Final

Cards (259)

  • Nekton: pelagic animals that are powerful enough swimmers to move actively at will in the water column.
  • Nekton are difficult to study as:
    • They move fast
    • Are hard to catch
    • Are normally quite large (hard to keep in captivity)
  • Much of the ecology of nekton is inferred by anatomical and physiological studies.
  • Abiotic factors affecting nekton
    • Light
    • Temperature
    • Density
    • Currents
  • Nekton's vast environment:
    • Is profound 3-D
    • Has no large solid substrate
    • Has virtually no bearings
    • Has no firm support
  • Nekton adaptations:
    • Great mobility
    • Nervous & sensory systems
    • Fast swimming speeds
    • Camouflage
    • Floatation
  • For epipelagic nekton, the priority is to stay afloat.
  • Nekton adapt for buoyancy with:
    • Gas/swim bladder systems
    • Swim quickly to avoid sinking
    • Gas filled cavities
    • Use of lipids in the body
  • Swim bladders absorb or secrete gas to adjust the depth.
  • Swim bladders can be physoclistous (isolated) or physostomous (controllable or connected to gas exchange).
  • Fish have no muscular control over their swim bladder.
  • Swim bladders can be potentially dangerous when a fish descends or ascends as gas may expand or shrink too fast.
  • Rete mirabile: a counter-current exchange structure of capillaries that allows gas uptake in a fish with a swim bladder.
  • The oxygen tension is always greater in the venous than in the arterial blood of the rete mirabile. This causes diffusion.
  • Oxygen released from hemoglobin is free in the venous capillary and will diffuse across into the arterial capillary in the rete mirabile.
  • Gas filled cavities are a common means of buoyancy in mammals and birds.
  • The use of lipids in the body is a common means of buoyancy in fast swimming fish, birds, and mammals.
  • Nekton adapted locomotion as the movement through water requires adaptations to create the propulsive force and reduce the resistance.
  • Nekton adapt for locomotion with:
    • Side to side motion
    • Movement of fins/limbs
  • Organisms create a side to side motion with trunk muscles arranged as a series of W shaped bands.
  • In side to side motion of organisms, muscles contract in sequence from anterior to posterior and alternately from one side to the other.
  • In side to side motion of organisms, undulations can occur throughout the entire body, part of the body, or be limited to the tail.
  • In general, relatively short, stubby fishes are faster than very long, narrow fishes.
  • In the movement of fins/limbs for locomotion, the body remains stationary, and the fins or paddle shaped limbs are moved in one of several ways to cause forward motion.
  • The speed of movement of locomotion through fins/limbs depends on the frequency of the stroke.
  • Types of resistance/drag to movement:
    • Frictional resistance
    • Form resistance
    • Induced drag
  • Frictional resistance is minimum in spherical objects.
  • Form resistance: drag is proportional to the cross sectional area of the object, and hence minimal in relatively long and thin objects.
  • To propel a body through water requires more energy than to move the same body at the same speed through air.
  • Caudal fin = tail fin
  • Fast swimming fish have caudal fins with high aspect ratios.
  • Fill in the following labels:
    A) Aspect ratio
    B) Height
    C) Area
  • Induced drag: with increasing speed or size, laminar flow is disrupted and forms vortices and eddies.
  • Eddy: circular movement of water in the opposite direction of water flow.
  • The best streamlined bodies have a teardrop shape and recessed protruding structures.
  • Nekton adapted for defense and camouflage with:
    • Development of a ventral keel
    • Cryptic coloration
  • The need for elaborate defensive mechanisms is somewhat reduced when able to camouflage.
  • The development of a ventral keel creates camouflage as when light enters the water as a cone, part of it is reflected/scattered, illuminating the animal from above and creating a shadow under the animal. If the body has a sharp ventral edge (keel) which illuminates the ventral side.
  • The development of cryptic coloration as blue and green are dominant colors in the ocean. Many nekton will have dark blue/green on the dorsal side, and silver/white on the ventral side to blend in from any perspective.
  • Types of cryptic coloration:
    • Mimicking
    • Disruptive coloration
    • Avoiding predation