8 The Water Column: Nekton
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| 8 The Water Column: Nekton
Marine Biology: Function, Biodiversity, Ecology
By Jeffrey S. Levinton
Nekton: Defini6ons •
that can swim strongly enough to move counter to modest water currents Nekton: Constraints
• Nekton: live under high Reynolds number, meaning that iner;al forces dominate over viscous forces •
•
Read Hot Topics 8.1, p. 179-‐180 • Quiz on Wednesday Fish
• Chondrichthyes -‐ car;laginous fishes including sharks, skates, rays (Elasmobranchs) -‐ car;laginous skeleton, replaceable tooth rows, 5 or more gill slits •
-‐ bony fishes, true bony skeleton -‐ much more diverse than Chondrichthyes, teeth fixed in jaws, single gill opening Chondrichthyes Osteichthyes Form and Swimming
Swimming of fish
• Swimming usually involves undula;on of en;re body
Components of force during swimming Dactylopteridae, Flying Gurnards Swimming In powerful swimmers undula opposed to eel, where undula Oxygen Use
• Water over gills •
diffuses into gills •
flow -‐ countercurrent exchange -‐ same principle as for gill flow in crabs and heat conserva;on in dolphins (ch. 4) Gill filaments of a fish and countercurrent exchange
Buoyancy
• Fish can regulate bulk chemistry • Sharks -‐ high lipid content -‐ reduces bulk density • Bony fish -‐ lower salt content than sea water -‐ reduces bulk density • Swim Bladder -‐ most bony fish Buoyancy
• Most bony fish -‐ swim bladder; fish can acquire air at surface and esophagus is connected to swim bladder •
•
Buoyancy: Swim Bladder
exchange to retain oxygen
Fish Feeding
• Two mechanisms in water column: suc;on (oral cavity expansion) and ram feeding (gill exit) •
some have specialized crushing teeth (puffer fish, some sculpins) •
suspension feed , trap zooplankton, phytoplankton, or par;culate organic maTer on gill rakers Frogfish suck! Family Antennaridae hYp://www.divephotoguide.com/underwater-‐ photography-‐scuba-‐ocean-‐news/scubazoo-‐s-‐ jason-‐isley-‐tells-‐story-‐behind-‐capturing-‐his-‐ amazing-‐frogfish-‐behavior-‐videos/
A shell-‐crushing fish, sculpin Asemichthys taylori Pacific Northwest, U. S. A. Vulmer, the crushing mouthpart Snail shell with punctures X ray of bivalves in fish gut Suspension feeding of a basking shark Moray eel everts pharyngeal jaws to seize prey
Sensory Percep6on
• Lateral line system -‐ Eyes -‐ fish o_en have excellent vision • Otoliths in contact with hairlike fibers Mesopelagic Fishes
• Fish living 150-‐2000 m •
mouths for feeding on large prey •
purpose of counterillumina;on -‐ camouflage to blend in with low light from above Chauliodus has specialized backbone to accommodate opening of large mouth to consume prey Loosejaw Malacosteus niger, light-‐emiang organs in infrared, can see prey one meter away, prey see nothing Deriva light, detected by re Mammals
Cetaceans: whales and porpoises Pinnipeds: seals, sea lions, walruses Mustelids: sea oYers Sirenians: sea cows, dugongs
Whales and Porpoises
• All belong to the Cetacea •
toothed whales (e.g., sperm whale, porpoises) •
baleen whales -‐ feed by means of baleen, which strains macrozooplankton, megazooplankton Whales and Porpoises
• All homeothermic •
mammals •
means of flukes Odontoce6
• Toothed, usually good hunters, feed on squid, fish, small mammals • Good divers • Oral communica •
Many species have bulbous melon, filled with •
Usually social, killer whales live in pods, Mys6ce6
• Adults have horny baleen plates, which strain zooplankton •
(e.g., northern right whale) are con;nuous ram feeders •
(e.g. Blue) are intermiTent ram feeders, periodically squeeze water out of large mouth chamber Ventral furrows Con;nuous ram feeding
ram feeding
{ Mys North Atlan Mys Baleen plate of a beached finback whale Other Marine Mammals
• Pinnipeds include seals, sea lions, walruses -‐ have hair but lack thick blubber of cetaceans •
family Mustelidae Sea oTer, Enhydra lutris Family Mustelidae Sirenians
• Includes manatee, dugong, ex Cow
• Sluggish, herbivorous • Live in inshore waters, estuaries Florida manatee Trichechus manatus Diving by Marine Mammals
• Must breathe at surface •
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to abdominal organs
Gas Bubble Problems
• Upon ascent, gas bubbles may be released in blood stream as pressure decreases -‐ The Bends •
marine mammals don’t breathe air under pressure at depth, like human divers •
between the lungs and rest of circulatory system and have small lung capacity Seabirds
• Penguins -‐ flightless, southern hemisphere, high la countercurrent heat exchange in circula and feet, colonial breeders •
Petrels -‐ great gliders, colonial breeders, o_en divers •
Pelicans -‐ generally tropical, heavy, diverse hun •
Gulls, auks, puffins -‐ feed on fish, o_en very Marine Biology: Function, Biodiversity, Ecology, 4/e Levinton Copyright © 2014 by Oxford University Press
(fulmar), (b) plunge diving (gannet), (c) diving from air (tern), (d) underwater pursuit diving using wings (puffin), and (e) use of feet in underwater propulsion (shag). (A_er Furness and Monaghan, 1987) Marine Biology: Function, Biodiversity, Ecology, 4/e Levinton Copyright © 2014 by Oxford University Press
Heron Island, Great Barrier Reef, Australia) is an effec mollusks such as limpets and bivalves. Note its robust bill, used for
bashing shells against rocks and severing adductor muscles. (Photograph by Jeffrey Levinton)
Marine Biology: Function, Biodiversity, Ecology, 4/e Levinton Copyright © 2014 by Oxford University Press
sandpiper, marbled godwit, and northern phalarope, with detail of webbed foot. (A_er Schneider, 1983)
Marine Biology: Function, Biodiversity, Ecology, 4/e Levinton Copyright © 2014 by Oxford University Press
wing display, trying to lure a poten from its nearby ground nest. (Courtesy of Peter Davis)
Seabirds • O_en colonial breeders • Believed to be monogamous • Courtship involves elaborate displays • Crowded breeding sites, o_en with several species, protected from predators such as mammals, predatory birds • Feeding involves either diving or underwater swimming • Long-‐distance migra Preda
Northern gannet, Morus bassanus Marine Biology: Function, Biodiversity, Ecology, 4/e Levinton Copyright © 2014 by Oxford University Press
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