Chapter 3
Molles: Ecology 3 rd Ed.
z 71% of earth’s surface is covered by water:
9 97% Oceans
9 2% Polar Ice Caps and Glaciers
9 1% Freshwater in lakes, streams, ground
Molles: Ecology 3 rd Ed.
z The hydrologic cycle exchanges water 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 3 rd Ed.
z Heat z Evaporation z Clouds z Precipitation
9 Evaporation
9 Consumed by organisms
9 Groundwater
9 Surface water
ƒ Rivers, Ponds, Streams >> Ocean
Molles: Ecology 3 rd Ed.
1

Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
z Three major basins: z z
Pacific
Atlantic
Total Area
180 million km 2
106 million km 2 z Indian 75 million km 2
Depth
4,000m 2
3,900m 2
3,900m 2
Molles: Ecology 3 rd Ed.
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
Molles: Ecology 3 rd Ed.
2

Molles: Ecology 3 rd Ed.
Light
Temperature
Circulation
Salinity
Organism
Molles: Ecology 3 rd Ed.
z Oceanic Zone: Areas beyond continental shelf
9 Epipelagic
9 Mesopelagic
0 - 200m
200 – 1,000m
9 Bathypelagic 1,000 – 4,000m
9 Abyssal 4,000 – 6,000m
9 Hadal 6,000m + z Benthic: Habitat on bottom of ocean z Pelagic: Habitat off the bottom of the ocean
Molles: Ecology 3 rd Ed.
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
Molles: Ecology 3 rd Ed.
3

z Salinity: Amount of dissolved salt in water
9 Open ocean 34g/kg water
ƒ Lowest salinity occurs near equator where precipitation exceeds evaporation
ƒ Highest salinity occurs in subtropics where evaporation exceeds precipitation z Oxygen: Typically concentration is highest near ocean surface, and decreases with depth. Minimum usually < 1,000m
Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
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
Molles: Ecology 3 rd Ed.
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
Molles: Ecology 3 rd Ed.
4

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 similar to terrestrial forests
ƒ Canopy at water’s surface
Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
5

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 and diverse ecosystems
Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
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
Molles: Ecology 3 rd Ed.
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
Molles: Ecology 3 rd Ed.
6

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
Molles: Ecology 3 rd Ed.
z Estuaries: found where rivers meet the sea z Salt Marshes and Mangrove Forests are concentrated along low-lying coasts
9 All are driven by ocean tides and river flow
ƒ Transports organisms, nutrients, oxygen, and removes waste
9 Extremely vulnerable to human intrusion
Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
7

Molles: Ecology 3 rd Ed.
z Rivers and Streams can be divided along three dimensions:
9 Length: pools, runs, riffles, rapids
9 Width : wetted / active channels
9 Vertical: water surface, column
ƒ Benthic
¾
Hyporheic Zone: Trans. between surface water and groundwater.
–
Phreatic Zone: Beneath Hyporeic
Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
8

Molles: Ecology 3 rd Ed.
z Temperature:
9 Closely tracks air temp.
z Dissolved Salts:
9 Reflects history of leaching in the basin z Oxygen:
9 Inversely correlated with temp.
ƒ Usually not limiting factor in river systems z Human Influence:
9 Long and intense
ƒ Transportation, Irrigation, Waste Disposal
Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
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
Molles: Ecology 3 rd Ed.
9

Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
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
Molles: Ecology 3 rd Ed.
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
Molles: Ecology 3 rd Ed.
10

Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
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 thermally stratified as they warm
Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
11

Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
Molles: Ecology 3 rd Ed.
12

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.
Molles: Ecology 3 rd Ed.
13