Chapter 6
 Coral reefs—form in clear, worm coastal water of the tropics and subtropics
o Formed by massive colonies of polyps
o Help moderate atmospheric temperature by removing CO2 from the atmosphere
o Act as natural barriers that help protect 14% of the world’s coastlines from
erosion by battering waves and storms
o Provide habitats for a variety of marine organisms
 Aquatic Environments
o Saltwater and freshwater aquatic life zones cover almost three-fourth of the
earth’s surface
o Most of it saltwater—71%
o The major types of organisms found in aquatic environments are determined by
the water’s salinity
o Classified into two major groups
 Saltwater or marine—estuaries, coastlines, coral reefs, coastal marshes,
mangrove swamps, and oceans
 Freshwater—lakes, ponds, streams, rivers, and inland wetlands
o Aquatic systems contain floating, drifting, swimming, bottom-dwelling, and
decomposer organisms
o Plankton—consists of weakly swimming, free-floating
 Phytoplankton—includes many types of algae
 Zooplankton—consist of primary consumers that feed on phytoplankton
and secondary consumers that feed on other zooplankton (they range from
single-celled protozoa to large invertebrates such as jellyfish)
 Ultraplankton—extremely small photosynthetic bacteria may be
responsible for 70% of the primary productivity near the ocean surface
o Nekton—strongly swimming consumers such as fish, turtles, and whales
o Benthos—bottom dwellers such as barnacles and oysters that anchor themselves
to one spot, worms that burrow into the sand or mud, and lobsters and crabs that
walk along the bottom
o Decomposers—break down the organic compounds in the dead bodies and wastes
of aquatic organisms into simple nutrient compounds for use by aquatic producers
o Life in most aquatic systems is found in surface, middle, and bottom layers
 Environmental factors, temperature, access to sunlight for photosynthesis,
dissolved oxygen content and availability of nutrients such as
carbon/nitrogen/phosphorus for producers, determines the types and
numbers of organisms found in these layers
 Euphotic zone (upper layer in deep water habitats): sunlight can penetrate
 There is more oxygen near the surface because of the oxygen-producing
photosynthesis takes place there
 As it get lower, oxygen level fall because of the aerobic respiration
 Less oxygen dissolves in the deeper colder water
 In shallow water nutrients are of abundance, unlike in the open ocean
 Organisms at the bottom of the dark ocean or deep lake depend on animals
or plant plankton to die and drift down to the bottom of the ocean

These organisms take long to reproduce, so they are especially
vulnerable to depletion from overfishing
Saltwater Life Zones
o Coastal Zone: Most of the Action is
 Makes up less than 10%, but contains 90% of all marine species
 Warm, nutrient-rich, shallow water that extends from the high-tide mark
on land to the gently sloping, shallow edge of the continental shelf
 Human activities severely affect it
 Have high net primary productivity, thanks to the zones ample sunlight
and plant nutrients that flow from land are distributed by tidal flows and
ocean currents
o Estuaries and Coastal Wetlands: Center of Productivity
 Highly productive ecosystems
 Estuary—where river meats sea (fresh and saltwater)
 Runoff and pollution from the streams mix in as well
 Coastal wetlands—land areas covered with water all or part of the year
 River mouths, inlets, bays, sounds, salt marshes in temperate zones
and mangroves in tropical ones
 Life here adapts to daily and seasonal changes in tidal and river
flow and land runoff of eroded soil sediment and other pollutants
 Rapid circulation of nutrients by tidal flows
 Mangrove forests—the tropical equivalent of salt marshes
 These trees can grow in salt water and have extensive roots that
often extend above the water, where they get oxygen and help the
plant with changing water levels
 Estuaries and coastal marshes provide ecological and economic services.
 Filter toxic pollutants, excess plant nutrients, sediments, and other
pollutants.
 Reduce storm damage by absorbing waves and storing excess
water produced by storms and tsunamis.
 Provide food, habitats and nursery sites for many aquatic species
Rocky and Sandy Shores: Living with the Tides
o Organisms have survived to the harsh and changing conditions of this area
o Gravitational pull by moon and sun causes tides.
o Intertidal Zone: area of shoreline between low and high tides.
o The organisms must be able to adapt to the changing salinity
 Most of them hold onto something, dig in, or hide in protective shells
o Barrier Islands: Low, narrow, sandy islands that form offshore from a coastline
 Primary and secondary dunes on gently sloping sandy barrier beaches
protect land from erosion by the sea
Threats to coral reefs: Increasing Stress
o Biologically diverse and productive coral reefs are being stressed by human
activities.
o Coral reefs can only live between 18-30 oC – a change in one degree could cause
bleaching
 Also people touching and breaking parts of can cause bleeching
Biological Zones in the Open Sea: Light Rules
o Brightly light surface, dimly lit middle, and dark bottom zone
o Euphotic zone: brightly lit surface layer.
 Nutrient levels low dissolved O2 high, photosynthetic activity.
o Bathyal zone: dimly lit middle layer.
 No photosynthetic activity, zooplankton and fish live there and migrate to
euphotic zone to feed at night.
o Abyssal zone: dark bottom layer.
 Very cold, little dissolved O2
 The animals get their nutrients from marine snow—a shower of dead or
decaying organisms
Effects of Human Activities on Marine Systems: Red Alert
o Human activities are destroying or degrading many ecological and economic
services provided by the world’s coastal areas.
Freshwater Life Zones
Freshwater System
o Freshwater life zones include:
 Standing (lentic) water such as lakes, ponds, and inland wetlands.
 Flowing (lotic) systems such as streams and rivers
Lakes: Water-Filled Depressions
o Littoral Zone: Top of the water
o Limnetic Zone: the main part of the water, first layer into the water
o Profundal zone: Below limnetic zone, no photosynthesis, animals have adapted to
the colder water
o Benthic Zone: filled with decomposers and is filled with nutrients from the
dead/decaying fish
o During summer and winter in deep temperate zone lakes become stratified into
temperature layers and will overturn.
 This equalizes the temperature at all depths.
 Oxygen is brought from the surface to the lake bottom and nutrients from
the bottom are brought to the top
Effects of Plant Nutrients on Lakes: Too Much of a Good Thing
o Plant nutrients from a lake’s environment affect the types and numbers of
organisms it can support
o Oligotrophic lake: poorly nourished, usually newly formed lake with small supply
of plant nutrient input.
o Eutrophic lake: well nourished, over time, sediment, organic material, and
inorganic nutrients wash into lakes causing excessive plant growth.
 Cultural eutrophication: Human inputs of nutrients from the
atmosphere and urban and agricultural areas can accelerate the
eutrophication process
o Mesotrophic lake: in between
Freshwater Streams and Rivers: From the Mountains to the Oceans
o Water flowing from mountains to the sea creates different aquatic conditions and
habitats
o Surface water—precipitation that does not sink into the ground or evaporate
o Runoff—surface water that flows into streams
o Watershed/drainage basin—is the land area that delivers runoff, sediment,
dissolved substances to the stream
o Three zones:
 Source zone
 Rapids, high in the mountains, dissolve a lot of oxygen from
the air
 Cold, clear, swift
 Fish that live there are adapted to the cold and they must be
able to swim in the currents , have flat bodies to fit under
stones
 Mosses and algae attach to rocks
 Transition zone
 Streams merge together, slower and more cloudy
 Less dissolved oxygen
 Warmer and less oxygen
 Floodplain zone
 High temperatures and less dissolved oxygen than the other
two zones
 Slow-moving rivers
 Because of the runoff, the water is muddy and contains high
concentrations of suspended particulate matter (silt)
 Eventually hits the sea
 Dams and levees have been built to control water flows in New
Orleans.
 Reduction in natural flow has destroyed natural wetlands.
o Causes city to lie below sea-level (up to 3 meters).
o Global sea levels have risen almost 0.3 meters since
1900
Freshwater Inland Wetlands: Vital Sponges
o Inland wetlands act like natural sponges that absorb and store excess water from
storms and provide a variety of wildlife habitats.
o Filter and degrade pollutants.
o Reduce flooding and erosion by absorbing slowly releasing overflows.
o Help replenish stream flows during dry periods.
o Help recharge ground aquifers.
o Provide economic resources and recreation
o