Chapter 7

Chapter 7

Aquatic Biodiversity

Euphotic zone- layer of water where sunlight can penetrate

What is the concentration of dissolved O2 at the surface ? at 1000 m ?

What is the concentration of dissolved CO2 at the surface? at 1000 m ?

Explain why dissolved O2 levels are so high near the surface.

Explain why dissolved CO2 levels are so low near the surface.

Explain why the O2 becomes less concentrated and the CO2 becomes more concentrated in deeper waters.

How would you expect this graph to change at night ? Why ?

How should the pH change with depth during the day ? Explain.

Graph page 146

Aquatic Life ZonesSaltwater or

Marine · Estuaries · Coastlines · Coral reefs · Coastal marshes · Mangrove

swamps · Ocean

Freshwater · Lakes and ponds · Streams and

rivers · Inland wetlands

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

Fig. 6-1a, p. 126

Natural capital: a healthy coral reef in the Red Sea covered by colorful algae These diverse and productive ecosystems are being damaged and destroyed at an alarming rate.

Fig. 6-1b, p. 126

Bleached Coral Reef That has lost most of its algae 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.

Coral Reefs-built from accumulatedlayers of calcium carbonate, CaCO3 laid

down by relatives of sea anemones.• 1. Most of these organism require warm shallow water• 2. Many live in a symbiotic relationship with green algae known as zooxanthellae • 3. A very diverse marine environment• 4. The Great Barrier Reef off the coast of Australia is one of the largest

Value of coral reefs

• Provide valuable habitat• Provide humans with seafood• Pharmaceuticals• Recreation/tourism dollars

Human Impacts• Covered with silt from inland logging• In 1980’s coral bleaching occurred stressed

corals expelled zooxanthellae algae• Thought to be related to warming of the seas. Corals can recover because• 1. Hold a secret reserve of algae• 2. Can take on other algae species when one species leaves• 3. Seasonally lose up to 75% of algae• Diving and snorkeling Overfishing• Agricultural and industrial pollutants in runoff.

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.

Fig. 6-2, p. 127

Land–ocean hemisphereOcean hemisphere

and 50% of its land–ocean hemisphere (right). Freshwater systems cover less than 1% of the earth’s surface.

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)

AQUATIC ENVIRONMENTS

Figure 6-3

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.

The Coastal Zone

Figure 6-5

The Open OceanLife Zones Euphotic Zone 1.Light 2. Dissolved Oxygen 3. Nutrients

upwellings 4.Organisms Bathyal Zone 1.Light 2. Organisms Abyssal Zone 1.Light 2.Oxygen 3. Nutrient levels

Marine Ecosystems

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

Figure 6-4

Major Human Impacts Salt Marshes, Mangrove Forests, Sea-grass

Meadows- Filled in for coastal development

Aquaculture of shrimp Beaches-

Erosion Benthic Habitat- Bottom trawlers Coral Reefs- Ocean warming, pH changes

associated with global warming.

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

Estuaries &Associated Coastal Wetlands

Located at the mouth of rivers and streams Fresh and salt water mix Highest NPP of any ecosystem because · 1. Nutrient runoff from land · 2. Tides circulate nutrients and remove

wastes · 3. Light penetrates the shallow water · 4.Plant carry out photosynthesis and trap

detritus Organisms must deal with daily changes in

temperature and salinity.

Saltwater marshes

Found associated with temperate estuaries Dominated by salt tolerant grasses Important services · 1. Habitat · 2. Sediment and pollution trapping · 3. Storm buffering Most are being covered over for coastal

development

Mangrove Forests

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

Figure 6-8

Mangrove Forests-tropical equivalent of saltwater marsh

Network of roots of the mangrove trees are important nurseries of many commercially important fish and shellfish (shrimp)

Branches of mangrove trees provide important habitat for nesting birds: pelicans, herons, egrets.

Roots stabilize submerged soil preventing coastal erosion

Storm buffer Being harmed by: Logging Coastal development · Aquaculture

Intertidal Zone- betweenhigh and low tide

· Organisms must contend with changing levels of water

In rocky shoreline habitat, most organisms are anchored in some way and have a

way to seal off their bodies to prevent moisture loss when the tide goes out. Most sandy beach organisms either burrow

in the sand or travel in and out with the tide.

The importance of sea grass High NPP make them important producers in

shallow water Roots stabilize sediments reducing erosion Provide food and habitat for many marine

species, sea turtles, manatees, ducks and geese Chinook salmon and eelgrass

Kelps Beds Formed from species of

marine algae Many are anchored to the

bottom and have air filled bags to allow the upper part of the plant to float to the top

equivalent to the forest biome on the land

Kelp beds or forests provide habitat and food for many species

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.

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

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.

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.

Ponds are generally shallow and have only one zone-light reaches to the bottom

Figure 6-14

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).

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?

Fig. 6-15, p. 137

Pond snail

Benthic zone

Profundal zone

Limnetic zone

Sunlight

Blue-winged teal

Muskrat

Plankton

Bloodworms Northern pikeYellow

perch

Diving beetle

Littoral zone

Painted turtleGreen

frog

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

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.

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.

Physical Properties of water

Approaches maximum density at 4oC At temperatures cooler than 4oC water

becomes less dense and it floats and freezes as temperatures drop to 0oC At temperatures greater than 4oC water

becomes less dense and it floats

Seasonal Overturn in Lakes

Fall Overturn- Surface waterscool to 4oC (39oF)and descend to the bottom

Nutrients Oxygen levels

Spring Overturn- Surface waterswarm to 4oC anddescend through the colder lessdense watersbeneath.

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

Fig. 6-17, p. 139

Source Zone

Rain and snow

Lake GlacierRapids

WaterfallTributary

Flood plain Oxbow lake

Salt marshDelta Deposited

sedimentOcean

SedimentWater

Floodplain Zone

Transition Zone

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.

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

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.

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.

Impacts of Human Activities on Freshwater Systems

These wetlands have been ditched and drained for cropland conversion.

Figure 6-19