Chapter Concepts
z The hydrologic cycle exchanges water
Chapter 3
LIFE IN WATER
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among reservoirs
z The biology of aquatic environments
corresponds broadly to variations in physical
factors such as light, temperature, and water
movements, and to chemical factors such as
salinity and oxygen
Molles: Ecology 3rd Ed.
The Hydrologic Cycle
The Hydrologic Cycle
z 71% of earth’s surface is covered by water:
9 97%
9 2%
9 1%
Oceans
Polar Ice Caps and Glaciers
Freshwater in lakes, streams, ground
z Heat
z Evaporation
z Clouds
z Precipitation
9 Evaporation
9 Consumed
by organisms
9 Groundwater
9 Surface water
ƒ
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Rivers, Ponds, Streams >> Ocean
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1
Natural History of Aquatic Environments:
Deep Blue Sea
z Three major basins:
Total Area
z Pacific
z Atlantic
z Indian
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180 million km2
106 million km2
75 million km2
Depth
4,000m2
3,900m2
3,900m2
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Deep Blue Sea
z Littoral (intertidal zone) – Shallow shoreline
z Neritic – Coast to margin (200 m) of
continental shelf
9 Epipelagic
zone (surface-200 m)
9 Mesopelagic zone (200-1000 m)
9 Bathypelagic zone (1000-4000 m)
9 Abyssal zone (4000-6000 m)
9 Hdal zone
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Deep Blue Sea
z Oceanic Zone: Areas beyond continental
shelf
9 Epipelagic
9 Mesopelagic
9 Bathypelagic
9 Abyssal
9 Hadal
0 - 200m
200 – 1,000m
1,000 – 4,000m
4,000 – 6,000m
6,000m +
z Benthic: Habitat on bottom of ocean
z Pelagic: Habitat off the bottom of the ocean
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Light
Temperature
Circulation
Salinity
Organism
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Deep Blue Sea
z Approximately 80% of solar energy striking
the ocean is absorbed in first 10m
9 Very
little, if any penetrates past 600m
z Sunlight increases velocity of water (temp.)
9 Rapid
motion decreases density, thus warm
water floats on top of cooler water
z Thermocline – Layer of water through which
temp. changes rapidly with depth
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3
Deep Blue Sea
z Salinity: Amount of dissolved salt in water
9 Open
ƒ
ƒ
ocean 34g/kg water
Lowest salinity occurs near equator where
precipitation exceeds evaporation
Highest salinity occurs in subtropics where
evaporation exceeds precipitation
z Oxygen: Typically concentration is highest
Deep Blue Sea
z Photosynthetic organisms are limited to
upper epipelagic zone (euphotic zone)
9 Phytoplankton
and zooplankton
9 Due to size, oceans contribute ¼ of total
photosynthesis in the bioshpere
z Chemosynthesis occurs near undersea hot
springs
near ocean surface, and decreases with
depth. Minimum usually < 1,000m
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Deep Blue Sea
z For most of human history, vastness of
oceans has acted as a buffer against
human intrusion
z New Human-induced threats:
9 Overharvesting
9 Dumping
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4
Life in Shallow Marine Waters
z Reef Categories:
9 Fringing
Reefs: hug shore of continents
9 Barrier Reefs: stands between open sea
and lagoon
9 Coral Atolls: Coral inlets built up from
submerged ocean island
z Kelp Beds
9 Structure
ƒ
similar to terrestrial forests
Canopy at water’s surface
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Life in Shallow Marine Waters
z Reefs and Kelp Beds both grow in surface
waters with sufficient light for photosynthesis
9 Both
limited by temperature
z Currents deliver oxygen and nutrients, and
remove waste products
9 Biological
productivity may depend on flushing
action
z Reefs and Kelp Beds among most productive
Marine Shores (Intertidal)
z Intertidal Zone can be divided vertically:
9 Supratidal
Fringe: Covered by high tide
9 Upper Intertidal: Covered only during highest
tides
9 Lower Intertidal: Uncovered during lowest
tides
9 Subtidal: Covered by water even during
lowest tides
and diverse ecosystems
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Molles: Ecology 3rd Ed.
Marine Shores
z Two most important water movements
affecting distribution and abundance of
intertidal organisms are waves and tides
9 Semidiurnal
Tides: 2 periods of low and high
tides daily
9 Diurnal Tides: Single low and high tide each
day
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Marine Shores
z Inhabitants of intertidal zone are adapted to
amphibious existence
9 Differential
tolerances to periodicity of air
exposure leads to zonation of species
z Due to increased accessibility, intertidal
zones are experiencing increasing human
exploitation
Estuaries, Salt Marshes, and Mangrove
Forests
z Estuaries: found where rivers meet the sea
z Salt Marshes and Mangrove Forests are
concentrated along low-lying coasts
9 All
ƒ
are driven by ocean tides and river flow
Transports organisms, nutrients, oxygen, and
removes waste
9 Extremely
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vulnerable to human intrusion
7
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Rivers and Streams
z Rivers and Streams can be divided along
three dimensions:
9 Length:
9 Width
:
9 Vertical:
ƒ
pools, runs, riffles, rapids
wetted / active channels
water surface, column
Benthic
¾ Hyporheic Zone: Trans. between surface
water and groundwater.
– Phreatic Zone: Beneath Hyporeic
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8
Rivers and Streams
z Light Considerations:
9 How
much light shines on the surface
9 How far light penetrates the water column
z Turbidity:
9 Erosion
from land
9 Suspended bottom sediments
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Rivers and Streams
z Temperature:
9 Closely
tracks air temp.
z Dissolved Salts:
9 Reflects
history of leaching in the basin
z Oxygen:
9 Inversely
ƒ
correlated with temp.
Usually not limiting factor in river systems
z Human Influence:
9 Long
ƒ
and intense
Transportation, Irrigation, Waste Disposal
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9
Rivers and Streams
z Nutrient Levels
9 Oligotrophic:
low biological production,
although often well oxygenated
9 Eutrophic: high biological production, but
may be depleted of oxygen
z Human Populations have had profound,
usually negative effect
9 Municipal
and Agricultural run-off
9 Exotic Species – Zebra Mussels
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Molles: Ecology 3rd Ed.
Lakes
z Most of the world’s freshwater resides in a
few large lakes
9 Great
Lakes contain 20% of freshwater in
the world
Structure:
9 Littoral
Zone: Shallows
9 Limnetic Zone: Open lake
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Lakes
z Vertical Distribution:
9 Epilimnion:
warm surface layers
9 Metalimnion: (Thermocline) – temp changes
substantially with depth
9 Hypolimnion: – cold dark waters
z Color:
9 Depends
on light absorption and bio. activity
z Stratification:
9 Become
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thermally stratified as they warm
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12
Summary
z Hydrologic Cycle exchanges water among
different holding areas
z Biology of aquatic organisms is largely
determined by physical and chemical
factors
9 Light,
temp, salinity, oxygen, etc.
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