life near the surface shipley marine biology summit high school
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Life Near the SurfaceLife Near the Surface
Shipley Marine BiologyShipley Marine Biology
Summit High SchoolSummit High School
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: 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:
No substrate for attachment No bottom for burrowing or deposit feeding Places to hide from predators are extremely
limited Predators cannot easily “sneak up” on their prey
for the same reason!
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
Life Near the Surface
Plankton Division by Size
Plankton Division by Time in the Plankton
Holoplankton – the entire life of the organism is spent in the plankton
Meroplankton – only a portion of the life of the plankton is spent in the plankton (larval forms of fish, molluscs, crustaceans, etc) –seen at right
Phytoplankton – plankton that generate
energy by means of primary production (autotrophs)
Zooplankton – plankton that are heterotrophs
Plankton Classification by Trophic Status
Phytoplankton Diatoms
Mainly reproduce by cellular division (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)
Dinoflagellates
Each of the 1200 species has unique shape reinforced by plates of cellulose
Two flagella 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
Red 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
Phytoplankton
Coccolithophorids
Occur in neritic and oceanic waters Shells of calcium carbonate Also exist in large numbers in nutrient poor
areas Can survive low light conditions as well Often thrive in areas devoid of other
plankton due to low light or low nutrient conditions
Phytoplankton
Silicoflagellates
Star-shaped internal skeleton of silica Two flagella of varying lengths Silicoflagellates tend to be abundant where
diatoms are also common; the skeletons of both groups are of similar size, composition, and geologic range and are thus commonly found together.
Like the diatoms, the silicoflagellates are especially abundant in areas of upwelling and in equatorial waters but are also abundant at high latitudes.
Phytoplankton
Major Groups of Marine Phytoplankton
Zooplankton Copepods
Small crustaceans
Dominant 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
Other zooplankton include a variety of
protistan flagellates and protists that move by way of pseudopods such as foraminiferans and radiolarians.
Zooplankton
Zooplankton Salps (top right) and
larvaceans (bottom right) are pelagic tunicates that can utilize mucous nets to capture food particles
Salps can be solitary as seen at right or occur in large floating colonies
Zooplankton Pteropods are
planktonic molluscs The foot found in all
molluscs is modified into two parts that serve as “wings” for this animal
Can be found in epipelagic or deeper waters
Eat phytoplankton and other zooplankton
Arrow worms are elongate plankton that
are predators of smaller zooplankton
They somewhat resemble fish larvae and are thought to be distant relatives of the chordates
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
Zooplankton
Meroplankton only spend a portion of their life
as plankton and include larval fish, molluscs, echinoderms, and crustaceans
Meroplankton
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 such as octopus, squid and cuttlefish, crustaceans and more!
Nekton
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”
Life in the Epipelagic
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
Some organisms increase buoyancy by containing
droplets of compartments of lipid which tends to float
Such organisms include 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!)
Increasing Buoyancy
The “Floaters” Floating organisms are
classified as neuston (float just beneath surface) and pleuston (some “parts” float above and some “parts” float below surface
At the top right, notice the pleustic Portuguese man ‘o war (Physalia) and the neustic Janthina (purple mollusc at bottom left of photo)
At the bottom right, notice the pleustic Velella
Both Physalia and Velella use similar air filled sacs
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
Predation and Protection from Predation
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
Sense Organs – Remote Sensing
Both cartilaginous and bony fish have a lateral line for remote sensing of water movement that can indicate prey or predators are nearby
Dolphins and other cetaceans use
echolocation to navigate pelagic waters
They also use this remote sense to find prey and avoid predators
Sense Organs – Remote Sensing
To blend in with their environment, organisms
can have different types of protective coloration: Countershading Camouflage Transparency
Protective Coloration
Countershading In counter shaded
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
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
Camouflage
Another way to hide is to lack coloration
completely
This is the case with most jellyfish, comb jellies, salps, larvaceans, and many zoo- and phytoplankton
Transparency
Epipelagic predators must be able to swim
quickly to capture prey This is accomplished by a streamlined body to
reduce drag, a strongly forked caudal tail to increase thrust and a narrow caudal preduncle to concentrate energy on the caudal fin
Swimming
Vertical Migrations The diagram to the
right shows the vertical migrations of copepods between day and night
These copepods move into deeper waters during the day to avoid predators
At night, they move back into shallower waters to feed on phytoplankton
This predator avoidance comes with a cost – it takes more energy to migrate than to stay in one place
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
All pelagic food webs begin with either
phytoplankton, either directly or as dissolved organic material (DOM)
Remember that cyanobacteria are very important producers as well
Where do the Food Webs Begin?
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
Imagine that you are a diatom in the winter near the Arctic Circle!
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
Limitations to Primary Productivity
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, mucous and the like)
Primary production is higher in areas of upwelling
El Nino occurs as trade winds along the
Pacific coast of South America decrease This decrease in the winds causes
upwelling in that area to drop This drop and at times, complete
cessation of upwelling, causes effects all the way up the food chain
When primary production drops, each organism that depend on that production will suffer to include zooplankton, fish, marine mammals, turtles, birds, etc.
El Nino and the Ocean’s Productivity