Transcript Chapter 6 Aquatic Biodiversity

Chapter 6
Aquatic Biodiversity
AP Environmental Science
Edinburg North High School
Chapter 6: Aquatic Biodiversity
Focus Questions:
• What are the basic types of aquatic life zones,
and what factors influence the kinds of life they
contain?
• What are the major types of saltwater life zones,
and how do human activities affect them?
• What are the major types of freshwater life
zones, and how do human activities affect them?
Core Case Study:
Why Should We Care about Coral Reefs?
• Coral reefs
– Warm coastal waters
– Marine equivalents of tropical rainforest (Fig. 6-1a)
– Polyps (jellyfish relative), CaCO3, symbiotic
zooxanthellae
– 0.1% of world’s ocean area
• Ecological and economic services
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Moderate atmospheric temperature
Natural barriers protective 15% of world’s coastline
Provides habitats for marine organisms
Produce one-tenth of global fish catch
Building materials for poor countries
Ecotourism
• Conservation
– 20% of the world’s coral reefs lost to coastal
development, pollution, overfishing, warmer
oceans, and other stresses
– Another 30% will be lost in next 20-40 yr
– Coral bleaching, linked to warmer water and
silt from land (Fig. 6-1b)
I. Aquatic Environments
• The Water Planet: Saltwater and Freshwater
– Oceans cover 71% earth’s surface, freshwater
< 1% (Fig. 6-2)
– Major types of organisms determined by salinity.
– Aquatic life zones classified into two major types:
• Marine, or saltwater, includes estuaries, coastlines, coral reefs,
coastal marshes, mangrove swamps, and oceans.
• Freshwater, includes lakes, ponds, streams, rivers, and inland
wetlands.
– Distribution of the worlds major saltwater oceans, coral
reefs, mangroves and freshwater lakes and rivers
(Fig. 6-3)
– Play vital roles in ecosystems and human
systems
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Biological productivity
Climate
Biogeochemical cycles
Biodiversity
Fisheries: fish and shellfish
Oil, natural gas, and minerals
Recreation and transport routes
• What kinds of organisms live in aquatic life
zones?
– Plankton
• Phytoplankton
• Zooplankton
• Ultraplankton
– Nekton
– Benthos
– Decomposers
• Life in Layers
– Three main layers: surface, middle, and bottom
– Factors that determine the distribution and
abundance of organisms:
• Temperature, light, DO, nutrients
– Photosynthesis confined to upper layer, or
euphotic zone.
• Depth depends on water clarity.
– Nutrients (nitrates, phosphates, iron, and others)
more limited in open ocean.
• Upwellings (see Suppl. 10) however has high NPP.
– Most deep bottom organism depend on dead
debris that falls to the bottom.
II. Saltwater Life Zones
• Why should we care about the oceans?
– They provide many important ecological and
economic services (Fig. 6-4).
– We know less about the oceans and
freshwater systems than we do about the
surface of the moon.
• Further study could yield immense ecological and
economic benefits.
• The Coastal Zone: Where Most of the
Action is
– Two major life zones: coastal and open ocean
(Fig. 6-5).
– Extends from high tide mark to end of continental
shelf.
• Relatively shallow, nutrient-rich
• Numerous interaction with land, so easily affected by
human activities.
– Only 10% of the world’s ocean area, but contains
90% of marine species
– Site of most large commercial fisheries
– High NPP because of ample nutrients and
sunlight.
• Estuaries and Coastal Wetlands: Centers of
Productivity
– Estuary – area where rivers meet the sea
• Seawater mixes with freshwater along with nutrients
and pollutants (Fig. 6-6)
– Coastal wetlands – coastal land areas covered
with water all or part of the year
• River mouths, inlets, bays, sounds, and salt marshes
(Fig. 6-7; in temperate areas) and mangrove forests in
tropical zones (in tropical areas).
• Significant daily and seasonal changes in tidal and
river flows, and land runoff of sediment and other
pollutants
– Estuaries and coastal wetlands very productive
– Mangrove forests are the tropical equivalents of
salt marshes.
• 70 % of gently sloping sandy and silty coastlines in
tropical and subtropical regions.
• Mangrove trees can grow in saltwater (Fig. 6-8).
• Systems provide important ecological and economic
services
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Filter toxic pollutants, excess nutrients, and sediments.
Reduce storm damage
Provide food, habitats, and nursery sites
Intact mangroves worth $200,000-$900,000/km2
• Based on sustainable fishing and fuel wood use; does
not include ecological services.
• 10-45x more worth than when cleared for aquaculture
• Protecting mangrove forest cost only $1000/km2
• More than a third of the world’s have been destroyed.
– For shrimp farms, crops, and coastal development
– Bangladesh and the Philippines have lost almost ¾
• Rocky and Sandy Shores: Living with the
Tides
– Gravitational pull from the sun and the moon
causes tides to rise and fall every 6 hours
(depending).
– Intertidal zone – area of the shoreline
between low and high tides.
– For an organism, lots of physical and
physiological stress.
• Crashing waves
• High and low tides – periodic immersion and
emersion
• Changing levels of salinity
– Rocky shores (Fig 6-9a)
• Are pounded by waves
• Numerous pools and other niches in the intertidal
zone
• Remarkable number of niches in response to daily
and seasonal changes in
– Temperature
– Water flow
– Salinity
– Barrier beaches, or Sandy Shores (Fig. 6-9b)
• Gently sloping shores
• Many critters burrow into the sand
• Variety of shorebirds with specialized feeding niches
(Fig. 4-8)
– Barrier Islands (Fig. 6-10)
• Low, narrow, sandy islands that form offshore from
a coastline.
• Prime targets for development
– Examples: Atlantic City, NJ; Palm Beach, FL; South
Padre Island, TX
– Development prone to destruction from mother nature
• Flooding, beach erosion, and hurricanes
– According to climate models many of the world’s barrier
islands may be under water by end of century.
• Undisturbed barrier islands
– One or more rows of sand dunes
– Dunes act as a line of defense against storm surges
– Development disrupts these natural barrier island
formations
• “People inaccurately call these human-influenced
events ‘natural disasters’.”
• Threats to Coral Reefs: Increasing Stresses
– Coral reefs found in clear,warm tropical and
subtropical waters
• Thrive in clear, warm, fairly shallow water of constant
salinity.
• Temperature range (18–30 oC); bleaching can be
triggered with an increase of just one degree.
– One-fourth of all marine species (Fig. 6-11)
• Biodiversity can be reduced by:
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Severe storms
Freshwater floods
Invasion of predatory fish
Human activities (Fig. 6-12)
– Loss of Coral Reefs
• 20% are so damaged that they are unlikely to
recover
• By 2050, 30-50% could be lost due to climate
change, habitat loss, pollution, and overfishing
• Only 300 of 6000 reefs are protected (at least on
paper)
– Ecology and Economy
• Worth an estimated $100,000-$600,000 km-2 y-1 from
small-scale sustainable fishing, tourism, and pet
trade.
– Does not include ecological services
– If included, much cheaper to protect than to use them
unsustainably
– There is evidence that coral reefs can recover.
• protection by restricted fishing
• reducing inputs of nutrients and other pollutants
• Biological Zone in the Open Ocean: Light
Rules
– Open sea – at edge of continental shelf.
– Divided into three vertical zones depending on
light availability (Fig. 6-5)
– Euphotic zone – brightly lit upper zone
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Phytoplankton carry out photosynthesis
Nutrients low except at upwellings
DO high
Populated with fast-swimming predatory fish
– Bathyal zone – dimly lit middle zone
• No photosynthesizers
• Zooplankton and smaller fish
– Migrate to surface to feed at night.
– Abyssal zone – lowest zone, dark and very
cold, and has little DO
• Contains enough nutrients to support a large
number of species
• Ocean floor is complex
– Mid-Atlantic Ridge
– Canyons
– Trenches deeper than the height of Mt. Everest
• Food rains from above, called marine snow
– Deposit feeders
– Filter feeders
– Average productivity and NPP per unit area is
low except at equatorial upwellings
• Absolute productivity is large because ocean
covers large area.
• Productivity increase as latitude increases.
• Effect of Human Activities on Marine
Systems: Red Alert
– Humans have an affinity for the coast
– Ecological and economic services being
degraded or destroyed (Fig. 6-13)
– In 2006, 45% of world’s pop. and more than
half in the US lived near the coast
– By 2010, 80% projected to live near the coast
III. Freshwater Life Zones
• Freshwater Systems
– 1% of earth’s surface
– Lentic, or standing: lakes, ponds, and inland
wetlands.
– Lotic, or flowing: streams and rivers
– Ecological and economic services (Fig. 6-14)
• Lakes: Water-Filled Depressions
– Large natural standing bodies of standing
freshwater formed from precipitation, runoff, and
groundwater seepage.
• Causes of depressions:
– Glaciation, crustal displacement, and volcanic activity
– Water supplied by rainfall, melting snow, and
streams
– Vary tremendously in size, shape and nutrient
availability
– Four distinct zones defined by depth and
distance from shore (Fig.6-15)
• Littorral zone
– Shallow, near shore to depth rooted plants cannot grow
– Most productive zone
– Biodiversity high: algae, rooted plants, turtles, frogs,
crayfish, bass, perch, carp
• Limnetic zone
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Open sunlit layer away from shore
Main photosynthetic body of the lake
Primary organism: phyo- and zooplankton
Large fish inhabit this zone, move into littoral zone to feed
and reproduce
• Profundal zone
– Open water where it is too dark for photosynthesis
– Fish adapted to lakes cooler, darker and lower oxygen levels
• Benthic zone
– Bottom of the lake
– Decomposers, detritus feeders, and fish that move from one
zone to another.
– Nourished from limnetic and littoral, and sediments that
wash in
– Thermoclines form in winter ad summer, but mix
in the fall and spring.
• These overturns mix the water equalizing
temperature, taking oxygen to the bottom, and
nutrients to the top.
• Effects of Plant Nutrients on Lakes: Too Much of a
Good Thing
– Lake classified according to their nutrient content and
primary productivity.
• Oligotrophic – poorly nourished (Fig. 6-16a)
– Newly formed, deep, steep banks
– Low NPP  clear water
– Small populations of phytoplankton and fish (e.g., smallmouth bass
and trout)
• Eutrophic – well-nourished (Fig. 6-16b)
– Excessive phosphates and nitrates  high NPP
– Sediments, organic material, and inorganic nutrients have washed
in
– Plant growth and decomposition
– Typically shallow, murky brown or green w/ poor visibility
• Cultural eutrophication
• Many lakes are mesotrophic
• Freshwater Streams and Rivers: From
Mountains to the Oceans
– Surface water – precipitation that does not
sink into the ground or evaporate.
– Runoff – surface water that flows into streams
– Watershed, or drainage basin – land area that
delivers runoff, sediment, and dissolved
substances into a stream.
– Most streams begin in elevated areas (e.g.,
mountains, hills)
– Flow from a mountain can be divided in to three different
life zones (Fig. 6-17):
• Source zone (or headwaters)
– Usu. Shallow, cold, clear, and swiftly moving  high O2
– Low production  lack of nutrients and phytoplankton
– Nutrients mostly from once living material (leaves, branches,
insects)
– Plants, algae and mosses that attach to rock
– Fish and other animals have compact or flattened bodies to live
under stones
• Others with streamlined, muscular bodies to swim in strong
currents.
• Transition zone
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Merging of headwaters forming wider, deeper, and warmer streams
Gentler slopes with fewer obstacles
Higher turbidity, slower moving, less oxygen
More phytoplankton, and cool and warm-water fishes with less
oxygen requirements.
• Flood plain zone
– Streams join into wider, deeper rivers that flow across broad,
flat valleys
– Water usu. w/ higher temp and less DO
– Support large populations of producers: algae,
cyanobacteria, and rooted aquatics along the shore
– Muddy and contains high concentration so suspended silt
– Main channels support distinctive varieties of fish (e.g., carp
and catfish)
– Backwaters support species similar to lakes
– Mouth of river may be divided in to many channels as is flows
through the delta
• Sediments deposit here and in the coastal wetlands and
estuaries.
– Coastal deltas, wetlands and inland floodplains
are important parts of earth’s natural capital.
• Relatively high diversity and productivity
• Absorb floodwater and protect against tropical storms
and tsunamis
– Human activities have degraded or destroyed
the natural protection of coastal surface
formations
• Hurricanes, typhoons and tsunamis become partially
unnatural disasters (see Case Study, p. 140)
– Streams shape the land over which they pass.
– Watershed must be the focus when we wish to
protect streams and rivers from excessive inputs
of nutrients and pollutants.
• Freshwater Inland Wetlands: Vital Sponges
– Inland wetlands – lands covered with freshwater
all or part of the time, excluding lakes, reservoirs,
and streams, located away from coastal areas.
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Marshes
Swamps (Fig. 6-18)
Prairie potholes
Floodplains
Arctic tundra in summer
– When a wetland is dry, a wetland may be
recognized by soil composition and certain
plants.
– Highly productive
– Habitats for game fish, muskrats, otters, beavers,
migratory waterfowl, and other birds
– Inland wetlands provide free ecological and
economic services.
• Filter and degrade toxic wastes and pollutants
– In US, worth at least $1.6 billion/yr
• Reduce flooding and erosion by absorbing and
releasing stormwater slowly, and by absorbing
overflows from streams and lakes
– In US, worth $3-4 billion/yr
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Help replenish stream flows during dry periods
Help recharge groundwater aquifers
Help maintain biodiversity
Supply valuable products such as fish and shellfish,
blueberries, cranberries, wild rice, and timber
• Provide recreation for birdwatchers, nature
photographers, boaters, anglers, and waterfowl
hunters
• Impacts of Human Activities on Freshwater
Systems
– Four major impacts
• First, dams, diversions, or canals fragment about 40%
of world’s 237 large rivers.
• Second, flood control levees and dikes alter and
destroy aquatic habitats.
• Third, cities and farmlands as pollutants and excess
nutrients to watershed.
• Fourth, draining or filling of inland wetlands to grow
crops (Fig. 6-19) or have been converted with
concrete, asphalt, and buildings.
• Case Study: Inland Wetland Losses in the United
States (Science and Politics)
– In US 95% of wetlands are freshwater; remaining are
saltwater or coastal.
– Alaska has more wetlands than the other 49.
– More than half the inland wetlands in continental US
have been lost since the 1600s.
• 80% for crops
• Rest for mining, forestry, oil and gas extraction, highways, and
urban development
• Iowa has lost 99%
– Loss of this natural capital has been an important factor
in increased flood and drought damage.
– Other countries too: France and Germany lost 80%
A Healthy Coral Reef (Fig 6-1a)
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Bleaching in Coral Reefs (6-1b)
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The Ocean Planet (Figure 6-2)
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Distribution of Major Oceans, Coral Reefs, Mangroves, and
Freshwater Lakes and Rivers (Figure 6-3)
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(Fig. 6-4)
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Major Ocean Life Zones (Fig. 6-5)
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Back to
Open Sea
Sediment Plume at Mouth of Madagascar’s
Betsiboka River (Fig. 6-6)
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Components and Interactions in a
Temperate Salt Marsh Ecosystem (Fig. 6-7)
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Mangrove Forest in Daintree National Park
In Queensland, Australia (Fig. 6-8)
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Specialized Niches in a Rocky
Shore (Fig. 6-9)
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Specialized Niches in a Sandy
Shore (Fig. 6-9b)
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Typical Barrier Island Profile
(Fig. 6-10)
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Components and Interactions in a
Coral Reef Ecosystem (Fig. 6-11)
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Major Threats to Coral Reefs (Fig 6-12)
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Major Human Impacts on the World’s
Marine Systems (Fig. 6-13)
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Major Ecological and Economic Services
(Fig. 6-14)
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Life Zones in a Temperate Zone
Lake (Fig. 6-15)
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Oligotrophic Lake (Fig. 6-16a)
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Eutrophic Lake (Fig. 6-16b)
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Three Zones in the Downhill Flow of Water
(Fig. 6-17)
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Cypress Swamp in Tennessee (Fig. 6-18)
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Prairie Pothole Wetland That Has Been
Ditched and Drained for Cropland (Fig. 6-19)
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