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Aquatic Biodiversity
Chapter 8
8-1 What Is the General Nature of
Aquatic Systems?
 Concept 8-1A Saltwater and freshwater aquatic
life zones cover almost three-fourths of the earth’s
surface with oceans dominating the planet.
 Concept 8-1B The key factors determining
biodiversity in aquatic systems are temperature,
dissolved oxygen content, availability of food and
availability of light and nutrients necessary for
photosynthesis.
8-1 What Is the General Nature of
Aquatic Systems?
 Aquatic life zones cover almost three-fourths of
the earth’s surface
• Saltwater: marine
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Estuaries
Coastal wetlands
Coral reefs
Mangrove forests
Open Ocean
• Freshwater
• Lakes
• Rivers and streams
• Inland wetlands
Most Aquatic Species Live in Top, Middle,
or Bottom Layers of Water
 Aquatic systems contain floating, drifting, swimming,
bottom-dwelling, and decomposer organisms.
• Plankton: important group of weakly swimming, freefloating organisms
• Phytoplankton (plant), Zooplankton (animal),
Ultraplankton (photosynthetic bacteria)
• Necton: fish, turtles, whales
• Benthos: bottom dwellers (barnacles, oysters)
• Decomposers: breakdown organic compounds
(mostly bacteria)
Most Aquatic Species Live in Top, Middle,
or Bottom Layers of Water
 Types and numbers of organism found depend on:
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Temperature
Access to sunlight for photosynthesis
Dissolved oxygen content
Nutrient availability
 These characteristics vary with depth.
 Euphotic zone (“well lit” in Greek)
• The upper layer through which
sunlight can penetrate.
8-2 Why Are Marine Aquatic Systems Important?
 Concept 8-2 Saltwater ecosystems are
irreplaceable reservoirs of biodiversity and
provide major ecological and economic services.
8-2 Why Are Marine Aquatic Systems Important?
 The oceans that
occupy most of the
earth’s surface provide
many ecological and
economic services.
 Scientists estimate
that marine systems
provide $12 trillion in
goods and services
per year – 70% more
than terrestrial
ecosystems.
Estuaries and Coastal Wetlands Are
Highly Productive
 The coastal zone: the warm, nutrient-rich, shallow
water that extends from the shoreline to the 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.
• Subject to human disturbance because of high
populations along ocean coastlines.
Estuaries and Coastal Wetlands Are
Highly Productive
 Estuaries are where fresh
water rivers empty into the
salt water oceans.
• The fresh water is less
dense so it floats on top of
the more dense salt water.
 Estuaries include river
mouths, bays, salt
marshes, and mangrove
forests.
Estuaries and Coastal Wetlands Are
Highly Productive
 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 and habitats for many aquatic species.
Rocky and Sandy Shores Host Different
Types of Organisms
 Intertidal Zone: the area of a shoreline between
low and high tides.
 Organisms living in the intertidal zone have
evolved a number of ways to survive under harsh
and changing conditions. They must deal with
daily changes in temperature, salinity, wave
action, and being left “high and dry”.
Coral Reefs Are Amazing Centers
of Biodiversity
 Coral reefs form in clear,
warm coastal waters of the
tropics and subtropics.
• Very important that they have
consistently warm water
 They are home to a huge
amount of biodiversity
• 25% of all marine species
• “Rain Forest of the Ocean”
Core Case Study:
Why Should We Care about Coral Reefs?
 Biodiversity
 Important ecological and economic services:
• Moderate atmospheric temperatures
• Act as natural barriers protecting coasts from
erosion
• Provide habitats
• Support fishing and tourism businesses
• Provide jobs and building materials
• Studied and enjoyed
Core Case Study:
Why Should We Care about Coral Reefs?
 Degradation and decline:
• Pollution
• Overfishing
• Warmer ocean temperatures
• Causing coral bleaching
• Increasing ocean acidity
• Dissolving coral (calcium carbonate)
The Open Sea and Ocean Floor Host a
Variety of Species
 Euphotic zone: brightly lit surface layer
• Nutrient levels low, dissolved O2 high, plenty of
photosynthetic activity.
 Bathyal zone: dimly lit middle layer
• No photosynthetic activity, zooplankton and fish live
there and migrate to euphotic zone to feed.
 Abyssal zone: dark bottom layer
• Very cold, little dissolved O2.
• High nutrient levels – filter down from the layers above
• Upwelling – nutrients are brought to the surface by currents
Major Life Zones and Vertical Zones in an Ocean
8-3 How Have Human Activities Affected
Marine Ecosystems?
 Concept 8-3 Human activities threaten aquatic
biodiversity and disrupt ecological and economic
services provided by saltwater systems.
8-3 How Have Human Activities Affected
Marine Ecosystems?
 Major threats to marine systems:
• Coastal development
• Overfishing
• Runoff of nonpoint source
pollution
• Point source pollution
• Habitat destruction
• Introduction of invasive species
• Climate change from human
activities
• Pollution of coastal wetlands and
estuaries
8-4 Why Are Freshwater Ecosystems Important?
 Concept 8-4 Freshwater ecosystems provide
major ecological and economic services and are
irreplaceable reservoirs of biodiversity.
8-4 Why Are Freshwater Ecosystems Important?
 Freshwater life zones
include:
• Standing (lentic) water
• lakes, ponds, and inland
wetlands
• Flowing (lotic) systems
• streams and rivers
Water Stands in Some Freshwater Systems
and Flows in Others
 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, sun-lit)
• Profundal zone (deep, open water, too dark for
photosynthesis)
• Benthic zone (bottom of lake, nourished by dead matter)
Distinct Zones of Life in a Fairly Deep
Temperate Zone Lake
Turnover in a Lake
 During the summer and winter, lakes become stratified
into temperature layers.
 In the spring and fall, the temperature equalizes and the
lakes “overturn”.
• Oxygen is brought from the surface to the lake bottom and
nutrients from the bottom are brought to the top.
Some Lakes Have More Nutrients Than Others
 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.
• Mesotrophic (medium nourished) lake: most lakes
are in between
• Eutrophic (well nourished) lake: Over time, sediment,
organic material, and inorganic nutrients wash into
lakes causing excessive plant growth.
Some Lakes Have More Nutrients Than Others
 Cultural eutrophication:
• Human inputs of nutrients from the atmosphere and
urban and agricultural areas can accelerate the
eutrophication process.
Freshwater Streams and Rivers Carry Water
from the Mountains to the Oceans
 Water flowing from mountains to the sea creates
different aquatic conditions and habitats.
Freshwater Streams and Rivers Carry Water
from the Mountains to the Oceans
 Watershed
or drainage basin
• the land area that delivers
runoff, sediment, and
dissolved substance to a
stream or river.
 The larger the watershed,
the larger the river it feeds
into.
Freshwater Inland Wetlands
Are Vital Sponges
 Inland wetlands act like
natural sponges that
absorb and store excess
water from storms and
provide a variety of
wildlife habitats.
Freshwater Inland Wetlands
Are 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.
8-5 How Have Human Activities Affected
Freshwater Ecosystems?
 Concept 8-5 Human activities threaten
biodiversity and disrupt ecological and economic
services provided by freshwater lakes, rivers,
and wetlands.
8-5 How Have Human Activities Affected
Freshwater Ecosystems?
 Human activities are disrupting the freshwater
ecosystems in many ways:
• Construction of dams and canals on 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.