how to hide in the sea ) transparency mirroring cryptic coloration counter-illumination

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 5-10 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...

DAY DAYNIGHT

10

200

Z (m)

New moon

Full moon

Nocturnal migrations

DAY DAYNIGHT

10

200

Z (m)

Twilight migrations

Three kinds of migrations...

Three kinds of migrations...

DAY DAYNIGHT

10

200

Z (m)

Reverse migrations

Why vertically migrate?

Reduce light-dependent mortalityMetabolic 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

Measured at 10 C

Tuna

Vent fish

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.

Large hinged jaw that can accommodate large prey

Viperfish

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ViperfishChauliodus macouni(depth 80-1600m)

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.

•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!

Coloration and Body Shape

Photophores on lower or ventral surface makes the silhouettes hard to see when they are viewed through water.

Value of Photophores

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

Bioluminescence

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.

Finding mates is a problem in the dark

So animals use…

1. Bioluminescence

2. Chemical signals

3. Hermaphroditism

4. Male Parasitism

Sex in the Deep Sea

Benthic Fish

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)

Nature of Life in the Deep Sea Benthos

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.

2 200 20,000 (um)

Snow

Bodies

Cells

cell chainplankton

fecesaggregates Willie

X

1-10 m

50 m

100 m

2000 m

Available towater columnprocesses

Reduction in Vertical Flux over Depth

1 2 3The Martin Curve

Martin and Knauer 1981

50% losses by 300 m75% losses by 500 m90% losses by 1500 m

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.

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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).

(Know the difference between bioluminescence and fluorescence and phosphorescence)

ALL PHYLA of animals have luminescent members

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Adaptations for Bioluminescence

Decoys: Long duration, broad wavelength, intenseFalse sense of size: Peripherally located, broad wavelengthBlind/confuse predator: Bright flash, broad wavelengthBlink and Run: Bright flash or luminescent cloudLure Prey: located near or in mouthBurglar alarm: bright, long duration

How does duration, intensity and wavelength serve an adaptation?

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BarreleyeMacropinna microstoma (Depth 100-900m)

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HeadlightfishDiaphus theta(depth 0-800m)

Northern PearleyeBenthalbella dentata(depth 500-1000m)

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Robust BlacksmeltBathylagus milleri(depth 60-1000m)

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Animal Adaptations in the Bathypelagic Mid-water Realm

Conservation of Energy

Blob sculpin(b)Psychrolutes phrictus

•Loss of muscularity and skeletal mass

•Low protein content in muscle

•Reduced eyesight

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Eelpout

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Giant grenadierAlbatrossia pectoralis Gigantism