I.
Physical Environment
C.
Salinity
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Usually expressed in ‰ (g per kg)
“Average” sea water ~34.7 ‰
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33-37 ‰ in open ocean (very consistent)
Fresh water < 0.5 ‰
Brackish water – 0.5-17 ‰
Consistent in open ocean
Variable in shallow areas and near sources
of fresh water
Ion composition consistent throughout
ocean
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Osmoregulation energetically expensive
Most marine organisms are osmoconformers
Fig. 2-4
Fig. 4-5
I.
Physical Environment
D.
Pressure
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Increases predictably with depth
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10 m = 1 atmosphere (14.7 psi)
Pressure @ 3700 m = 5450 psi
Affects gas-filled structures
Constrains vertical movements of many
animals
I.
Physical Environment
E.
Density
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Sea water 830x denser than air
Reduces need for substantial support structures
Marine organisms have adaptations for buoyancy,
not support
Examples:
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Fishes have light, flexible bones and swim bladders
filled with gas/lipid
Whales have hollow bones filled with lipid
Most marine plant species are microscopic, floating
organisms
Many marine macrophytes use gases for buoyancy
Many organisms live in permanent suspension
(bacteria, viruses)
High density of sea water also influences:
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Locomotion (less energy required than in air)
Feeding (enables suspension feeding)
Communication (efficient sound transmission)
I.
Physical Environment
F.
Gas Availability
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Oxygen concentrations in sea water much
lower than in air (~0.001% vs. 21%)
More soluble at lower temperatures
Concentrations affected by biological
activity
Aerobic organisms may be limited in
design, metabolic activity and distribution
by
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Oxygen availability
Ability to carry out rapid gas exchange
I.
Physical Environment
G. Viscosity
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Stickiness to objects due to adhesion
Objects moving through water drag some
water with them
Many aquatic animals have adaptations to
manipulate drag
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Reduce: fast-swimming species (squid, tuna)
Use: some suspension feeders
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Link
I.
Physical Environment
H.
Surface Tension
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Stickiness at the surface due to cohesion
Water surface can support weight of very
small organisms
Air-water interface supports numerous
organisms
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Microbes in surface films
Halobates
Fig. 4-2
I.
Physical Environment
I.
Water vs. Air
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J.
Dehydration not a problem (most terrestrial
organisms expend energy avoiding
desiccation)
Some marine organisms expend energy
getting rid of water
Nutrient Availability
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Food availability decreases with depth
Sea water contains many dissolved
chemicals that can be absorbed directly
II.
Zonation
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Important concept in biological oceanography
Construct created by humans, but zonation has a
basis in ecological reality
Pelagic/Benthic
A.
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B.
Pelagic = “open sea”
Benthic = “bottom”
“Reverse benthic”
Neritic/Oceanic
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Neritic zone overlies continental shelf
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Bounded by land and 200 m isobath (typically),
representing edge of continental shelf
Exception: Ross Sea (shelf to 800 m depth)
Some neritic zones are wide (E. Coast of US); others are
narrow (W. Coast of S. America)
Oceanic zone overlies deeper water
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Overall, 92% of World Ocean is oceanic
Fig. 2-24
II.
Zonation
C.
Depth Zones
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1.
Limits subjective & variable, ecologicallybased
Pelagic
a.
Epipelagic (0-200 m)
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Definition based mainly on downwelling light
intensity
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Functionally similar to euphotic zone
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Nearly all photosynthetic marine organisms
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Epipelagic organisms adapted to well-lighted
environment with few horizontal obstructions
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Air-sea interface important to some organisms
II.
Zonation
C.
Depth Zones
1.
Pelagic
b.
c.
Mesopelagic (200-1000 m)
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Extends from lower limit of epipelagic zone to nominal
depth of maximum sunlight penetration
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Organisms typically non-photosynthetic
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Some may migrate into surface waters periodically
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Organisms adapted to low-light, fairly high-pressure
environment with limited food availability and
relatively cold temperatures
Bathypelagic (1000-4000 m)
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Extends from lower limit of mesopelagic zone to
~mean depth of ocean
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Organisms typically non-migratory
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Low densities and difficulty of sampling limit
knowledge of organisms
II.
Zonation
C.
Depth Zones
1.
Pelagic
d.
e.
Abyssopelagic (4000-6000 m)
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Conditions similar to bathypelagic zone
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Organisms living in association w/sea floor show very
different adaptations vs. purely pelagic organisms
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Bottom-associated (benthopelagic, nektobenthic)
animals often active scavengers and/or predators,
skilled at detecting, localizing & utilizing scarce food
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Benthopelagic species typically w/larger eyes and
less watery tissues than species not associated with
sea floor
Hadopelagic (6000-11,000 m)
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Includes trenches; maximum depth of ocean
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Pelagic trench fauna very poorly studied
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Food resources often more plentiful than in
abyssopelagic zone
II.
Zonation
C.
Depth Zones
2.
Benthic
a.
b.
Supralittoral (Above mean high water)
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“Splash zone” (Ex: La Bufadora)
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May be immersed during storms and unusual high
tides
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Organisms adapted to almost constant exposure to
terrestrial conditions but also must be able to cope
with aquatic conditions periodically
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Conditions may be highly variable
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Harsh conditions  few organisms in this zone
Littoral/Intertidal (Mean high water to mean low water)
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Immersed at high tide, exposed at low tide
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Organisms must be able to cope with complete
exposure and complete immersion every day
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High light levels may support extensive populations of
photosynthetic organisms