Aquatic Biomes - Comprehensive Notes

Aquatic Biomes

Reminders and Announcements

  • Finish Chapter 24 on Aquatic biomes.
  • Lecture assignment 9 and makeup lecture assignment are due Friday.
  • Issue with images in assignment 9 has been resolved.
  • Final exam is on Thursday, May 8 at 2:00pm.
  • One lab assignment remains, so do a careful job!

Distribution of Aquatic Organisms

  • Communities of plants, algae, and animals are distributed according to several factors:
    • Photic zone: The region where light is available for photosynthesis.
    • Benthic realm: The bottom region of an aquatic biome.
    • Aphotic zone: The depth of water where light is insufficient for photosynthesis.
    • Depth of water.
    • Distance from shore.
  • Ponds and lakes may be stratified both horizontally and vertically.

Horizontal and Vertical Stratification

Vertical Stratification:

  • Photic zone: Light is available for photosynthesis.
  • Profundal zone (aphotic zone): Beyond the depth of effective light penetration.
  • Benthic zone: Bottom region that is the primary place of decomposition.

Horizontal Stratification:

  • Littoral zone: Shallow-water zone in which light reaches the benthic zone.
  • Limnetic zone: Open water in the photic region.
  • Plankton: Includes phytoplankton (photosynthetic algae and bacteria) and zooplankton (small animals that feed on phytoplankton).
  • Nekton: Free-swimming animals, such as fish.

Limnetic Zone

  • Phytoplankton and zooplankton dominate the limnetic zone.
  • Fish comprise most of the nekton in the limnetic zone.
  • Distribution of fish is influenced by food supply, oxygen, and temperatures.

Benthic Realm in Lakes and Ponds

  • The benthic realm is:
    • At the bottom of all aquatic biomes.
    • Made up of sand and organic & inorganic sediments.
    • Occupied by communities of organisms that may include algae, aquatic plants, worms, insect larvae, molluscs, and microorganisms.
  • Dead material that “rains” down from the productive surface waters of the photic zone is a major source of food for animals of the benthic realm.

Lake Types

  • Eutrophic Lake: Has a high surface-to-volume ratio and is often surrounded by nutrient-rich deciduous forest and/or farmland.
  • Oligotrophic Lake: Has a low surface-to-volume ratio, and the water receives little nutrient input.
  • Dystrophic Lake: Receives large amounts of organic matter from the surrounding land.

Stream Characteristics

  • Current velocity is affected by:
    • Shape and steepness (width, depth, bottom roughness).
    • Intensity of rainfall or rapidity of snowmelt.
  • As the gradient decreases, the width, depth, and volume of water increase.
  • Two habitat types:
    1. Turbulent riffle: Sites of primary production in a stream.
    2. Quiet pool: Current velocity slows enough for organic matter to settle; sites of decomposition and production of carbon dioxide.

Watersheds and Stream Order

  • Watershed: All the land that drains into a given body of water.
  • Near the source of a stream, the water is usually: cold, low in nutrients, and clear.
  • Downstream, the water is usually: warmer, murkier, wider, and slower.
  • Stream order:
    • Headwater streams (first to third order).
    • Medium-sized creeks and streams (fourth through sixth order).
    • Rivers are orders greater than 6.

Streamflow

  • The ecology of a stream ecosystem is determined largely by its streamflow, which is the water discharge occurring in the natural channel.
  • The rate at which water flows through the stream channel influences:
    • Water temperature.
    • Oxygen content.
    • Rate of nutrient spiraling.
    • Physical structure of the benthic environment.
    • Organisms living in the stream.

Stream Life Adaptations

  • Animals in fast-water streams require high {O_2}.
  • High stream velocity adaptations:
    • Stream-lined form and flattened and broad body shape.
    • Protective cases.
    • Sticky undersurfaces.
  • Low stream velocity adaptations:
    • Larger gills.
    • Air breathing.
    • Surface swimming.
    • Burrowing.

Aquatic Invertebrate Feeding Groups

  • Gougers: Burrow into waterlogged limbs and trunks of fallen trees.
  • Grazers: Feed on the algal coating of substrates.
  • Shredders: Feed on organic material and its decomposers.
  • Collectors: Feed on particulate organic matter produced by shredders.

Stream Order and Width

  • The diagram illustrates the relationship between stream order and width, as well as the import of FPOM (Fine Particulate Organic Matter) at different stream orders.

Estuaries

  • Transition between river and ocean.
  • Variable salinity (brackish).
  • Most productive ecosystem on Earth.
  • Nutrients and {O_2} are carried into the estuary by tides.
  • Nursery ground for shrimp, scallops.
  • The aquatic biomes are NOT a limitless resource!

Marine Biomes

  • Benthic zone: Bottom region of the ocean.
  • Pelagic zone: Whole body of water.
    • Neritic province: Water that overlies the continental shelf.
    • Oceanic province: Water that overlies the abyssal plane.

Living in the Pelagic Zone

  • Dominant autotrophs are phytoplankton.
  • Major herbivores are zooplankton.
  • Phytoplankton: Photosynthetic protists (e.g., diatoms, dinoflagellates).
  • Zooplankton: Small herbivore animals (0.5 – 5.0 mm) that feed on protists (e.g., copepods, small shrimp/krill).
  • Nanoplankton: Bacteria (heterotrophic and cyanobacteria).

Benthos

  • Animals that inhabit the deep water have special adaptations for securing food:
    • Luminescent lures.
    • Mimicry of prey.
    • Extendable jaws.
    • Expandable abdomens.
  • Two-thirds of mesopelagic species are bioluminescent.

Coral Reefs

  • Occur in the photic zone of warm tropical waters.
  • Water temperature and salinity are high, and CO_2 is low.
  • Corals = complex, modular, cnidarians that secrete a hard external skeleton.
  • Symbiotic relationship with zooxanthellae (photosynthetic algae).

Types of Coral Reefs

  • Fringing reefs: grow seaward from the rocky shores of islands and continents.
  • Barrier reefs: parallel shorelines of continents and islands and are separated from land by shallow lagoons.
  • Atolls: are rings of coral reefs and islands surrounding a lagoon, formed when a volcanic mountain subsides beneath the water’s surface.

Productivity in the Oceans

  • Limited by photic region size.
  • Thermocline prevents nutrient movement from the deeper to surface waters.
  • Movement of nutrients is determined by:
    • Seasonal breakdown of the thermocline and subsequent turnover.
    • Upwelling of deeper nutrient-rich waters to the surface.
  • Coastal regions exhibit the highest productivity.