1. Chapter 16
The Ocean Depths

3. “Inner Space”
Dark, cold, inhabited by bizarre fearsome looking creatures
Humans can only venture into this mysterious realm only with the aid of elaborate, specially designed craft – element of risk as well

4. Least known of all our planet’s environments
Ocean depths include a number of distinct habitats

6. Mesopelagic lies below the epipelagic “middle pelagic”
Still has some dim light – not enough for photosynthesis

7. Deep Sea
Below the mesopelagic
No sunlight at all

8. Several Different Habitats are found in the ocean depths
Each has a distinct community of organisms
All of them lack primary production of food by photosynthesis
Depend on organic matter produced in the surface layers of the ocean for food

9. Characteristics of the Habitat
Life is much less abundant below the photic zone
Most food particles get eaten before they sink into deeper water
Deep-water organisms depend on the surface for food and oxygen

10. There is a gradual thermohaline circulation to even the deepest parts of the sea, bringing life-giving oxygen
To sink all of this way the oxygen-rich surface water must become very dense (cold and salty)

11. Great Ocean Conveyor
Surface overturn reaches the bottom in the Atlantic south of Greenland and just north of Antarctica
After the water sinks, it spreads through the Atlantic and into the other ocean basins
The water eventually rises to the surface and flows back to the Atlantic
Thought to play a role in regulating earth’s climate

12. The Twilight World

13. The Twilight World The mesopelagic is a world of twilight
Dim light during the day is enough to see by
As the depth increases the sea gets darker
1000m (3,300 ft) there is no light at all
The absence of light marks the end of the mesopelagic zone

14. Temperature at a given depth in the mesopelagic varies much less than in the epipelagic
Main thermocline is in the mesopelgaic
Organism that move up and down in the water column encounter larger changes in temperature

15. The Animals of the Mesopelagic

16. Mesopelagic supports a rich and varied community of animals, which are often called midwater animals

17. Zooplankton
Major group of animals in the mesopelagic zooplankton are much the same as those in the epipelagic
Krill and copepods dominate
Krill and most mesopelagic shrimps have a common adaptation of midwater animals – photophores or light organs – specialized structures that produce light

18. Figure 16.02

19. The light produced is known as bioluminescence
Ostracods can be very abundant – group of crustaceans
Arrow worms or chaetognaths – important midwater predators

20. Jellyfish, siphonophores, comb jellies, larvaceans and pteropods are also common
Squids have photophores which are typically arranged in different patterns for each species

21. Figure 16.04

23. Midwater Fishes Most are quite small (2 to 10 cm) (1 to 4 in long)
Bristlemouths and lanternfishes are the most abundant
Most abundant fish on earth (Cyclothone signata)

24. Viperfish
Dragon-fishes
Barracudinas
Sabertooth fishes
Lancetfishes
Snake mackerels
Cutlass fishes

26. Adaptations of Midwater Animals
They are well adapted to their unique environment

27. Feeding and Food Webs
Most of the food produced in the epipelagic is used there
About 20% of the surface primary production sinks to the mesopelagic
Mesopelagic is chronically short on food
Abundance of midwater organisms reflects the productivity of the waters above

28. Many of the characteristics of midwater animals are related to the lack of food
Large mouth
Hinged, extendable jaws
Fearsome teeth
Very broad diets and eat just about anything
Large jaws allow them to eat just about anything

30. Two groups of Midwater Animals
One group stays in the mesopelagic (non-migrators)
One group migrates to the surface each night (Migrators)

31. Figure 16.09

32. Nonmigrators
A few species of small zooplankton, mainly copepods and krill
These organisms filter out detritus and small amounts of zooplankton that sink
Fecal pellets are an important part of the detritus eaten by mesopelagic filter feeders

33. Most non-migrating midwater animals are fishes, shrimps and squids
Sit and wait predators
Have a number of adaptations that reduce their energy requirements
Flabby, watery flesh
No swim bladder – too much energy required to fill and deflate it

34. Have soft weak bones
Have lost the defensive structures like spines and scales – reduce weight and make them more neutrally buoyant
Are not streamlined – do not swim much

35. Vertical Migration and the Deep Scattering Layer
Do not have to sit and wait for food to come to them
Swim up at night to feed in the rich surface layers and during the day they descend several hundred meters or more
Spend the day in a lethargic stupor

36. Vertical Migration Adaptations
Well developed muscles and bones
Retain the swim bladder for buoyancy
Swim bladder can be filled with fat which does not expand when the pressure changes
Can tolerate temperature changes

37. Importance of Vertical Migration
Transports food into the deep water
Vertical migrators carry products of surface production down with them
Greatly increases the food in the mesopelagic
Many non-migrating species feed heavily on the migrators
Have more muscle so they are a more nutritious meal

38. Sense Organs
Have eyes that are large and unusually sensitive – fish, squid, shrimps
Tubular eyes – some mid-water fishes have – complex visual system that is almost like having two pairs of eyes – very acute vision in the direction the eyes point

40. Coloration and Body Shape
Mesopelagic predators rely heavily on vision
Camouflage is perhaps even more important than in the epipelagic – basic strategies remain the same
Countershading, transparency, reduction of the silhouette

42. Transparency
Common in the shallower and better-lit parts of the mesopelagic
Copepods, jellyfish, shrimps, bristlemouth fish
Deeper – tend to be more silvery
Deepest darkest part – black or red – no red light appear black

43. Countershading Black backs and silvery sides
To reduce the silhouette they have laterally compressed bodies which reduces the size of the body outline

44. Bioluminescence Allows organisms to mask their silhouette
Bioluminescent photophores produce light that breaks up the silhouette and helps the animal blend in
Counter illumination – the emission of light by midwater animals to match the background light

45. Many mesopelagic animals can control the brightness of the light they produce and match it to the brightness of the light coming down from above

46. The ways to produce light
Photophores
Animal’s own specialized tissue
Symbiotic bacteria that live inside the light organ

47. Important Functions of Bioluminescence
Counter illumination
The pattern of photophores is different among species and even between sexes – communicate and attract mates
Bioluminescent secretions may serve as a defense mechanism
Light to lure prey
Light around eyes to help them see

48. The Oxygen Minimum Layer
Midwater organisms have to deal with a shortage of oxygen in the water
Oxygen enters the water in two ways: gas exchange with the atmosphere and as a by product of photosynthesis
Once a water mass leaves the surface and descends into mesopelagic depths there is no way for it to gain oxygen

49. Water becomes depleted in oxygen often in fairly defined layers around 50 m (1,600 ft)
Known as the oxygen minimum layer
Oxygen concentration can drop to practically nothing

50. The water below the oxygen minimum layer retains most of the oxygen it had when it left the surface since there is little decomposition and respiration

52. Adaptations to Little Oxygen
Large, well developed gills
Relatively inactive
Complex biochemical adaptations like hemoglobin that functions well at low oxygen concentrations

53. The World of Perpetual Darkness

54. Lies below the mesopelagic
Sunlight never penetrates here
Largest habitat on earth and contains about 75% of the planets liquid water

55. The Pelagic Depth Zones of the Deep Sea
Bathypelagic zone (1,000-4,000 m 3,300-13,000 ft)
Abyssopelagic zone (4,000-6,000 m 13,000 to 20,000 ft)
Hadopelagic or Hadal pelagic zone – waters of the trenches (6,000 m and below)

56. Each of the depth zones supports a distinct community of animals
They have many things in common

58. Conditions of the Deep Pelagic Environment
The environment is very stable
Always dark
Always cold (1 to 2 C or 35 F)
Salinity and other chemical properties are uniform
No countershading
Most zooplankton are drab gray or off-white, fish are black, shrimps are bright red

59. Bioluminescence is very common – not used for counterillumination and these organisms have fewer photophores
Used for attracting prey, communication and courtship
Becomes less common the deeper you go
Functional small eyes in the upper deep sea

60. Fishes of the deep parts of the deep sea are blind or have very small eyes

61. The Lack of Food

62. Organisms face a continual shortage of food
Only about 5% of the food from above makes it down to the waters of the deep sea
The animals do not make vertical migrations
Deep sea animals are few and far between

63. Most common, bristlemouths are small 50 cm (20 in) but they are larger than mesopelagic fishes
It is believed that deep sea fishes put their energy into growth and therefore reproduce slowly and late in life
Adaptations to food shortages are similar to the mesopelagic but they are accentuated

64. Adaptations to lack of food in the deep sea
Fish are sluggish and sedentary
Flabby, watery muscles, weak skeletons, no scales and poorly developed respiratory, nervous and circulatory systems
No swim bladders
Have huge mouths and can consume prey much larger than they are

65. Many have stomachs that can expand to accommodate large prey
Swallowers (Saccopharynx)
Gulpers (Euryphyarynx)
Anglerfishes – dorsal fin is a modified pole with a fleshy bit of tissue on the end

68. Sex in the Deep Sea

69. Finding a mate can be difficult
Most are hermaphrodites so that any two fish of a species can breed
Bioluminescence, pheromones (special chemicals that a male can detect and follow), male parasitism (male bites on to the female and stays)

70. The Deep Sea Floor

71. Shares many characteristics of the pelagic waters above it
Absence of light
Constant low temperature
Great hydrostatic pressure
Communities are different than the pelagic waters because there is a bottom

72. Scientist know more about the deep sea benthos than the deep sea pelagic organisms
However only 500 m2 (5,400 ft2) of the 270 million km2 (105 million mi2) of deep sea floor have been studied

73. Feeding in the Deep Sea
Food shortage is critical however, once the food lands on the bottom it remains until it is found and eaten unlike the pelagic waters above
Rain of organic matter from above is more like a drizzle

74. Meiofauna, tiny organisms that live among the sediment particles are the most numerous organisms of the deep sea
Suspension feeders are rare
Deposit feeders are common – many are infauna burrowing through the sediment, some are epifauna resting on the sediment
Polychaete worms are the most abundant macrofauna

75. Crustaceans
Bivalve mollusks
Sea cucumbers

79. Predators of the Deep Sea
Fairly rare
Sea stars, brittle stars, crabs
Fishes, squids
Sea spiders (pycnogonids)
Inverts of the deep sea are often much larger than their shallow water counterparts – deep sea gigantism

80. Tripod fishes
If a large piece of food makes it to the bottom amiphods are usually the first to find it
Fish that come quick are: grenadiers or rattails, brotulas, cusk eels, deep sea spiny eels, hagfishes – tend to be larger, more active and more muscular than bathypelagic fishes

81. The Nature of Life in the Deep-Sea Benthos
Life proceeds at a very different pace
Animals grow very slowly, probably because of lack of food
Live for a long time
Low temperature and high pressure may slow down the processes of life
Or they may need to live a long time to store up enough energy to reproduce

82. Eggs are usually large with a good supply of food of the larva to make it through its early stages without eating
Deep sea animals only produce a few eggs

83. Figure 16.27

84. Hot Springs, Cold Seeps and Dead Bodies

85. 1977 rich flourishing communities are found around the deep sea hydrothermal vents – Alvin
Around the vents there were gigantic worms, clams, dense clusters of mussels, shrimps, crabs and fishes
Vent communities vary considerablely from place to place
Over 400 species have been found around different vents

86. Primary producers are chemosynthetic archaea and bacteria
Hot water rising from the vents is rich in hydrogen sulfide which is toxic to most organisms but is also an energy rich molecule
Chemosynthetic prokaryotes use the energy in hydrogen sulfide to make inorganic matter – they are the base of the food chain

87. Many vent organisms have symbiotic bacteria that live within them and provide them with organic matter

89. Cold Seeps
Places mostly along continental margins or in sediment rich basins where hydrogen sulfide and methane seep out from the sea floor
Chemosynthetic prokaryotes use these molecules to support a community

90. Dead Bodies
After scavengers eat a whale the decomposing remains produce hydrogen sulfide and methane and can support a community similar to the vents and seeps

91. Spring, Seep and Body Communities
Organisms enjoy an energy rich environment and grow fast and large
Specialized habitats that are tiny oases separated by vast distances
Unreliable energy sources

92. The End