The Deep Ocean, Part 1

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The Deep Ocean,Part 1

• Lecture 7
• Marine Biology

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Deep Sea Research
The deep ocean is largely unknown. Most work
is by expensive submersible expeditions and,
previously, by trawling
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Benthic Zonation
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Deep Sea Faunal Zones
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Light Penetration
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Discoveries

• The base of food web is comprised of fecal
  pellets/detritus of epipelagic copepods.
•  
• Vertical migration discovered during WWII with
  advent of sonar
• noted false bottom at night - large schools of
  migrating mesopelagic fishes and squids or krill.

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Discoveries, cont.
Referred to as Deep Scattering Layer   During
daylight hours - 300-500 m depth During
nighttime hours - surface   Migrations impt. in
transporting food to midwater depths and below.  
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Differences in Mesopelagic and Bathypelagic
Fishes
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Features adapted to mid-water (mesopelagic)
fishes

• Use countershading or counter-illumination
• Most deepwater fishes (mesopelagic) migrate to
  the surface at night and return to depth during
  daylight hours.
• possess a swim bladder
• well developed muscles and bones and can tolerate
  temperature variation. 
• Those species that do not migrate lack all of the
  above.

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The Mesopelagic Zone and Below

• - some light but not sufficient for
  photosynthesis
•  
• below mesopelagic, it is perpetually dark
• without photosynthesis, organisms depend on
  organic matter falling from surface.
• One exception - vent communities (next lecture).
•  
• - consequences
• - low food supply and fewer organisms
• 5 to 10x fewer organisms
• - most food gets eaten on way down to bottom.
•  
•  - fauna dominated by mid-water fishes - all
  small, 1-4"

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Pressure
Effects of Pressure in the Deep Sea - Pressure
can have negative effects on enzyme systems -
At the sea surface air exerts 1 atm14.7 lbs/m2
or 1 kg/cm2 for each 10m of depth   - So,
pressures occur up to 1,000 atm in the ocean,
with an of average of 200-600 atm   -
Proteins membranes are influenced by pressure
- evolution acts to reduce the sensitivity of
cellular structures at higher activation
energies but lower catalytic efficiency.
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Pressure, cont.

• Effects similar to that of changing temperature
• - high pressure leads to lower metabolic rate
• - lipids in cells undergo phase change when
  pressure goes up
• - reduced fluidity of membrane affects
  morphology of cells
•  
• Argument - low metabolism could be overcome with
  evolution of
• cell/enzyme system to become more efficient,
• but no selection for this since low metabolism
  is favored in
• nutrient poor deep sea environment.
•  
• Pressure also lowers ability to accrete CaCO3
• Ca HCO3 dissociation favored.

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Deep Sea Food Sources
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Characteristics of Deep Sea Organisms
Tissues of deep sea organisms are more depleted
in protein lipids, lower caloric content - more
like jellyfish   Exception to small size is seen
in some invertebrates - very large amphipods (1
ft), referred to as deep sea gigantism  
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Deep Sea Fishes

• Most abundant species belong to two groups
• Lanternfish (Myctophids) and Bristlemouths
• - 90 of midwater fishes.
• One species of Bristlemouth,
• Cyclothone sigmata,
• may be most abundant
• fish on earth.
• Others include viperfish,
• hatchetfish, dragonfish,
• many eel-like fishes.

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Anglerfish

• male attaches to female body, shares circulatory
  system
• - referred to as male parasitism
• - price paid by female to insure reproductive
  success.

• Invertebrates have other strategies
• - aggregate (probably through pheromones or other
  chemical signals)
• - separate sexes are the rule here.

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Deep Ocean Organisms
Anglerfishes
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Deep Sea Organisms, cont.
Spineback eel
viperfish
Peraphila jelly
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Deep Sea Organisms, cont.
Ophiura
Mastigoteuthis
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Deep Sea Organisms, cont.
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Deep Sea Organisms, cont.
Giant hatchetfish
Finned octopus (jelly-like)
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Deep Sea Organisms, cont.
collapsible urchin
Chauliodus
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Deep Sea Organisms, cont.
Blacklip ratfish
deepwater ctenophore
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Deep Sea Organisms, cont.
Atolla
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Adaptation to Darkness
Good vision in poor light - facilitated by
large, sensitive eyes - evolution of tubular
eyes or lobed eyes that allow both vertical
and lateral vision. - able to distinguish
between natural light and bioluminescence
(blue light) - allows predators to find prey.
- this adaptation is ubiquitous in fish,
octopus and krill which live in the
mesopelagic zone.
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Bioluminescence

• Some organisms possess photophores on underside
• predator looking up sees broken pattern,
• blends with surface
• - association with light emitting bacteria.
• luciferin oxidized by enzyme luciferase to
• produce blue light at 460-480 nm.

 Function Attract prey Communicate
Courtship/mating
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Adaptations
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Adaptations to Sediments

• Organisms have developed many ways to prevent
  sinking into the
• deep-sea mud.
• - Burrowing - Many small organisms, e.g. worms,
  bivalves.
• - Stay above the mud by
• Stalks - sessile organisms, such as pennatulids
• Stilts - errant animals, such as sea-spiders,
  crabs and fish
• Float - fish utilize swim-bladders, though this
  poses problems due
• to pressure. Elasmobranchs have fatty livers to
  aid buoyancy,
• while some species convert heavy tissue such as
  bone to water.
• Climb - utilize the sessile organisms to climb
  away from the mud.
• Munida (a squat lobster) uses the glass sponge
  Pheronema as a
• burrow.

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Adaptations, cont.
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Light Organs in Fish
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Light Organs in Squid
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Adaptations Hinged Jaw

• Fish are small because food is limited
• large mouth, protrusible jaws
• teeth increase ability to
• capture prey
• Prey can be equal or greater
• in size than themselves.

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Hinged Jaws
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EyeAdaptations
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Patterns of Species Diversity

• highest in bathypelagic
• biomass in regions reflect overlying
  productivity in surface waters.

In many ways this environment is analogous to
deserts  -Patchy environment - at times major
windfalls - big fish and whales die and sink
rapidly to bottom - referred to as whale falls or
fish falls
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Species Patterns Abundance and Biomass
1. Abundance The general trend as you move
down the continental slope is for high
abundance above 1km and then a steady decrease in
animal numbers with depth, leveling out at
the abyssal plain to a constant low
abundance. 2. Biomass. Follows a similar trend
to abundance, with decreasing total biomass
with increasing depth
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Organism Size
For many of the main groups of organisms (e.g.
fish), there is an increase in the size of the
individual organism with depth. The presence
of giant organisms in comparison with coastal
regions is a feature of the abyss
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Diversity
From the data obtained by deep-sea surveys, there
appears to be an increase in diversity (e.g.
number of species) peaking between 2-3 km
depth. From here, the number of species present
decreases. However, this area has been one of
intensive sampling in order to catch the more
sparsely distributed organisms, so species
richness could be purely a function of sampling
effort.
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Diversity, cont.
If the number of species for a given area of sea
bed is plotted against number of individuals, it
can be seen that there is a linear relationship
regardless of depth or location. Species
richness is therefore a function of abundance.
Recent studies off the east coast of USA
suggest a very high diversity in the deep-sea
(estimates up to 10 million species!)
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Species Composition
The bathymetric gradient down the slope is a
gradient of environmental stress comparable
with the salinity gradient in estuaries and the
exposure gradient on rocky shores. As a result,
a sequential distribution of similar species is
apparent down the slope.
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Main Groups of Organisms
Organisms can be classified by size Megafauna
are those visible in photographs and large enough
to be caught in trawls Macrofauna are
organisms smaller than this, but generally gt1mm
Meiofauna and micro-organisms are those
passing through a 1mm (or 0.5mm) sieve. a
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Deep Ocean Community Structure

• Few suspension feeders
• slow water movement
• levels of suspended organic matter too low to
  support suspension feeding

• Most invertebrates are deposit feeders
• - i.e., ingest organic enriched sediments.

Life is in slow lane - reproduction low but
constant - no seasonality - very constant
environment, physically speaking. Interesting
results in low density, but high diversity of
species.