Chapter 15
Life Near the Surface
Life Near the Surface
• Pelagic – water column away from bottom
or shore
• Epipelagic – sea surface to depth of about
200 meters
– The epipelagic can be divided into (1) neritic
waters over the continental shelf and (2)
oceanic waters that are not over the
continental shelf
Life Near the Surface
• Epipelagic oceanic ecosystems:
– Warmest portion of the water column
– Most well lit portion of the water column (light
can be limiting in high latitudes and at night,
however)
– There are vast stretches of water that support
primary production
– This primary production support organisms in
this community as well as organisms in other
communities via water currents
Life Near the Surface
• Disadvantages of the Epipelagic oceanic
ecosystem:
– No substrate for attachment
– No bottom for burrowing or deposit feeding
– Places to hide from predators are extremely
limited and prey often can spot predators
Life Near the Surface
• Plankton:
– Thrive in the epipelagic
– Plankton are organisms that cannot fight
against the prevailing water currents
– These organisms may be microscopic or not
– Plankton are classified in numerous ways
including by size, by trophic status and by the
length of time spent in the plankton
Plankton Division by Size
(Know Net)
Plankton Division by Time in the
Plankton
• Holoplankton –
the entire life of
the organism is
spent in the
plankton
• Meroplankton –
spend only a
portion of their
life as plankton
(larvae of
molluscs (a),
brittlestars (b),
sea stars (c),
polychaetes (d)
crustaceans(e)
and fish
Plankton Classification by Trophic
Status
• Phytoplankton – plankton that generate
energy by means of primary production
(autotrophs)=cyanobacteria, diatoms,
dinoflagellates, green algae, red algae,
brown algae
• Zooplankton – plankton that are
heterotrophs=ciliates, radiolarians,
foramniferans, copepods, tunicates,
pteropods (gastropod) and larvae
Phytoplankton
• Diatoms
– Mainly reproduce by _____
(a form of asexual
reproduction)
– Extremely important
primary producers
– Common in all marine
waters
– May be solitary cells or a
colony of cells
– Can be pennate (elongate)
or centric (circular)
Phytoplankton
• Dinoflagellates
– Each of the 1200 species has unique shape reinforced
by plates of cellulose
– Two _____ in grooves on body that produce spinning
motion
– Also reproduce by cellular division
– Some are bioluminescent
– Some are toxic such as the species that cause ____
Tide or Pfiesteria
– they are particularly prevalent in warm waters and
“bloom” readily when nutrients are plentiful
Phytoplankton
• Cyanobacteria
– Some can go through nitrogen fixation which
improves growth in low nutrient conditions
– Also an extremely important primary producer
– Many grow in filamentous colonies with other
cyanobacterial cells
– Other are solitary cells
Zooplankton
• Copepods
– Small crustaceans
– Dominate the
zooplankton,
perhaps making up
to 70% of
zooplankton
– Copepods feed on
phytoplankton as
well as other
zooplankton
– They, in turn, serve
as a major source
of food for other
organisms
Zooplankton
• Other zooplankton include a variety of ciliates and other
protists that move by way of pseudopods such as
foraminiferans and radiolarians.
Foramniferan catching a copepod in its long, thin pseudopods
Zooplankton-Tunicates
• (Salps (top right) and
larvaceans (bottom
right)) are pelagic
tunicates that can
utilize mucous nets to
capture food particles
Zooplankton
• Pteropods are planktonic
•
•
•
molluscs (gastropods)
The foot is modified into
two parts that serve as
“wings” used for
swimming
Can be found in
epipelagic or deeper
waters
Eat phytoplankton and
other zooplankton
Zooplankton
• Jellyfish and comb jellies are not small organisms
• However, they are considered by some biologists to be
plankton because they cannot fight the prevailing water
currents in most cases
• Both organisms are carnivorous
Life in the Epipelagic
• Living in this environment means finding
ways to STAY AFLOAT
• This can be accomplished in various ways
including air or lipid filled compartments
(increases buoyancy) or by increasing
surface area and “drag”
Increasing Drag and Surface Area
• Some organisms
•
•
increase their surface
area by being flat (as
seen top right)
Others have a variety of
spines or appendages
to increase their surface
area (bottom right)
In both cases,
increasing the surface
area promotes “drag” or
water resistance which
helps keep these
organisms afloat
Increasing Buoyancy
• Some organisms increase buoyancy by
containing droplets or compartments of lipid
which tends to float
• Lipids are used in this way by diatoms,
copepods and many larval forms
• Other organisms trap air in various
structures or compartments to increase
buoyancy
• Such organisms include cyanobacteria,
cnidarians and even fish (swim bladder)
Nekton
• Nekton are organisms that can fight
against the prevailing water current and
purposefully move in any direction they
choose
• Examples of nekton found in the pelagic
zone are fish, sea turtles and sea snakes,
marine mammals, cephalopods, and some
larger crustaceans.
Predation and Protection from
Predation
• Since organisms have virtually no places
to hide, they must have other means for
finding prey or avoiding being prey
• Fast swimming, protective coloration,
migrations and a variety of sense organs
are used to accomplish this
Sense Organs
• Eyes –
– eyes can be used to form images or simply to
sense light/dark or patterns
– Most organisms is this environment have well
developed eyes
– Eyesight is used to capture prey, avoid being
prey, find mates and stay in groups (as
applicable)
Sense Organs – Remote Sensing
• Both cartilaginous
and bony fish
have a _____ line
for remote
sensing of water
movement that
can indicate prey
or predators are
nearby
Sense Organs – Remote Sensing
• Dolphins and other cetaceans use their _____
for echolocation to navigate pelagic waters
• They also use the melon to find prey and avoid
predators
Protective Coloration
• To blend in with their environment,
organisms can have different types of
protective coloration:
– Countershading
– Camouflage
– Transparency
Countershading
• In _____ organisms, the
ventral side of the
organism is lighter than
the dorsal side
• This aids the organism in
“blending in” because if
they are seen from
above, their darker dorsal
side blends in with the
darker water below
• However, if they are seen
from below, their lighter
ventral side blends in
with the better lit water
above
Camouflage
• As an example, the sargassum fish, Histrio histrio, is an
•
example of a pelagic organism that uses camouflage for
protection from predators
This fish looks very much like the Sargassum macroalgae
it calls home
Transparency
• Another way to hide is to lack coloration
completely
• This is the case with most jellyfish, comb jellies,
and pelagic tunicates, as well as many zoo- and
phytoplankton
Swimming
• Epipelagic predators must be able to swim quickly to
•
capture prey
This is accomplished by a streamlined body to reduce
drag and a strongly forked caudal tail to increase thrust.
Pelagic Food Webs
• The diagram to
•
the right shows
one example of a
food web and
how the web
changes over the
life cycle of one
species
This is a common
feature of pelagic
food webs – an
organism will not
feed on the same
type of
organisms
throughout their
life
Where do the Food Webs Begin?
• All pelagic food webs begin with either
phytoplankton, either directly or as
dissolved organic matter (DOM), which
comes from viral action.
Limitations to Primary Productivity
• Primary production can be limited by light
– even though there is normally plenty of
light in the pelagic environment, light is
not present at night or for long stretches
in high latitudes at certain times of the
year
Limitations to Primary Productivity
• Primary production can also be limited by
essential nutrients such as nitrogen (most
important) or phosphate
• Bacteria are important “recyclers” of these
nutrients as they break down organic
matter and cyanobacteria fix nitrogen
Areas of Upwelling
• The heating and
cooling of surface
waters can cause
deeper water to be
brought to the surface
in certain areas
• The diagram to the
right shows this
process, called
upwelling
• Upwelling brings vital
nutrients to the
surface (these
nutrients were lost
from the pelagic as
DOM, fecal matter,
and mucous)
• Primary production is
higher in areas of
upwelling