876 - HMS Challenger collects >4000 new species from deep ocean

1929-1934 - Beebe and Barton dive in bathysphere, observe in situ life

1960 - Piccard and Walsh reach ocean's deepest point (~10916m) in bathyscaphe Trieste

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Early Notions in Deep-Sea Ecology

1843 - Forbes proposed 'azoic theory' = no life beyone 600m

  • Based on dredging observations in Aegean Sea

Theory refuted by 3 expiditions - all dredged to deeper depths and collected specimens

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Misconceptions about Ocean Mapping

Often repeated that only 5% Earth's oceans is mapped = NOT TRUE

All been mapped at low resolution (~5km)

Earth is dynamic - hard to create map that applies constantly

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Deep Ocean Habitats - Dysphotic Zone

Twilight zone

Mid-water depths - 200-1000m

High productivity

Down-welling sunlight but insufficient for photosynthesis 

Bottom of zone ultimate limit of sun's rays

90% animals bioluminescent

Most numerous vertebrates on Earth

Greatest animal migration - diel vertical migrations of deep-water zooplankton

  • Move to surface at dusk to feed on phytoplankton
  • Move down at sunrise to avoid predators

Largest invertebrate species e.g. Giant squid, colossal squid

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Deep Ocean Habitats - Aphotic Zone

Midnight Zone

From ~1000m (to around 4000m)

No down-welling sunlight by 1000m

Bioluminescence used but NOT for counter-illumination

Prey increasingly scarce so adaptations for predation important

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Deep Ocean Habitats - Continental Slopes

Drop very slowly (gentle) but sometime very steep

Areas of steeper slope - exposed rock for suspension feeder colonisation

Cut by submarine canyons (old river beds) - important in transferring material

Deep water corals form thickets - support diverse assemblages of polychaetes, ophiuroids, fish

  • Corals are scleractinians (stony) = filter feeders (no symbiotic zooxanthellae)
  • Growth slow as result (2-25mm per year) = vulnerable to bottom-trawling damage

Chemosynthetic cold seep habitats present here

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Deep Ocean Habitats - Abyssal Plains

Flattest part of surface topography (<1:10000)

Abyssal hills occur - most abundant seabed feature

Underlying crustal topography obscured by <3km thick sediment = soft-sediment environments

High species richness of macrofauna living in sedmient

High species richness of sediment meiofauna

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Deep Ocean Habitats - Seamounts

Active or extinct undersea volcanoes rising >1000m above seafloor

>39000 worldwide but <300 visually surveyed

Steep slopes = bare rock surfaces for suspension feeder attachment

Enhanced flow around seamounts = increased food for suspension feeders

Taylor column effect (rotating fluids disturbed by solid body form columns) traps larvae

Pressure from deep-sea trawling

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Deep Ocean Habitats - Mid-Ocean Ridges

65000km chain of undersea volcanoes

Can be a rift

Rocky-deep sea habitat (similar to seamounts)

Non-chemosynthetic fauna less well-studied than at hydrothermal vents in ridges

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Deep Ocean Habitats - Ocean Trenches

Poorly studied

Animal life observed at oceans deepest point (~10916m)

Limited knowledge from scientific trawls and lander deployments

Renewed interest in vehicles may improve knowledge

Ecological questions:

  • Do trenches concentrate organic input?
  • Do fauna exhibit biogeographic patterns?
  • Do taxa have physiological depth limits?
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Bioluminescence

Created by oxidation of luciferin substrate via luciferase enzyme (exact chemicals involve vary)

Animals obtain chemicals from food or bioluminescent bacteria in photophore organs

Most blue wavelength - attenuates less rapidly and matches down-welling light

Uses:

  • Counter-illumination (only dysphotic)
  • Signalling to conspecifics
  • Catching prey
  • Evading predators
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Counter-Illumination

Dysphotic zone only - downwelling irradiance casts 'shadow'

Many predators have sensitive upward-looking eyes to detect shadows e.g. tube-eye, barrel-eye fish

Bioluminescence breaks up or mashs silhouettes

Matches downwelling irradiance = camouflage

Alternative to counter-illumination = transparent bodies to cast no shadows

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Signalling to Conspecifics

Attract mates or social purposes

Examples in cephalopod molluscs - firefly squid

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Catching Prey

Bioluminsecent lures e.g. angler fishes

Iluminating prey during hunting e.g dragonfish

Dragonfish:

  • Emit red light from suborbital photophores
  • Invisible to most animals
  • Eyes contain chlorophyll that boosts colour range
  • = Illuminate prey without prey realising
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Evading Predators

Confuse predators - expel bioluminescent fluid

May also discourage predators - burglar alarm hypothesis = display or expelling sticky fluid attracts predators' predator and threatens them

Example - bloodybelly comb jellies

  • Expel red light from transparent stomachs when eating
  • Masks bioluminescent prey 
  • = Avoids detection by predators
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Living Under Pressure

Pressure increases ~1atm per 10m = 5000m = >50,600kPa

Internal and external pressure equalised as solids and liquids incompressible = no structural adaptations to pressure and do not 'explode' at surface

Pressure can trap water on unfolded protein surface - prevents folding into enzymes

  • Prevention using chaperone molecules = remove water and promote correct folding

Example - TMAO

  • Fish and decapod crustaceans 
  • TMAO concentrations increase with depth
  • Elasmobranch fish (sharks, rays etc) - high TMAO concentratios at surface = adaptation to osmotic stress
  • Inability to accumulate sufficient TMAO limits elasmobranch fish to <3000m
  • Hypothesis that teleost fish may not live at bottom of ocean
  • Other taxa use different chaperones = live in hadal zones
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Predation

Prevalent in aphotic and dysphotic

Ambush predation - lower energetic cost than active hunting

Adaptations for predation and to evade predation - evolutionary arms race

Predators tackle large prey = flexible jaws and expandable stomachs

  • Dragonfishes - additional neck joint = wide jaw opening
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Suspension Feeding

Need to escape boundary - seabed friction reduces flow

  • Long stalks
  • Climbing and colonise upstanding features

Anchor if stalked = limit distribution if no hard substrata available

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Deposit-Feeding

Extract organic matter from sediment

3 types of gut:

  • 'Batch-reactor'
    • Ophiuroids
    • One entrance and exit
    • Episodic input and output times
  • 'Continous-flow stirred-tank reactor'
    • Decapods
    • Seperate entrance and exit
    • Episodic input and output times
  • 'Plug-flow reactor' 
    • Holothurians
    • Seperate entrance and exit
    • Continous input and output
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Scavenging

Olfactory and other sensory adaptations to detect food falls e.g. dead fish

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Exploiting Larger Organic Falls

Some organic input much larger than particulates in size e.g. animal carcasses and wood falls

Taxa specialists in exploiting resources, using partnerships with symbiotic bacteria

  • Xylophagidae wood-eating bivalves
  • Osedax spp. bone eating polychaetes (zombie worms) - digest any bone
    • Burrows in plesiosaur fossils
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Finding a Mate

Pairing behaviour

  • Finds member of opposite sex and sticks with it until mating
  • Holothurian double excretion tracks on seabed

Accessory Dwarf Males

  • Male parasitic on larger female = ensures mating
  • Angler fish suborder Ceratioidei
  • Osedax spp. polychaetes and xylophagidae molluscs

Opportunistic Mating Behaviour 

  • Squid and cephalopod moluscs shoot spermatophores at female for sperm transfer
  • Deep-sea males found with spermatophores attached to them = shooting them at anything

Possible Aggregation of Broadcast Spawners

  • External fertilisation method where unfertilised gametes released in water at same time
  • Aggregations e.g. echinoids - adaptation to improve fertilisation success
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Deep Ocean Evolutionary History

Most species smaller than shallow water relatives - lack of food?

Few exhibit gigantism e.g. isopods, chephalopods, amphipods

Example of Island Rule - colonists tend to evolve contrasting body sizes to ancestors

  • Deep ocean recolonised repeatedly follow Ocean Anoxic Events in geological past
  • Ocean Anoxic Events - mass extinction where oceans less oxygenated due to changing ocean currents/global climate change
  • After recolonisation, colonists have few predators = larger than normal
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Anthropogenic Impacts

Fisheries - increase has impacted slope and seamount habitats

  • Bottom trawling damages seabed habitats
  • Stony corals take long time to recover, as do many species due to slow growth/maturity times

Litter - modern litter and clinker

  • Clinker - damage seafloors and create new exposed areas for suspension feeder attachment

Microplastics -accumulate in high concentration which explains missing plastic/garbage patches

  • Dilutes marine snow - affects deposit feeders

Pollution - accidents from gas and oil may look cleared up but found in high concentration in deep

Potential - Seabed Mining at hydrothermal vents and seamounts

  • Impacts poorly understood so studies to reduce effects necessary
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Declines in Biomass in Deep Ocean

Two main patterns:

  • Decline in biomass with depth
  • Decline in biomass with distance from land
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