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Lecture 34: NEKTONIC ORGANISMS

Powerpoint Lecture Slides

General characteristics
Representatives
Invertebrates
Fish

Sharks, rays, etc.
Bony fish
Shallow-water
Deep-water

Cetaceans -- whales and porpoises
Other mammals
Reptiles
Migration during life cycle -- some examples

GENERAL CHARACTERISTICS

o Individual control over movement -- swimmers o Mode of nutrition: Herbivores Carnivores (predators, scavengers)
o Vertebrates dominate the nekton

INVERTEBRATE NEKTON -- relatively few representatives

o Large shrimp o Cephalopods (class of Mollusca): Chambered Nautilus Squid Cuttlefish

FISH -- THE DOMINANT TYPE OF NEKTONIC LIFE

o Distributed world-wide o Occur at all depths Concentrated in the epipelagic (photic) zone (0-200m) Deep-water and bottom dwellers also
Cartilagenous fish: skeletons of cartilage, not bone Sharks Wide-spread, epipelagic Active predators; some are plankton feeders Skates and rays Shallow-bottom dwellers Carnivores; BUT ALSO plankton feeders!
Bony fish: (includes most eels) Epipelagic representatives (commercially fished) Tuna, Salmon -- predators Herring, Anchovy -- plankton feeders Coastal bottom-dwellers (commercially fished) Halibut, Sole Deep-sea (>200m) bony fish General features -- adaptations: Small (<10 cm) Large mouths, well-developed teeth Low rates of metabolism Large, light sensitive eyes Luminsecent -- light-producing organs Protective evasion Attraction of prey Mate selection Representative deep-sea fish: Cyclothone, Lantern fish Abundant mesopelagic fish Members of the "Deep-Scattering Layer" Hatchetfish Eyes and mouth directed upward Angler fish Luminous moveable lure Parasitic male attached to body of female

CETACEANS

Evolved from a common terrestrial ancestor Baleen whales -- filter-feeders (plankton, small fish) All other whales, porpoises, dolphins Toothed Fast-swimming predators
OTHER MARINE MAMMALS Pinnepeds ("feather-footed") Seals, Sea Lions, Walruses Habitat: polar, midlatitudes require shore and sea-ice areas Also evolved from common terrestrial carnivore Sea cows -- Manatees, Dugongs: tropical herbivores Sea otters Habitat: cold, coastal waters Nutrition: carnivores of benthic organisms like clams
MARINE REPTILES Few species, but successful Representatives: Turtles Crocodiles Snakes Marine Iguanas
MIGRATION OF NEKTONIC SPECIES -- SOME NOTABLE EXAMPLES Why do they have these arduous journeys? Migration links .... .. regions appropriate for reproduction ... regions of feeding for adults
Examples: California Grey Whales Pacific Salmon Skipjack Tuna Atlantic Eels Spawn at sea; adults migrate to fresh-waters Atlantic Green Turtles

Nekton

Nekton have individual control over their movement. All nekton are heterotrophic, either herbivores (grazers) or carnivores (predators and scavengers). Vertebrates dominate the nekton.

1.) Invertebrate nekton. There are relatively few species, although members of this group are abundant. They include large shrimp and several cephalopods (a class of the Mollusca): Chambered Nautilus Squid Cuttlefish

2.) Fish (vertebrates) are the dominant nekton. They are distributed world-wide and can occur at all depths. However, most fish are concentrated in the epipelagic zone (= photic zone, 0-200 m).
Cartilagenous fish . . have skeletons of cartilage, not bone. Sharks are wide-spread, epipelagic members of this group. Most sharks are active predators, some of the large varieities are actually plankton eaters. Skates and rays are also cartilageneous. They inhabit the bottom of shallow sea-floor. Some are carnivores; others are plankton feeders.

Bony fish . . (including most eels) are abundant throughout the oceans. Representative fish that are harvested commercially include:

tuna and salmon -- epipelagic predators
herring and anchovies -- epipelagic plankton feeders
halibut and sole -- coastal bottom-dwellers, carnivores
Coastal bottom-dwellers (commercially fished)

Deep-sea (>200m) bony fish . . must have special adaptations to survive in the harsh environment of the deep ocean:

Small (<10 cm)
Large mouths, well-developed teeth to ingest the unpredictable sinking of food particles or encounter with a prey.
Low rates of metabolism.
Large, light sensitive eyes

Representative deep-sea fish

cyclothones and lantern fish may be the most abundant mesopelagic fish. They are members of the "deep scattering layer."
hatchetfish have their eyes and mouth directed upward. Why?....That's where food comes from.
angler fish have a moveable luminous lure to attract prey. This species also solves the problem of reproduction by having the male as a parasite attached to the body of the female.

Cetaceans

are mammals, and include whales, dolphins, and porpoises. All cetaceans evolved from a common terrestrial (land) ancestor tens of millions of years ago. Dolphins, porpoises, and some of the whales are fast-swimming predators. Baleen whales are filter feeders.

Other Marine Mammals

Pinnepeds include seals, sea lions, and walruses. Like the cetaceans, pinnepeds also evolved from a common terrestrial carnivore. They are found in mid-latitude and polar oceans. Pinnepeds cannot spend long periods of time under-water. They require shore (islands) and areas of sea ice to rest and reproduce.
Manatees and dugongs are tropical herbivores. They can inhabit fresh water as well as sea water.
Sea otters live in cold, coastal waters. They are carnivores, usually feeding on benthic shellfish.

Marine Reptiles.

There are relatively few species, but all are successful in the ocean. Representatives include:

Turtles
Crocodiles
Snakes
Marine Iguanas

Migration of Nekton -- Some notable examples.

Several varieties of fish, reptiles, and mammals migrate long distances during their life cycles. For these animals, migration links regions that are appropriate for reproduction with regions of feeding for adults. Examples of long-distance migrators are:

California Grey Whales
Pacific Salmon
Skipjack Tuna
Altlantic Eels
Atlantic Green Turtles

The following is a list of the representative pelagic organisms (live in the water column) that were discussed in lecture and described in the readings. Students should be able to identify the habitat and mobility (i.e., planktonic versus nektonic) and know a little about the general characteristics of these organisms:

PLANKTON

Phytoplankton
Diatoms Dinoflagellates Coccolithophores

Zooplankton Protozoans Foraminifera Radiolaria
Crustaceans Copepods Euphausids ("krill')
Others Jellyfish (Coelenterates) Comb jellies (Ctenophores) Planktonic snails (pteropods) Meroplankton -- eggs, larvae, juveniles
Bacteria

NEKTON
Invertebrates Cephalopods -- Nautilus, squid
Cartilagenous Fish Sharks Skates, Rays
Bony Fish Tuna, Salmon Herring, Anchovy Halibut, Sole
Deep-water Bony Fish Cyclothone Lantern fish Hatchetfish Angler fish
Marine Mammals Cetaceans Baleen whales Other whales, dolphin, porpoises Pinnepeds -- walruses, seals, sea lions Others Manatees, dugongs Sea otters
Marine Reptiles Turtles Crocodiles Snakes Iguanas
Migratory fish, mammals, reptiles California grey whales Pacific salmon Skipjack tuna Atlantic eels Atlantic green turtles

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