Life in Water

Chapter 3

The Hydrologic Cycle

§       Over 71% of the earth’s surface is covered by water:

v  Oceans contain 97%.

v  Polar ice caps and glaciers contain 2%.

v  Freshwater in lakes, streams, and ground water make up less than 1%.

Ocean Structure

§       Oceanic environments are divided into vertical and horizontal zones

Physical Conditions

§       Physical conditions affect the ecological characteristics of oceanic environments

§       Light = critical for Photosynthesis

§       Temperature = affect rates of photosynthesis, nutrient transport and distributions of organisms

§       Chemical Composition = lots of salt

§       Oxygen

Light

§       Rapidly absorbed by water

§       ~ 80% of solar energy is absorbed in first 10 m.

v   Red, orange, yellow and green absorbed most rapidly

v   Below ~ 50 m only blue wavelengths left

§       Photic Zone = Top 150 m.  Enough light for photosynthesis

§       Aphotic zone = below 150 m.  No photosynthesis

Temperature

§       Affects rates of photosynthesis, nutrient transport and distributions of organisms

§       Sunlight increases velocity of water.

v    Rapid motion decreases density, thus warm water floats on top of cooler water.

v    Thermocline: Layer of water through which temperature changes rapidly with depth.

§    Creates thermal stratification.

Chemical Conditions

^§        Primary salts Na⁺, Mg²⁺, Cl^-

§       Salinity = measure of [salt] in seawater

v  open ocean, salinity 34 - 36.5 ppt.

§    Lowest salinity occurs near equator where precipitation exceeds evaporation.

§    Highest salinity occurs in subtropics where evaporation exceeds precipitation.

Oxygen

§       A liter of air contains ~ 200 ml of oxygen at sea level

§       A liter of seawater contains a maximum of 9 ml of oxygen.

v  Typically concentration is highest near ocean surface, and decreases with depth.

§    Minimum usually < 1,000m.

Water Movements

§       Oceans are never still.

§       Three major types

v   Surface currents = gyres caused by wind within major ocean basins

§    Generally transport warm water from equator poleward, moderating clomate at temperate latitude

v   Deep ocean currents = created as cold polar water sinks and moves towards the equators

v   Upwelling = brings deep, cold nutrient and oxygen rich water to the surface

Oceanic Circulation

Upwelling

Nutrient Cycling and Retention

§       More “open” in oceanic than terrestrial environments

§       Both oceanic and terrestrial = productivity is a function of photosynthesis, major difference in terms of nutrient cycling and storage

v   Terrestrial systems = nutrients stored and recycled between living organisms and soil (stay in system)

v   Oceanic systems = nutrients tend to sink to deeper parts of the ocean and rest in sediments

§       Oceanic systems tend to be nutrient poor

Productivity

§       Productive oceanic systems are those with high rates of photosynthesis and good nutrient storage and retention

§       Include places like:

v  Estuaries, salt marshes and mangroves

v  Coral reefs

Coral reefs

§        Found only where conditions are favorable to the corals and symbiotic algae (zooxanthellae)

v     Warm, shallow water, with lots of light and little variation in salinity (shallow tropics)

§        Extremely diverse systems (“the oceans rainforests)

§        High productivity because:

v     Physical conditions favors photosynthesis (light, temperature)

v     Symbiosis between coral, zooxanthellae recycles nutrients

§     Zooxanthellae photosynthesize during day, transfer C-compounds to corals

§     Corals feed on plankton, transfer nitrates, phosphates to zooxanthellae

v     Reef acts as a nutrient trap

v     Reef provides structure for huge diversity

Coral Reefs - Types

Estuaries, Salt Marshes, and Mangroves

§       Estuaries are found where rivers meet the sea.

§       Salt Marshes and Mangroves are concentrated along low-lying coasts.

v  All driven by ocean tides and river flow.

§    Transport organisms, nutrients, oxygen, and remove wastes.

v  Extremely vulnerable to human intrusion.

Salt Marshes and Mangrove Forests

Estuaries, salt marshes and mangroves

§       Complex landscapes = floods with the tides

§       Dominated by herbaceous vegetation = diversity not high, but productivity high

v    Physical conditions variable, often good for photosynthesis

§    Light levels high, but varies with tides

§    Temperature and salinity also varies with tides

v    Tidal action major reason for high productivity = tides bring in nutrients, oxygen and removes wastes

v    “tight” nutrient recycling = large community of detritovores keep nutrients within the system