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., 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.

Mesopelagic Crustaceans

Typical Mesopelagic Fish

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 NIGHT Z (m) New moon Full moon Nocturnal migrations

DAY NIGHT Z (m) Twilight migrations Three kinds of migrations...

DAY NIGHT Z (m) 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

O 2 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

Photophores Specialized light structures that make “living light” or bioluminescence.

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

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

36 Viperfish Chauliodus macouni (depth m)

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 are believed to be unable to afford the energetic cost of swimming fast, spines, or scales so they… Camouflage with countershading (dark on top, light bottom or sides) Are transparent = see through them (in upper mesopelagic – jellies, shrimp, etc) Reduce their silhouette (bioluminescence on bottom) With blue-green light they control! Coloration and Body Shape

Summary