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