Chapter 16 The Ocean Depths

Life in the mesopelagic and deep sea is linked to plankton and light intensity in the water.

Nightly Migrations ~11 cm/sec (~4 BL/sec)

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

In the end, it’s all about fitness… Cumulative risk from predation must be balanced by energetic benefit going to reproduction. ‘better hungry than dead’

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.

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

Large hinged jaw that can accommodate large prey

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!

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

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

Typical Characteristics of deep-sea pelagic fish

Comparing mid-water and deep-water 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

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)

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)

Amount of nutrients at different depths is controlled by photosynthesis, respiration, and the sinking of organic particles. Nutrients are recycled but sink!

The deep currents are part of the great ocean conveyor. Small variations in the conveyor produce big changes in weather patterns around the world (El Nino). Large changes create ice ages.

Deep water originates at the cold surface at the poles. Cold water sinks and spreads out along the bottom.

Midwater shrimp experiment

Deep-sea Hydrothermal vents harbor rich communities. The primary production that supports these communities comes from microbial chemosynthesis, not photosynthesis. Tubeworms have symbiotic bacteria in them that take the hydrogen sulfide or methane from vents, or dead bodies and make energy rich molecules to feed the worms!

50 A Review of Abiotic Properties of the Deep Sea metazoans per 100 m Z (m) 2 bumps

51 A Review of Abiotic Properties of the Deep Sea metazoans per 100 m Z (m) 2 bumps

52 The Deep Scattering Layer

53 Sound Scattering Layer Swim bladders Air bubbles Hard bodies Compressibility of jellies

54 Sound Scatterers Who are they? Fishes (e.g., myctophids or lanternfish) Crustaceans (copepods, krill) Jellies (siphonophores, medusae)

55 Contribution of Migrators to DOC Production in the Mesopelagic Steinberg et al % of total carbon

56 Animal Adaptations in the Mesopelagic Food Oxygen Light

57 Mesopelagic

58 How to hide in the sea (Johnsen 2003) Transparency Mirroring Cryptic coloration Counter-illumination

59 Transparency (jellies, etc.) Light passing through is about the same as the downwelling ambient Reflection and refraction from animal exceeds upwelling light

60 Cryptic coloration and mirrored surfaces mirrored fish White ventral surface is best under all situations Dorsal surface never perfectly cryptic

61 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

62 Luciferan + Oxygen Oxyluciferan + Light Luciferase (oxidation) Oxidation of LUCIFERAN catalyzed by LUCIFERASE Luciferan either acquired by diet or by synthesis

63 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?

64 Crested Bigscale Poromitra crassiceps (depth m)

65 Barreleye Macropinna microstoma (Depth m)

66 Headlightfish Diaphus theta (depth 0-800m) Northern Pearleye Benthalbella dentata (depth m)

67 Viperfish Chauliodus macouni (depth m)

68 Robust Blacksmelt Bathylagus milleri (depth m)

69

70 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

71 Eelpout

72 Giant grenadier Albatrossia pectoralis Gigantism