Ch 8
8 The Water Column: Nekton Notes for Marine Biology:
Function, Biodiversity, Ecology By Jeffrey S. Levinton Nekton: Defini6ons • Nekton: organisms living in the water column 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 • Boundary layer on fast moving forms is thin • Minimizing pressure drag is important for fast and con;nual mo;on Nekton -‐ Principal Members •
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Cephalopods Fish Mammals Sea birds Rep<les -‐ Sea Turtles 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 • Osteichthyes -‐ 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<on may be concentrated in tail, as in tuna (right), as opposed to eel, where undula<ons are more evenly distributed through long body Oxygen Use • Water over gills • Water flows over gill lamellae and oxygen diffuses into gills • Blood flow is in opposite direc;on of water 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 • Gas gland -‐ gas uptake and release • Rete mirabile -‐ intertwined capillaries and veins -‐ countercurrent exchange to retain oxygen near the gas gland Buoyancy: Swim Bladder Rete mirabile: countercurrent exchange to retain oxygen Fish Feeding • Two mechanisms in water column: suc;on (oral cavity expansion) and ram feeding (gill exit) • Many fish chew prey by means of teeth; some have specialized crushing teeth (puffer fish, some sculpins) • Some species suspension feed, trap zooplankton, phytoplankton, or par;culate organic maTer on gill rakers Frogfish suck! Family Antennaridae hYp://www.divephotoguide.com/underwater-‐
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amazing-‐frogfish-‐behavior-‐videos/ Vulmer, the crushing mouthpart Snail shell with punctures X ray of bivalves in fish gut A shell-‐crushing fish, sculpin Asemichthys taylori Pacific Northwest, U. S. A. 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 • Fish have well developed eyes, o\en large mouths for feeding on large prey • Many have ventral photophores, serves 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<ve of chlorophyll has antenna for infrared, transfers to b-‐g light, detected by re<na 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 • Odontoce; toothed whales (e.g., sperm whale, porpoises) • Mys;ce; baleen whales -‐ feed by means of baleen, which strains macrozooplankton, megazooplankton Whales and Porpoises • All homeothermic • Reproduce much the same as terrestrial mammals • Posterior strongly muscular -‐ propulsion by means of flukes Odontoce6 • Toothed, usually good hunters, feed on squid, fish, small mammals • Good divers • Oral communica<on common • Many species have bulbous melon, filled with oil -‐ func<on could be sound recep<on • Usually social, killer whales live in pods, maternally dominated Odotocete Killer whale, Orcinus orca Mys6ce6 • Adults have horny baleen plates, which strain zooplankton • Right whales (e.g., northern right whale) are con;nuous ram feeders • Rorqual whales (e.g. Blue) are intermiTent ram feeders, periodically squeeze water out of large mouth chamber Con;nuous ram feeding IntermiTent ram feeding {
Ventral furrows Mys<cete feeding with baleen plates North Atlan<c Right whale, Eubalaena glacialis Mys<cetes: humpback whale (rorqual whale) breaching Baleen plate of a beached finback whale Other Marine Mammals • Pinnipeds include seals, sea lions, walruses -‐ have hair but lack thick blubber of cetaceans • Sea oTers belong to the otherwise terrestrial family Mustelidae Australian sea lion Neophoca cinerea Family Mustelidae Sea oTer, Enhydra lutris Sirenians • Includes manatee, dugong, ex<nct Stellar Sea Cow • Sluggish, herbivorous • Live in inshore waters, estuaries Florida manatee Trichechus manatus Diving by Marine Mammals • Must breathe at surface • Problem: oxygen for long dives • Most have increased volume of arteries and veins • Have increased blood cell concentra;on • Can decrease heart beat rate and O2 consump;on • Can restrict peripheral circula;on and circula;on to abdominal organs Gas Bubble Problems • Upon ascent, gas bubbles may be released in blood stream as pressure decreases -‐ The Bends • Not as bad a problem as you might think, because marine mammals don’t breathe air under pressure at depth, like human divers • Seals and whales can restrict circula;on between the lungs and rest of circulatory system and have small lung capacity Seabirds • Penguins -‐ flightless, southern hemisphere, high la<tude, divers, insulated by blubber and feathers, countercurrent heat exchange in circula<on to wings and feet, colonial breeders • Petrels -‐ great gliders, colonial breeders, o_en divers from air • Pelicans -‐ generally tropical, heavy, diverse hun<ng from diving to underwater swimming • Gulls, auks, puffins -‐ feed on fish, o_en very abundant FIG. 8.36 Methods by which seabirds obtain prey: (a) feeding from surface (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
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FIG. 8.39 The sooty oystercatcher Haematopus fuliginosus (seen here on Heron Island, Great Barrier Reef, Australia) is an effec<ve predator on 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
FIG. 8.37 Some of the diversity of shorebirds: ruddy turnstone, purple 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
FIG. 8.38 A piping plover, Charadrius melodus, with a decep<ve broken wing display, trying to lure a poten<al predator (the photographer) away from its nearby ground nest. (Courtesy of Peter Davis) Marine Biology: Function,
Biodiversity, Ecology, 4/e
Levinton
Copyright © 2014 by Oxford University
Press
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<on between nes<ng and feeding areas is common •
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Preda<on on juvenile black albatross by shark Northern gannet, Morus bassanus BOX FIG. 8.1 Tucker, a mixed-‐breed Labrador retriever who has been trained to sniff and locate floa<ng orca scat at the sea surface, off San Juan Island, Washington. (Courtesy of Sam Wasser) Marine Biology: Function,
Biodiversity, Ecology, 4/e
Levinton
Copyright © 2014 by Oxford University
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