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Chapter 8
Biodiversity in Aquatic
Systems
Key Concepts
 Factors
that influence aquatic
systems
 Saltwater life zones
 Freshwater life zones
 Human activities that affect
aquatic systems
Lakes
Rivers
Coral reefs
Mangroves
Aquatic Life Zones
Aquatic life zones = aquatic biomes
2 major types
1. saltwater or marine: estuaries,
coastlines, coral reefs, coastal
marshes, mangrove swamps, oceans
2. freshwater: lakes, ponds, streams,
rivers, inland wetlands
What lives in water?
 Phytoplankton:
plant plankton;
producers
 Zooplankton: animal plankton;
herbivores
 Nekton: consumers; strong swimmers;
fish, whales, turtles
 Benthos: bottom-dwellers; barnacles,
worm that burrow, lobsters, crabs
 Decomposers: bacteria
© 2004 Brooks/Cole – Thomson Learning
Advantages
Advantages
Water
buoyancy
Constant
temperature
Nourishment
from dissolved
nutrients
Easy dispersal
Less exposure
to UV
radiation
Dilution of
pollutants
Disadvantages
Can tolerate a narrow
range of temp.
Exposure to
pollutants
Fluctuating
population size
Aquatic offspring
separated from
parents
What Factors Limit Life?

Temperature

Access to sunlight for photosynthesis
(mainly euphotic zone)

Dissolved oxygen: high near surface
(photosynthesis), low in deep, cool water

Availability of nutrients: fewer nutrients
available in deep area (lower net primary
productivity)
Saltwater Life Zones
 Oceans
cover 71% of the planet
 Oceans
contain 250,000
species of plants and animals
 Oceans
provide many
ecological and economic
services
Marine Systems
Marine
Systems
Figure 7-6
Page
147
Economic Services
Ecological Services
•
Climate moderation
• CO2 absorption
• Nutrient cycling
• Habitats and nursery areas
for marine and terrestrial
species
• Biodiversity
Animal and pet feed
Pharmaceuticals
Harbors and transportation
routes
Recreation
Employment
Offshore oil and natural gas
Minerals
Ocean Life Zones
1.
2.
3.
4.
Coastal Zone: shallow, nutrient-rich,
warm, extends to continental shelf,
90% all ocean species (high or low
NPP?)
Euphotic Zone: upper zone,
photosynthesis, low nutrient levels,
dissolved O2 high
Bathyal Zone: dimly lit, no producers
Abyssal Zone: dark, deep ocean,
dissolved O2 low
Coral Reefs




1.
2.
3.
Form in clear, coastal waters
Oldest, most diverse ecosystems
Complex interaction between organisms
Vulnerable to damage because:
Grow slowly
Disrupted easily
Thrive only in warm, clear, shallow water
Coral Reef
Threats to Coral Reefs
Ocean warming
Algae growth from fertilizer runoff
Rising sea levels
Increased UV exposure from ozone
depletion
Using cyanide and dynamite to
harvest coral reef fish
Coral removal for building material,
aquariums, and jewelry
Damage from anchors, ships,
and tourist divers
 Coral
Bleaching: whitening of corals, due
to stress or death of their symbiotic
protozoa (zooxanthellae), or due to the
loss of pigmentation within the protozoa
 Under
stress, corals may expel their
zooxanthellae, which leads to a lighter or
completely white appearance (“bleached”)
Coral bleaching can be induced by:

increased (most commonly) or reduced water
temperatures
 increased solar radiation
 changes in water chemistry
 starvation caused by a decline in zooplankton
 increased sedimentation (due to runoff)
 pathogen infections
 changes in salinity
 wind
 low tide air exposure
 fishing
Highly Productive Areas

Estuaries: where saltwater mixes with
freshwater (ecotone)
 Coastal wetlands: land areas covered with
water (river mouths, inlets, bays)
 Mangroves: forest swamps; protect coastlines
and coral reefs; important habitat
* constant water movement stirs up nutrients,
making estuaries and wetlands very productive
areas
Estuary
Mangrove
Intertidal Zone
 Area
of shoreline between low and high
tides
 Stressful zone
 Animals may be crushed or swept away
may be immersed during high tide
may be left to dry during low tide
 Salinity is constantly changing
 Example: rocky shores, barrier beaches
Rocky Shores and Barrier Beaches
 Intertidal
Zones
 Both have great variety of species,
lots of available niches
 Rocky shores have lots of pools in
rocks where animals live
 Barrier Beaches-most animals
survive by burrowing, digging,
tunneling in the sand
Rocky Shore Beach
Barrier Beach
Barrier Islands

Long, thin, low offshore islands of sediment
 Parallel to the shore
 Protect mainland by dispersing storm waves
(“barrier”)
Human Impact on Marine
Systems







½ world’s original wetlands (91% Ca) have
been destroyed
35% mangroves destroyed
70% beaches eroding rapidly
Boats with chains/nets destroy ocean bottom
habitats
27% coral reefs severely damaged
11% coral reefs destroyed
Prediction: 70% coral reefs destroyed by
2050
Megalodon Shark
 Miocene
Period-20 mya
 60 ft long; jaws 5 ft long
Freshwater Life Zones


1.
2.


Less that 1% salt concentration
2 types:
Standing: lakes, ponds
Flowing: streams, rivers
Freshwater systems cover less than
1% of earth’s surface
Runoff from land provides FW zone
with organic matter, nutrients,
pollution
© 2004 Brooks/Cole – Thomson Learning
Freshwater Systems
Economic Services
Ecological Services
• Climate
moderation
• Nutrient cycling
• Waste treatment and
dilution
• Food
• Drinking water
• Irrigation water
• Hydroelectricity
• Flood control
• Transportation corridors
• Habitats for aquatic
and terrestrial
species
• Genetic resources and
biodiversity
• Scientific information
• Recreation
• Employment
Freshwater Life Zones
 Littoral
zone: shallow, sunlit water
surface near shore
 Limnetic zone: open, sunlit water
surface away from shore; main
photosynthetic part
 Profundal zone: deep, open water; too
dark for photosynthesis
 Benthic zone: bottom of the lake, cool
temp, low oxygen levels (why?)
How do Plant Nutrients affect
Lakes?
 Lakes
are classified according to:
nutrient content and productivity
 Newly-formed lake = oligotrophic lake
(poorly nourished); clear water
 Established lake= eutrophic lake (wellnourished); murky water
 Cultural eutrophication: human inputs
of nutrients accelerates eutrophication
Seasonal Changes in Lakes

Thermal stratification: three distinct layers
with different temperatures
1.
Epilimnion: upper layer of warm water, high
dissolved oxygen (warm water on top, less
dense)
Thermocline: cooler “middle” layer, moderate
levels of dissolved oxygen
Hypolimnion: lower layer of cold water, low
concentration of dissolved oxygen (more dense)
2.
3.
Seasonal Changes in Lakes
Seasonal Changes in Lakes,
cont.

Fall: surface water cools, thermocline
disappears as warm water becomes colder
(and more dense)
fall overturn: brings nutrients from
bottom to top, brings dissolved oxygen from
surface to bottom
 Winter: cold temp, water separates into
different densities
 Spring: surface water sinks (becomes more
cold dense)
spring overturn: brings nutrients from
bottom to top, brings dissolved oxygen from
surface to bottom
Streams and Rivers
 Remember
hydrologic cycle!
 Runoff: precipitation that does not sink
into the ground or evaporate--flows into
streams
 Watershed: land area that delivers
runoff to a stream
 Small streams join to form rivers; rivers
flow downhill to the ocean (hydrologic
cycle)
Stream and River--Life Zones
1.
2.
3.
Source zone: cold, clear water (from
mountains) rushes over waterfalls and
rapids; dissolves large amounts of oxygen
with turbulence; cold water fish and lots of
algae and mosses on rocks
Transition zone: streams merge to form
wider streams; fewer obstacles; warmer
water supports more producers
Floodplain zone: streams move across
valleys; slow-moving; warmer temp; less
dissolved oxygen; muddy, lots of silt
Rain and snow
Lake
Glacier
Rapids
Waterfall
Tributary
Flood plain
Oxbow lake
Salt marsh
Delta
Ocean
Deposited
sediment
Source Zone
Transition Zone
Water
Floodplain Zone
Sediment
Inland Wetlands
 Land
covered with freshwater all
or part of the time
 Includes: marshes, swamps,
prairie potholes (from glaciers),
floodplains, bogs
 Important for flood control
Freshwater marsh
Cypress Swamp
Prairie Potholes
Human Impact of Freshwater
Systems
 60%
of world’s rivers are fragmented by
dams and canals (destroys wildlife
habitats by reducing water flow)
 Flood control levees destroy habitats,
eliminate wetlands (fish breeding
grounds)
 In U.S., 53% of inland wetlands have
been drained or filled and covered with
asphalt/concrete for buildings
How Sustainable are Aquatic
Ecosystems?

Most pollutants end up in the ocean
 Aquatic life zones are constantly renewed
because:
1. water is purified by hydrologic cycle
2. nutrients cycle in and out
3. populations can be replenished
 However, this can happen ONLY if overpolluting and over-fishing do not occur!!