8 The Water Column: Nekton Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S....
-
Upload
harvey-simmons -
Category
Documents
-
view
218 -
download
3
Transcript of 8 The Water Column: Nekton Notes for Marine Biology: Function, Biodiversity, Ecology By Jeffrey S....
8 The Water Column: NektonNotes for Marine Biology: Function, Biodiversity,
EcologyBy Jeffrey S. Levinton
©Jeffrey S. Levinton 2001
Nekton: Definitions
• 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 inertial forces dominate over viscous forces
• Boundary layer on fast moving forms is thin
• Minimizing pressure drag is important for fast and continual motion
Nekton - Principal Members
• Cephalopods
• Fish
• Mammals (cetaceans, otters)
• Birds (divers)
Chambered nautilus
Cephalopods (Phylum Mollusca)
Cephalopods
• Phylum Mollusca
• Mouth - powerful beak
• Mantle + siphon = rapid movement
• Squids and octopus have an ink gland; ink expulsion confuses predators
Cephalopod Buoyancy
• Gas production
• Nautilus - chambers
• Cuttlefish - cuttlebone + osmotic pump
Cuttlebone of cuttlefish
Fish
• Chondrichthyes - cartilaginous fishes including sharks, skates, rays - cartilaginous skeleton, replacable tooth rows
• Osteichthyes - bony fishes, true bony skeleton - much more diverse than Chondrichthyes, teeth fixed in jaws
Form and Function
• Form of fishes strongly related to their locomotion type and feeding ecology
Form and Function 2
• Rover predators long and torpedo-shaped, with fins spaced - maneuverability
Tuna
Form and Function 3
• Surface-oriented fishes (e.g. flying fishes) mouth oriented upward to capture prey at surface
Flying fish
Form and Function 4• Bottom fish - variable, but often flattened
to be close to bottom
Flounder
Form and Function 5
• Deep-bodied fish - flattened laterally, excellent at maneuvering, not prolonged swimmers
Butterfly fish
Form and Function 6
• Eel-like fish - well adapted to moving in crevices, such as moray eels
Form and Swimming
• Form is a combination of three modes:
• Acceleration
• Cruising
• Maneuvering
Form and Swimming 2
Swimming• Swimming usually involves undulation of
entire body
Components of force during swimming
Swimming
• Swimming usually undulation of body
• Bony fishes use vertebral column as a skeleton to oppose muscular action
• Sharks - helical external meshwork of collagen against which muscular action works
Oxygen Use
• Water over gills
• Water flows over gill lamellae and oxygen diffuses into gills
• Blood flow (hb) is in opposite direction of water flow - countercurrent exchange - same principle as for heat conservation in dolphins (ch. 4)
Gill filaments of a fish
Buoyancy
• Fish can regulate bulk chemistry
• Sharks have high lipid content - reduces bulk density
• Bony fish have lower salt content than sea water - reduces bulk density
• Swim Bladder - most fish
Buoyancy
• Most bony fish have a swim bladder; fish can acquire air at surface and esophagus is connected to swim bladder
• Gas gland facilitates gas uptake and release• Rete mirabile - intertwined capillaries and
veins that use 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: suction and ram feeding
• 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 particulate organic matter on gill rakers
A shell-crushing fish, sculpin Asemichthys tayloriPacific Northwest U. S. A.
Vulmer, the crushingmouthpart
Snail shell withpunctures
X ray of bivalves in fish gut
Suspension feeding of a basking shark
Sensory Perception
• Lateral line system - mechanoreceptors used in spatial location, perception of approaching stimuli (e.g., predators)
• Eyes - fish often have excellent vision
• Otoliths - suspended and in contact with hairlike fibers, gives information on spatial orientation
Schooling
• Behaviorally based aggregation of fish• Most tightly schooling species have silvery sides• Schools sometimes in the form of “fish balls”• Behavior related to predation; fish leaving
school are attacked successfully• Schooling may also reduce drag, save on
energetic cost of swimming
Body temperature
• Most fishes - temperature conformers• Tunas and relatives, some sharks, use
countercurrent heat exchange to reduce heat loss - have elevated body temperature
• Elevated body temperature allows higher metabolic rate, localized heating of nervous system in some species (e.g., swordfish)
Mesopelagic Fishes 3
• Fish living 150-2000 m
• Fish have well developed eyes, often large mouths for feeding on large prey
• Many have ventral photophores, serves purpose of counterillumination - camouflage to blend in with low light from above
Chauliodus has specialized backbone to accommodate Opening of large mouth to consume prey
Location of ventral photophores on some deep-water fish
Mammals
Cetaceans: whales and porpoisesPinnipeds: seals, sea lions, walrusesMustelids: sea ottersSirenians: sea cows, dugongs
Whales and Porpoises
• All belong to the Cetacea
• Odontoceti include toothed whales (e.g., sperm whale, porpoises)
• Mysticeti include 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
Odontoceti
• Toothed, usually good hunters, feed on squid, fish, small mammals
• Good divers• Oral communication common• Many species have bulbous melon, filled
with oil - function could be sound reception• Usually social, killer whales live in pods,
maternally dominated
Killer whale, Orcinus orca
Mysticeti
• Adults have horny baleen plates, which strain zooplankton
• Right whales are continuous ram feeders
• Rorqual whales (e.g. Blue) are intermittent ram feeders, periodically squeeze water out of large mouth chamber
Ventral furrows
Continuousram
feeding
Intermittentram
feeding
Other Marine Mammals
• Pinnipeds include seals, sea lions, walruses - have hair but lack thick blubber of cetaceans
• Sea otters belong to the otherwise terrestrial family Mustelidae
Seal
SeaLion
Australian sea lion
Sea otter, Enhydra lutris
Sirenians
• Includes manatee, dugong, extinct Stellar Sea Cow
• Sluggish, herbivorous
• Live in inshore waters, estuaries
Florida manatee
Diving by Marine Mammals• Must breathe at surface• Problem of having enough oxygen for long dives• Most have increased volume of arteries and veins• Have increased blood cell concentration• Can decrease heart beat rate and O2 consumption• Can restrict peripheral circulation and
circulation to abdominal organs
Gas Bubble Problems 3
• 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 circulation between lungs and rest of circulatory system and have small lung capacity
The End