MARS 3450, 9 October 2012NektonSampling can be a challenge…Nekton, Part 1•Capable of active locomotion in the water•Most are vertebratesDomain EukaryaKingdom AnimaliaPhylum ChordataSubphylum Vertebrata•Seven Classes of Vertebrata•No marine amphibiansExceptions: cephalopods, krill, shrimp, etc.!But only six have marine membersSumich 1992MammalsBirdsReptilesAmphibians•Three classes of fishAgnatha, Chondrichthyes, Osteichthyes•Oldest vertebrates•14,000 marine species•Temperatures to -1.9oC•Life span to 100 years or more•Size range: 10 mm to 12 m•60% of all known fish species are marineNekton Part 1Science 305:472. 2004.Stout Infantfish7 mm, 1 mgCoral lagoons in AustraliaCastro and Huber 2003Common namesfor subclassesClass Agnatha•Cartilagenous skeleton•No paired fins•No jaws•Round muscular mouth, rows of teeth•No scales•Elongate, cylindrical body•Two groups: hagfish, lampreys“Jawless Fish”Lots of mucus!•Unpalatable•Reduce frictionHagfish•Strictly marine•Scavengers•Locate food with tentacles•Bore into food with toothed tongue•43 species•“slime eels”http://naturefilmsnetwork.comLampreys•Mostly freshwater, some marine•Reproduce in freshwater•Parasitic; rasp with teeth until bloodflows, secrete anticoagulant•Some adults don’t feed•41 speciesDeep sea whale carcassHagfish in the Deep Sea•Scavenging on whale carcass•Feed by rasping fleshClass Chondrichthyes•Cartilaginous skeleton•Moveable jaws•Well-developed teeth•Paired fins•Small scales: denticles•Ventral mouth•5-7 pairs exposed gill slits•Spiracles: openings behind eyes for breathing•Carnivores: fish, mollusks, crustaceans•Three groupsSharks, skates, rays, ratfishCartilaginous FishSharks•Well-developed caudal fin, asymmetrical•Two dorsal fins, first large and triangular•Fins stiff and fleshy; don’t fold•Sexually dimorphic – males have “claspers”•Conveyer belt teeth: embedded in soft tissue, replaced continuallytailHammerhead and White Tip Reef Sharks•Cleaner station for parasites•Exposed gill slitsCastro and Huber 2003Skates and Rays•Flattened body•Demersal•Gill slits on bottom•Flat, expanded pectoral fins,fused with head•Feed on clams, small fish, plankton•Stingrays have poison glandsRatfish (Chimeras)• Deep Sea• Feed on crustaceans,mollusks, worms• http://seattletimes.com/html/pacificnw/2012531495_pacificpratfish15.htmlLive near the sea floorManta Ray•Feeding on planktonBat Ray•Feeding on benthic invertebratesClass Osteichthyes•Bony skeleton•Moveable and paired fins•Flexible and symmetrical caudal fin•True scales; thin and flexible•Mouth forward•Gill cover: operculumBony fishCastro and Huber 2003Chondricthyes vs.OsteichthyesVery maneuverable,swim backwards,keep stationaryNot maneuverableMorphologyCastro and Huber 2003Chondricthyes vs.OsteichthyesMouth need not be open to breatheOperculum forces water over gillsSwim with mouth openRespirationSharks, raysBony fishMore flexibility inlifestyle!Sumich 1992Coelacanth•First specimen caught in 1938•Second in 1952•Deep water (>200 m)A Coelacanth in Paris! Latimeria chalumnae1997:Two specimens in IndonesiaLatimeria menadoensisNekton Adaptations•BuoyancyAdaptations of nektonic organisms: fishBones, cartilage, shells: 2.0, 1.05, 2.0 g/cm3Seawater: 1.02 g/cm3Store oils and fat (0.9 g/cm3) Oversized livers in sharks, mackerel, tunaAir bladders (air is 0.1% as dense as water)Rigid: nautilisNon-rigid: swim bladdersConstant SwimmingIon ReplacementThe problem!Bony fishFins provide liftLevinton 2001Rete Mirable (“wonderful net”)Countercurrent systemHow do gases get into a swim bladder?Some species can gulp airLactic acid secretedHemoglobin releases oxygenNeed to allow vertical movementthrough the waterRapidly vents swim bladderSlowly vents swim bladderPhysostomusPhysoclistousHow do gases get out of a swim bladder?PerchesTarpon, carp•Unique Sensory OrgansAdaptations of nektonic organisms: fishCastro and Huber 2003Lateral lines•Gelatin-filled canals•Lined with sensory organs•Vibrations tranmitted to nerves•Detect low frequency soundMinute vibrations of foodNavigate from reflected wavesCoordinate schooling•Unique Sensory OrgansAdaptations of nektonic organisms: fishElectroreception•Cartilaginous fish•Network of pores/pits on head•Ampullae of Lorenzini•Connected to lateral lines•Detect electrical currents at distance of <1m•Use to locate preyNekton, Part 2•Vertebrates evolved in the marine environment•Invaded land 350 million years ago (limbs, lungs)•Some re-invaded the ocean•Legacies of terrestrial ancestorsAll retain lungs, not gillsSome return to land to reproduceIncomplete return to the seaMust surface to breathe airNektonPart 2Sumich 1992MammalsBirdsReptilesAmphibiansHall IllustrationOrder: Testudines (Chelonia)Class: Sauropsida (Reptiles)•Dry skin, covered with scales•Leathery shell covering eggs•Ectotherms•Marine reptiles have specialized gland for salt secretion•Seven species•Shell is fused to backbone, can’t retract head•Live primarily in warm seas•One herbivore (Green turtle; 300 lbs)•One jellyfish-eater (Leatherback; 1300 lbs)•Others omnivorous•Local turtle: Loggerhead (350 lbs) Characteristics of marine reptilesSea Turtles•Return to land to lay eggs•Sexual maturity takes 10-30 yrs•Long migrations between feeding and nesting grounds•Females reproduce every 2-4 yrs•Females mate offshore, lay eggs on beach•Lay ~100 eggs into sand nest•Eggs hatch after ~60 days•Temperature influences sex ratio: higher temps = >Sea TurtleReproductiveBehavior(>1000 miles!)GreenSeaTurtle•Eastern Pacific Leatherback populations are declining•Mortality from fisheries? egg harvesting? climate?Sea TurtlePopulationDynamicsInterval between “remigration” events for femalesPlaya Grande, Costa RicaTemperature affects NPPIncludes sea surface temperature# of nesting femalesSaba et al. 2007Sea Turtle Nesting•Females come ashore•Timed with neap tideOrder: Squamata Class: Sauropsida (Reptilia)Sea Snakes and Marine Iguanas•Indian and Pacific Ocean, tropical seas •Paddle-shaped tail •Salt glands•Most reproduce in the ocean; eggs develop in reproductive tract (live birth) •Carnivores (feed on fish, eggs) •Some have toxic venomE Pennisi Science 2012;338:1143-1143Are you thirsty? Harvey Lillywhite has tested hundreds of sea snakes to see if they will drink fresh water. They