1. 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

2. 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

3. 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

4. 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)

5. Just keep swimming, just keep swimming
Paired fins combined with a tail and a relatively inflexible body propel nekton through the water

6. 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

7. 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

8. 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)

9. 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

10. Cephalopods
Pelagic cephalopods move by swimming with special fins and/or by squirting jets of water from interior cavities
“jet propulsion”
fins
Water enters mantle cavity
Water exits from funnel or siphon
fins

11. 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
Shell of cuttlefish internalized and can function as ‘air bladder’ maintaining air spaces between septa

12. You will never be as cool as a cephalopod
Mimic octopus
Vampire squid from hell

13. 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

14. 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

15. 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)

16. 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

18. 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

19. 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

20. 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

21. Dramatic decline in shark populations
Myers, et al. 2007

22. 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

23. 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

24. 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)

25. Our Local Sea Turtles Leatherback Green Loggerhead Hawksbill
scienceblogs.com
Leatherback
Green
Loggerhead
fisheriesoxford/ research/fwh/ seaturtles.html
Hawksbill
Kemp’s Ridley

26. 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

27. Trends in nesting leatherback turtles in the Pacific
Fourth largest nesting colony in the world; French Guiana and Suriname now host the largest nesting pops
Lewison, R., S. Freeman & L.B. Crowder. 2004

28. Map of Reported Longline Effort, inc. all Tuna & Swordfish for 2000
1.4 Billion Hooks Deployed Every Year
Lewison, R., S. Freeman & L.B. Crowder Quantifying the effects of fisheries on threatened species: the impact of pelagic longlines on Loggerhead and Leatherback Sea Turtles

29. 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

30. 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

31. 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!

32. 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)

33. 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)
orders

34. 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

35. 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

36. 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

37. Baleen whales

39. Save the 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!!!

40. 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

41. 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!

42. Sea Otters

43. Sea otter as a keystone species

44. 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)

45. The Florida Manatee