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ANIMALS OF THE PELAGIC ENVIRONMENT
I. STAYING ABOVE THE OCEAN FLOOR
A. OVERVIEW
1.) Pelagic organisms that are suspended in seawater comprise most of the
ocean’s biomass.
> Lucky for phytoplankton, they are light and have enough frictional
resistance to stay up there
2.) In order to maintain their depth (in surface waters for food purposes), pelagic
marine animals must either increase their buoyancy OR continually swim (against
the pressure that is exerted on them).
B. GAS CONTAINERS
1.) Air is 1000 times less dense than water, therefore even a small amount of air
inside a marine organism would increase its buoyancy.
2.) Cephalopods (cephalo = the head, podium = a foot) have rigid gas containers
in their bodies.
> http://www.youtube.com/watch?v=QMFqV4SJLWg
3.) Figure 15-1 explains three different genera (plural of genus) with varying gas
containers
a.) Nautilus has a pressure of 1 atm inside its gas container, so it must stay
above 500 meters to avoid collapse.
4.) Swim Bladders are used by some slow-moving fish in order to achieve
neutral buoyancy. On the other hand, active swimmers (tuna) have no swim
bladder.
a) Figure 15-2 shows an example of a swim bladder.
b) It is an internal organ that either expands or contracts, depending on
depth. Thus, fish must remove or add gas to maintain a constant volume.
i) Some fish have a pneumatic duct that connects the swim
bladder to their esophagus, allowing for exchange of gases.
ii) Some fish do not have a pneumatic duct, so the exchange of
gases must happen between their blood and the swim bladder.
This process takes much longer, and thus, this fish cannot
withstand rapid changes in depth.
iii) At deeper levels (7000 m) gas compression is around 700
atmospheres, making the gasses less dense than water,
approximately the same as fat. Thus, some fish have special
organs that are filled with fat, not gas.
C. ZOOPLANKTON (FLOATING HETEROTROPHS)
1.) Microscopic Zooplankton (pictures on p.428)
a.) RADIOLARIANS
i) These are single-celled animals that build their tests out of what?
ii) How do they stay afloat?
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b.) FORAMINIFERS
i) These are single-celled animals that build their tests out of what?
ii) The test is segmented or chambered with a prominent opening.
c.) COPEPODS
i) These are shrimplike animals of the subphylum Crustacea.
ii) They have a hard exoskeleton.
 http://img.dailymail.co.uk/i/pix/2007/11_01/sealifeDM
0511_1024x681.jpg
 http://www.dailymail.co.uk/sciencetech/article491916/Under-microscope-Just-splash-seawater-aliveplankton.html
 http://www.youtube.com/watch?v=mUIOdyBdVqU&fe
ature=related
2.) Macroscopic Zooplankton
a.) KRILL
i) These are mini-shrimp-like animals that are no longer than 5 cm.
ii) They are abundant near Antarctica
b.) CNIDARIANS
i) These are animals with soft bodies (more than 95% water) and
tentacles that are armed with what?
ii) They were formally known as coelenterates.
iii) There are two basic groups, hydrozoans and scyphozoans
aa.) HYDROZOANS
> Portuguese Man-of-War
> Their gas chambers, called pneumatophores,
serve as floats and sails, allowing the wind to push
them across the ocean.
bb.) SCYPHOZOANS
> Jellyfish
> They move by muscular contraction. Water
enters the cavity under the bell ad it forced out
when muscles that circle the bell contract.
> Sensory organs that are light sensitive or gravity
sensitive are spaced around the outer edge of the
bell. Since they feed by going up and down, this is
important.
>
http://www.youtube.com/watch?v=K9cFbJ8qYWg
&feature=related
> http://www.youtube.com/watch?v=Id53jmsdxfQ
**There are two other classes of Cnidarians: (1) Anthozoans
(anemones, corals, etc.) and (2) Cubazoans (box jellies)
c.) TUNICATES
i) These are barrel-shaped animals with two openings (an incurrent
opening for inflow and an excurrent opening for outflow).
ii) Salps are tunicates.
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iii) Tunicates move by jet propulsion (water through them).
iv) http://www.youtube.com/watch?v=dWA3OI-sh8g
d) CTENOPHORES
i) These are gelantinous, spherical animals with 8 rows of hairlike
iridescent cilia. Each ctenophore also has a pair of tentacles with
adhesive pads for catching prey.
ii) A common variety is the “sea gooseberry”
iii) http://www.youtube.com/watch?v=Wm5ZdKKqkyI
e) CHAETOGNATHS
i) These are “arrowworms” that dart through the water and eat prey
with impressive mouthparts.
D. NEKTON (SWIMMING ORGANISMS)
1.) This group can include squid, fish and marine mammals.
2.) Swimming squid, for example, have no hollow chambers and therefore require
more energy to stay in the upper water of the oceans without sinking.
3.) Squid swim around by trapping water in a cavity between their body and the
pen-like shell and forcing it out through a siphon.
4.) Fish swim using contraction and relaxation of muscle sections called
myomeres. The backward pressure of thee fish’s body and fins produced y the
movement of this wave provides the forward thrust.
5.) FIN DESIGNS IN FISH
a) Most active fish use two sets of paired fins (pelvic and pectoral) to turn,
brake, and balance. Vertical fins (dorsal and anal) serve as stabilizers.
b) The caudal fin is the most important in propelling the fish. The
efficiency of the caudal fin depends on its shape and can be represented by
the aspect ratio. [ = (fin height)2 / fin area ]
c) See attached page with slides
d) Sometimes, the fin is designed for other reasons (flying fish, stingray,
gurnard)
6.) DEEP-WATER NEKTON
a) For these creatures, their main food source is detritus. What is that?
b) The lack of abundant food limits the total biomass.
c) These deep-sea fish have special adaptations.
d) Figure 15-14
e) Eyes are more sensitive
f) Bioluminescence, which means they create light organically by using
photophores.
 attracting prey
 staking out territory
 communication / seeking a mate
 escaping form predators by creating a flash of light
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II. ADAPTATIONS FOR SEEKING PREY
(1) Mobility (2) Speed
(3) Body Length
(4) Body Temperature (5) Circulatory System
A. LUNGERS VS. CRUISERS
1.) Lungers (eg grouper) wait for prey to come close by. Almost all of their
muscle tissue is white.
2.) Cruisers (eg tuna) actively seek prey. Most of their muscle tissue is red.
3.) Red muscle fibers contain more myoglobin (a red pigment with an affinity for
oxygen). Red fibers have more oxygen.
4.) So, why do they match with the types of fish?
B. SPEED AND BODY SIZE
1.) Generally, the larger the fish, the faster it can swim.
2.) Speed is sometimes given as “body lengths per time”
3.) What is the fastest fish in the ocean?
C. COLD-BLOODED VS. WARM-BLOODED
1.) Fish are mostly cold-blooded or poikilothermic, so their body temperatures
are nearly the same as their environment.
2.) Usually, they are not fast swimmers (mackerel, yellowtail, bonito are fast
swimmers, though).
3.) Fish that have temperatures much higher than their environment, which is
characteristic of warm-blooded or homeothermic organisms.
D. CIRCULATORY SYSTEM MODIFICATIONS
1.) A modified circulatory system helps mackerel sharks and tuna maintain their
high body temperatures. (only for warm-blooded animals)
2.) Most fish have a dorsal aorta located just beneath the vertebral column that
provides blood to the swimming muscles.
3.) As cool blood flows into red muscle tissue, muscle contractions happen, thus
creating heat, thus raising the temperature of the blood. So, to adapt to this, a fine
network of tiny blood vessels within the muscle tissue is designed to minimize
heat loss. These vessels, be it veins or arteries, are referred to as cutaneous (skin)
arteries and veins.
4.) This is a countercurrent heat exchange system
III. ADAPTATIONS TO AVOID BEING PREY
A. INTRODUCTION
1.) Trying to get food is a pretty big deal for living organisms. In fact, it’s mainly
what we do.
2.) Some are filter feeders, as in they move more leisurely as they filter their small
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prey from seawater.
3.) To avoid being prey (or become better predators themselves), organisms can
make adaptations dealing with speed, secreting poisons, and mimicry of other
poisonous or distasteful species, transparent color, camouflage, or countershading.
B. SCHOOLING
1.) School is a term used for large numbers of fish, squid, or shrimp that form
well-defined social groupings.
2.) Since they all move in the same pattern and same direction, spacing is an issue
(maintained either through lateral line (made up of neuromasts) or sight).
3.) Advantages include spawning advantages and protection from predators.
IV. MARINE MAMMALS
A. INTRODUCTION
1.) If an organism is in the class Mammalia, they have the following
characteristics:
 Warm-blooded
 Breathe Air
 Have hair in at least some stage of development
 Bear Live Young
 Females have mammary glands
2.) Marine mammals include at least 116 species within the orders Carnivora,
Sirenia and Cetacea
B. ORDER CARNIVORA
1.) Animals within order Carnivora have prominent teeth, including the cat and
dog families on land.
2.) Examples include: sea otters, polar bears, and pinnipeds (pinni = feather, ped
= foot). The name comes from organism’s prominent skin-covered flippers, such
as walruses, seals, sea lions, and fur seals.
3.) Refer to additional notes
C. ORDER SIRENIA
1.) Refer to additional notes
D. ORDER CETACEA (REFER TO HANDOUT FOR PICTURES)
1.) Refer to additional notes
2.) MODIFICATIONS
a.) For increase in swimming speed, cetaceans (along with their
streamlined bodies), their skin has a soft outer layer that is 80% water and
has narrow canals filled with spongy material. The soft layer decreases
the pressure differences at the skin-water interface by compressing when
pressure is high and expanding when pressure is low.
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b) For deeper dives, special structures allow them to use oxygen
efficiently and an ability to resist nitrogen narcosis.
3.) CETACEAN BREATHING (See Figure 15-24)
a.) Inhaled air finds its way to tin terminal chambers (alveoli).
b.) These are lined with a thin membrane that is in contact with a dense
bed of capillaries (?).
c) The exchange of gases between the inhaled air and the blood (O2 in,
CO2 out) occurs across this membrane.
d) This allows them to extract as much as 90% of oxygen from each
breath. (humans get 4-20% and take 15 breaths to 1to3).
e) Now, to use this oxygen, it must be stored and limited for the deep
dives.
f) Prolonged divers have such a large blood volume per unit of body mass,
this oxygen can be stored. (in the hemoglobin within red blood cells and
in the myoglobin (weigh less, carries more oxygen) in the muscles)
g) Also, they decrease energy going toward certain circulatory functions
(digestive tract, kidneys) so heart rate is reduced to 20%-50%. (None
happens in common dolphin, the whale, or bottlenose dolphin)
4.) NITROGEN NARCOSIS
a) When humans descend using compressed gas (including N2 and O2),
the can experience “the bends” or decompression sickness. This happens
from going too deep or staying too long at a depth more than 30 meters.
b) The lungs cannot remove the excess gases fast enough, reduced air
pressure causes small bubble to form in the blood.
c) The bubbles interfere with blood circulation, causing severe pain, sever
physical debilitation, or even death.
d) Cetaceans collapse their rib cage as well, removing all air from alveoli
in lungs. Thus, preventing the blood from absorbing additional gases,
therefore no nitrogen narcosis.
e) Maybe no sensitivity?
5) SUBORDER ODONTOCETI (toothed whales)
a) This includes the killer whale, sperm whale, porpoises, and dolphins
b) DIFFERENCE BETWEEN DOLPHINS AND PORPOISES
 Porpoises are smaller
 Porpoises have a more stout body shape while Dolphins have
are elongated and streamlined.
 Porpoises have a blunt snout, while dolphins have a longer
rostrum
 Teeth of dolphins end in points, while the teeth of porpoises are
blunt or flat
6) SUBORDER MYSTICETI
a) Refer to additional notes
b) Grey whales migrate from their cold-water summer feeding grounds in
the Arctic to warm, low-latitude lagoons in Mexico during winter for
breeding and birthing purposes.