1. Chapter 6
Aquatic Biodiversity

2. Chapter Overview 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?

3. Updates Online
The latest references for topics covered in this section can be found at the book companion website. Log in to the book’s e-resources page at to access InfoTrac articles.
InfoTrac: Down the bayou: a marine biologist, a community, and the resolve to preserve an ocean's bounty. Taylor Sisk. Earth Island Journal, Autumn 2006 v21 i3 p27(6).
InfoTrac: A scourge of the '70s returns to Great Lakes. The Christian Science Monitor, March 30, 2006 p14.
InfoTrac: The fate of the ocean. Julia Whitty. Mother Jones, March-April 2006 v31 i2 p32(15).
National Oceanic and Atmospheric Administration: Fisheries
Amazon Conservation Association: Amazon Rivers Project

4. Core Case Study: Why Should We Care About Coral Reefs?
Coral reefs form in clear, warm coastal waters of the tropics and subtropics.
Formed by massive colonies of polyps.
Figure 6-1

5. Figure 6.1
Natural capital: a healthy coral reef in the Red Sea covered by colorful algae (left) and a bleached coral reef that has lost most of its algae (right) because of changes in the environment (such as cloudy water or too warm temperatures). With the algae gone, the white limestone of the coral skeleton becomes visible. If the environmental stress is not removed and no other alga species fill the abandoned niche, the corals die. These diverse and productive ecosystems are being damaged and destroyed at an alarming rate.
Fig. 6-1a, p. 126

6. Figure 6.1
Natural capital: a healthy coral reef in the Red Sea covered by colorful algae (left) and a bleached coral reef that has lost most of its algae (right) because of changes in the environment (such as cloudy water or too warm temperatures). With the algae gone, the white limestone of the coral skeleton becomes visible. If the environmental stress is not removed and no other alga species fill the abandoned niche, the corals die. These diverse and productive ecosystems are being damaged and destroyed at an alarming rate.
Fig. 6-1b, p. 126

7. Core Case Study: Why Should We Care About Coral Reefs?
Help moderate atmospheric temperature by removing CO2 from the atmosphere.
Act as natural barriers that help protect 14% of the world’s coastlines from erosion by battering waves and storms.
Provide habitats for a variety of marine organisms.

8. AQUATIC ENVIRONMENTS
Saltwater and freshwater aquatic life zones cover almost three-fourths of the earth’s surface
Figure 6-2

9. Land–ocean hemisphere
Figure 6.2
Natural capital: the ocean planet. The salty oceans cover 71% of the earth’s surface. About 97% of the earth’s water is in the interconnected oceans, which cover 90% of the planet’s mostly ocean hemisphere (left) and 50% of its land–ocean hemisphere (right). Freshwater systems cover less than 1% of the earth’s surface.
Ocean hemisphere
Land–ocean hemisphere
Fig. 6-2, p. 127

10. AQUATIC ENVIRONMENTS
Figure 6-3

11. What Kinds of Organisms Live in Aquatic Life Zones?
Aquatic systems contain floating, drifting, swimming, bottom-dwelling, and decomposer organisms.
Plankton: important group of weakly swimming, free-floating biota.
Phytoplankton (plant), Zooplankton (animal), Ultraplankton (photosynthetic bacteria)
Necton: fish, turtles, whales.
Benthos: bottom dwellers (barnacles, oysters).
Decomposers: breakdown organic compounds (mostly bacteria).

12. Life in Layers
Life in most aquatic systems is found in surface, middle, and bottom layers.
Temperature, access to sunlight for photosynthesis, dissolved oxygen content, nutrient availability changes with depth.
Euphotic zone (upper layer in deep water habitats): sunlight can penetrate.

13. SALTWATER LIFE ZONES
The oceans that occupy most of the earth’s surface provide many ecological and economic services.
Figure 6-4

14. Harbors and transportation routes
Natural Capital
Marine Ecosystems
Economic
Services
Ecological
Services
Climate moderation
Food
CO2 absorption
Animal and pet feed
Nutrient cycling
Pharmaceuticals
Waste treatment
Harbors and transportation routes
Reduced storm impact (mangroves, barrier islands, coastal wetlands)
Coastal habitats for humans
Figure 6.4
Natural capital: major ecological and economic services provided by marine systems. Scientists estimate that marine systems provide $21 trillion in goods and services per year—70% more than terrestrial ecosystems. QUESTION: Which two ecological services and which two economic services do you think are the most important?
Habitats and nursery areas
Recreation
Employment
Genetic resources and biodiversity
Oil and natural gas
Minerals
Scientific information
Building materials
Fig. 6-4, p. 129

15. The Coastal Zone: Where Most of the Action Is
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.
The coastal zone makes up less than 10% of the world’s ocean area but contains 90% of all marine species.
Provides numerous ecological and economic services.
Subject to human disturbance.

16. The Coastal Zone
Figure 6-5

17. High tide Coastal Zone Open Sea Sun Low tide Sea level Photosynthesis
Euphotic Zone
Estuarine Zone
Continental shelf
Bathyal Zone
Twilight
Abyssal Zone
Figure 6.5
Natural capital: major life zones in an ocean (not drawn to scale). Actual depths of zones may vary.
Darkness
Fig. 6-5, p. 130

18. Marine Ecosystems
Scientists estimate that marine systems provide $21 trillion in goods and services per year – 70% more than terrestrial ecosystems.
Figure 6-4

19. Figure 6.6
Natural capital degradation: view of an estuary taken from space. The photo shows the sediment plume at the mouth of Madagascar’s Betsiboka River as it flows through the estuary and into the Mozambique Channel. Because of its topography, heavy rainfall, and the clearing of forests for agriculture, Madagascar is the world’s most eroded country.
Fig. 6-6, p. 130

20. Estuaries and Coastal Wetlands: Centers of Productivity
Estuaries include river mouths, inlets, bays, sounds, salt marshes in temperate zones and mangrove forests in tropical zones.
Figure 6-7

21. Herring gulls
Peregrine falcon
Snowy
Egret
Cordgrass
Short-billed
Dowitcher
Marsh
Periwinkle
Phytoplankton
Smelt
Figure 6.7
Natural capital: some components and interactions in a salt marsh ecosystem in a temperate area such as the United States. When these organisms die, decomposers break down their organic matter into minerals used by plants. Colored arrows indicate transfers of matter and energy between consumers (herbivores), secondary or higher-level consumers (carnivores), and decomposers. Organisms are not drawn to scale. The photo below shows a salt marsh in Peru.
Zooplankton and
small crustaceans
Soft-shelled
clam
Clamworm
Bacteria
Producer to
primary
consumer
Primary to
secondary
consumer
Secondary to
higher-level
consumer
All consumers
and producers
to decomposers
Fig. 6-7a, p. 131

22. Figure 6.7
Natural capital: some components and interactions in a salt marsh ecosystem in a temperate area such as the United States. When these organisms die, decomposers break down their organic matter into minerals used by plants. Colored arrows indicate transfers of matter and energy between consumers (herbivores), secondary or higher-level consumers (carnivores), and decomposers. Organisms are not drawn to scale. The photo below shows a salt marsh in Peru.
Fig. 6-7b, p. 131

23. Mangrove Forests
Are found along about 70% of gently sloping sandy and silty coastlines in tropical and subtropical regions.
Figure 6-8

24. Estuaries and Coastal Wetlands: Centers of Productivity
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.

25. Rocky and Sandy Shores: Living with the Tides
Organisms experiencing daily low and high tides have evolved a number of ways to survive under harsh and changing conditions.
Gravitational pull by moon and sun causes tides.
Intertidal Zone: area of shoreline between low and high tides.

26. Rocky and Sandy Shores: Living with the Tides
Organisms in intertidal zone develop specialized niches to deal with daily changes in:
Temperature
Salinity
Wave action
Figure 6-9

27. Rocky Shore Beach Hermit crab Sea star Shore crab High tide Periwinkle
Sea urchin
Anemone
Mussel
Low tide
Sculpin
Figure 6.9
Natural capital: living between the tides. Some organisms with specialized niches found in various zones on rocky shore beaches (top) and barrier or sandy beaches (bottom). Organisms are not drawn to scale.
Barnacles
Kelp
Sea lettuce
Monterey flatworm
Nudibranch
Fig. 6-9, p. 132

28. Barrier Beach Beach flea Peanut worm Tiger Beetle Blue crab Clam Dwarf
Olive
High tide
Sandpiper
Ghost
Shrimp
Low tide
Silversides
Figure 6.9
Natural capital: living between the tides. Some organisms with specialized niches found in various zones on rocky shore beaches (top) and barrier or sandy beaches (bottom). Organisms are not drawn to scale.
Mole
Shrimp
White sand macoma
Moon snail
Sand dollar
Fig. 6-9, p. 132

29. 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.
Figure 6-10

30. Primary Dune Secondary Dune Grasses or shrubs
Bay or Lagoon
Ocean
Beach
Trough
Back Dune
Intensive recreation,
no building
No direct passage
or building
Limited
recreation
and walkways
No direct passage
or building
Most suitable
for development
Intensive
recreation
Grasses or shrubs
Bay shore
No filling
Taller shrubs
Taller shrubs and trees
Figure 6.10
Natural capital: primary and secondary dunes on gently sloping sandy barrier beaches help protect land from erosion by the sea. The roots of grasses that colonize the dunes help hold the sand in place. Ideally, construction is allowed only behind the second strip of dunes, and walkways to the beach are built over the dunes to keep them intact. This helps preserve barrier beaches and protect buildings from damage by wind, high tides, beach erosion, and flooding from storm surges. Such protection is rare because the short-term economic value of oceanfront land is incorrectly considered much higher than its long-term ecological value. Rising sea levels from global warming may put many barrier beaches under water by the end of this century.
Fig. 6-10, p. 133

31. Threats to Coral Reefs: Increasing Stresses
Biologically diverse and productive coral reefs are being stressed by human activities.
Figure 6-11

32. Green sea turtle Banded coral shrimp Symbiotic algae
Gray reef shark
Green sea
turtle
Sea nettle
Fairy basslet
Blue
tangs
Parrot fish
Sergeant major
Hard corals
Brittle star
Algae
Banded coral
shrimp
Phytoplankton
Symbiotic
algae
Coney
Figure 6.11
Natural capital: some components and interactions in a coral reef ecosystem. When these organisms die, decomposers break down their organic matter into minerals used by plants. Colored arrows indicate transfers of matter and energy between producers, primary consumers (herbivores), secondary or higher-level consumers (carnivores), and decomposers. Organisms are not drawn to scale. See photos of a coral reef in Figure 6-1 and photo 10 in the Detailed Contents.
Zooplankton
Blackcap basslet
Sponges
Moray
eel
Bacteria
Producer to
primary
consumer
Primary to
secondary
consumer
Secondary to
higher-level
consumer
All consumer
and producers
to decomposers
Fig. 6-11, p. 134

33. Natural Capital Degradation
Coral Reefs
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
Figure 6.12
Natural capital degradation: major threats to coral reefs. QUESTION: Which three of these threats do you think are the most serious?
Fig. 6-12, p. 135

34. Biological Zones in the Open Sea: Light Rules
Euphotic zone: brightly lit surface layer.
Nutrient levels low, dissolved O2 high, photosynthetic activity.
Bathyal zone: dimly lit middle layer.
No photosynthetic activity, zooplankton and fish live there and migrate to euphotic zone to feed at night.
Abyssal zone: dark bottom layer.
Very cold, little dissolved O2.

35. Effects of Human Activities on Marine Systems: Red Alert
Human activities are destroying or degrading many ecological and economic services provided by the world’s coastal areas.
Figure 6-13

36. Natural Capital Degradation
Marine Ecosystems
Half of coastal wetlands lost to agriculture and urban development
Over one-third of mangrove forests lost to agriculture, development, and aquaculture shrimp farms
Beaches eroding because of coastal development and rising sea level
Ocean bottom habitats degraded by dredging and trawler fishing
At least 20% of coral reefs severely damaged and 30–50% more threatened
Figure 6.13
Natural capital degradation: major human impacts on the world’s marine systems. QUESTION: Which two of these threats do you think are the most serious?
Fig. 6-13, p. 136

37. FRESHWATER LIFE ZONES Freshwater life zones include:
Standing (lentic) water such as lakes, ponds, and inland wetlands.
Flowing (lotic) systems such as streams and rivers.
Figure 6-14

38. Habitats for many species
Natural Capital
Natural Capital
Freshwater Systems
Ecological
Services
Economic
Services
Climate moderation
Nutrient cycling
Waste treatment
Flood control
Groundwater recharge
Habitats for many species
Genetic resources and biodiversity
Scientific information
Food
Drinking water
Irrigation water
Hydroelectricity
Transportation corridors
Recreation
Employment
Figure 6.14
Natural capital: major ecological and economic services provided by freshwater systems. QUESTION: Which two ecological services and which two economic services do you think are the most important?
Fig. 6-14, p. 136

39. Lakes: Water-Filled Depressions
Lakes are large natural bodies of standing freshwater formed from precipitation, runoff, and groundwater seepage consisting of:
Littoral zone (near shore, shallow, with rooted plants).
Limnetic zone (open, offshore area, sunlit).
Profundal zone (deep, open water, too dark for photosynthesis).
Benthic zone (bottom of lake, nourished by dead matter).

40. Lakes: Water-Filled Depressions
During summer and winter in deep temperate zone lakes the 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.
What causes this overturning?

41. Lakes: Water-Filled Depressions
Figure 6-15

42. Sunlight Painted turtle Green frog Blue-winged teal Muskrat Pond snail
Littoral zone
Limnetic zone
Figure 6.15
Natural capital: distinct zones of life in a fairly deep temperate zone lake.
Diving beetle
Plankton
Profundal zone
Benthic zone
Northern pike
Yellow perch
Bloodworms
Fig. 6-15, p. 137

43. Effects of Plant Nutrients on Lakes: Too Much of a Good Thing
Plant nutrients from a lake’s environment affect the types and numbers of organisms it can support.
Figure 6-16

44. Effects of Plant Nutrients on Lakes: Too Much of a Good Thing
Plant nutrients from a lake’s environment affect the types and numbers of organisms it can support.
Oligotrophic (poorly nourished) lake: Usually newly formed lake with small supply of plant nutrient input.
Eutrophic (well nourished) lake: Over time, sediment, organic material, and inorganic nutrients wash into lakes causing excessive plant growth.

45. Effects of Plant Nutrients on Lakes: Too Much of a Good Thing
Cultural eutrophication:
Human inputs of nutrients from the atmosphere and urban and agricultural areas can accelerate the eutrophication process.

46. Freshwater Streams and Rivers: From the Mountains to the Oceans
Water flowing from mountains to the sea creates different aquatic conditions and habitats.
Figure 6-17

47. Oxbow lake Deposited sediment
Rain and snow
Glacier
Lake
Rapids
Waterfall
Tributary
Flood plain
Oxbow lake
Salt marsh
Deposited sediment
Delta
Ocean
Source Zone
Transition Zone
Figure 6.17
Natural capital: three zones in the downhill flow of water: source zone containing mountain (headwater) streams; transition zone containing wider, lower-elevation streams; and floodplain zone containing rivers, which empty into the ocean.
Water
Sediment
Floodplain Zone
Fig. 6-17, p. 139

48. Case Study: Dams, Wetlands, Hurricanes, and New Orleans
Dams and levees have been built to control water flows in New Orleans.
Reduction in natural flow has destroyed natural wetlands.
Causes city to lie below sea-level (up to 3 meters).
Global sea levels have risen almost 0.3 meters since 1900.

49. Freshwater Inland Wetlands: Vital Sponges
Inland wetlands act like natural sponges that absorb and store excess water from storms and provide a variety of wildlife habitats.
Figure 6-18

50. Freshwater Inland Wetlands: Vital Sponges
Filter and degrade pollutants.
Reduce flooding and erosion by absorbing slowly releasing overflows.
Help replenish stream flows during dry periods.
Help recharge ground aquifers.
Provide economic resources and recreation.

51. Impacts of Human Activities on Freshwater Systems
Dams, cities, farmlands, and filled-in wetlands alter and degrade freshwater habitats.
Dams, diversions and canals have fragmented about 40% of the world’s 237 large rivers.
Flood control levees and dikes alter and destroy aquatic habitats.
Cities and farmlands add pollutants and excess plant nutrients to streams and rivers.
Many inland wetlands have been drained or filled for agriculture or (sub)urban development.

52. Impacts of Human Activities on Freshwater Systems
These wetlands have been ditched and drained for cropland conversion.
Figure 6-19