MAY 2011
Oceanography Ch # 14
Animals in the Pelagic Environment.
Introduction
Pelagic Organisms (Phytoplankton) make up more than 50% of the Ocean
biomass. They live in the water column penetrated by light. They can stay afloat
as a result of their size or appendages, or ability to produce droplets of oil, or
attaching themselves to floating objects, or swimming continuously or they have
gas containers or have only soft body parts.
14 – 1. Staying above the Ocean floor
Organisms increase buoyancy – with gas containers in their bodies.
Examples: Cephalopods regulate the amount of air in the container, but they
must stay above 50 met depth.
Organisms use swim bladders. These Slow swimmers add or remove gas
through ducts to change their depth. (maintain a constant pressure). Swimmers
living on the sea floor do not have a swim bladder. The gas composition for
shallow water dwellers is 20% Oxygen (similar to the atmosphere). Deep water
dwellers may store gas up to 90% Oxygen. Many animals that venture very deep
often have special organs in which fat is substituted for air (0.7 gms/cubic cm).
Floating Heterotrophs range in size from Microscopic Zooplanktons with
hard tests (2nd. Largest biomass in the ocean) to large species (jellyfish) with
gelatinous bodies. Their density is reduced to stay afloat. Example: Radiolarians
are abundant, single celled, extract silica from the water and make intricate
patterns to increase surface area and surface tension.
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Foraminifera are also single celled, barely macroscopic. Some species are
benthic, make hard shells by extracting CaCO3. They have segmented chambers
with openings at one end.
Copepods are shrimp-like, microscopic, crustacean, have a hard
exoskeleton, segmented and jointed legs.
Macroscopic Zooplanktons –
Krill are large enough to be seen without a scope. There are > 1500 species.
Coelenterates have hollow soft bodies. Hydrozoans – Portuguese Man O War.
Nektons (Swimming) Organisms.
Squids, marine mammals, and fish can swim as fast as any fish of
comparable size. Use Jet propulsion. Fish locomotion - wave of the lateral body
curvature passes from front to back. Fins are used for swimming and staying
afloat. Tail fin provides thrust. Can migrate long distances.
Deep sea fish have special adaptations, good sensory devices and
bioluminescence, which allow for survival in complete darkness. – large eyes,
dark color, smell to track food, large sharp teeth, expandable bodies and hinge
jaws.
The Diversity of Planktonic Animals
Microscopic Zooplankton –
Radiolarians, are single-celled. Has a hard shell, ornamental, with spikes
and spines, composed of silica. Ornaments increase surface area and may be a
defense mechanism.
Foraminifers – benthic species with chambers in a hard shell of CaCO3. A
component of deep sea sediments.
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Copepods – shrimp-like animals. Has a hard exoskeleton, segmented with
jointed legs, forked tails and elaborate antennae, lays eggs. There are > 7500
species.
Macroscopic Zooplankton –
Krill - Resembles a mini shrimp, up to 2 inches long, > 1500 species. Very
abundant around Antarctica.
Hydrozoan is not self propelled, but pushed by the wind. Example: The
Portuguese man-of-war. Poisonous to humans.
Jellyfish – move through muscular contractions.
Swimming Organisms
Nektonic organisms- Example: Squid, an active predator of small fish. It has
a long slender body with paired fins, and hollow chambers (see p.428).
Fish – locomotion through lateral wave of its body. Fins provide the forward
thrust.
Fin design in Fish
Pelvic (underside) and pectoral are used to turn, brake and balance.
Vertical fin serves as stabilizers.
Rounded fins are flexible and are used for accelerating and maneuvering at
slow speeds.
Forked fins and truncate fins are flexible and are used for propulsion (in
faster fishes)
Lunate fins on fast cruising fish (Tuna) are used very efficiently for
propulsion.
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14 -2. Adaptations for seeking prey
Lungers (grouper) wait patiently, use short bursts of speed to capture prey.
Its muscle color reflect how O2 is used. All muscle tissue is white. Have a truncate
caudal fin, used for speed and maneuverability.
Cruisers have red muscle tissue and a much greater Oxygen supply. Speed –
fast when hunting for food but faster when trying to escape a predator. Generally,
the larger a fish is, the faster it can swim. The Yellow fin Tuna has been clocked at
75 km/hr (about 20 body lengths/sec).Toothed whales are also fast. Killer whales
speed sometimes exceed 55 km/hr.
Cold- Blooded vs Warm- Blooded Organisms
Cold blooded fish are not fast. Their body temp is similar to the surrounding
water. Warm blooded temp range from 86 to 95 Deg F. Or 5 Deg C. difference
from the water temp.
Adaptations for Deep Water Nektons
Food source is detritus. They have small populations, use sensory devices to
collect food. They have light producing cells (photophores) and use
bioluminescence to attracting others.
Most shrimp and squid have photophores cells and can bioluminesce.
Bioluminesence attracts prey, or is used to attract a mate or to escape a predator.
Deep water nektons have large, sharp teeth, hinged jaws, expandable bodies and
huge mouths.
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14 -3. Adaptations of Pelagic Organisms (to avoid being a prey).
Schooling. – during spawning, for invading new territory and for protection
against predators.
Other adaptations – secrete poisons, mimicry of other species, camouflage
and counter-shading.
14 -4. Characteristics of Marine Mammals.
Seals, sea lions, manatees, porpoises, dolphins and whales.
Fossils of whales have been discovered in China, India, and Pakistan. They
indicate a possible land origin about 50 MMy ago.
Mammalian characteristics include: warm – blooded, breathe air, have hair,
bear live young and females have mammary glands.
Other Carnivores are the sea otters, polar bears, walruses, seals, sea lions
and fur seals (pinnipeds)
Otters have no blubber, but dense fur, eat shell fish, crustaceans. They inhabit
kelp beds and use rocks to break shells.
Polar Bears have massive webbed paws, are excellent swimmers and feed mainly
on seals.
Walruses have ivory tusks, which are used to kill their prey.
Seals lack ears and prominent front flippers. They have claws, a different hip
structure from sea lions or fur seals. They propel themselves with their rear
flippers.
Manatees and Dugongs (sea cows) belong to the Order Sirena. Manatees
have nails on their front flippers, similar to elephants. Dugongs live in the Indian
ocean and the western Pacific. They eat shallow water grasses – true vegetarians.
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Whales, Dolphins and Porpoises are from the Order Cetacea. They are cigar
shaped, insulated with a thick blubber layer, have an elongated skull with blow
holes on the top of the skull. They have very few hair and a horizontal tail fin and
are all excellent swimmers. They have adapted with a streamline body,
specialized skin, can dive to great depths (2800 meters), use oxygen efficiently.
Effects of deep Diving
Nitrogen narcosis – Nitrogen dissolves in the body, to give a feeling of
drunkenness, when one dives too deep ( >30 met) or stays too long at depth. If
one returns too quickly to the surface, decompression sickness strikes (bends). It
is similar to opening a carbonated soda – bubbles interfere with the blood
circulation.
Characteristics of Toothed Whales.
They use their teeth to hold and orient fish , squid, etc. before swallowing.
They also have the ability to use sound to communicate and locate them-selves.
Intelligence wise, they have a large brain cavity, highly convoluted cells.
Baleen whales are the largest (Blue, hump back, fin back and gray whales). Baleen
is used to separate small prey and to concentrate them. The gray whale has short
coarse baleen, the Rorqual has short baleen and the Right whale has long fine
baleen.
Dolphins and Porpoises – differences
Dolphins can leap out of the water while swimming. Their teeth are pointed.
Some dolphins in the wild have assisted drowning humans. They can be trained to
respond to hand signals. Porpoises are smaller and more stout, and have blunt,
flat teeth.
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14-5. Why do Gray Whales migrate?
First: They can grow to 50 ft long, weigh 35 Tons and up to 60 years. They feed on
cold water sea floor organisms. Theories to explain their migration patterns are:
 A relic of te ice age
 May leave habitat to escape a predator Killer whale
 Follow the food source.
They breed and give birth off Baja California. Their timing may be linked to
physical oceanographic conditions. First to leave are pregnant females, then nonpregnant mature females, followed by immature females, mature males and last
are immature males. Their return journey is in the opposite order.
The Gray whale are on the endangered species list.
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