Transcript 2010, final lecture 10, Mesopelagic Depths_Habitat2

Environmental Characteristics• of
the Epipelagic Zone

Three dimensiorality-no cues for orientation

No solid substrate-no shelter and no support
Characteristic Features of
Nektonic Species

Great speed

Great sensory abilities especially where
navigation is concerned

Counter-shading camouflage
Buoyancy adaptations-swim bladders,
accessory air sacs, reduced bone content, high
lipid content

Characteristics Features of
Nektonic Species (2)

Both r-selected (tunas, marlins, ocean sunfish,
which produces millions of eggs, and grow
extremely rapidly), and K-selected forms
(sharks, which may produce only a few to
tens of embryos and grow and mature quite
slowly)
Epipelagic Nekton

Holoepipelagic forms (spend their entire life in
the upper water column of the open ocean):
flying fishes, tunas, marlins, swordfish

Meroepipelagic forms (spend a part of their life
in the upper part of the water column in the
open ocean): herrings, salmon,
halfbeaks, mammals, turtles, penguins
Growth

Growth rates are usually very high in epipelagic
forms. However, longevity is usually not great
(Example: r-selected large tunas live for only 510 years, while K-selected sharks may live for
20-30 years, and mammals may live for even
longer periods).
••
Migration

Many pelagic organisms migrate very long
distances. Why should they do this?

Possible explanations include:(1) Exploit
different food supplies in areas where food is
abundant; (2) spawn young in warm waters
where growth rates will be high; and (3)
spawn where predators are less abundant.
How to hide in the sea
)
•
•
•
•
Transparency
Mirroring
Cryptic coloration
Counter-illumination
Transparency
(jellies, etc.)
Light passing
through is about
the same as the
downwelling
ambient
Reflection and
refraction from
animal exceeds
upwelling light
Cryptic coloration and
mirrored surfaces
mirrored fish
•White ventral surface is best under all
situations
•Dorsal surface never perfectly cryptic
Diagram showing how a keel on
the ventral surface of an animal
eliminates he dark shadow
normally cast downward by an
unkeeled animal. The presence of
the shadow means that an animal
living deeper and looking upward
would see the unkeeled nektonic
animal due to the shadow, but
would not see the keeled animal,
which would blend into the lighted
background. (Modified from Y. G.
Aleyev, Nekton, Dr. W. Junk BV.,
1977. Reproduced by permission
of Kluwer Academic Publishers.)
Fast swimming fishes with warm bodies have streamlined bodies and heavily muscled tails
with crescent shaped caudal fins. The ones illustrated here are three tunas: the bluefin (a),
the skipjack (b), and the wahoo (c), and a mackerel shark, the mako (d).
Typical adaptations of epipelagic fishes.
Three views of a tuna showing the adaptations necessary for fast movement.
(A) Front view. (B) Side view. (C) Top view.
Life in the
mesopelagic
and deep sea
is linked to
plankton
and light
intensity in
the water.
Animal Adaptations in the Mesopelagic
Mid-water Realm
Vertical Migrations of Animals
Diel (daily) vertical migrations: cycle is coupled to
downwelling light (the ‘Zeitgeber’ or ‘time-giver’)
Three kinds of migrations...
10
New moon
Z (m)
Full moon
200
DAY
NIGHT
DAY
Nocturnal migrations
Three kinds of migrations...
10
Z (m)
200
DAY
NIGHT
DAY
Twilight migrations
Three kinds of migrations...
10
Z (m)
200
DAY
NIGHT
DAY
Reverse migrations
Why vertically migrate?
Reduce light-dependent mortality
Metabolic advantage
• Light damage avoidance
• Minimize horizontal advection (use deep
counter-currents)
• Prevent over-grazing
• Maximize genetic exchange
• Minimize competition
Adaptations of Vertical migrators like the Lanternfish
on left and non-migrators like dragonfish on right.
1. Well developed muscles and bones
2. Swim bladder of air or fat
3. Withstand extreme temperature changes
O2 Minimum Layer
Torres et al.
Reduced with depth
Tuna
Vent fish
Measured at 10 C
Fish activity decreases with depth
Theusen and Childress
Only visual predators show this decrease in activity
Oxygen binding capacity of
OMZ animals
Summary of Low oxygen adaptations
Reduced oxygen consumption with depth
Results in reduced athleticism
Oxygen binding high
Mesopelagic Crustaceans
Photophores
Specialized light structures that make “living light”
or bioluminescence.
Typical Mesopelagic Fish
Rectangular midwater trawls used to collect
mesopelagic organisms. Net has remote control to
open only at certain depths.
As more
shallow fish are
over fished
other deeper
fish like this
black scabbord
fish are being
caught. This is
one way that we
have learned
more about fish
from deeper
depths.
Viperfish
Large hinged jaw that can accommodate large prey
Viperfish
Chauliodus macouni
(depth 80-1600m)
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Many non-migrators like this Rattrap Fish eat the more
muscular migrators because they have more protein!
Tubular eyes like this midwater bristlemouth fish,
with acute (great) upward vision.
Coloration and Body Shape
•Midwater predators rely on sight.
•Midwater prey cannot afford energy cost of swimming
fast, spines, or scales so they…
•Camouflage with countershading
(dark on top, light bottom or sides)
•Transparency = see through them
(in upper mesopelagic – jellies, shrimp, etc)
•Reduce the silhouette (bioluminescence on bottom)
With blue-green light they control!
Value of Photophores
Photophores on lower or ventral surface makes the
silhouettes hard to see when they are viewed through water.
Bioluminescence
Living light is used for…
1) Counterillumination to mask silhouette
2) Escape from Predators with confusing light
3) Attract or see prey
4) Communication and Courtship
Summary
Typical Characteristics of deep-sea pelagic fish
Tremendous pressure of 1,000 atmospheres or 14,700 psi
1. Tough to visit and bring fish back alive
2. Metabolism affected by pressure
3. Molecular adaptations to allow enzymes to work under
extreme pressures.
Sex in the Deep Sea
Finding mates is a problem in the dark
So animals use…
1. Bioluminescence
2. Chemical signals
3. Hermaphroditism
4. Male Parasitism
Benthic Fish
Nature of Life in the Deep Sea Benthos
Reduced eyes or are completely blind
(Live in complete darkness)
Huge mouths to eat prey larger than themselves
(Scarce food -less than 5% from higher waters)
No vertical migrations to richer surface waters
(small to reduce metabolic demands; flabby muscles,
weak skeletons, no scales, and poorly developed
respiratory, circulatory, and nervous systems)
Nature of Life in the Deep Sea Benthos
Slow Pace
(Save Energy)
Low Temp and High Pressure
(slow pace)
Live Long and Large
(up to 100 years)
Produce fewer larger eggs
(a lot of food for larva)
Dominated by Deposit Feeders
(eat marine snow)
Marine Snow Particles
Marine Snow Particles
Discarded feeding houses
Marine Snow Particles
‘Comets’
Aggregates
Contribution of Marine Snow to Vertical Flux
Narrow window of particle sizes which are large
enough to sink but numerous enough to be widely
distributed.
Cells
Snow
Bodies
2
200
20,000 (um)
cell
chain
plankton
feces
aggregates
Willie
X
1-10 m
50 m
Available to
water column
processes
100 m
2000 m
Reduction in Vertical Flux over Depth
1
The Martin Curve
50% losses by 300 m
75% losses by 500 m
90% losses by 1500 m
Martin and Knauer 1981
2
3
Explanations for the Shape of the Martin Curve
• Bacterial decomposition = remineralization of Carbon
• Cryptic swimmer distribution
• Smaller, slower sinking particles at depth
Composition of Marine Snow
Once living material (detrital) that is large enough to
be seen by the unaided eye.
Described first by Suzuki and Kato (1955)
High C:N makes for poor food quality.
• Senescent phytoplankton
• Feeding webs (e.g., pteropods,
larvaceans)
• Fecal pellets
• Zooplankton molts
Formation of Marine Snow
Type A: Mucous feeding webs are discarded
individually.
Type B: Smaller particles aggregate into larger,
faster sinking particles.
Aggregates
Extreme Deposition: Food Falls
• Rare events (not recorded in traps)
• Deposit large amounts of high quality organic
materials to sea floor (low C:N)
• Rapid sinking, reach 1000s of meters in few days
• Large bodies that remain intact (whales, fish,
macroalgae, etc)
Amount of nutrients at
different depths is
controlled by
photosynthesis,
respiration, and
the sinking of
organic particles.
Nutrients are
recycled but sink!
Deep water originates at the cold surface at the poles.
Cold water sinks and spreads out along the bottom.
Sound Scatterers
Who are they?
Fishes (e.g., myctophids or lanternfish)
Crustaceans (copepods, krill)
Jellies (siphonophores, medusae)
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Animal Adaptations in the Mesopelagic
 Food
• Oxygen
• Light
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Mesopelagic
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Animal Adaptations in the Mesopelagic
Mid-water Realm
Bioluminescence
Production of light by organisms through chemical
reaction (kind of chemiluminescence).
ALL PHYLA of animals have luminescent members
(Know the difference between bioluminescence
and fluorescence and phosphorescence)
66
Adaptations for Bioluminescence
Decoys: Long duration, broad wavelength, intense
False sense of size: Peripherally located, broad wavelength
Blind/confuse predator: Bright flash, broad wavelength
Blink and Run: Bright flash or luminescent cloud
Lure Prey: located near or in mouth
Burglar alarm: bright, long duration
How does duration, intensity and wavelength serve an
adaptation?
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Barreleye
Macropinna microstoma
(Depth 100-900m)
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Headlightfish
Diaphus theta
(depth 0-800m)
Northern Pearleye
Benthalbella dentata
(depth 500-1000m)
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Robust Blacksmelt
Bathylagus milleri
(depth 60-1000m)
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Animal Adaptations in the Bathypelagic
Mid-water Realm
Conservation of Energy
•Loss of muscularity
and skeletal mass
•Low protein content in
muscle
•Reduced eyesight
Blob sculpin(b)
Psychrolutes phrictus
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Eelpout
73
Giant grenadier
Albatrossia pectoralis
Gigantism
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