Biology 205Ecology and Adaptation

Lecture 4Life in Water

Dr. Erik D. Davenport

Lecture outline

Hydrologic cycle.

Aquatic environmental factors: what, why and how are they distributed in different aquatic systems.

The responses of living organisms to these factors in different aquatic systems.

Water on Earth

-Water covers 71% of the earth.

– The ocean contains over 97% of total water.

– The polar ice caps and glaciers contain additional 2%.

– Only 1% of the water is freshwater that is in lakes, rivers, and actively exchanged groundwater.

“Distribution of water is not static.”

– Heat– Evaporation– Clouds– Precipitation

Evaporation Consumed by

organisms Groundwater Surface water

“The Hydrologic cycle exchanges water among reservoirs .”

The hydrologic cycle is powered by solar radiation.

“Reservoirs” are places where water is stored for some period of time during the hydrologic cycle.

“Turnover times vary among reservoirs”

Turnover time: is the time that required for entire volume of a particular reservoir to be renewed.

volume/exchange rate.

air ~ 9 days. ocean ~ 3,100 years.

LargestOcean Basins:

Pacific : ~180 million km2

Atlantic: ~106 million km2

Indian: ~75 million km2

Deepest Ocean– Marianas - 10,000 m

deep (west Pacific)– Would engulf Mt.

Everest with 2 km to spare.

Ocean Structure:

Oceanic Zone:– Epipelagic 0 - 200 m– Mesopelagic 200 - 1,000 m– Bathypelagic 1,000 - 4,000 m– Abyssal 4,000 - 6,000 m– Hadal 6,000 + m

Benthic: Habitat on bottom. Pelagic: Habitat off the bottom.

“Oceans are never still.”Wind-driven surface currents across open ocean create gyres that move right in the Northern Hemisphere and left in the Southern Hemisphere.

Deepwater currents cause upwelling.

Light Penetration in the Ocean – Approximately

80% of solar energy striking the ocean is absorbed in first 10 m.

– Very little, if any penetrates past 600 m.

– Leaves approximately 3,400 m of deep black water with only light produced by bioluminescence.

Temperature

Satellite Sea Surface Temperature from NOAA

Temperature in the Ocean – Warm water will decreases density, thus warm water floats on top of cooler water.

– Ocean water temperature is more stable than terrestrial temperature.

– Thermocline: a layer of water where temperature changes rapidly with depth (usually above 200m).

Creates thermal stratification.

Salinity

Salinity in the Ocean Salinity is the amount of salt dissolved in water.

Salinity unit: parts per thousand (‰) or ppt, so 34 ppt means 34 g of salt in 1 kilogram of water.

Precipitation affects salinity.

Salinity in the Ocean– In the open

ocean, salinity varies from about 34 ppt to 36.5 ppt.

– Lowest salinity occurs near equator where precipitation exceeds evaporation.

– Highest salinity occurs in subtropics where evaporation exceeds precipitation.

Oxygen in the Ocean– A liter of air

contains about 200 ml of oxygen at sea level, while a liter of seawater contains a maximum of 9 ml of oxygen.

– Typically concentration is highest near ocean surface, and decreases with depth. Why?????

– Minimum usually < 1,000m.

Biology in the ocean

Ecologists classify ocean habitat and their organisms on the basis of light levels, depth, and bottom type.

• In the deep of the ocean, there are some chemosynthetic communities.

• Photosynthetic organisms are limited to the lighted epipelagic zone. (also called euphotic zone)

• The most significant photosynthetic organisms are phytoplankton, which are microscopic organisms that drift with the current.

Female deep-sea angler fish with her male partner.

Human Influences on the Ocean

For most of human history, vastness of oceans has acted as a buffer against human intrusion. But things have changed.

Over-harvesting Ocean Dumping

Shallow Marine Waters

Among the most productive and diverse of all ecological systems in

the biosphere are:

“Shallow waters along the continents and islands support marine communities of very high diversity

and biomass”

• Kelp: seaweed in the temperate latitude.

• Coral: only in tropical area.

Coral Reef

Reefs and kelp beds both grow in surface waters with sufficient light for photosynthesis.

Both limited by temperature.

Currents deliver oxygen and nutrients, and remove waste products.

Biological productivity may depend on flushing action

Kelp Forest

Marine Shore

Marine shore: Life between low and high tides

Marine shores are the most dynamic environments in the biosphere.

It can be divided into sandy and rocky shore.

Wide variation in light intensity.

Diurnal tides: Single low and high tide each day.

“Most important water movements affecting distribution

and abundance of intertidal organisms are waves and tides.”

Semidiurnal tides: Two periods of low and high tides daily.

Marine Shores Intertidal Zone can be divided vertically:– Supratidal Fringe:

Covered by highest tides.

– Upper Intertidal: Covered only during high tides.

– Lower Intertidal: Uncovered during lowest tides.

– Subtidal: Covered by water even during lowest tides.

Marine Shores

Inhabitants of intertidal zone are adapted to amphibious existence.– Differential tolerances to

periodicity of air exposure leads to zonation of species.

Due to increased accessibility, intertidal zones are experiencing increasing human exploitation.

Estuaries, Salt marshes and mangrove forests

Salt marshes and mangrove forests are the transition between land and sea, however, salt marshes are distributed mainly along the sandy shores from temperate to high latitude, and mangrove forests are in subtropical and tropical shores.

What is estuarine? The area where rivers meet the sea.

Salt marsh

Mangrove

Estuary

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Salt marsh and mangrove swampsFigure 3.22

3-10     Source: Chapman 1977, Long and Mason 1983

Physical conditions

Experience the significant variations in tidal level.

Exposed to highly light variations. Ocean tide and river flow drive the complex

water movements in the estuaries. And further influence the nutrients delivery, oxygen distributions, etc….

Extremely vulnerable to human intrusion.

Salinity may fluctuate widely, particularly where the tidal and river flow are substantial.

Rivers and Streams

Riparian zone is a transition area between the aquatic and upland terrestrial environments.

Rivers and streams can be divided along three dimensions:

Length: Pools, runs, riffles, rapidsWidth: Wetted / active channelsVertical: Water surface, column

Major Rivers

Rivers and StreamsStream Order

– First Order - Headwater

– Second Order - Joining of two first order.

– Third Order - Joining of two second order.

Rivers and streams are vertically divided into water surface, water column, and bottom (benthic).

Hyporheic Zone: Transition between surface water and groundwater.Phreatic Zone: Groundwater

Rivers and Streams - Physical Conditions

Light– How much light shines on the surface.– How far light penetrates the water column.

Water Movements– Erosion from land.– Suspended bottom sediments.

Temperature– Closely tracks air temperature.

Rivers and Streams

Chemical Conditions – Salinity

Reflects history of leaching in the basin.– Oxygen

Inversely correlated with temperature. Human Influence

– Long, intense history of human use. Transportation, Irrigation, Waste Disposal.

Lakes Most of the world’s freshwater resides in a few

large lakes.– Great Lakes of North America contain 20% of freshwater

in the world.

Lake Structure

Lakes - Physical Conditions

Light– Lake color depends on light absorption and biological

activity. Temperature

– Lakes become thermally stratified as they warm. Water Movement

– Wind-driven mixing of the water column is ecologically important.

Seasonal Temperature Changes

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Oligotrophic and eutrophic lakesFigure 3.39

3-22

Oligotrophic lake: well-mixed lakes of low biological productive, and have high oxygen concentration.

Eutrophic lakes: lakes with high biological productivity, and also associated with low or depleted oxygen concentration.

Lakes - Chemical Conditions

Oxygen– Oligotrophic: Low biological production, although

often well oxygenated.– Eutrophic: High biological production, but may be

depleted of oxygen.

Lakes - Human Influences

Human populations have had profound, usually negative effect.– Municipal and agricultural run-off ------ increase of

the nutrient concentration. Why excess nutrients input is bad for lakes?

– Exotic species - Zebra Mussels

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Species introduced to the Great LakesFigure 3.40

3-23     Source: Mills et al. 1994

Review

Hydrologic Cycle Deep Blue Sea Shallow Marine Waters Marine Shores Estuaries, Salt Marshes, and Mangrove

Forests Rivers and Streams Lakes