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)
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
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.
C. Temperaturethermocline 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.
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
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
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)
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
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
III. Marine Shores: Life between High tides and Low tides (intertidal zones)
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
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
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
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
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
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
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
Salinity
Very low salinity
Oxygen
Oxygen content is inversely correlated with temperature
Polluted river water have low oxygen content
Biology ( fig 3.34)
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.
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
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)
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.