Transcript 5 The Water Column: Nekton

8 The Water Column: Nekton
Notes for Marine Biology:
Function, Biodiversity, Ecology
By 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
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Cephalopods
Fish
Mammals (cetaceans, otters)
Birds (divers)
Cephalopods (Phylum Mollusca)
Chambered nautilus
Cephalopods
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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 torpedoshaped, 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
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Form is a combination of three modes:
Acceleration
Cruising
Maneuvering
Form and Swimming 2
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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
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
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
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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 porpoises
Pinnipeds: seals, sea lions, walruses
Mustelids: sea otters
Sirenians: 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
Continuous
ram
feeding
Ventral furrows
Intermittent
ram
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
Sea
Lion
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