Oceanography 100
P Anderson
Chapter 14
Animals of the Pelagic Environment
Pelagic organisms
• Organisms that live in the pelagic environment:
– Live suspended within the water column
– Can float or swim
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Have adaptations that allow them to stay above the ocean floor
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Rigid gas containers
Swim bladder
Ability to float
Microscopic floating organisms:
Radiolarians
• Radiolarians produce a hard test composed of silica
• Tests have projections to increase surface area
Foraminifers
• Foraminifers produce a hard test composed of calcium carbonate
• Test is segmented or chambered
Copepods
• Copepods have a hard exoskeleton and a segmented body with jointed legs
• Relatives of shrimp, crabs, and lobsters
Krill
• Krill are related to copepods but are larger in size
• Abundant in Antarctic waters, where they are a favorite food of the largest whales
Macroscopic floating organisms: Coelenterates
• Coelenterates are soft-bodied organisms including:
– Siphonophores (Portuguese man-of war)
– Scyphozoans (jellyfish)
Swimming organisms (nekton)
• Larger pelagic organisms can swim against currents and often migrate long distances
• Nektonic organisms include:
– Squid
– Fish
– Marine mammals
Fish: Adaptations
• Feeding styles: Lungers versus cruisers
– Lungers sit and wait for prey to come close by
– Cruisers actively seek prey
• Cold-blooded versus warm-blooded
– Most fish are cold-blooded
– A few active fish are warm-blooded
• Many fish school to avoid predators
Fish: Deep-water nekton
• Adaptations of deep-sea fish:
– Good sensory devices
– Bioluminescence
– Large, sharp teeth
– Large mouths and expandable bodies
– Hinged jaws
Marine mammals
• Characteristics of marine mammals:
– Warm-blooded
– Breathe air
– Have hair (or fur)
– Bear live young
– Females have mammary glands that produce milk for their young
Marine mammals: Order Carnivora
• All members of order Carnivora have prominent canine teeth
• Includes:
– Sea otters
– Polar bears
– Pinnipeds (flipper-footed)
• Walrus
• Seals
• Sea lions/fur seals
Differences between seals and sea lions/fur seals
• Seals:
– Lack ear flaps
– Have small front flippers
– Have claws
– Cannot rotate hind flippers beneath themselves
Marine mammals: Order Sirenia
• Sirenian characteristics:
– Large body size
– Sparse hair all over body
– Vegetarians
– Toenails (on manatees only)
• Includes:
– Manatees
– Dugongs
Marine mammals: Order Cetacea
• Cetacean characteristics:
– Blowholes on top of skull
– Skull telescoped (streamlined shape)
– Very few hairs
• Includes:
– Whales, dolphins, and porpoises
Marine mammals: Order Cetacea Two suborders
• Suborder Odontoceti (toothed whales)
– Echolocate (send sound through water)
– Includes killer whale, sperm whale, dolphins, porpoises, and many others
• Suborder Mysticeti (baleen whales)
– Have rows of baleen plates instead of teeth
– Includes blue whale, finback whale, humpback whale, gray whale, and many others
Differences between dolphins and porpoises
• Dolphins have:
– An elongated snout (rostrum)
– A sickle-shaped (falcate) dorsal fin
– Teeth that end in points
Generation of Odontoceti echolocation clicks
• Sound is bounced off objects to determine:
– Size
– Shape
– Distance
– Internal structure
Mysticeti: The baleen whales
• Mysticeti whales have baleen instead of teeth
• Baleen plates:
– Hang as parallel rows from the upper jaw
– Are made of keratin
– Are used as a strainer to capture zooplankton
– Allows baleen whales to eat krill and small fish by the ton
Types of baleen whales
• Baleen whales include three families:
– Gray whale (a bottom-feeder with short baleen)
– Rorqual whales (medium-sized baleen)
•
Balaenopterids (blue whales, finback whales, and other large whales )
•
Megapterids (humpback whales)
– Right whales (surface skimmers with long baleen)
An example of migration: Gray whales
• Gray whales undertake the longest annual migration of any mammal:
– Spend wintertime in birthing and breeding lagoons in Mexico
– Spend summertime feeding in highly productive Arctic waters