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Chapter 6

Aquatic Biodiversity

Chapter Overview Questions

Ø What are the basic types of aquatic life zones and what factors influence the kinds of life they contain?

Ø What are the major types of saltwater life zones, and how do human activities affect them?

Ø What are the major types of freshwater life zones, and how do human activities affect them?

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Core Case Study: Why Should We Care About Coral

Reefs?

Ø Coral reefs form in clear, warm coastal waters of the tropics and subtropics. l  Formed by

massive colonies of polyps.

Figure 6-1

Core Case Study: Why Should We Care About Coral

Reefs?

Ø Help moderate atmospheric temperature by removing CO2 from the atmosphere.

Ø Act as natural barriers that help protect 14% of the world’s coastlines from erosion by battering waves and storms.

Ø Provide habitats for a variety of marine organisms.

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AQUATIC ENVIRONMENTS

Ø Saltwater and freshwater aquatic life zones cover almost three-fourths of the earth’s surface

Figure 6-2

AQUATIC ENVIRONMENTS

Figure 6-3

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What Kinds of Organisms Live in Aquatic Life Zones?

Ø Aquatic systems contain floating, drifting, swimming, bottom-dwelling, and decomposer organisms. l  Plankton: important group of weakly swimming,

free-floating biota. •  Phytoplankton (plant), Zooplankton (animal),

Ultraplankton (photosynthetic bacteria) l  Necton: fish, turtles, whales. l  Benthos: bottom dwellers (barnacles, oysters). l  Decomposers: breakdown organic compounds

(mostly bacteria).

Life in Layers

Ø Life in most aquatic systems is found in surface, middle, and bottom layers.

Ø Temperature, access to sunlight for photosynthesis, dissolved oxygen content, nutrient availability changes with depth. l  Euphotic zone (upper layer in deep water

habitats): sunlight can penetrate.

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SALTWATER LIFE ZONES

Ø The oceans that occupy most of the earth’s surface provide many ecological and economic services.

Figure 6-4

The Coastal Zone: Where Most of the Action Is

Ø The coastal zone: the warm, nutrient-rich, shallow water that extends from the high-tide mark on land to the gently sloping, shallow edge of the continental shelf.

Ø The coastal zone makes up less than 10% of the world’s ocean area but contains 90% of all marine species. l  Provides numerous ecological and economic

services. l  Subject to human disturbance.

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The Coastal Zone

Figure 6-5

Marine Ecosystems

Ø Scientists estimate that marine systems provide $21 trillion in goods and services per year – 70% more than terrestrial ecosystems.

Figure 6-4

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Estuaries and Coastal Wetlands: Centers of Productivity

Ø Estuaries include river mouths, inlets, bays, sounds, salt marshes in temperate zones and mangrove forests in tropical zones.

Figure 6-7

Mangrove Forests

Ø Are found along about 70% of gently sloping sandy and silty coastlines in tropical and subtropical regions.

Figure 6-8

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Estuaries and Coastal Wetlands: Centers of Productivity

Ø Estuaries and coastal marshes provide ecological and economic services. l  Filter toxic pollutants, excess plant nutrients,

sediments, and other pollutants. l  Reduce storm damage by absorbing waves

and storing excess water produced by storms and tsunamis.

l  Provide food, habitats and nursery sites for many aquatic species.

Rocky and Sandy Shores: Living with the Tides

Ø Organisms experiencing daily low and high tides have evolved a number of ways to survive under harsh and changing conditions. l  Gravitational pull by moon and sun causes tides. l  Intertidal Zone: area of shoreline between low

and high tides.

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Rocky and Sandy Shores: Living with the Tides

Ø Organisms in intertidal zone develop specialized niches to deal with daily changes in: l  Temperature l  Salinity l  Wave action

Figure 6-9

Barrier Islands

Ø Low, narrow, sandy islands that form offshore from a coastline.

Ø Primary and secondary dunes on gently sloping sandy barrier beaches protect land from erosion by the sea.

Figure 6-10

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Threats to Coral Reefs: Increasing Stresses

Ø Biologically diverse and productive coral reefs are being stressed by human activities.

Figure 6-11

Fig. 6-12, p. 135

Ocean warming Soil erosion Algae growth from fertilizer runoff Mangrove destruction Bleaching Rising sea levels Increased UV exposure Damage from anchors Damage from fishing and diving

Natural Capital Degradation

Coral Reefs

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Biological Zones in the Open Sea: Light Rules

Ø Euphotic zone: brightly lit surface layer. l  Nutrient levels low, dissolved O2 high,

photosynthetic activity. Ø Bathyal zone: dimly lit middle layer.

l  No photosynthetic activity, zooplankton and fish live there and migrate to euphotic zone to feed at night.

Ø Abyssal zone: dark bottom layer. l  Very cold, little dissolved O2.

Effects of Human Activities on Marine Systems: Red Alert

Ø Human activities are destroying or degrading many ecological and economic services provided by the world’s coastal areas.

Figure 6-13

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FRESHWATER LIFE ZONES

Ø Freshwater life zones include: l  Standing (lentic)

water such as lakes, ponds, and inland wetlands.

l  Flowing (lotic) systems such as streams and rivers.

Figure 6-14

Lakes: Water-Filled Depressions

Ø Lakes are large natural bodies of standing freshwater formed from precipitation, runoff, and groundwater seepage consisting of: l  Littoral zone (near shore, shallow, with rooted

plants). l  Limnetic zone (open, offshore area, sunlit). l  Profundal zone (deep, open water, too dark for

photosynthesis). l  Benthic zone (bottom of lake, nourished by dead

matter).

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Lakes: Water-Filled Depressions

Ø During summer and winter in deep temperate zone lakes the become stratified into temperature layers and will overturn. l  This equalizes the temperature at all depths. l  Oxygen is brought from the surface to the lake

bottom and nutrients from the bottom are brought to the top.

Ø What causes this overturning?

Lakes: Water-Filled Depressions

Figure 6-15

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Effects of Plant Nutrients on Lakes: Too Much of a Good Thing

Ø Plant nutrients from a lake’s environment affect the types and numbers of organisms it can support.

Figure 6-16

Effects of Plant Nutrients on Lakes: Too Much of a Good Thing

Ø Plant nutrients from a lake’s environment affect the types and numbers of organisms it can support. l  Oligotrophic (poorly nourished) lake: Usually

newly formed lake with small supply of plant nutrient input.

l  Eutrophic (well nourished) lake: Over time, sediment, organic material, and inorganic nutrients wash into lakes causing excessive plant growth.

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Effects of Plant Nutrients on Lakes: Too Much of a Good Thing

Ø Cultural eutrophication: l  Human inputs of nutrients from the atmosphere

and urban and agricultural areas can accelerate the eutrophication process.

Freshwater Streams and Rivers: From the Mountains to the Oceans

Ø Water flowing from mountains to the sea creates different aquatic conditions and habitats.

Figure 6-17

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Case Study: Dams, Wetlands, Hurricanes,

and New Orleans Ø Dams and levees have been built to control

water flows in New Orleans. Ø Reduction in natural flow has destroyed

natural wetlands. l  Causes city to lie below sea-level (up to 3

meters). l  Global sea levels have risen almost 0.3 meters

since 1900.

Freshwater Inland Wetlands: Vital Sponges

Ø  Inland wetlands act like natural sponges that absorb and store excess water from storms and provide a variety of wildlife habitats.

Figure 6-18

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Freshwater Inland Wetlands: Vital Sponges

Ø Filter and degrade pollutants. Ø Reduce flooding and erosion by absorbing

slowly releasing overflows. Ø Help replenish stream flows during dry

periods. Ø Help recharge ground aquifers. Ø Provide economic resources and recreation.

Impacts of Human Activities on Freshwater Systems

Ø  Dams, cities, farmlands, and filled-in wetlands alter and degrade freshwater habitats. l  Dams, diversions and canals have fragmented about 40%

of the world’s 237 large rivers. l  Flood control levees and dikes alter and destroy aquatic

habitats. l  Cities and farmlands add pollutants and excess plant

nutrients to streams and rivers. l  Many inland wetlands have been drained or filled for

agriculture or (sub)urban development.

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Impacts of Human Activities on Freshwater Systems

Ø These wetlands have been ditched and drained for cropland conversion.

Figure 6-19