Chapter 15
Life Near the Surface
Vast open sea – pelagic realm
Contains almost all of the liquid
water on earth
How the Open Sea Effects
You
Regulates our climate
Conditions our atmosphere
Provides food and many
resources
Life in the Pelagic
Pelagic organisms live
suspended in their liquid medium
Lacks the solid physical
structure provided by the bottom
No place for attachment, no
bottom for burrowing, nothing to
hide behind
Epipelagic
Upper pelagic
Zone from the surface down to a
given depth commonly 200 m
(650 ft)
Warmest
Best lit
Similar to the photic zone (area
where photosynthesis can occur)
I.
Pelagic
1. Epipelagic
2. Mesopelagic
3. Bathypelagic
4. Abyssopelagic
II. Benthic
5. Littoral, Sub-littoral
6. Bathyal
7. Abyssal
8. Ultra-abyssal
Two Main Components
1.Coastal or Nertic – epipelagic
waters that lie over the
continental shelf
Lies close to shore
Supports most of the world’s
marine fisheries production
2.Oceanic part
Waters beyond the continental
shelf
The Organisms of
the Epipelagic
The Pelagic Realm
Fueled by solar energy captured
in photosynthesis
Nearly all primary production
takes place within the epiplagic
system itself
Gets almost no external input of
organic matter
Supplies food to other
communities
Lacks deposit feeders
Suspension feeders are very
common
There are also many large predators
like fishes, squids and marine
mammals
The Plankton: A
New
Understanding
Scientist used to study
plankton by catching
them in tow nets
This practice limited
what organisms were
caught
Recent developments in
collecting plankton have lead to
the discovery of many new groups
of plankton and have changed
how the plankton interactions are
currently looked at
Plankton can be grouped
based on their size
Picoplankton – smallest
Nanoplankton
Microplankton
Mesoplankton
Macroplankton
Megaplankton – largest
Phytoplankton – perform
photosynthesis
Zooplankton – cannot perform
photosynthesis - heterotrophs
Phytoplankton –
Major Groups
Net Plankton (Micro, Meso,
Macro)
Diatoms – found everywhere –
important primary producers
Dinoflagellates found
everywhere, most common in
warm waters – common red tide
organisms
Dinoflagellates
Diatoms
Colonial cyanobacteria
(Trichodesmium) – mainly tropical –
can fix atmospheric nitrogen – causes
red tides in the Red Sea
Nanoplankton
Coccolithophorids – important
primary producers in nutrient
poor waters
Cryptophytes – very important
primary producers
Silicoflagellates – sometimes
form blooms
Coccolithophorids
Picoplankton
Unicellular cyanobacteria
(Prochlorococcus) dominant
primary producers, especially in
nutrient poor water
Various protists – presence of
many groups recently discovered
ZooPlankton
Phytoplankton form the base of
the food web
Solar energy that they capture
and store in organic matter is
passed on to the other creatures
of the epipelagic from minute
zooplankton to gigantic whales
Herbivores eat phytoplankton
Zooplankton are by far the most
important herbivores in the
epipelagic
Very few zooplankton are strict
herbivores – will eat other
zooplankton
Most zooplankton species are
primarily carnivorous and
hardly eat phytoplankton at all
Protozoan Zooplankton
Protozoans can catch tiny
picoplankton and nanoplankton
Without protozoans, much of the
primary production in the epipelagic
would go unutilized
Flagellates, Ciliates,
Foraminiferans, Radiolarians
Foraminiferans
Radiolarians
Copepods
Small crustaceans
Dominate the net zooplankton
Most abundant members of the
net zooplankton practically
everywhere in the ocean – 70% or
more of the community
Major carnivores
Copepods
Other Crustaceans –
Shrimp-Like Krill
Not as abundant as copepods
but often aggregate into huge
dense swarms
Dominate the plankton in the
polar seas
Efficient filter feeders – diatoms
are a favorite food, also eat
detritus
Relatively big – up to 6 cm
Eaten by fishes, seabirds, great
whales
Krill
Non-Crustacean
Zooplantkon
Salps – transparent, planktonic
herbivores – filter out plankton
by pumping water through a
sieve-like sac or a fine mucus net
Larvaceans – float inside a
house they make of mucus – beat
tail to move water through the
house – food particles are caught
in a complicated mucus net that is
inside the house
Pteropods – mollusks – small
snails that have a foot that has
been modified to form a pair of
wings that they flap to stay afloat
Arrow Worms or chaetognaths
– extremely important predators
in the zooplankton – feed mostly
on copepods
Jellyfish and
siphonophores –
large, weak
swimmers that drift
with the currents –
carnivore
Holoplankton
Spend their whole lives as
plankton
Meroplankton
Many fish and invertebrates
have planktonic larvae
Temporary members of the
plankton
Small larvae feed on
phytoplankton
Larger larvae feed on
zooplankton
Larvae can grow while in the
plankton and change trophic
levels
The Nekton
Large strong swimmers
Fishes, marine mammals, squids,
turtles, sea snakes, penguins
Carnivorous
Planktivorous nekton – eat
plankton – include herrings,
sardines and anchovies, whale
shark and the basking shark
Herring
Anchovies
Sardines
Most species of nekton eat other
nekton
Fishes, squids and large
crustaceans are the main foods
Epipelagic predators are not
fussy, just need to be the right
size
In general the larger the
predator the larger the prey
Herrings (small fish) –
zooplankton
Sperm whale largest of nekton
– giant squid 10 m (33 ft long)
Living in the Epipelagic
Demands of the environment
cause organisms to have certain
adaptations
Two main problems
Need to stay in the epipelagic
zone
Need to eat and avoid being
eaten
Staying Afloat
Cells and tissues are denser
than water – naturally sink
Shells and skeletons are even
more dense
Phytoplankton need to stay for
sun and the others need to stay so
they can get prey
How to stay afloat if you
can not swim
Increase the water resistance so
that you sink slower
Make yourself more buoyant
Increased Resistance
Drag – resistance to movement
through water or any other
medium
Small organisms – drag mostly
depends on surface area – higher
the surface area the slower the
organism sinks – reason
plankton are so small
Shape influences surface area –
parachute shape slows sinking
(jellyfish)
Flat shapes slow sinking
Long projections or spines
increase surface area and
therefore decrease the rate of
sinking
Forming chains slows sinking
Swimming organisms rarely
have spines as this would
increase water resistance and
make swimming harder
They generally have
adaptations that reduce drag
Increase Buoyancy
Reduces the tendency to sink
Store lipids (Oils or fats)
Lipids are less dense so they
tend to float
Diatoms, copepod and fish eggs
contain a drop of oil
Many adult fish store lipids –
especially sharks and tuna
Whales, seals and other marine
mammals have a great deal of
buoyant fat in a thick layer of
blubber under the skin
Pocket of gas is another
adaptation
Bony fish have swim bladders –
disadvantage – gases expand and
contract as the fish moves in the
water column
The Floaters
Neuston – organisms that live
right at the sea surface but
remain underwater
Pleuston – organisms whose
bodies project through the sea
surface into the air
Most common method is to have
a gas-filled structure
By-the-wind-sailor – (Velella) –
colonial jellyfish-like cnidarian
that is specialized as a float
Portuguese man-of-war
(Physalia) – powerful sting –
part of the colony acts as a sail
Violet shell (Janthina)- makes a
rafts of mucus filled with bubbles
from which it hangs upside down
Physalia
Velella
Velella
Janthina
Predators and their Prey
Many of the adaptations of
epipelagic animals are related to
their need to find food and at the
same time avoid being eaten
Sense Organs
Highly developed
Vision is important – many have
good eyesight
Vision is especially important to the
nekton because there are no solid
structures to avoid concealment
Lateral line – remote sensing
system that sense vibrations in
the water – used to stay with
school mates and detect
predators
Coloring and Camouflage
Protective coloration or
camouflage
Nearly universal among
epipelagic organisms that are
large enough to be seen
One way – transparent –
jellyfish, salps, larvaceans, comb
jellies
Countershading – dorsal surface
(back) is dark usually green, blue or
black and the belly (ventral surface) is
white or silver
Looking down – ocean depths are
dark blue and it is hard to see the prey
Looking up – bright light is filtered
down and it is hard to see the prey
Laterally compressed bodies are
also common – reduce the size of
the silhouette
Silvery sides – reflect light –
help to blend in
Vertical bars or irregular
patterns – help to break up their
outline in the dappled under
water light
Swimming: The Need for
Speed
Whether the prey gets away or
the predator gets a meal depends
on which swims faster
Emphasis is on sheer speed
Epipelagic contains the worlds
most powerful swimmers
Practically all epipelagic nekton
have streamlined bodies that
make swimming easier & more
efficient
Do not have features that
increase resistance (like spines,
bulging eyes)
Laterally compressed bodies are
also common – reduce the size of
the silhouette
Firm and Muscular
Force is delivered mainly by the tail
The tail is high and narrow
Fins tend to be stiff – provides
maneuverability and lift
Fishes have two types of muscle
– red and white – red muscle gets
its color from the high
concentration of myoglobin
(stores oxygen)
Red muscle – best suited for
long sustained effort – for
sustained cruising
White muscle – provides short
burst of power
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
Vertical Migration
Pelagic waters are dangerous
but they also contain the most
food
Some zooplankton spend only
part of their time near the surface
and then retreat to safer, deeper
water
Usually live at least 200m or
650 ft down
Epipelagic Food
Webs
Of great interest, especially
because epipelagic fishes provide
food and employment to millions
Trophic Levels and
Energy Flow
Very complex
Epipelagic contains vast
numbers of different species
Feeding habits of most of them
are poorly known
Most of the animals eat a
variety of prey often from
different trophic levels
Most epipelagic animals
consume different prey at
different times in their lives
The basic flow of energy in the
epipelagic can be depicted as
phytoplankton  zooplankton 
Small nekton  Large nekton
top predators
Epipelagic food chains usually
have many steps and are
generally longer than in other
ecosystems
Tropical usually have more
levels than colder waters
Epipelagic is an exception to the
10% rule
Herbivores pass on 20% and the
carnivores pass on more than
10% also
Patterns of
Production
Epipelagic food webs are
complex but they all share one
simple feature: primary
production by phytoplankton is
the base
Some areas of the epipelagic are
among the most productive on
earth and some are “deserts”
Phytoplankton need 2 main
things to perform
photosynthesis:
Sunlight
Supply of essential nutrients
Ocean Productivity
Red areas
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Light Limitation
Must get all their light during
the day
May be light-limited during the
winter
Total primary production also
depends on how far down light
penetrates into the water column
Nutrients
Nitrogen, iron and phosphorus
play a major part in controlling
primary production
Nitrogen is most often the
limiting nutrient
Most nutrients come from
recycling
Much of the organic matter ends
up as detritus (fecal pellets, dead
bodies)
Often the detritus sinks past the
epipelagic zone before it releases
its nutrients
Deep water is usually nutrient
rich
Seasonal Patterns
Can cause nutrient laden cold
water to come to the surface
As the water cools it sinks,
breaks up the thermocline and
allows surface waters to mix with
deep nutrient rich water
Upwelling
Caused by Ekman Transport
Occur mainly along the eastern
sides of ocean basins where the
prevailing winds blow parallel to
the coast
Ekman transport carries the
warm surface water offshore
This allows the deeper nutrient
rich water to move to the surface
Major coastal upwelling areas
are among the most productive
waters of the epipelagic
In the pacific there can be
equatorial upwelling