Nekton

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

12. You will never be as cool as a cephalopod • 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 www.islandream.com/sangalakigallery7.htm http://www.itsnature.org/sea/other/colossal-squid/ www.flickr.com/photos/maxcdc/3615629745/

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) http://www.greatturtlerace.com/

25. Our Local Sea Turtles scienceblogs.com http://fwie.fw.vt.edu www.underwater.com.au Leatherback Green Loggerhead www.dnr.state.md.us/fisheriesoxford/research/fwh/seaturtles.html Hawksbill Kemp’s Ridley http://www.costaricaturtles.com/costa_new_seaturtles.html

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 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. 2004. 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)

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