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Chapter 16 - Animals in the Pelagic Environment

This chapter focuses on higher-level organisms in the marine environment, specifically vertebrates, all of which are pelagic animals that can swim (or fly) in the open ocean or coastal marine environments. (The previous Chapter 15 focuses on invertebrates - most of which are either attached or live on or with the seabed (the benthic environment).


Vertebrates are a large group of animals distinguished by the possession of a backbone or spinal column. They belong in the taxa:

Kingdom Animalia    
  Phylum Chordates  
    Subphylum Vertebrata

Click on thumbnail images for a larger view.
Fish fossil from WyomingFig. 16-1. This Wyoming fish fossil displays a well preserved backbone (spinal column). Backbones or spinal columns are common to all vertebrates.


Classes in Vertabrata in the Marine Environment

CLASS Examples
Mammalia Whales, seals, sea lions, otters, polar bears (mammals)
Amphibia Frogs, salamanders (amphibians are rare in marine environments but a few species exist in near-marine settings)
Reptilia Snakes, turtles, lizards (crocodillians, iguanas)
Aves Birds
Osteichthyes Fish with bony skeletons
Chondrichthyes Fish with cartilage skeletons- sharks (very old fish with cartilage, some are up to 280 million years old)


Example of the Taxonomy of Whales

Example: Taxonomy of Whales
kingdom             kingdom: Animalia
  phylum           phylum: Chordata
(subphylum: vertebrata)
    class         class: Mammalia
      order       order: Cetacea
        family     Mysteceti (mustache whales)
Odontoceti (toothed whales)
Archeoceti (ancient whales - now extinct)
          genus   one or several genus within families
            species one or more species within a genus


Characteristics of All Marine Mammals

  • Land-dwelling ancestors
  • Warm-blooded
  • Breathe air
  • Hair/fur
  • Bear live young
  • Mammary glands for milk
  • Life habit is to live in or near seawater or freshwater.

Fig. 16-2. Are humans marine vertebrates

Taxonomy of marine vertebrates include:



(have prominent canine teeth)
  FAMILY Mustelidea Sea otters Among the smallest of marine mammals, range: North Pacific, largest member of the weasel family. Each carries a pebble tool to break open shells.
  FAMILY Ursus • Polar bears Live in the arctic circle, primary diet of seals, lives on ice, snow, open ocean.
  FAMILY Pinnipeds    
    GENUS • Walruses Range is in the Arctic and subarctic in Northern Hemisphere on continental shelves. Large tusks and whiskers used for foraging for bivalves on seabed.
    GENUS • Seals Fin-footed ( flippers ), semi-aquatic marine mammals, 33 extant species worldwide.
    GENUS • Sea lions Sea lion have external ear flaps, long fore flippers, the ability to walk on all fours, and are voracious eaters. Six species worldwide, except N. Atlantic.
    GENUS • Fur seals Similar to sea lions (smaller), 1 species in North Pacific, 7 species in S. Hemisphere; have external ear flaps, long fore flippers, ability to walk on all fours.

Examples of Marine Carnivores
Otter Polar bear walrus Colony of Walruses
Fig. 16-3. Sea otter Fig. 16-4. Polar bears Fig. 16-5. Walrus Fig. 16-6. Walruses on ice.
Monk seal Steller sea lion Steller sea lion colony fur seals
Fig. 16-7. Monk seal Fig. 16-8. Steller sea lion Fig. 16-9. Steller sea lion colony Fig. 16-10. Fur seals




(Aquatic herbivores living in coastal areas)
  FAMILY • Manatees (tropical Atlantic Ocean)
  FAMILY • Dugongs (Indian and western Pacific Oceans)

Examples of Sirenia
Fig. 16-11. Manatees Fig. 16-12. Dugong


ORDER Cetacea Cetaceans have elongated skull with blowholes on top, use echolocation: they emit
click-like noises and get return—used to detect fish, and can be used to stun fish. Cetacea have large brains relative to body size; can communicate with each other, many are considered trainable.


Toothed whales:
    FAMILY • dolphins (Delphinidae) - seven genera with about 40 species, worldwide
    FAMILY • porpoises (Phocoenidae) - Compared with dolphins, porpoises have shorter beaks and flattened, spade-shaped teeth.
    FAMILY • killer whales (technically a subfamily of dolphins, called "blackfish" or orcas - 6 species)
    FAMILY • beaked whales (have prominent noses [or nose -like features] - 22 species)
    FAMILY • Sperm whales - largest of the toothed whales, 3 species, (They use echolocation to hunt giant squid.)


Baleen whales (Baleen is fibrous plates in whale mouths used to sieve prey items.)
    FAMILY • Right whales (Balaenidae): 4 species live in northern oceans, mostly North Atlantic
    FAMILY (1species) • Rorquals whales (9 species, worldwide), includes:
* Blue whale
- largest of all mammal species - up to 30 m (98 ft), 180 tons
    FAMILY • Humpback whales (1 species) - found in all oceans
    FAMILY • Gray whales (1 species) - live in coastal waters of the Northern Pacific only

Examples of Cetaceans
Dolphin Porpoises killer whale narwhales
Fig. 16-13. Dolphin Fig. 16-14. Porpoises Fig. 16-15. Killer whale Fig. 16-16. Narwhales
Sperm whale Blue whale Humpback whale Baleen whale
Fig. 16-17. Sperm whale Fig. 16-18. Blue whale Fig. 16-29. Humpback whale Fig. 16-20. Atlantic right whale (baleen showing)


Migration of Gray Whales on the West Coast

Gray whales are probably the most commonly sighted whales in the coastal waters of California. Gray whales have the longest migration of any mammal species, about 10,000 miles 16,000 km) every year.

Gray Whales have a routine. They spend the winter months (December to April) in their birthing and mating grounds the shallow bays and lagoons in and around the southern Baja California and southern Gulf of California (Figure 16-23).

Gray Whales begin their northward migration in late February to May along the coastline, following the spring blooms of phytoplankton and zooplankton. They are frequently seen moving in small groups (pods) several hundred yards beyond the breaker zones to about 4 kilometers (2.5 miles [4 km]) from shore. Their destination is the rich summer feeding grounds along coastal Alaska and the Bering Sea, a distance of about 5,000-7,000 miles (8,000 to 11,000 km). Adult males and juveniles arrive in northern waters in June; females and young offspring leave and arrive a little later. They spend the summer (June to October) feasting. The first to head south are the pregnant females, followed by the others, some of whom don't make it as far south as Mexico if food resources are available farther north.
Gray whale
Fig. 15-21.
Gray whale
nutrients supply in temperate regions
Fig. 15-22.
Temperate zone productivity by seasons.
Whale migration
Fig. 16-23. Migration pattern of gray whales along the West Coast of North America.

Marine Reptiles

Compared with the number of reptiles groups and species on Earth, relatively few are adapted to marine environments. The earliest marine reptiles appear in the Permian Period. Many groups emerged in the Mesozoic Era including more familiar varieties including ichthyosaurs, plesiosaurs, and mosasaurs. Many varieties of the Mesozoic Era vanish at the K/T Boundary extinction.


  ORDER Crocodiles
  ORDER Lizards
  ORDER Sea Turtles
  ORDER Sea Snakes


There are 23 living crocodilian species in both terrestrial aquatic and coastal marine environments. Crocodilians are found in the tropical to subtropical regions on all continents (not Antarctica); they're found in over 90 countries and islands. They are unable to survive and reproduce successfully in cold climates.
What's the difference between an alligator and a crocodile?

American Alligator

American Crocodile

Habit: feisty Habit: more feisty, but shy and reclusive
Habitat: freshwater to brackish water Habitat: brackish to salt water
Color: gray to black Color: greenish gray
Encounters with humans: common Encounters with humans: not so common
Diet: most everything, fish, birds, pets
Diet: mostly fish
Maximum size: `12 feet Maximum size: ~13 feet
Characteristics: Alligators snout is blunt and shovel like (used like a shovel too) Characteristics: Crocodile snout is pointed with more teeth sticking out (better for catching fish)
Range in US: Gulf & Atlantic coasts (TX to SC) Range in US: South Florida only
Example: Figure 16-25 Example: Figure 16-26
Americal Alligator
Fig. 16-24.
American crocodile
Fig. 16-25.

Marine Lizards

The only marine lizard is the Galápagos marine iguana (Amblyrhynchus cristatus)—found only on the Galápagos Islands. This iguana lives along rocky island shorelines and can dive over 9 m (30 ft) into the water to forage for its main diet of red and green algae (Figure 16-27).
Fig. 16-26.
Galápagos marine iguana

Extinct Large Marine Reptiles

Aquatic reptiles first noted from the Permian Period. There were many varieties of large marine reptiles during the Mesozoic Era. All vanished at the end of the Cretaceous Period (about 65 million years ago).

Ichthyosaurs: Triassic to Late Cretaceous

Plesiosaurs: Early Jurassic - Late Cretaceous

Mosasaurs: Late Cretaceous

The ancient marine reptiles illustrated convergent evolution - they had terrestrial ancestors like dolphins and whales.
Fig. 16-27.
A fossil ichthyosaur from Berlin-Itchtyosaur State Park, Nevada

Sea Turtles

There are seven species of sea turtles worldwide. Sea turtles sea turtles can be found in all oceans except for the polar regions, along the continents shelves and islands. They are known to nest in more than 80 countries. Sea turtles first appear in the geologic record in early Cretaceous time (land proto-turtles appeared in Permian time).

Unlike land turtles, sea turtles are unable to pull their heads or appendages into their shells. Sea turtle shells are lighter and more hydrodynamic than terrestrial turtle shells. There flippers enable them to swim long distances. Male sea turtles spend their entire lives at sea. Females return to the same beaches they were born on about every two years to lay eggs.

All adult green sea turtles are herbivores, feeding on algae, sea grasses, and other vegetation. Juvenile are carnivorous, feeding on jellies and other invertebrates. Large adult green sea turtles can weigh upward of 400 pound and over 1 meter.

Leatherback turtles are carnivorous, migrating thousands of miles each year to feed on jellyfish.
Leatherback Turtles can weigh as much as 1500 pounds and reach lengths of over 2 meters.

Sea Turtles

Green sea turtle

Leatherback sea turtle

Loggerhead sea turtle
Sea Turtle (Carribean) Leatherback sea turtle Loggerhead sea turtle
Fig. 16-28. Green sea turtle Fig. 16-29. Leatherback sea turtle Fig. 16-30. Loggerhead sea turtle.


Sea Snakes

There are about 50 species. They live in tropical waters of the west Pacific Ocean, around Australia, and in the Indian Ocean. Sea snakes inhabit marine environments for most or all their lives.

Sea snakes are generally non aggressive, brightly colored, with small mouth and fangs.

Sea snakes have very powerful venom.
An average of about 20 deaths per year happen from fishermen trying to remove them from nets.
Sea snake
Fig. 16-31.
Sea snake.


There are many varieties of seabird (too many to discuss here!). Here are characteristics of seabirds:
• Seabirds are found on all continents and islands around the world.
• Seabirds can be highly pelagic, coastal, or partly terrestrial.
• Most species nest in colonies (dozens to millions of birds)
• Seabirds live longer, breed later, and have fewer young.
• Many species undertaking long annual migrations, crossing the equator or even circumnavigating the Earth.
• Seabirds feed both at the ocean's surface,below it, and even on each other.
• All seabirds share feed in saltwater (some may feed in both sea and terrestrial sources).
• Wing morphology and body shape depends the niche a species or family has evolved.
-- Longer wings and low wing loading are typical of more pelagic species,
-- Diving species have shorter wings.
-- Seabirds like albatross and pelicans use dynamic soaring to take advantage of wind deflected by waves to provides lift.
• Seabirds also almost always have webbed feet.
• Salt glands in their nasal cavities are used to excrete the salt they ingest by drinking and feeding.
• Birds appear in the Mesozoic Era, but modern seabirds proliferated in the Paleogene (after the K/T extinction).


Seagull Arctic tern Pelican Penguins
Fig. 16-32. Seagull Fig. 16-33. Arctic tern Fig. 16-34. Pelican Fig. 16-35. Penguins



There are many varieties of fish (too many to discuss here!). Here are important facts about fish.
Fish are found in nearly all aquatic environments (land & sea), and all depths of the oceans.
Fish are all aquatic, gill-bearing, craniate (head-bearing) animals that lack limbs with digits.
Fish groups account for more than half of all vertebrate species.

At 32,000 species, fish exhibit greater species diversity than any other group of vertebrates.
* almost 28,000 known extant (not yet extinct) species,
~27,000 are bony fish,
~970 sharks, rays, and chimeras.
* over 100 hagfish and lampreys.
* many extinct varieties.

Most fish are ectothermic (cold-blooded), allowing their body temperatures to vary as ambient temperatures change some of the large active swimmers (examples white shark and tuna can hold a higher core temperature).

Fish are abundant in most bodies of water, all parts (depths) of the oceans.

Fish Evolution

Amphibians, reptiles, birds and mammals) and fish share a common evolutionary ancestry.
The earliest fish-like organisms appeared during the Cambrian period. (However, they lacked a true spine, but possessed notochords.)
Fish evolve through the Paleozoic era, diversifying into a wide variety of forms.

Many Paleozoic fishes developed external armor that protected them from predators. The first fish with jaws appeared in the Silurian period, after which many (such as sharks) became formidable marine predators rather than just prey.

Osteichthyes Fish with bony skeletons
Chondrichthyes a class of fishes that have the cartilaginous skeletons, rather than bone—they have jaws, paired fins, scales, a heart with its chambers in series. Subclass Elasmobranchii (includes sharks, rays, skates, sawfish), and subclass Holocephali (include chimaeras). Some lineages are up to 280 million years old.

Examples of Osteichthyes (bony fish)

Giant Oarfish Anchovies in a school Marlin Schooling tuna
Fig. 16-36. Oarfish (a species with ancient roots) Fig. 16-37. Anchovies Fig. 16-38. Marlin Fig. 16-39. Blue fin tuna

Examples of Chondrichthyes (Sharks and Rays)
Great White Hammerhead Whale Shark (Gulf of Mexico) Manta rays
Fig. 16-40. Great white shark Fig. 16-41. Hammerhead shark Fig. 16-42. Whale shark Fig. 16-43. Manta Rays


Adaptations to the Marine Environment

• Ability to float
(Zooplankton – some produce fats or oils to stay afloat)
• Ability to swim
(Nekton – larger fish and marine mammals)

Propulsion and movement of fish -
the body plan of fish reflect adaptations to feeding on prey and fleeing predators.
Width/Length Ratio

Tuna - .28
Dolphin - .25
Swordfish - .24
Whale - .21

Most efficient is about.25, but there is a size-scale factor.
Ratio produced from natural selection “the fittest survive and produce offspring”
Fig. 16-42. Swordfish

Compare with Surfboard Design!

Type Width Length Ratio Comments
Short Board 19 ¼" 6’4” 0.25 Small – medium waves
PT (Ebenizer Townsend, 1798) 19 ¼" 6'7" 0.24 Large waves
Average Long Board 22" 9'0" 0.20 Like a whale – scale factor
Average Surf Board 18 ¼" 6’2” 0.25 rapid turns, harder to control


Kinds of Zooplankton

Includes organisms described as floaters and drifters. All forms are invertebrates.
Microscopic Zooplankton
Radiolarians, Foraminifers, Copepods

Macroscopic Zooplankton:
• Krill ( resemble mini shrimp or large copepods, critical in Antarctic food chains)
Fig. 16-43.
Fig. 16-44.
Floating Macroscopic Zooplankton include:

Portuguese man-of-war (have gas-filled float)
Jellyfish (have soft, low-density bodies; there are hundreds of species)

Many species of portuguese man-of-war and jellyfish can sting or produce potent toxins.
Portugese man-of-war
Fig. 16-45.
Portuguese man-of-war
Jellyfish floating
Fig. 16-46.
Swimming (Nekton) Organisms

Includes all fish, squids, sea turtles and sea snakes, and marine mammals.

• Swim by trapping water and expelling it (squid, octopus)

• Swim by curving body from front to back (fish, etc.)
Fig. 16-47.
Adaptations for Finding Prey

Lungers wait for prey and pounce (example: grouper).

Cruisers actively seek prey (example: tuna). They typically hunt in packs.
Fig. 16-48.
Groupers are lungers
Bluefin tuna
Fig. 16-49.
Tuna are cruisers
Adaptations to Avoid Predation
Hiding: includes Transparency, Camouflage and Countershading
Poison (to touch or eat: examples: sea snakes, blowfish, lion fish)
Schooling (safety in numbers, appear as a larger unit, maneuvers confuse predators)

Video: Schooling anchovies at Scripps Pier (Scripps Institute of Oceanography)
Fig. 16-50.
Lionfish are highly poisonous.

Protecting and Preserving Marine Life: A Most-Essential Goal For the 21st Century

The efforts of human exploitation of ocean resources have had catastrophic effects on marine life. The large disasters of modern times have brought attention to some of the problems (i.e. The Alaska-Exxon Valdez oil spill (1989), the destruction of Kuwait's oil fields in the 1st Gulf Wa (1991)r, and the BP Deepwater Horizon Oil Spill in the Gulf of Mexico (2010) are high-profile examples of marine ecosystem disasters (each having long-term impacts). However, it is the small scale, daily exploitation impacts of a growing human population that is having catastrophic effects on marine ecosystems (and human communities that rely on marine resources).

* 80% of available fish stock are now fully exploited, overexploited, or depleted/recovering.
* Large predatory fish reduced are greatly reduced in populations.
* Global warming of ocean waters is causing havoc on marine ecosystems: warmer water increases metabolism needs of marine life, affecting their life and reproduction cycles. In addition, thicker thermoclines reduce upwelling of nutrient-rich waters, reducing primary production.

Many countries are now using Fisheries Management. Fisheries management involves regulation, education, enforcement, with an effort to create self-sustaining ecosystems.

Much work needs to be done!

Feeding Frenzies (YouTube videos)

Anchovies in Santa Cruz:
Sharks along North Carolina beach
Sardines, dolphins, birds, sharks, whales
Sei whale feeding
Chapter 16 quiz questions