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

Nekton• 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

Why water aerobics are a great workout

• 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

Just keep swimming, just keep swimming

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

• Reduces drag– torpedo shape most effective

Mahi mahi (dolphinfish)

Just keep swimming, just keep swimming

• 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

Staying 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

Invertebrate Nekton• 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 mollusks

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

• They are the most highly evolved of all mollusks

• Cephalopods (“head feet”) have heads surrounded by feet divided into tentacles

• Only nautiluses retain an exterior shell

Cephalopods• Pelagic cephalopods move by swimming with

special fins and/or by squirting jets of water from interior cavities

• “jet propulsion”Water enters mantle cavity

Water exits from funnel or siphon

fins

fins

Cephalopods

• 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

You will never be as cool as a cephalopod

• Mimic octopus http://www.youtube.com/watch?v=H8oQBYw6xxchttp://www.youtube.com/watch?v=ygh1-ul6E94

• Vampire squid from hellhttp://www.youtube.com/watch?v=S3CJIKKSUpg

www.islandream.com/sangalakigallery7.htm http://www.itsnature.org/sea/other/colossal-squid/ www.flickr.com/photos/maxcdc/3615629745/

Pelagic Arthropods

• 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

Who are you calling ‘shrimp’?

• 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

Shrimp collected in Great South Bay, NY; 2009

Fish are 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)

Class Osteichthyes (Bony Fish)

• 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

Class Chondrichthyes (Cartilaginous Fish)

• 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

You are more likely to die from a dog bite (or lightening) than a shark bite…• 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

Fish are friends, not food…

• 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

all-creatures.org

Dramatic decline in shark populations

Myers, et al. 2007

Marine Amphibians?• 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

Marine Reptiles

• 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

Marine Reptiles

• 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)http://www.greatturtlerace.com/

Our Local Sea Turtles

Leatherback

http://fwie.fw.vt.edu

Green

scienceblogs.com www.underwater.com.au

http://www.costaricaturtles.com/costa_new_seaturtles.html

Loggerhead

Hawksbill Kemp’s Ridley

www.dnr.state.md.us/fisheriesoxford/research/fwh/seaturtles.html

Sea Turtles

• 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

Lewison, R., S. Freeman & L.B. Crowder. 2004

Trends in nesting leatherback turtles in the Pacific

Lewison, R., S. Freeman & L.B. Crowder. 2004. Quantifying the effects of fisheries on threatened species: the impact of pelagic longlines on Loggerhead and

Leatherback Sea Turtles

Map of Reported Longline

Effort, inc. all Tuna & Swordfish for 2000

1.4 Billion Hooks Deployed Every Year

Marine Birds• Birds evolved from reptiles and

retain some reptilian features– Scaly legs and claws

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

• Birds evolved a lightweight skeleton for efficient flight

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

• 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!

Tubenoses

• 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

• 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)

Marine Mammals

• 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

Order Cetacea

• 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

Order Cetacea

• 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

Baleen whales

• 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!!!

Save the Whales!

Order Carnivora

• 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

Order Carnivora

• 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!

Sea Otters

Sea otter as a keystone species

Order Sirenia

• 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)

The Florida Manatee