Marine Biology (Chapter 15)

1. LIFE NEAR THE
SURFACE
CHAPTER 15

2. ◦ Pelagic realm – vast
open sea.
◦ It holds all the liquid
water on earth, the water
planet.
◦ It lacks solid physical
structure.

3. How open sea affects us?
1. It regulates our climate
2. Conditions our atmosphere
3. Provides food and other resources

4. EPIPELAGIC
◦ Shallowest; upper pelagic realm
◦ The zone from the surface down to a depth of 200 m
(650 ft).
◦ Generally the warmest, and best lit.
◦ Primary production takes place.
◦ Photic zone – the layer from the surface of the depth
where light limits photosynthesis.

7. Two main components:
1. Coastal or Neritic – lie over the continental shelf.
◦ relatively close to the shore
◦ supports most of the world’s marine fisheries.
2. Oceanic – surface water beyond the continental
shelf.

8. THE ORGANISMS OF THE EPIPELAGIC
◦ Pelagic realm is fueled by solar energy captured in
photosynthesis.
◦ Epipelagic supply food to other communities;
◦ intertidal zone
◦ aphotic zone
◦ Epipelagic lacks deposit-feeders.

9. THE PLANKTON
Mostly small microscopic organisms carried
about by water currents, having little or no ability
to swim horizontally, but can swim vertically.

10. 1. Femtoplankton – composed of viruses (virioplankton)
2. Picoplankton – consists of archaea and bacteria
3. Net plankton – they can be caught in nets (e.g. micro-,
meso-, macro-, and megaplankton)

11. 4. Phytoplankton – microscopic autotrophs (plants),
single celled or loose aggregates restricted to the photic
zones
5. Zooplankton – most microscopic heterotrophs,
singled celled to large multicellular animals
A. Holoplankton – spend their entire life in the plankton
B. Meroplankton – spend part of their life in the plankton

18. PHYTOPLANKTON

19. ◦ Single-celled microscopic organisms dispersed
throughout the epipelagic zone.
◦ They produce more than 95% of photosynthesis in
the ocean.
◦ This accounts for half of all primary production and
nearly half the oxygen in our atmosphere.

20. ◦ Extremely important
phytoplankton
◦ Most abundant in both near
the coast and open ocean.
◦ Common in temperate and
polar regions and other
nutrient-rich waters.
DIATOMS

21. ◦ Important in both neritic and
oceanic waters, but prefer
warm areas.
◦ Most abundant in tropic areas.
◦ May be better-adapted to low-
nutrient conditions.
◦ May grow explosively in huge
numbers (bloom), sometimes
called red tides.
DINOFLAGELLATES

22. ◦ Abundant in nutrient-poor waters.
◦ Nitrogen-fixing bacteria.
◦ Most abundant picoplankton and
account for at least half the ocean’s
total primary production.
◦ Trichodesmium – grows in
filamentous colonies that can be
caught in nets.
CYANOBACTERIA

23. ◦ Prochlorococcus – most abundant
of all marine phytoplankton.
◦ It is dominant in nutrient-poor
tropical and subtropical waters.
◦ Synechococcus – very abundant in
polar waters.

24. ◦ Eukaryotes make up less
than 5% of the total
picoplankton cells in water.
◦Their ecological role in the
phytoplankton is poorly
known.
PROTISTS

25. A. COCCOLITHOPHORIDS
◦ Abundant group of phytoplankton.
◦ They do best in open ocean but also occur in coastal waters.
B. CRYPTOPHYTES
◦ Very plentiful in neritic waters.
◦ Very important in the economy of the sea.
C. SILICOFLAGELLATES
◦ Occasionally bloom
◦ Important primary producers.

28. ZOOPLANKTON

29. ◦ The animals that of the pelagic region.
◦ Only organisms that can feed directly on phytoplankton.
◦ Herbivorous zooplankton are the primary link of the
flow of energy through the food web.

30. ◦ Most zooplankton are carnivores and few are strict
herbivores.
◦ Most nektonic animals begin life as members of the
zooplankton community.
◦ As the zooplankton grow and improve their
swimming capabilities, they eventually graduate to the
status of nekton.

32. ◦ They can catch tiny picoplankton and nanoplankton.
◦ Without protozoans, much of the primary production in the
epipelagic would go unutilized.
◦ Flagellates, ciliates, foraminiferans, and radiolarians.
◦ Many grazing protozoans are capable of photosynthesis,
so they also act as members of the phytoplankton.
PROTOZOANS

33. Foraminiferans Radiolarians

34. ◦ Small crustacean dominate
the net zooplankton.
◦ Most abundant in ocean;
◦ 70% or more.
◦ Most numerous group of
animals on earth.
COPEPOD

35. ◦ Major carnivores; though
most copepods eat at least
some phytoplanktons, many
also eat other zooplanktons.
◦ A few copepods are
exclusively carnivorous.
◦ They generally catch their
prey with their claw-like
appendages.

37. ◦ Krill – shrimp-like often aggregate into huge, dense swarm.
◦ Prefer cold oceanic waters, they sometimes dominate
zooplankton in polar seas.
◦ Filter-feeders, capturing phytoplankton.
◦ They also eat small zooplankton and detritus.
◦ 6 cm (2.5 in) in size.
OTHER CRUSTACEANS

38. ◦ A few larger crustaceans also occur in the net zooplankton.
◦ E.g. decapods like crabs, shrimps, etc.
◦ Decopods are almost exclusively carnivorous.

39. 1. SALPS – transparent, planktonic relatives of the sea squirt, or
turnicates, that live on the bottom.
◦ They catch phytoplankton by filtering water through a sieve-
like sac or fine mucus net.
2. LARVACEANS – float inside a house they make of mucus.
◦ They beat tail to move water through the house.
◦ Food particles are caught in mucus that is secreted inside the
house.
NON-CRUSTACEAN ZOOPLANKTON

43. VIDEO 1
VIDEO 2
VIDEO 3

44. 3. PTEROPODS – a group of
molluscs, also includes
phytoplankton grazers.
◦ Small snails in which the foot
has been modified to form a
pair of wings that they flap to
stay afloat.
◦ Some feed in phytoplankton
using mucus nets or threads.

45. ◦ Larvaceans, salps, and some pteropods feed with mucus
nets or threads.
◦ They are among the few zooplankton that can eat
picoplankton and nanoplankton.
◦ Discarded larvacean houses are an important source of
detritus in epipelagic.

46. 4. ARROW WORMS or CHAETOGNATHS
◦ Feed mostly on copepods.
◦ They have a major role in epipelagic food web.
5. JELLYFISHES, SIPHONOPHORES and
COMB JELLIES.
◦ Quite large but weak swimmers and drift with the current as
part of the plankton.
◦ They are carnivorous.

48. 6. OCEAN SUNFISH
(Mola mola)
◦ Grows to 2,300 kg (5,000 lb)
◦ Swims weakly and
sometimes considered a
member of the zooplankton.

49. VIDEO 4

50. ◦ Holoplankton – spend their whole lives in the plankton
◦ Meroplankton – the larval stages of invertebrates and
fishes that spend only part of their lives in the
zooplankton.
◦ Nearly all marine fishes have planktonic larvae.

52. THE NEKTON

53. ◦ They are large, strong swimmers.
◦ It includes fishes, marine mammals, squids, turtles, sea
snakes and penguins.
◦ All nekton are carnivorous.
◦ Most species of nekton eat other nekton.
◦ Planktivorous nekton – eat planktons (e.g. herring,
sardines, anchovies, whale shark, basking shark, and
baleen whales).

54. ◦ Lanternfishes – stay deeper water during day and
swim up into epipelagic at night, consume large
amounts of zooplankton.
◦ Sperm whale (Physeter catodon) – largest of all
nekton except baleen whale, eats giant squid more
than 10 m (33 ft) long.

56. LIVING IN THE
EPIPELAGIC

57. ◦ Two main adaptations needed of an organism living
in epipelagic:
1. The need to stay in the epipelagic
2. The need to eat and avoid being eaten.

58. STAYING AFLOAT
◦ Cells and tissues are denser than water.
◦ Shells and skeletons are even more dense.
◦ Phytoplankton have to stay in relatively shallow water to
get enough light for photosynthesis.

59. How can you stay afloat if you cannot swim?
◦ To increase water resistance
◦ To be more buoyant

60. Increased Resistance
◦ Drag – resistance to movement through water or any
other medium.
◦ For small organisms, drag depends most on surface
area: the higher the surface area, the higher the water
resistance and the slower the organism to shrink.
◦ They have more surface area per unit volume than large
organisms.

61. ◦ Common adaptations that can increase surface area:
1. Organism’s shape
◦ parachute-like shaped of jellyfish
◦ extremely flat shapes of many planktons
2. Long projections or spines
3. Many phytoplankton form chains

64. Increased Buoyancy
1. Storage of lipids, such as oils and fats, in the body.
◦ Many planktons – diatoms, copepods, fish eggs and
larvae – contain oil droplets.
◦ Many adult epipelagic fishes also gain buoyancy by
storing lipids. (e.g. sharks, tunas). They have poorly
developed swim bladder.
◦ Lipids are less dense so they tend to float.

65. ◦ Epipelagic shark – have enlarged livers with very high
oil content.
◦ Whales, seals and other marine mammal have a great
deal of buoyant fat in a thick layer of blubber under the
skin.
2. A blubber provides insulation from cold as well as
buoyancy.

66. 3. Pocket of gas
◦ Cyanobacteria – have tiny gas bubbles, or vacuoles,
inside their cell. They are able to change the number and
buoyancy of the vacuoles. It allows them increase
buoyancy to move up in the water column or decrease it
to sink.
◦ Most epipelagic bony fish have swim bladders for
buoyancy.
◦ Gas-filled bladder or float – disadvantage: gases expand
and contract as the fish moves in the water column and
the pressure changes.

68. 4. Control the composition of the body fluid.
◦ excluding heavy ions like sulfate and magnesium; and
replacing them with lighter ones – ammonium and chloride,
◦ organisms can reduce their density and become more buoyant.

69. The Floaters
◦ Neuston – organisms that live right at the sea but remain
underwater.
◦ Pleuston – organisms whose bodies project through the
sea surface into the air.
◦ The most common method of doing this is to have some
sort of gas-filled structure to provide buoyancy.

70. ◦ By-the-wind sailor (Velella)
◦ a colonial, jellyfish-like cnidarian, is specialized as a float.
◦ Portuguese man-of-war (Physalia)
◦ a siphonophore, is a famous for its powerful sting.
◦ Violet shell (Janthina)
◦ makes a raft of mucus filled with bubbles from which it hangs
upside down; predator of Portuguese man-of-war.
◦ Glaucus
◦a nudibranch, stays afloat by swallowing a bubble of air. It feeds
on the by-the-wind sailor, and its relative, disk-shaped Porpita.

72. VIDEO 5
VIDEO 6

73. VIDEO 7

74. ◦ Water strider (Halobates)
◦ the only insect that
lives in the open ocean.
Skims over the water
surface.
VIDEO 8

75. PREDATORS AND
THEIR PREY

76. SENSE ORGANS
◦ Most epipelagic animals have highly developed sense
organs to help them detect prey and enemies.
◦ VISION is important since the epipelagic has plenty of
light to see by, during the day.
◦ Many zooplanktons have well-developed eyes, though
most can’t see actual images, they can detect motion,
shapes, and shadows.

77. ◦ Copepods and other zooplankton use vision to locate
prey and avoid predator.
◦ Squid, fishes and marine mammals all have good
eyesight.
◦ Vision is especially important to nekton in the
epipelagic because there are no solid structures that
can be used for concealment.

78. ◦ Lateral line – remote sensing system of fishes which
is extremely sensitive to vibrations in the water.
◦ Echolocation – another remote sensing system found in
dolphins and other cetaceans. It is a built-in sonar which
allows them to locate prey at a distance.

79. COLORATION AND CAMOUFLAGE
1. Protective coloration, or camouflage
◦ nearly universal among epipelagic animals.
◦ jellyfishes, salps, larvaceans, and comb jellies are probably
best at being invisible.
◦ zooplanktons are partially invisible.

81. 2. Countershading
◦ the dorsal surface is dark and ventral is white or silver is
widespread among epipelagic nekton.
◦ most epipelagic fishes have silvery sides to reflect light,
where it blend in against the background whether they are
viewed from above or below.

83. ◦ Flying fishes (Cypselurus)
◦ have evolved a distinctive
defense to make them hard
to see.
◦ when threatened, they burst
out of the water an glide
through the air on their
greatly enlarged pectoral
fins.

84. SWIMMING: THE NEED FOR SPEED
◦ Epipelagic contains the world’s most powerful swimmers.
◦ All epipelagic nekton have streamlined bodies that make
swimming easier and more efficient.
◦ They have often smooth body surface; with usually small
scales or none at all.
◦ Fishes produces mucus that actually lubricates the body
surface, allowing them to slip the water even more easily.

85. ◦ They are also firm and muscular.
◦ Force is delivered mainly by the tail which is high and
narrow.
◦ Fins tend to be stiff – provides maneuverability and lift at
high speed.
◦ Two kinds of muscles:
1. Red muscle – it has a high concentration of myoglobin that
can store a lot of oxygen. Best suited for long and sustained
effort.
2. White muscle – provides short burst of power.

86. ◦ Epipelagic sharks, tuna and billfishes have evolved a
system to conserve the heat generated by their muscles
and keep their internal temperatures above that of the
surrounding water.
◦ Rete mirable or “wonderful net”
◦ special arrangement of the blood vessels of most
“warm-blooded fishes”

88. VERTICAL MIGRATION
◦ Zooplankton stay below (200 m) the photic zone during the day,
and they migrate to the surface to feed at night.
◦ Explanations for vertical migration of zooplanktons:
1. To avoid predators
2. They may be able to slow their metabolism and conserve
energy by spending part of their time in the deep water, which
is cold and reduces their body temperature. This is somewhat
like sleep or hibernation.
3. They migrate to avoid toxins produced by some phytoplankton.