Download Chapter 17

The Open Ocean
Chapters 6, 10, 12, 17
Regions of the Open Sea
• Vertical zonation depends on penetration
of sufficient sunlight to support
photosynthesis
– photic zone—receives enough light for
phytoplankton to survive
– aphotic zone—light rapidly disappears until
the environment is totally dark
• Epipelagic zone—the location of pelagic
animals in the upper 200 m of the ocean
Life in the Open Sea
• Classification of plankton
– taxonomic groups
•
•
•
•
seston—particles suspended in the sea
tripton—non-living seston
phytoplankton—primary producers
zooplankton—heterotrophic eukaryotic microbes
that float in the currents
• bacterioplankton—archaeans and bacteria
• viriplankton—free viruses (the most abundant
plankton of all)
Life in the Open Sea
• Classification of plankton (continued)
– functional groups
• akinetic—plankton that don’t move at all
• kinetic—plankton that can move
– size
• original scheme (based on collection method):
macroplankton, microplankton, nanoplankton
• newer classifications: femtoplankton, picoplankton,
mesoplankton, macroplankton, megaplankton
Life in the Open Sea
• Classification of plankton (continued)
– life history
• holoplankton—organisms that are planktonic
throughout their lives
• meroplankton—planktonic larvae that will grow into
non-planktonic organisms
Life in the Open Sea
• Classification of plankton (continued)
– spatial distribution
• neritic—distinguished by presence of
meroplankton and diverse diatoms
• oceanic—less diverse diatoms or invertebrate
meroplankton; more salps, larvaceans,
arrowworms and sea butterflies
• neuston—plankton that life close to the water’s
surface
• pleuston—plankton which break the surface of the
water with their gas bladders or bubbles
Life in the Open Sea
• Patchiness in the open sea
– plankton occur in patches (localized
aggregations), often around upwellings
– micropatchiness occurs throughout the photic
zone when marine microbes become attached
to particles of organic matter, especially
marine snow
• marine snow—strands of mucus secreted by
zooplankton that form translucent, cob-webby
aggregates
Life in the Open Sea
• Plankton migrations
– many open-ocean zooplankton migrate from
the surface to nearly 1.6 km deep each day
• provides access to phytoplankton in the photic
zone
• reduces predation by plankton-eating fishes in the
epipelagic zone
– deep scattering layer—a mixed group of
migratory zooplankton and fishes that are
densely packed
Plankton
• Diatoms
• Dinoflagellates
• Foraminiferans
Plankton
• Protozoans
Life in the Open Sea
• Megaplankton
– cnidarian zooplankton
• largest plankton are jellyfishes
Life in the Open Sea
• Megaplankton
– molluscan zooplankton
• pteropods (sea butterflies) have a foot with 2 large
wing-like projections and a greatly reduced
(thecosome pteropods) or absent (gymnosome
pteropods) shell
• pteropod ooze—calcareous sediments formed
from shells of dead thecosome pteropods
• purple sea snails produce bubble rafts
• nudibranchs
Life in the Open Sea
• Megaplankton (continued)
– urochordates
• salps
• pyrosomes—close relatives of salps that produce
colonies name up of hundreds of individual
animals joined to form a hollow cylinder up to 14 m
long
• larvaceans
Life in the Open Sea
• Nekton
– invertebrates
• squids
– fish
• billfish—species with an enlongated upper jaw
(bill) and no teeth
• tuna
• ocean sunfish
• sharks
• manta rays
Fishes
• Fishes are vertebrates—animals that
possess vertebrae, a series of bones or
cartilages that surround the spinal cord
and help support the body
• Primitive fishes lacked paired fins and
jaws
• Adaptation of jaws and paired fins allowed
fish to more efficiently obtain food
Jawless Fishes
• Class Myxini (hagfish) and class
Cephalospidomorphi (lampreys)
• Lack both jaws and paired appendages
• Have skeletons of cartilage (no bone)
• Lack scales
• Hagfish also lack vertebrae (some
scientists consider them invertebrates)
Cartilaginous Fishes
• Class Chondrichthyes
– e.g. sharks, skates, rays, chimaeras
•
•
•
•
Skeleton of cartilage
Possess jaws and paired fins
Have placoid scales
2 major groups:
– holocephalans (chimaeras or ratfish)
– elasmobranchs (2 body forms: streamlined or
dorsoventrally flattened)
Sharks
• Excellent swimmers with streamlined
bodies
– swim with powerful, sideways sweeps of the
caudal fin (tail)
– heterocercal tail—caudal fin in which the
dorsal lobe is longer than the ventral
• Males have claspers—modified pelvic fins
which transfer sperm from the male to the
female
Sharks
• Maintaining buoyancy
– sharks sink if they stop swimming
– large livers produce squalene—an oily
material with a density less than seawater
– squalene offsets the shark’s higher density to
help maintain buoyancy
Shark Sensory Systems
• Vision
– a clear nictitating membrane covers and
protects each lidless eye
– many species seem to have color vision
• Olfaction
– more important than vision – almost 2/3 of the
shark’s brain cells are involved in processing
olfactory information
– sharks are sometimes referred to as
“swimming noses”
Shark Sensory Systems
• Lateral line system
– consists of canals running the length of the
animal’s body and over the head
– canals open to the outside at regular intervals,
allowing free movement of water over the
neuromasts (sensory receptors) within
– neuromasts detect vibrations in the fluid which
alert the shark to movements in the water,
possibly made by prey animals
Shark Sensory Systems
• Ampullae of Lorenzini
– organs scattered over the top and sides of the
animal’s head
– sense electrical currents in the water
Digestion in Sharks
• Blade-like, triangular teeth in the mouth
grasp prey and tear off chunks
• Food is swallowed whole (sharks cannot
move their jaws back and forth to chew)
• Food passes through stomach to a short
intestine containing a spiral valve
– spiral valve—a structure which aids in
absorption by slowing the movement of food
and increasing the surface area
Osmoregulation in Sharks
• Maintain an internal solute concentration >
or = to the seawater
– retain large amounts of nitrogenous wastes,
mostly urea and trimethylamine oxide (TMAO)
• Gills and rectal gland (a large structure
that empties into the intestine) work to
excrete excess sodium chloride
• Kidney excretes other salts
Reproduction in Sharks
• Sperm produced in paired testes are
transferred to the female through grooves
in the claspers
• Oviparity
– most primitive mode
– eggs are laid outside the body and the
embryos develop in a protective case
– e.g. whale sharks, bullhead sharks
Reproduction in Sharks
• Ovoviviparity
– most common mode
– eggs hatch within the mother’s uterus but no
placental connection is formed
• young are nourished by yolk from the egg
– e.g. basking sharks, thresher sharks, saw
sharks, sand tiger
Reproduction in Sharks
• Viviparity
– most recent mode to evolve
– either the young directly attach to the
mother’s uterine wall or the mother’s uterus
produces “uterine milk” that is absorbed by
the embryo
– e.g. requiem sharks, hammerhead sharks
Skates and Rays
• Have flattened bodies adapted to a bottom
existence
• Greatly enlarged pectoral fins that attach
to the head
• Reduced dorsal and caudal fins
• Eyes and spiracles (openings for the
passage of water) on top of the head
• Gill slits on the ventral side
• Specialized pavement-like teeth are used
to crush prey (e.g. invertebrates)
Differences between Skates and
Rays
Rays: swim by moving
fins up and down
streamlined tails with
venomous barbs or
spines
larger size
ovoviviparous
Skates: create a wave
from the forward to
backward fin edges
fleshier tails with small
fins and no spines
smaller size
mostly oviparous
Defense Mechanisms
• Electric rays have electric organs that can
deliver up to 220 V
• Stingrays have hollow barbs connected to
poison glands
– treatment for stingray wounds: submerge in
hot water to break down protein toxin
• Sawfishes and guitarfishes have a series
of (non-venomous) barbs along their
pointed rostrums
Bony Fishes
• Class Osteichthyes
• Very diverse 25,000 species
• Most forms have: swim bladder (or lung),
bone, bony scales, and fin rays
• 2 major lineages:
– lobefins (subclass Sarcopterygii) –
coelacanths, freshwater lungfish
– ray-finned fishes (subclass Actinopterygii)
Ray-Finned Fishes
• 2 major groups:
– subclass Chondrostei – primitive forms with
heterocercal tails, primarily cartilage skeleton,
ganoid scales
• ganoid scales—thick, heavy scales which give the
fish an armored appearance
Ray-Finned Fishes
– subclass Neopterygii – homocercal tails,
cycloid or ctenoid scales, more maneuverable
fins
• homocercal tails—tails with dorsal and ventral
flanges nearly equal in size; vertebral column
usually does not continue into the tail
• cycloid & ctenoid scales—scales that are thinner
and more flexible; less cumbersome for active
swimmers
Ray-Finned Fishes
• Possess unpaired median fins and paired
fins, providing better control of movements
• Median fins consist of 1 or more dorsal
fins, caudal fin, and usually anal fin
– help maintain stability while swimming
• Paired fins consist of pectoral and pelvic
fins
– both used in steering
– pectoral fins also help to stabilize the fish
Body Shape
• Fusiform body shape—streamlined shape
with a very high and narrow tail
– efficient movement for active swimmers
Body Shape
• Laterally
compressed
or deep body
– allows
navigation
through
grass or
corals
Body Shape
• Depressed or flattened bodies
– bottom-dwelling fishes
Body Shape
• Globular bodies, enlarged pectoral fins
– appropriate for sedentary lifestyle
Body Shape
• Long, snake-like bodies, absent or
reduced pelvic and pectoral fins
– useful for burrowing, living in tight spaces
Fish Coloration
• 2 basic types of fish colors:
– pigments (biochromes)
– structural colors
• Pigments—colored compounds found in
chromatophores
– chromatophores—irregularly-shaped cells,
usually appearing as a central cell body with
radiating processes
– fish can alter color by moving pigments
between the central core and processes
Fish Coloration
• Structural colors—colors produced by light
reflecting from crystals located in
specialized chromatophores
– iridophores—chromatophores used to
produce structural colors
– colorless, relatively immobile crystals produce
mirror-like silver or iridescence
Fish Coloration
• Countershading is seen in open ocean fish
– obliterative countershading—coloration in
which the back (dorsum) is dark green, dark
blue or gray, and the shades grauate on the
sides to the belly’s pure white
• Disruptive coloration—background color of
the body is usually interrupted by vertical
lines; may be an eyespot
– more difficult for predators to see the fish
Fish Coloration
• Cryptic coloration—coloration which
blends with the environment
– used for camouflage
Fish Coloration
• Poster colors—bright, showy color
patterns
– may advertise territorial ownership, aid
foraging individuals to keep in contact, or be
important in sexual displays
– aposematic (warning) coloration—bright
coloration to warn predators that the fish is
too venomous or spiny to eat
Buoyancy Regulation
• Most fish use a swim bladder—a gas-filled
sac that helps offset the density of the
body and regulates buoyancy
– the fish can adjust the amount of gas in the
swim bladder to maintain depth
– gas is added as the fish descends and
removed as it ascends
Buoyancy Regulation
• 2 methods for adjusting the amount of gas
in the swim bladder
– gulping air from the surface or spitting air out
as needed
– gas gland—a specialized gland which fills the
swim bladder from gases dissolved in the
blood
• fish with a gas gland empty gas from the swim
bladder through diffusion into the blood
• Active swimmers do not have swim
bladders, and must keep swimming
Nervous System and Senses
• Nervous system consists of: brain, spinal
cord, peripheral nerves, and various
sensory receptors
• Olfaction
– olfactory pits—blind sacs opening to the
external environment that contain olfactory
receptors
– size varies with dependence of fish on
olfaction
Nervous System and Senses
• Taste and hearing
– taste receptors may be located on the surface
of the head, jaws, tongue, mouth and barbels
(whisker-like processes about the mouth)
– bony fishes have a lateral line system for
detecting movement in the water
– ears are internal and have a detection range
of 200 to 13,000 hertz
• human range = 20 to 20,000 hertz
Nervous System and Senses
• Vision
– no eyelids
– usually don’t need to adjust pupil size
because of the low quantity of light
– entire lens moves back and forth to focus
– eyes are usually set on the sides of the head
– most have monocular vision
– shallow-water species can perceive color
Feeding Types
• Carnivores (e.g. pufferfish, groupers)
– most bony fishes are carnivores
– prey are usually seized, swallowed whole
• chewing would block water flow past gills
• Herbivores (e.g. surgeonfish, parrotfish)
– feed on a variety of plants and algae
– teeth often broad and flat with a sharp edge to
scrape food from surfaces
– may have gizzard-like stomach to grind
vegetable matter
Feeding Types
• Filter feeders (e.g. anchovies, larvae)
– feed on plankton
– typically use gill rakers—projections from the
gill arches which filter phyto- and zooplankton
from seawater
– most travel in large schools, and are an
important food source for larger carnivores
Adaptations to Avoid Predation
• Many exhibit elaborate camouflage
• Pufferfishes and porcupinefish inflate their
bodies to deter predators
• Flying fishes use enlarged pectoral fins to
glide through the air and escape
• Pearlfish hide in other organisms
• Parrotfish secrete a mucus cocoon
• Surgeonfish are armed with razor-sharp
spines
Adaptations to Avoid Predation
• Clingfishes use a sucker to attach to rocks
so predators can’t dislodge it
• Triggerfish projects spines to deter
predators or wedge itself into cracks
• Scorpionfish and stonefish have venom
glands for self-protection
Reproduction in Bony Fishes
• Gonads are paired structures suspended
from the roof of the body cavity by
mesenteries (membranes)
• Sperm and eggs pass to the outside
through ducts, except in salmon
• Egg and sperm development is usually
seasonal
• Variation in the level of pituitary and
gonadal hormones controls the
reproduction process
Reproduction in Bony Fishes
• Pelagic spawners (e.g. tuna, wrasses)
– release vast quantities of eggs into the water
for fertilization by males
– fertilized eggs drift with the currents
– no parental care
• Benthic spawners (e.g. smelt)
– non-buoyant eggs with large yolks
– no parental care
– pelagic or benthic embryos/larvae
Reproduction in Bony Fishes
• Brood hiders (e.g. grunion)
– species that hid their eggs in some way but
exhibit no parental care
• Guarders (e.g. damselfish)
– species that care for their offspring until they
hatch and, frequently, through their larval
stages
• Bearers (e.g. jawfish, seahorses)
– species that incubate their eggs until they
hatch (in the mouth or a special pouch)
Reproduction in Bony Fishes
• Hermaphroditism—individuals have both
testes and ovaries at some time in their
lives
– occurs in at least 14 bony fish families
– synchronous—possessing functional gonads
of both sexes at one time
– sequential—changing from one sex to another
• protogyny—changing from female to male
• protandry—changing from male to female
Life in the Open Sea
• Nekton (continued)
– reptiles
• yellow-bellied sea snakes
– birds and mammals
• penguins
• whales
Characteristics of Marine
Mammals
• Class Mammalia
• Most have an insulating body covering of
hair
• Homeothermic
– allows activity day and night, and adaptation
to a wide range of habitats
• Mothers feed their young with milk
– mammary glands—special glands in the
female that secrete milk
Characteristics of Marine
Mammals
• Most marine mammals are placental
mammals—animals that retain their young
inside their body until they are ready to be
born
– placenta—an organ present only during
pregnancy that sustains the young
• Feed at various trophic levels
Sea Otters
• Have thick fur with an underlying air layer
for insulation (instead of blubber)
• Short, erect ears
• Dexterous 5-fingered forelimbs
• Well-defined hind limbs with fin-like feet
• Usually stay within a mile of shore, near
coastal reefs and kelp beds
Sea Otters
• Females normally give birth to 1 pup on
shoreline rocks, and it soon follows its
mother into the sea
• Consume nearly 25% of their body weight
in food each day
– eat sea urchins, molluscs, crustaceans, some
species of fish
• Diurnal, gregarious, vocal and playful
• Nearly hunted to extinction for fur
Pinnipeds: Seals, Sea Lions,
and Walruses
• Suborder Pinnipedia (e.g. seals, elephant
seals, sea lions, walruses)
– pinniped—”feather-footed”
• Have 4 limbs like terrestrial animals, but
are more at home in the water
• Come shore to give birth and molt
– most also mate on shore, and some sleep on
land or ice floes to avoid entirely aquatic
predators
Pinnipeds: Seals, Sea Lions,
and Walruses
• Eat fish, invertebrates; some eat other
homeothermic animals
• Eaten by sharks, killer whales and humans
Pinniped Characteristics
• 3 families:
– eared seals (Otariidae)
– true seals (Phocidae)
– walruses (Odobenidae)
• Eared seals have small external ears and
swim using their forelimbs
• Phocids (true seals) lack external ears and
swim with a sculling movement of their
hind flippers
Pinniped Characteristics
• Walruses swim with a combination of the 2
methods
• Pinnipeds have spindle-shaped bodies
• Many have several thick layers of
subcutaneous fat
• Round is carried on a distinct neck
• Large brains, well-developed senses
• 2 pairs of limbs are modified into flippers
Swimming and Diving
• Fast swimmers and expert divers
• Adaptations for diving
– exhale before diving to decrease buoyancy
– metabolism slows by 20% and heart rate
decreases while under water
– blood redistributed to direct oxygen to vital
organs such as the brain and heart
• Weddell seals and northern elephant seals
known for deep diving
Reproduction in Pinnipeds
• Most congregate on well-established
breeding beaches to mate/give birth
• Some species are polygynous—bulls
establish harems of 15 or more females
• Males arrive to establish territories;
females arrive, give birth to pups, then
mate again
Reproduction in Pinnipeds
• Gestation = 9-12 months
• Lactation period (length of time pups
nurse) depends on species and habitat
– coldest habitats = shortest lactation
– nursing stresses the mother and she loses
weight
– some breed on pack ice, and must wean pups
before it breaks up and becomes dangerous
to the pups
Eared Seals
• Sea lions
– e.g. California sea lion, the intelligent trained
seal seen in zoos and circuses
– highly social; congregate when on shore
• Fur seals
– distinguished from sea lions by thick, wooly
undercoats
– coats are prized in the fur market, so hunting
is limited to avoid decimating the population of
fur seals
Phocids, or True Seals
• Forelimbs are set closer to the head and
smaller than the hind limbs
– less adapted to life on land
– move on land by dragging their bodies
• Most congregate during breeding season;
males establish territories but mate with
only 1 female
• Most abundant: crabeater seal, which
actually eats plankton such as krill
Phocids, or True Seals
• Harbor seals are a familiar type
• Harp seal pups have a white coat, and are
thus prized in the fur market
Phocids, or True Seals
• Leopard seal is the only phocid that eats
homeothermic prey, including other
phocids, penguins, and seabirds
Phocids, or True Seals
• Elephant seals are the largest, and bulls
have a unique proboscis that amplifies
their roar and attracts mates
Walruses
• Lack external ears but have a distinct neck
and hind limbs that can be used for
walking on land
• Canine teeth of the upper jaws of males
have developed into tusks
– used to fight with other males or hoist the
animal onto ice floes
• Typical family group = 1 dominant bull with
a harem of up to 3 females and 6 calves of
various ages
Walruses
• Reproduction
– 11-month gestation period
– 1 or 2 calves stay with the mother until they
are 4 or 5 years old
– old bulls sometimes kill young
• Found in the Arctic region
• Eat fishes, crustaceans, molluscs and
echinoderms
• Eskimos are allowed to hunt them for
meat, but not for their tusks
Sirens: Manatees and Dugongs
• Order Sirenia (sirenians)
• Confined to coastal areas and estuaries of
tropical seas
• Similarities to whales
– streamlined, practically hairless bodies
– forelimbs that form flippers, tail flukes
– vestigial pelvis without hind limbs
• Completely aquatic
• Gentle and often trusting of humans
Dugongs
•
•
•
•
Strictly marine
Live in coastal areas of Indian Ocean
Feed on shallow-water grasses
Dugongs are distinguished anatomically
from manatees by:
– larger heads
– shorter flippers
– notched tail
Manatees
• Inhabit both the sea and inland rivers and
lakes
• Have smaller heads, longer flippers than
dugong, and rounded tails
• Mate and give birth under water
– male remains with female after breeding
• Strict vegetarians that consume large
amounts of shallow-water plants
• Motorboat propellers are the greatest
danger to northern manatees
Steller’s Sea Cow
• This Arctic sirenian is now extinct
• Species was first observed and recorded
by Georg Wilhelm Steller
• After his expedition brought furs from the
Commander Islands, this area developed
a reputation for furs which attracted
hunters
• The hunters used Steller’s Sea Cow as a
food source, and hunted the species to
extinction
Cetaceans: Whales and their
Relatives
• Mammals most adapted to life at sea
• E.g. whales, dolphins, porpoises
• Cetaceans have fascinated humans for
centuries
• Cetaceans have frequently appeared in art
and literature
General Characteristics of
Cetaceans
• Thought to have evolved from terrestrial
carnivores (now extinct)
• Bodies closely resemble those of fishes
and are very streamlined
– blowhole—nostril at the top of the head
– uniformly thick layer of subcutaneous blubber
– streamlining of body results in lack of neck,
inability to move head separately
– internal ears with wax plugs
General Characteristics of
Cetaceans
• Bodies closely resemble those of fishes and
are very streamlined (continued)
– essentially hairless, except for a few hairs on the
head
– lack of sweat glands conserves water
– forelimbs modified into stabilizing flippers
– tail composed of flat flukes composed of dense
connective tissue is the main organ of
propulsion
– countercurrent circulatory system with cold
blood directed to un-insulated flippers conserves
heat
Adaptations for Diving
• Prior to dive, a whale inhales an enormous
breath, oxygen is rapidly transferred to
blood, and the whale exhales to reduce
buoyancy
• Proportionately large lungs with many
alveoli—small air sacs
– increases internal lung surface area exposed
to blood vessels
– allows for more efficient diffusion of gases into
and out of blood
Adaptations for Diving
• Lungs and rib cage structured to collapse
easily upon descent
– contain little air during a dive
– animal avoids problems of compression and
decompression while diving/surfacing
• During a dive:
– metabolism and heart rate decrease
– blood is preferentially shunted to vital organs
and tissues (e.g. brain, spinal cord)
Adaptations for Diving
• Medulla oblongata is less sensitive to CO2
levels in blood
– can hold breath without urge to breathe
• Large amounts of hemoglobin and
myoglobin
– hemoglobin—molecule in red blood cells
responsible for carrying oxygen
– myoglobin—molecule in muscle tissue that is
a reservoir of oxygen for muscle activity
Adaptations for Diving
• Muscles less sensitive to lactic acid
– lactic acid—a waste produced during vigorous
or extended muscle activity in the presence of
insufficient oxygen
• Exhalation of mucus from blowhole upon
surfacing helps eliminate nitrogen from
inhaled air, preventing the bends
– the bends—condition in which nitrogen gas
dissolved in blood comes out of solution and
forms gas bubbles
Adaptations for Diving
• Water is prevented from entering
respiratory passages
– larynx opens into the nasal chambers instead
of the back of the throat
– cetaceans can open their mouths under water
without food or water entering respiratory
passages
Reproduction and Development
• Many travel in pods (groups) of adults and
young
• Usually bear 1 offspring at a time
• Nursed on extremely rich milk
– 40-50% fat, 10-12% protein
– infant grows rapidly
– can produce sufficient body heat until blubber
layer has developed
Types of Whales
• 2 suborders
– Mysticeti – baleen whales
– Odontoceti – toothed whales
• Baleen whales lack teeth, and filter food
from the water using baleen
– largest whales are of this type
• Toothed whales feed on larger prey
– e.g. dolphins, killer whales
Baleen Whales
• Enormous plates of baleen
– each plate has an elongated triangular shape
and is anchored at its base to the gum of the
upper jaw
– composed of keratin—a tough protein—in
fibers fused except at the inner edge, where
they form a fringe
– hundreds of plates form a tight mesh
– used to capture plankton, especially krill, and
fish
Baleen Whales
• Whale feeds by swimming open-mouthed
through the water, then straining out water
through baleen
– bubble net—a ring of bubbles blown by a
humpback whale to trap krill near the surface
for collection
• Baleen is protected by the underlip when
the whale is not feeding
Baleen Whales
• Right whales (family Balaenidae)
– lack dorsal fins and grooves on throat and
chest
– name derived from identification of these
whales as the “right whales” for hunting
– one species, the Greenland or bowhead
whale, is the rarest of all whales
Baleen Whales
• Rorquals (family Balenopteridae)
– have dorsal fin and ventral grooves
• ventral grooves allow the throat to expand while
the animal is feeding
– slender, streamlined, fast swimmers
– blue whale is the largest whale
– fin whale is second largest
– humpback whale has hump on its back,
bosses (bumps) on its snout, and very long
pectoral fins
Baleen Whales
• Gray whale (Eschrictius gibbosus)
– only eastern Pacific population survived after
western Pacific and Atlantic populations were
hunted to extinction
– migrate from summer feeding grounds in
Bering Sea to waters off Baja California to
mate and give birth
– referred to as mossback whales owing to
large accumulations of barnacles on their skin
Toothed Whales
• Sperm whales (Physeter macrocephalus)
– 3rd largest animal with massive blunt snout
– have a series of humps on the rear third of the
body, no real dorsal fin
– aggressive attackers of squid and fish
– polygynous – males accompanied by several
females
– named for spermaceti—an oily, wax-like
substance in the animal’s head
Toothed Whales
• Sperm whales (continued)
– ambergris—a digestive product; a secretion
thought to function in protecting the enormous
digestive system from undigested squid beaks
and cuttlefish cuttlebone
– spermaceti was sought as a high-grade wax;
ambergris, as a base for perfumes
Toothed Whales
• White whales (family Monodontidae)
– beluga whales are unique for their white color,
are found in northern polar seas
– male narwhals have a tusk developed from 1
of 2 tooth buds; narwhals also inhabit Arctic
waters
Toothed Whales
• Porpoises (family Phocaenidae)
– porpoises have a rounded head with no beak
(dolphins have a beak)
– harbor porpoises are small cetaceans known
for great intelligence, and have a wide
distribution in the North Atlantic
– Dall’s porpoise is perhaps the first animal to
be protected by law – Europeans once
considered it a rare delicacy
Toothed Whales
• Dolphins (family Delphinidae)
– collectively referred to as delphinids
– common dolphin has a definite beak
separated from the snout by a groove; known
for encircling and following ships
– bottlenose dolphins are used in research on
cetacean intelligence, and as performing
animals at aquariums
– orca (killer whale) is the largest dolphin; only
cetacean that eats homeothermic prey (e.g.
seals, sea lions, penguins)
Toothed Whales
• Dolphins (continued)
– pilot whales have a globular head, projecting
forehead, and muzzle that forms a small beak
• known for beaching themselves in large numbers
Echolocation
• Ears are modified to receive a wide range
of underwater vibrations
• Echolocation allows cetaceans to
distinguish and hone in on objects
• Dolphins emit clicking sounds
– orientation clicks—low-frequency clicks that
give the animal a general idea of its
surroundings
– discrimination clicks—high-frequency clicks
that give the animal a precise picture of a
particular object
Echolocation
• No vocal cords; sounds are produced by a
ring of muscles in the larynx, which allows
control of air flow
• Sounds are directed by being focused in
the melon
– melon—an oval mass of fatty, waxy material
located between the blowhole and the end of
the head
• Clicking sounds bounce off objects;
echoes picked up by sensitive areas on
the lower jaw
Echolocation
• Echoes provide 4 types of information:
– direction from which echo is coming
– change in frequency
– amplitude
– time elapsed before the sound returns
• This reveals object’s range, bearing, size,
shape, texture and density
• Traveling dolphins move their heads side
to side and up and down, scanning for
objects
Survival in the Open Sea
• Remaining afloat
– swimming methods
• flagella, cilia, and jet propulsion
– dinoflagellates, coccolithophores, silicoflagellates, and
blue-green bacteria swim with flagella
– tintinnids, ciliates, and larvae use cilia
– jellyfish, siphonophores, salps, and squid use jet
propulsion
• appendages
– appendicular swimmers—organisms that use
appendages to swim (e.g. copepods, pteropods)
• undulations of the body
– e.g. arrowworms, larvaceans, worms, fish, whales
Survival in the Open Sea
• Remaining afloat (continued)
– reduction of sinking rates
• frictional drag – can be increased by decreasing
volume, flattening the body or increasing body
length
• buoyancy – increased by storage of oils,
increasing water content of the body, exchange of
ions, and use of gas spaces
Survival in the Open Sea
• Avoiding predation
– benefit of being less conspicuous
• countershading—having dorsal surfaces that are
dark blue, gray or green and ventral surfaces that
are silvery or white
• many planktonic species are nearly transparent
Survival in the Open Sea
• Avoiding predation
– safety in numbers
• animals such as siphonophores (e.g. Portuguese
man-of-war) increase chances of survival by
forming colonies
Ecology of the Open Sea
• Open sea is a pelagic ecosystem—one in
which the inhabitants live in the water
column
• Small, primary producing organisms have
a relatively high surface area
– allows them to absorb more nutrients from
surrounding seawater
Ecology of the Open Sea
• Productivity
– all higher forms of life rely on plankton
– water near the surface receives plenty of
sunlight, but few nutrients from land or the
sea bottom (except in rare areas of upwelling)
– phytoplankton productivity is low in tropical
waters
• arrangement of water in layers with little circulation
between prevents nutrients from being brought
from the sea bottom
Ecology of the Open Sea
• Food webs in the open sea
– dissolved and particulate organic matter
• phytoplankton release photosynthetic products as
DOM into surrounding seawater
• heterotrophic bacteria recycle DOM as they eat it
and then are eaten by nanoflagellates
• bacterial loop—process in which bacteria
metabolize DOM and return it to the water in an
inorganic form available to phytoplankton
• lysis of bacteria by viruses releases DOM and
particulate organic matter (POM)
Ecology of the Open Sea
• Food webs in the open sea (continued)
– efficiency of open-ocean food webs
• surprisingly efficient
• entire phytoplankton or bacterial production may
be consumed daily
• conversion rates (food to biomass) may be high
• food webs may have food chains with 5-6 links
• few large animals are supported away from
upwelling areas because of limited rate of primary
production and declining conversion efficiency
along the food chain