Aquatic Ecology

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Aquatic Ecology
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Two Major Types of Aquatic Life Zones

• Saltwater or marine
• Estuaries, coastlines, coral reefs, coastal
  marshes, mangrove swamps, and oceans
• Freshwater
• Lakes and ponds, streams and rivers, and inland
  wetlands
• Determining Factor Salinity

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Major Types of Organisms

• Phytoplankton plant plankton
• Free-floating microscopic cyanobacteria and algae
• The producers and the basis of the food chain
• Zooplankton animal plankton
• Nonphotosynthetic herbivores that feed on
  phytoplankton
• Secondary consumers that feed on other
  zooplankton
• Range from single-celled protozoa to large
  invertebrates such as jellyfish.

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Larger Organisms

• Nekton
• Fish, turtles, and whales
• Benthos
• Bottom-dwellers barnacles oysters that anchor
  to one spot
• Worms burrow into sand or mud
• Lobsters and crabs walk on the bottom
• Some are filter-feeders
• Decomposers
• Bacteria that break down organic compounds

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Key Characteristics of Aquatic Organisms

• Less pronounced and fixed physical boundaries
  therefore difficult to count and manage
  populations
• More complex and longer food chains
• More difficult to monitor and study because of
  their size and they are hidden from view

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Limiting Factors

• Aquatic life zones are divided into three layers
  surface, middle, and bottom
• Factors are
• Temperature
• Access to sunlight for photosynthesis
• Dissolved oxygen (DO) content
• Availability of nutrients such as carbon (CO2),
  nitrogen (NO3), and phosphorus (PO4) for
  producers

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Dissolved Oxygen

• Photosynthesis can take place only as deep as
  light can penetrate (euphotic zone)
• Oxygen gets in from photosynthesis and diffusion
  for air and is removed by aerobic respiration
  (includes decomposition)
• O2 can vary greatly in aquatic ecosystems
• Most aquatic organisms cannot survive below 5 ppm
  of DO
• DO and CO2 concentrations vary with depth

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Saltwater Life Zones
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Coastal Zone

• Warm, nutrient-rich, shallow water that extends
  from the high tide mark to the margin of the
  continental shelf
• Makes up less than 10 of ocean but contains 90
  of all marine species and is especially important
  to commercial fisheries.
• Gets
• Sunlight and nutrients

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Other Coastal Ecosystems

• Estuaries a partially enclosed area where
  seawater mixes with fresh water
• An ecotone
• Coastal Wetlands covered by water all or part
  of the year
• river mouths, inlets, bays, sounds, mangrove
  swamps, and salt marshes
• Temperature and salinity vary widely
• Tides, seasonal variation in water flow,
  unpredictable flows after heavy rains and floods
• VERY PRODUCTIVE AREAS!

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Other Coastal Ecosystems

• Intertidal zone area of shoreline between high
  and low tides
• Very stressful zone for organisms
• Wave stress
• Immersed during high tides and dry during low
  tides
• Changing levels of salinity
• Organisms usually cling to something, dig or hide
  in shells.

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What are Barrier Islands?

• Barrier Islands
• Long, thin, low offshore islands of sedement that
  generally run parallel to shore
• Help protect mainland
• Constantly shift

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Coral reefs

• Form in clear, warm, coastal waters in tropics
  and subtropics
• Have many types of organisms
• Attached corals, algae, and sponges
• Fishes
• Small organisms that bore into or attach
  themselves to coral
• Easily damaged, grow slowly, can survive only in
  clear, shallow, warm water
• Have been harmed by global warming
• They face many threats from pollution and other
  human activities.

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Open Sea

• Beyond the continental shelf
• Euphotic zone lighted upper area
• Photosynthesis
• Low nutrient levels
• High DO
• Bathyl zone dimly lit middle zone
• No photosynthesis
• Abyssal zone dark lower zone
• Very cold
• Little DO
• Many nutrients

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Some Open Sea Organisms

• Deposit feeders
• Take mud into their bodies and extract nutrients
  from it
• Filter feeders
• Pass water through or over their bodies and
  extract nutrients from it
• Average primary productivity NPP are low.

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Freshwater Life Zones

• Found where water with a dissolved salt
  concentration of less than 1 by volume either
  accumulates or flows through the surfaces of
  terrestrial biomes.
• Standing water lakes, ponds, inland wetlands
• Flowing water streams and rivers
• Covers less than 1 of the earths surface but
  ecologically and economically important
• Are very closely connected to terrestrial biomes
  due to nutrient run-off

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Life zones

• Ponds shallow light often penetrates to the
  bottom usually have only one zone
• Lakes deeper generally consist of four zones
  defined by depth and distance from shore
• Littoral zone shallow water near shore where
  rooted plants grow
• Limnetic zone open sunlit water away from shore
  as deep as sunlight penetrates
• Profundal zone deep open water that receives no
  sunlight cool so although oxygen is low, some
  fish live here.
• Benthic zone bottom of lake cool temperatures
  and low oxygen

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Characteristics of Freshwater

• Surface water forms when precipitation that does
  not sink into the ground or evaporate becomes
  run-off
• Watershed the land area that delivers run-off,
  sediment, and dissolved substances to a stream.
• Streams join together to form rivers
• Rivers flow downhill to the ocean

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Eutrophication Natural Aging of a Lake

• Classify lakes according to nutrient content and
  primary productivity
• OLIGOTROPHIC LAKE low nutrients
• Geographically young
• Deep
• Blue in color
• Colder
• Low populations of phytoplankton
• More desirable fish bass and trout
• Low NPP

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Eutrophication Natural Aging of a Lake

• EUTROPHIC LAKE many nutrients
• Old lake
• Shallow
• Green or brown in color (algae)
• Warmer
• Algal blooms are common
• Less desirable types of fish catfish, carp
• High NPP

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Sunlight
Narrow littoral zone
Little shore vegetation
Low concentration of nutrients and plankton
Sparse fish population
Limnetic zone
Sleepily sloping shorelines
Profundal zone
Sand, gravel, rock bottom
Oligotrophic lake
Sunlight
Wide littoral zone
Much shore vegetation
High concentration of nutrients and plankton
Dense fish population
Limnetic zone
Gently sloping shorelines
Figure 7-21Page 158
Profundal zone
Silt, sand, clay bottom
Eutrophic lake
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SEASONAL CHANGES IN LAKES

• Occurs in temperate lake
• Makes use of the property of water that it is
  less dense as a solid (0oC) then it is at a
  liquid (4oC)therefore ice floats on water.
• This causes THERMAL STRATIFICATION of deep lakes

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Summer

• Lakes have three distinct layers
• EPILIMNION upper layer of warm water high
  levels of DO
• THERMOCLINE layer where the temperature changes
  with depth usually 1oC/meter increase in depth
  moderate oxygen during summer acts as a
  barrier between epilimnion and hypolimnion
• HYPOLIMNION bottom layer of cold, dense water
  low DO
• To keep cool fish would be at the bottom but low
  DO there

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Fall Overturn

• Water begins to cool, becomes more dense and
  sinks to the bottom
• The thermocline disappears
• Water mixes nutrients are carried to the top
  and oxygen to the bottom. Fish can be found at
  all depths

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Winter

• Lake separates into layers again due to
  difference in density.
• Warmest (4oC)water is at the bottom
• Thermocline is reversed
• Coldest water is at the top and freezes forming
  ice which insulates and protects the lake.

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Spring Overturn

• Water begins to warm up
• Wind blows causing vertical currents
• Lake overturns again bring nutrients to the top
  and oxygen to the bottom

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Other Freshwater Biomes

• Inland wetlands land covered with water all or
  part of the year located away from the ocean
• Marshes have a few trees
• Swamps dominated by trees and shrubs
• Prairie potholes depressions formed by glaciers
• Floodplains receive water during heavy rains or
  floods
• Bogs and fens waterlogged peaty areas

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