Pelagic organisms that can actively swim (against a current) are known as nekton

Pelagic organisms that can actively swim (against a current) are known as nekton

• Pelagic organisms that can actively swim (against a current) are known as nekton

• Nekton includes vertebrates (animals with a backbone) and invertebrates (animals without a backbone)

• Examples of vertebrates: marine mammals, reptiles, birds & fish
• Examples of invertebrates: squid, octopus, shrimp and some crabs

To remain in surface waters (where the food supply is greatest), pelagic animals must increase their buoyancy or swim continually

• To remain in surface waters (where the food supply is greatest), pelagic animals must increase their buoyancy or swim continually

• Most pelagic fish have air bladders and generally have soft bodies devoid of hard, dense body parts

• Larger animals must exert more energy to propel through the water

Water is ~800 times denser than air, and 100 times more viscous

• Water is ~800 times denser than air, and 100 times more viscous

• Impedes moving effectively at low speeds

• Nekton have evolved special adaptations to efficiently move through the water column

Pelagic nekton usually have stream-lined shapes that make their propulsive efforts more effective

• Pelagic nekton usually have stream-lined shapes that make their propulsive efforts more effective

• Reduces drag

• torpedo shape most effective

Paired fins combined with a tail and a relatively inflexible body propel nekton through the water

• Paired fins combined with a tail and a relatively inflexible body propel nekton through the water

While fish undulate their tails from side to side to move, marine mammals move their tails up and down to generate thrust, and use flippers to propel and steer themselves through the water

• While fish undulate their tails from side to side to move, marine mammals move their tails up and down to generate thrust, and use flippers to propel and steer themselves through the water

Some fish (and all marine mammals, birds and reptiles) lack air bladders, and so depend on lipid reserves (ex. sharks) or blubber (marine mammals, penguins) to stay afloat

• Some fish (and all marine mammals, birds and reptiles) lack air bladders, and so depend on lipid reserves (ex. sharks) or blubber (marine mammals, penguins) to stay afloat

• Others must constantly expand energy to avoid sinking

Most nekton are vertebrates, however a few specialized invertebrates evolved the ability to swim (and hunt) actively in the water column

• Most nekton are vertebrates, however a few specialized invertebrates evolved the ability to swim (and hunt) actively in the water column

• Cephalopods (squids, octopus, cuttlefish, nautilus)
• Arthropods (shrimp, prawns, some crabs)

Cephalopods are a group of mollusks that include squid, nautilus, cuttlefish and octopus

• Cephalopods are a group of mollusks that include squid, nautilus, cuttlefish and octopus

• They are the most highly evolved of all mollusks

Pelagic cephalopods move by swimming with special fins and/or by squirting jets of water from interior cavities

• Pelagic cephalopods move by swimming with special fins and/or by squirting jets of water from interior cavities

• “jet propulsion”

Most cephalopods catch their prey with stiff adhesive discs on their tentacles

• Most cephalopods catch their prey with stiff adhesive discs on their tentacles

• Cephalopods (except nautiluses) contain a large ink sac used to deter (or numb) predators

• Cephalopods contain chromatophores – pigment-containing cells which enable them to camouflage against virtually any background

Mimic octopus http://www.youtube.com/watch?v=H8oQBYw6xxc

• Mimic octopus http://www.youtube.com/watch?v=H8oQBYw6xxc

• http://www.youtube.com/watch?v=ygh1-ul6E94

• Vampire squid from hell

• http://www.youtube.com/watch?v=S3CJIKKSUpg

Arthropods (“jointed feet”) are a group of invertebrates possessing an exoskeleton, segmented body, and jointed appendages

• Arthropods (“jointed feet”) are a group of invertebrates possessing an exoskeleton, segmented body, and jointed appendages

• Arthropods include copepods, barnacles, lobsters, crabs and shrimp

• Only shrimp (also referred to as “prawns”) and some specialized crabs are pelagic

There are ~2,000 species of pelagic shrimp which range in size from ½ inch to 8 inches

• There are ~2,000 species of pelagic shrimp which range in size from ½ inch to 8 inches

• Shrimp are a very important source of protein for higher trophic levels

Fish are the most abundant and successful group of vertebrates

• Fish are the most abundant and successful group of vertebrates

• There are more species of fish than species of all other vertebrates combined (includes all birds, reptiles, amphibians, and mammals)!!!

• Fish are divided into 2 groups:

• Bony Fish (Class Osteichthyes)
• Cartilaginous Fish (Class Chondrichthyes)

Bony fish are the most successful and abundant of the 2 groups of fishes (~27,000 species)

• Bony fish are the most successful and abundant of the 2 groups of fishes (~27,000 species)

• Osteichthyes possess a hard, strong, but lightweight skeleton made of calcium that supports them and is responsible for their success (and diversity) as a group

• Bony fish include tuna, cod, flounder, goldfish, and other familiar species

All members of the class Chondrichthyes have skeletons made not of bone, but of tough, elastic tissue called cartilage

• All members of the class Chondrichthyes have skeletons made not of bone, but of tough, elastic tissue called cartilage

• Includes:

• Sharks
• Skates
• Rays

• ~350 species of sharks; ~320 species of rays

• Nearly all are marine

More than 80% of all sharks are <2 meters in length (less than 6.6 feet)

• More than 80% of all sharks are <2 meters in length (less than 6.6 feet)

• Only a few of the remaining 20% are aggressive towards humans

• Many sharks exhibit countershading, appearing dark on top and light on the bottom

• Camouflage from above and below

In fact, sharks have WAY more to fear from humans than we do of sharks

• In fact, sharks have WAY more to fear from humans than we do of sharks

• Shark populations are in considerable decline worldwide

• 80% global decline in shark populations!
• 26-73 million sharks killed every year for their fins!
• Potential increases in diseased, unfit, and unhealthy prey individuals

Amphibians are thin-skinned animals that require moisture to keep from drying out

• Amphibians are thin-skinned animals that require moisture to keep from drying out

• “Amphibian” literally translates to “double life”

• Larval form uses gills for breathing

• There are NO marine amphibians; saltwater would result in rapid desiccation

Reptiles are cold-blooded, air-breathing animals with tough, scaly skin

• Reptiles are cold-blooded, air-breathing animals with tough, scaly skin

• Marine reptiles include:

• Sea turtles
• Sea snakes
• Marine crocodiles
• Marine lizards (iguanas)

• Marine reptiles are equipped with special salt glands to concentrate and excrete salts

8 species of sea turtles

• 8 species of sea turtles

• All are streamlined and adapted for life in the water

• Forelimbs are modified into flippers
• Hindlimbs act as rudders
• Cannot retract head or limbs

• Sea turtles spend their entire lives at sea; only females come ashore to lay eggs

• Homing (return to same beach where they were born to lay eggs)

Most of the world’s sea turtles are threatened or endangered

• Most of the world’s sea turtles are threatened or endangered

• Dangers include:

• Shrimp trawling
• Beach destruction; hardening of shorelines, bright lines, vehicles and dogs on beaches
• Long-line fishing
• Marine debris

Birds evolved from reptiles and retain some reptilian features

• Birds evolved from reptiles and retain some reptilian features

• Scaly legs and claws

• However, birds are warm-blooded and possess wings for flight

Only ~3% of all birds are marine birds

• Only ~3% of all birds are marine birds

• Marine birds, like reptiles, have salt-excreting glands to allow salt from their diet to drip out passages on their beaks

• All marine birds are tied to the land, in that they must return to land to breed and to lay their eggs

• Penguins and tubenoses are best adapted to the pelagic realm

Penguins have completely lost the ability to fly and instead traded their wings for flippers

• Penguins have completely lost the ability to fly and instead traded their wings for flippers

• Fatty insulation keeps penguins warm and allows them to maintain neutral buoyancy in the water

• All penguins are found in the Southern Hemisphere

• Believed to consume ~86% of all food taken by birds in the Southern Hemisphere!

The “tubenoses” include albatross and petrels

• The “tubenoses” include albatross and petrels

• A tubular nasal passage allows them to smell and locate patchily-distributed food at sea, and to help locate their own nests

• Albatross have the largest wingspan of any bird (up to 11 feet from tip to tip)

Marine mammals include the largest animals ever to have lived on Earth

• Marine mammals include the largest animals ever to have lived on Earth

• Mammals are warm-blood, air-breathing animals that give birth to live young, have mammary glands (females), and possess fur/hair

• Marine mammals include:

• Cetaceans (Whales, dolphins and porpoises)
• Seals, sea lions, walruses, and sea otters (Carnivores)
• Sirenians (manatees and dugongs)

All marine mammals arose from land ancestors and have become adapted to a marine existence

• All marine mammals arose from land ancestors and have become adapted to a marine existence

• Streamlined body shapes reduce drag

• Limbs have been modified into flippers

• They evolved means of retaining large quantities of oxygen to facilitate long dives

• Concentrated (highly saline) urine

Cetaceans are believed to have evolved from hooved land animals (ex. sheep, horse) which spent more and more time in productive, shallow waters searching for food

• Cetaceans are believed to have evolved from hooved land animals (ex. sheep, horse) which spent more and more time in productive, shallow waters searching for food

• Cetaceans include whales, dolphins, and porpoises

• Spindle-shaped body; forelimbs modified into flippers; tail with horizontal flukes; nearly hairless

Cetaceans are further divided into toothed whales and baleen whales

• Cetaceans are further divided into toothed whales and baleen whales

• Toothed whales include all the dolphins and porpoises, along with orca (killer whale) and sperm whales

• Baleen whales lack teeth and instead have baleen, a structure made of keratin, for filtering out small animals (ex. fish, krill) from the water; the largest of all animals

The great baleen whales have been hunted for several centuries for their meat and blubber which was processed into fuel, soaps and other products

• The great baleen whales have been hunted for several centuries for their meat and blubber which was processed into fuel, soaps and other products

• Many populations were decimated (and some have still not recovered)

• The North Atlantic Right Whale was most dramatically affected; only ~330 individuals remain!!!

The group Carnivora includes land predators ranging from dogs and cats to bears and weasels, but carnivores belonging to the group Pinnipedia (the pinnipeds) are nearly exclusively marine

• The group Carnivora includes land predators ranging from dogs and cats to bears and weasels, but carnivores belonging to the group Pinnipedia (the pinnipeds) are nearly exclusively marine

• Pinnipeds include:

• Seals
• Sea lions
• Walruses

Marine carnivores also include sea otters

• Marine carnivores also include sea otters

• Sea otters are found only in the Pacific Ocean, and have the densest fur of all animals

• Sea otters inhabit nearshore environments and dive to the sea floor to forage on mollusks, crustaceans and echinoderms (sea stars and urchins)

• A keystone species!

Sirenians include the manatee and dugongs

• Sirenians include the manatee and dugongs

• Sirenians are the only herbivorous marine mammal; feed on aquatic plants and algae

• Some species live in fresh and/or brackish water

• Inhabit temperate or subtropical waters

• Threatened by motor boat collisions, harmful algal blooms, and pollution (and severe winters)