Chapter 6

• Theory of symbiosis


  A theory holds that organelles such as chloroplasts and mitochondria were independent prokaryotes, which were later incorporated into eukaryotes
• Some species depend on fresh water for all stages of their life cycles
• Groups of freshwater animals

  • One group of marine origin - primary aquatic animals
  • A second group of terrestrial origin: Terrestrial systems and then colonized fresh water
• Biodiversity


  The variability of living organisms (marine, freshwater and land) and the ecological complexes to which they belong
• Factors influencing the distribution of aquatic organisms

  • Variations in salinity of estuaries
  • Alterations in the substratum in rivers
  • Gradients of conductivity in rivers and reservoirs (both horizontal and vertical)
  • Periods of drought and temporary desiccation of rivers and lakes
  • Intensity of underwater radiation
  • Horizontal and vertical gradients of dissolved oxygen
• Biotic factors

  • Exclusive competition
  • Effects of predation
  • Parasitism
  • Production of inhibitory substances
  • Chemical interactions between species, populations and communities
• Organisms and communities play an essential role in the operational processes of rivers, lakes, reservoirs and wetlands
• Dispersal


  Movement of particles of wind-blown dust, insects, birds, aquatic mammals, reptiles, amphibians and fish that carry algae, larvae and fish eggs, protozoa, eggs and resistant forms of aquatic organisms
• Extinctions of species result from human pressure and the introduction of exotic species
• Isolation in many aquatic ecosystems has resulted in speciation in mollusc, ostracod, Trichoptera and fish species
• Heterotrophic bacteria

  • Decompose organic matter in rivers and lakes and provide food for scavengers
• Chemolithotrophic bacteria


  • Responsible for the oxidation of Fe2 to Fe3, the oxidation of ammonia to nitrite and nitrate, and Hydrogen Sulfide to Sulfate
• Photosynthetic bacteria


  • Use H2S and CO2 as substrates
• Free-living bacteria that fix nitrogen have been identified in various inland aquatic environments
• Coliforms develop in the digestive tract of animals
• Aquatic fungi act as parasites or saprophytes that use organic matter for growth
• Freshwater sponges (Porifera) are important environmental indicators
• Rotifers

  Important component of zooplankton in lakes and reservoirs with short retention time
• Used to classify rotifers

  • Trophi (Structures)
  • Lorica (Cuticle)
• Crustaceans play an important role in the structure and function of lakes, rivers, reservoirs, estuaries and marine waters
• Fish are part of the nektonic (free-swimming) community and are economically, evolutionarily and ecologically important
• Types of diadromous fish

  • Anadromous - reproduce in fresh waters and live in marine waters, such as salmon
  • Catadromous - Breed in marine waters and live in fresh waters, such as the eel family Anguillidae
• Aquatic communities


  • Located in different regions and substrata
  • In open water or supported by different structures
• Plankton


  Inhabits open waters with limited capacity of locomotion and with systems that enable permanent or limited buoyancy
• Autotrophic and heterotrophic components of plankton

  • Phytoplankton
  • Zooplankton
• Benthos


  The communities distributed on the surface of sediment and sediment/water interface
• Main groups of benthic invertebrates

  • Insects
  • Annelids
  • Molluscs
  • Crustaceans
• Benthic fauna is a good indicator of the trophic conditions and degree of contamination of rivers and lakes
• Chironomus larvae resist low concentrations of dissolved oxygen
• Main features of macrophyte vegetation

  • Emergent macrophytes: produce aerial reproductive organs, are located in shallow regions (1.5 m of water)
  • Macrophytes with floating leaves: chiefly angiosperms occurring in regions with depths of 0.5 to 3.0 m
  • Submerged macrophytes: occur at all depths in the euphotic zone, but as angiosperms are limited to 10 m (1 atm of pressure)
  • Floating macrophytes: a group without roots in the substratum, which float freely, with various forms
• Migratory organisms

  • Neuston - In air-water interface (live at the surface of a body of water). Insect (water strider, whirligig beetles)
  • Tetoplankton - Organisms located at the bottom or on other organisms
  • Herpon - Microscopic organisms with slow sliding movement on the bottom
  • Plankton - Migratory organisms with low capacity for locomotion
• Organisms on Fixed Surface

  • Pecton - Organisms that live on a compact substratum, forming fine covers
  • Plocon - Filamented organisms that may become detached from their base with their mass at some distance from the base
  • Periphyton or Haptobenthos - Organisms that form masses several millimeters in height, generally on macrophytes, rocks and sediment
• Migratory with roots or with roots suspended in water

  • Pleuston - Floating plants
  • Megalopleuston - Plants submerged below the surface with no roots, often resting on the bottom
• Fixed on a substratum

  • Haptophytes - Plants with roots fixed on substratum, adapted to live in very intense running water
  • Rhizophytes - Submerged rooted plants in sediment