1. Chapter 15
Life Near the Surface

2. 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

3. 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

4. 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!

5. 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

6. Plankton Division by Size (Know Net)

7. 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

8. 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

9. 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)

10. 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

11. 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

12. 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

13. Zooplankton
Other zooplankton include a variety of protistan ciliates and protists that move by way of pseudopods such as foraminiferans and radiolarians.

14. Foramniferan catching a copepod in its long, thin pseudopods

15. Zooplankton-Tunicates
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

16. Zooplankton Pteropods are planktonic molluscs (gastropods)
The foot found in all molluscs 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

17. 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

18. 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 such as octopus, squid and cuttlefish, and crustaceans.

19. 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”

20. 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

21. Increasing Buoyancy
Some organisms increase buoyancy by containing droplets or 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)

22. 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

23. 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

24. 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)

25. 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

26. Sense Organs – Remote Sensing
Dolphins and other cetaceans use their _____ for echolocation to navigate pelagic waters
They also use this remote sense to find prey and avoid predators

27. Protective Coloration
To blend in with their environment, organisms can have different types of protective coloration:
Countershading
Camouflage
Transparency

28. 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

29. 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

30. Transparency Another way to hide is to lack coloration completely
This is the case with most jellyfish, comb jellies, tunicates like salps and larvaceans, as well as many zoo- and phytoplankton

31. 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.

33. 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

34. 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 death and emptying of cells and viral action

35. 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

36. 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

37. 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