Chapter 8 Aquatic Ecology
I. 8-1 Limiting Factors in Aquatic Environments
A. Two major types of aquatic life zones.
1. Saltwater or Marine (estuaries, coral reefs, coastlines)
2. Freshwater (ponds, lakes, streams)
Salinity - amount of various salts such as sodium chloride (NaCl)
dissolved in a given volume of water. (Types of organisms depend
on salinity of water)
B. Main Kinds of Organisms in Aquatic life zones
1. Plankton - weak swimming, free floating
a. 3 categories include phytoplankton, nanoplankton, zooplankton
i. phytoplankton primary producer for most food chains
ii. nanoplankton, recently discovered
ii. zooplankton, feed on phytoplankton
2. Nekton - strong swimming
a. fish,turtles, whales
3. Benthos - bottom dwelling
a. barnacles and oysters (stationary), lobsters move, these are
decomposers break down organic compounds in the dead bodies
and wastes of aquatic organisms.
C. Water’s Unique Properties
1. Fluctuations in temperature greatly reduce the risks of drying out or
becoming overheated or too cold.
2. nutrients are dissolved and readily available.
3. toxic metabolic wastes secreted by aquatic organisms are diluted and
dispersed.
D. 4 factors limit life at different depths in aquatic life zones.
1. Water temperature
a. temp falls with increase in depth, small changes in water
temperature can have a significant effect on the performance and
survival of aquatic organisms.
2. Access to sunlight for photosynthesis
a. Sunlight can only penetrate to a depth of 100 ft., thus
photosynthesis is confined mostly to this upper layer or
euphotic zone.
3. Dissolved oxygen content
a. Oxygen enters threw atmosphere and photosynthesis.
b. Near surface Oxygen levels are high b/c oxygen producing
organisms and photosynthesis. However, as one goes
deeper less light can penetrate and less photosynthesis takes
place. CO2 levels begin to increase b/c of aerobic respiration
by aquatic animals and decomposers.
4. Availability of nutrients
a. Phosphates are most limiting in freshwater
b. Nitrates are most limiting nutrient in saltwater ecosystem.
II. 8-2 Saltwater life zones
A. Why are the Oceans Important?
1. 71 % of earths surface
2. Help regulate the earth’s climate through evaporation (hydrologic cycle)
3. 250,000 known species of marine plants and animals.
4. Two major life zones (Coastal zone and Open Sea)
5. Coastal zone is the warm, nutrient-rich, shallow water that extends from the
high-tide mark on land to the gently sloping, shallows edge of the continental
shelf.
B. Estuaries and Tidal Ecosystems
1. Estuary - a partially enclosed area of coastal water where seawater mixes
with fresh water and nutrients from rivers, streams, and runoff from land.
a. constant water movement stirs up the nutrient-rich silt, making it
available to producers.
b. Temp. and salinity levels can vary b/c heavy rainfall, raising temps.
and lower salinity.
C. Coastal Wetlands
1. Coastal Wetlands - covered all or part of the year with salt water.
a. Breeding ground for waterfowl.
b. Help maintain quality of coastal waters by diluting, filtering, and
settling out sediments, excess nutrients, and pollutants. (KIDNEY FOR
CLAIRE)
2. About 3 % of wetland areas are coastal wetlands
a. grasses are dominant vegetation.
D. Mangrove Swamps
1. Mangrove swamps - area along warm tropical coasts that has to much silt to
produce coral reefs. (highly productive)
a. dominated by salt-tolerant trees or shrubs known as mangroves.
b. protects coastlines from hurricanes & breeding grounds for over
2000 species.
E. Rocky and Sandy Shores
1. Intertidal zone- area long shore-line between low and high tides.
a.Organisms here must be able to handle many different situations.
i. Heavy rain which changes salinity, to pounding surf
2. Rocky shores and barrier beaches both exist.
F. Barrier Islands and Coral Reefs
1. Barrier Islands - long, thin, low offshore islands of sediment that generally
run parallel to the shore.
a. islands protect the mainland from storms and erosion.
b. constant movement of sand from one place to another.
2. Coral Reefs form in clear warm coastal waters of the tropics and subtropics.
a. most biologically diverse life zones.
G. Impacts of humans in Coastal zones
1. Biggest problem is humans living in coastal areas.
a. 2025 estimated that 6.2 billion people live along coast.
b. Coastal ecosystems are vulnerable to toxic contamination b/c they
trap pesticides, heavy metals, and other pollutants.
c. Sewage treatment plants or septic tank systems big problem
2. Destruction of coral reefs
a. only 30% of coral reefs in world is stable.
H. What can be done about beach erosion?
1. Serious problem for gently sloping beaches and islands
2. sea level rising b/c of warmer climate has melted much ice and expanded
volume of seawater.
3. Several methods to prevent erosion
a. seawalls, breakwaters, importing sand, groins, jetties
4. Since 1965 US has spent over 3.5 billion on beach replenishing
5. Presently Flood insurance subsidies reduce risk of home owner and
protect them from $$$ loss.
I. Open Ocean and Biological Zones
1. Open Ocean - sharp increase in water depth at the edge of the continental
shelf separates the coastal zone from the open sea.
2. 3 vertical zones in open ocean
a. Euphotic zone where photosynthesis occurs in open sea.
i. 10% of marine species live here
ii. Nutrient levels low and dissolved oxygen high.
iii. Makes up 90% of ocean surface, it produces only about
10% of the world’s commercial fishing.
b. Bathyal zone and Abyssal Zone
i. dimly lit and completely dark
ii. no sunlight but have high levels of nutrients b/c dead and
decaying organisms fall to ocean floor.
iii. Deposit or Filter feeders take in water and nutrients and
extract it,
iv. Chemosynthesis to produce food (hydrothermal vents)
III. 8-3 Freshwater life zones
A. What are freshwater life zones?
1. dissolved salt concentration is less than 1%
2. Standing vs. flowing systems
a. Standing = lakes, ponds, inland wetlands
b. flowing = streams, rivers, creeks
3. Runoff provides freshwater for both standing and flowing systems.
B. What life zones are found in freshwater lakes?
1. Lakes fed by rainfall, melting snow, streams that drain into them.
2. 4 lake zones
a. littoral zone - most productive area in lake b/c abundant sunlight and
nutrients it gets from surrounding land.
i. high in biological diversity, large # of decomposers
b. limnetic zone- water surface layer away from shore and extends to
depth penetrated by sunlight.
c. profundal zone- deep open water where it is too dark for
photosynthesis. inhabited by fish adapted for cooler, darker waters.
d. benthic zone- inhabited by decomposers (bacteria, fungi)
C. How do plant nutrients affect lakes?
1. Oligotrophic lake (newly formed lake) Poorly nourished
a. small supply of plant nutrients and so it has low net primary
productivity. (typically blue to green)
b. low phytoplankton so low plant growth
2. Eutrophic lake (well-nourished)
a. sediment washes into oligotrophic lake and bottom sediment
begins to have more nutrients.
b. large populations of phytoplankton (typically brown or green in
color)
c. In summer some eutrophic lakes are depleted of dissolved oxygen
b/c plant growth is very rapid.
D. What seasonal changes occur in temperate lakes?
1. Water is densest as a liquid at 39degrees. (Ice Floats), this is good b/c
lakes would freeze from bottom up if not for water property.
2. Thermal Stratification - a lake becomes stratified into different temperature
layers that resist mixing b/c summer sunlight warms surface, making them less
dense.
a. Epiliminon - upper layer of warm water with high levels of dissolved
oxygen.
b. Hypoliminon - lower layer of colder, densewater usually with a
lower concenteration of dissolved oxygen b/c it is not exposed to
atmosphere.
c. Thermocline - middle layer, with water temps. change at a rapid rate
with increase in depth.
d. fall overturn - brings nutrients from bottom sediments to the surface
and sends dissolved oxygen from the surface to the bottom.
e. spring overturn - both the temperature of the lake and dissolved
oxygen levels are roughly the same at all depths.
E. What are the zones in Freshwater streams and rivers?
1. Surface water to Runoff to Watershed/drainage basin
a. runoff - when it flows into streams and eventually to the ocean as
part of the hydrologic cycle.
2. 3 river zones
a. Narrow zone (1st) - headwater or mountains highland streams of
cold, clear water rush over water-falls and rapids.
i. large amounts of oxygen dissolved from air.
ii. find cold water fish trout
b. Second Zone - headwater streams merge to form wider, deeper
streams that flow down gentler slopes with fewer obstacles.
i. warmer waters support more producers
c. Third Zone - streams join into wider and deeper rivers that meander
across broad, flat valleys.
i. Waters are often muddy b/c high concentration of
suspended particulate matter silt.
F. Why are freshwater inland wetlands important?
1. include marshes, prairie potholes, swamps, mud flats, floodplains, bogs,
wet meadows
2. Wetlands play an important role.
a. provide food for many species
b. improve water quality “nature’s kidney”
c. reduce flooding and erosion by absorbing stormwater
d. replenish groundwater
G. What impact do humans have on inland wetlands?
1. Most wetlands are lost to agriculture.
2. Federal Permits are now required to fill in wetlands
3. Mitigation banking - policy allows destruction of existing wetlands as long
as an equal area of the same type of wetland is created or restored.
8.4 Sustainability of aquatic ecosystems.
A. Why is an understanding of aquatic life zones important?
1. Everything is connected
B. How sustainable are aquatic ecosystems?
1. aquatic ecosystems are directly connected to everything upstream and
collect abuses from human activities and wetshed areas.
2. constantly renewed