Factors Affecting Life in Water

Concepts:

—Hydrologic cycle exchanges water among reservoirs.

—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.

 Aquatic  environments.

 Ocean

—-covers over 360 million km  of earth’s surface and consist of one continuous, interconnected mass of water.

—-  Pacific Ocean, Atlantic Ocean and Indian Ocean ( three major ocean basins)

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—Littoral zone – shallow shoreline under the influence of the rise and fall of the tides (10m deep)

—Neritic zone – extends from the coast to the margin of the continental shelf (200 m deep)

—Oceanic zone – beyond the continental shelf.

—Epilagic – 200 m deep

—Mesopelagic – 200 m to 1000 m deep

—Bathypelagic – 1000 m to 4000 m deep

—Abbysal zone – 4000 m to 6000 m deep

—Hadal zone – deepest part

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        Pelagic – organisms found off the bottom, regardless of the depth.

        Benthic – organisms on the bottom of the ocean

B.  Light
 

— 80% of the solar energy strikes the ocean and is absorbed in the first 10 m.

— in first 10 m, marine environment is bright with all the colors of the rainbow

— below 50 to 60 m it is blue twilight.

—at 600 m, the amount of sunlight that penetrates is approx. equal to the intensity of starlight in a clear night.

 

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C. Temperature

—thermocline separates the warm and cold layer of the ocean water.

— thermal stratification (layering of the water column by temperature.

—Temperate oceans are stratified only during summer and thermocline breaks during winter.

— Oceanic temperature are much more stable than terrestrial  temperature at all latitudes.

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 D.  Water movements

— wind drive current (surface current) that transport nutrients, oxygen and heat as well as organisms.

—deep water current is due to the sinking of cold, high density water .

 * upwelling -  movement of the deep ocean water to the surface

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 E.  Salinity

— amount of salt dissolved in water

—34 g of salt per 1 kg of water.

—lowest salinity where precipitation exceeds evaporation.

— high salinities when evaporation exceeds precipitation

 F.  Oxygen

— 1 L of air contains 200 mL of oxygen at sea level

— 1 L of water contains 9 mL oxygen

— oxygen decreases and reaches its minimum at 1000 m deep.

— oxygen increases progressively towards the bottom

 G.  Biology

— great diversity of life

— presence of zooplanktons and phytoplanktons

II.  Life in Shallow Marine Waters: Kelp Forests and Coral Gardens

 

 Kelp – found beyond intertidal zones, at temperate latitudes and over a solid bottom

—Brown and green seaweed

—Grows over 40 m in height

  Coral Reefs – middle latitudes at 30  N to S

—Animal species with so diverse in color and texture

—Depends their survival on photosynthesis by photosynthetic protist called zooxanthellae that live in their tissues

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 Structure: Coral Reefs

         Kinds:

— Fringing reef

—Barrier reef

—Atoll

        Kelp Forest Structure ( shown in the figure)

 Light

—Needs sufficient life to support photosynthesis

—Survives up to 100 m deep

 Temperature

—10  C to 20  C (kelp)

—18  C to 29  C (corals)

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 Water Movements

—Slight ocean current needed to deliver oxygen and nutrients and remove waste products

—Severe current destroys the two communities and requires many centuries to built up again.

 Salinity

—Fairly stable salinity ( corals )

—More tolerant to reduced salinity (kelp)

 Oxygen

—Well oxygenated water

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 Biology

    Coral Reefs:

—Threatened by predators like crown of thorns sea stars which eat corals.

—Sea urchin were infected by pathogens and attack both algae and corals which harms and at the same time benefit coral communities

—Reduced sea urchin population may reduce coral reproductive success

—Algal population compete with young corals for space

—Corals compete with each other

    Kelp Forest

—House epiphytic algae and sessile inverts

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III.  Marine Shores: Life between High tides and Low tides (intertidal zones)

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1. Supratidal Fringe or splash zone – seldom covered by high tides but is often wetted by waves

2. Intertidal zone  a) upper – covered during high tides

                                b) lower – uncovered during low tides

                           c) middle – covered and uncovered during average tides

3.   Subtidal zone – remains covered with water even during lowest tide

 

 Light

—At  high tide there is low light intensity

—Low tide, high light intensity

 Temperature

—Changes twice a  day

—Depends upon the geography

 Water movements

—Affected by tidal fluctuations

—Organisms are affected by wave action

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 Salinity

—Low tide increases salinity

—Rapid evaporation  during low tide increases salinity

 Oxygen

—Not a limiting factor in intertidal zone for two reason;

—Intertidal species are exposed to air at each low tide

—The water waves -swept shores is thoroughly mixed and therefore well oxygenated

—Oxygen may be low in sandy or muddy shores, sheltered bay where water circulation is weak.

 Biology

—Sea  stars, sea urchin, barnacles, mussels, seaweeds, kelp, animals that lives inside rocks

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IV.    Estuaries, Salt Marshes and Mangrove Forest

  Estuaries – found wherever river mouths meets the sea

                    - transition between river and sea

    Salt Marshes and Mangrove Forest

            - Concentrated along low lying coasts with sandy shores

            - Transition between land and sea

         

Water Movements

—Current transport organisms, renew nutrients and oxygen and removes wastes.

 Salinity

—Salinity fluctuate widely

—Salinity of estuaries is lower than sea water 

 Oxygen

—Oxygen content is often variable and reaches at extreme levels

 Biology

—Support great variety of life(birds, crocodiles, alligators, snakes etc

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V.  Rivers and streams

  - Formed from run off water 

Structure (fig  3.30)

    River and Streams Dimensions:

         Along lengths, based on their variation of flow

             1. Pools

             2. Runs

             3.Riffles

             4.Rapids

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Across their widths

— Wetted channel – contains water even  during low condition

—Active channel – extends out from one or both sides of the wetted channel

—Riparian zone – outside the active channel, transition between aquatic environment of the river and the upland terrestrial environment

 

Vertical division

— Water surface

—Water column

—Benthic zone – includes the surface of the bottom substrate and the interior of the substrate

  Hyporheic zone – a zone between areas of surface       water flow and ground water

  Phreatic zone -  area containing the groundwater

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 Light

—Affected by how far light penetrates into the water column and how much light shines on the surface

—Turbidity affects light intensity

—Rivers and streams are in intimate contact with the surrounding landscape and inorganic and organic materials continuously wash, fall or blow in rivers and streams

—River turbulence erodes bottom sediments and keeps them in suspension during floods

—Shading may cause decrease in the rate of photosynthesis by aquatic plants

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Temperature

—Temperature of the rivers and streams depend upon air temperature

Water Movements

—River current deliver food, remove wastes, renew oxygen and strongly affects the size, shape and behavior of river organisms

—River and stream current is affected by the occurrence of wet and dry seasons

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 Salinity

—Very low salinity

 Oxygen

—Oxygen content is inversely correlated with temperature

—Polluted river water have low oxygen content

 Biology ( fig 3.34)

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VI.  Lakes

—Basins in the landscape that collect water

—Are worked over by geological forces like shifting of the earth’s crust (tectonic), volcanism and glacial activity.

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Structure

—Littoral zone – shallowest waters along the lake shore, where rooted aquatic plants may grow

—Limnetic zone – open  lake

—Vertical divisions:

       Epilimnion – warm surface of the water

        Metalimnion – thermocline

       Hypolimnion – cold, dark waters

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 Light

—Lake color ranges from the deep blue of the clearest lakes to yellow, brown or even red

—Difference in color is affected by many factors especially lake chemistry and biological chemistry

—Surrounding landscapes delivers large quantities of nutrients, primary production is high and phytoplankton populations reduce light penetration( deep green in color)

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Temperature

—Lake temperature vary with latitude

—Temperate lakes are stratified during summer

—Tropical lakes are stratified the whole year round

 Water movements

—Lake movement is mainly due to the action of wind

Salinity

—Much more saline than estuarines but lesser saline than the ocean

—Lake volume also affects salinity

 Oxygen

—-well-oxygenated lakes (oligotrophic),have low biological production

—-low-oxygenated lakes(eutrophic) have high biological production

  Biology

  - different kinds of lakes vary in the presence of organisms because they vary in oxygen availability,    temperature and availability of nutrients.

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