The Earth's oceans are home to most of the planet’s biodiversity. Here we can find
mollusks, fish, whales, crustaceans, bacteria, fungi, sea anemones and many other animals. Animals have to deal with unique
living situations in all zones of the ocean. The ocean is a salty place that is often cold. Many animals have special adaptations
to handle this difficult environment. Most marine mammals have blubber to survive in the cold water, but sea otters are unique
because they don’t have blubber. Instead, they have fur more dense than any other mammal, with up to one million hairs
per square inch. Most people have ten times less than that on their heads! The ocean can also support very large life forms.
The blue whale is the biggest animal on earth. It can be over 100 feet long. Blue whales are so large that a small person
could crawl through their main arteries, and 20 people could stand on their tongue!
More detail on the
more complex organisms
A. All the pelagic
organisms below belong to the Phylum Chordata
- animals with gill slits and a cartilaginous skeletal rod at some stage of their development and the Subphylum Vertebrata - spinal column of vertebrae, red blood & 2 pairs of appendages
B. Fish dominate the nekton. They are found at all depths and
in all the oceans but their distribution patterns are determined directly or indirectly by their dependency on the
oceans' primary producers. Concentrated (50% of them) in upwelling
areas, shallow coastal areas and estuaries, which only represent about 2% of the ocean.
1. Wide variety of shapes related to their environment and behavior.
2. Schooling is common amoung certain types.
3. Divided on basis of whether they have a skeleton of cartilage or of
bone or whether they are jawless.
4. Most primitive fish - (Class Agnatha)
= lamprey, hagfish
5. Primitive cartilaginous - (Class Condrichthyes)
a. Sharks - cartilaginous skeleton and no gill covers
b. Predate mammals - first appeared 450 mya.
c. Extremely well-adapted to their environment
1) Good eyesight, excellent senses of smell, hearing, electrical impulses
(good navigators) & chemistry.
d. Many must swim perpetually to maintain position in water column and
get oxygen in through their gills.
e. Carnivores, planktivores and scavengers
f. Skates and rays are flattened, shark-type fish that have adopted
a bottom-dwelling life-style.
1) Planktivores, carnivores
FISH (Class Osteichthyes) - bony skeletons, scales, gill covers, swim bladder
a. Commercial Species of Bony Fish - sardine, anchovy, menhaden,
herring (planktivores) and mackerel, pompano,
tuna & swordfish (predatory) and flounder, halibut, turbot, sole (demersal = bottom fish) and perch and snapper (along
seafloor in the shallower, nearshore areas)
b. Most in surface layers (<200m) and are streamlined, active, predatory,
and capable of high-speed, long-distance travel.
c. Deep-sea species of bony fish-not well known (>200m)
1) Predators have highly specialized equipment for catching their
2) Usually large mouths and hinged jaws so they can take advantage
of the rare, large meals on which they subsist.
3) Many have specialized light organs to confuse predators or attract
C. Class Reptilia - sea snakes & turtles
1. Reptiles are few and far between
a. A few marine lizards (Galapagos)
b. Sea Snakes - about 50 kinds - extremely
poisonous, only in Pacific and Indian oceans - coastal
1) Some of their venom is 50X more potent than
c. Turtles - live in ocean but nest on land, 1 of 4 types=herbivorous,
while the other 3 are carnivorous.
D. Class Mammalia - Seals, manatees, whales, dolphins
herbivores ( Sirenians
(sea cows) – dugongs.manatees
b. Coastal carnivores
(spend most of lives in waters and come ashore to breed
1) Sea otter
(Sea lions, seals, and walruses)
c. Pelagic Forms (Cetaceans = whales, porpoises, and dolphins)
2. Because mammals
evolved from reptiles on land some 200 million years ago and no marine forms are known earlier than 60 mya,
it is believed that all marine forms evolved from some ancient land-dwellers.
herbivores ( Sirenians (sea cows) – dugongs & manatees
a. Much like elephants
and live as long (60-70 years)
b. Found south of North
Carolina on the east coast of the USA and along the Gulf Coast
c. Harmless, docile,
4. Coastal carnivores (spend most of lives in waters and come ashore to breed
a. Sea otter
(Sea lions, seals, and walruses)
E. Pelagic Mammals (Cetaceans = whales, porpoises, and dolphins )
1. Two types = Toothed whales (Odontoceti,
one blow hole) and Baleen (Mysticeti, two blow holes)
a. Cigar-shaped bodies
b. Nearly hairless
c. Insulated with thick
d. Forelimbs are modified
into flippers that move only at shoulder
e. Hind limbs are vestigial
(not attached to rest of skeleton)
f. Skull highly modified
1) One blow hole for toothed
2) Two blow holes
g. Propel themselves
by vertical movements of horizontal fluke (Tail)
2. Toothed whales
(Odontoceti) feed on fish and squid although the Killer Whale is know to feed on a variety of larger
animals, including other whales.
a. Killer Whales, Sperm
whales, porpoises and dolphins
3. Baleen (Mysticeti)
whales feed primarily by filtering krill, copepods and small fish at depths ranging from surface down to an including the
sediment of shallow ocean basins.
4. Modifications ot increase swimming speed
a. Cetaceans' muscles
are not vastly more powerful than other mammals
b. Modifications reduce
5. Modifications to
allow deep diving
a. Humans can free dive
to a maximum of 100 m and stay for 6 minutes.
b. Sperm whale dives
deeper than 2200 m (1.5 miles)
c. Elephant seal can
stay down for up to 2 hours.
d. Can alternate between
periods of normal breathing and cessation of breathing.
1) Cetaceans have
exceptionally large concentrations of capillaries that exchange gasses and hold air in lungs longer so can extract much more
of the oxygen (90%) than terrestrial mammals (20%)
2) Have much greater
blood volume per unit of body mass so can store more
3) Swimming muscles
can function without oxygen during dive
4) Other organs not
necessary during dive can be shut off from circulatory system (digestive tract, kidneys, etc.) so can reduce heart rate by
6. Baleen whales probably
evolved from toothed whales about 30 mya
a. Instead of teeth,
they have baleen, plate of horny material, that hang down from the upper jaw to serve as a sieve.
b. Blue, finback, humpback, right, gray, etc.
7. Some whales migrate seasonally many thousands of miles
a. California Gray-Arctic Ocean to Baja, California
b. Humpback-As far north as the Gulf of Alaska
and as far south as the Mariana and Hawaiian Islands