Aquatic Food Webs (DP IB Environmental Systems & Societies (ESS))

Aquatic Food Webs

• Aquatic food webs show how energy and nutrients move through freshwater and marine ecosystems

Phytoplankton

• Phytoplankton are microscopic organisms found in marine and fresh water bodies that can perform photosynthesis

  • Phytoplankton are not plants

  • They include a variety of autotrophic microorganisms, such as:

    • Algae (e.g. diatoms)

    • Cyanobacteria (prokaryotic organisms that are also known as blue-green algae)

• Role in food webs:

  • They form the base of most aquatic food webs

  • They capture solar energy and convert it into biomass through photosynthesis

  • They are consumed by primary consumers (zooplankton and small fish)

  • They contribute to oxygen production and nutrient cycling

Macrophytes

• Macrophytes are aquatic plants that are visible to the naked eye

• They can be:

  • Emergent: plants that grow above the water surface (e.g. cattails or bulrushes)

  • Submerged: plants that grow completely underwater (e.g. seagrass)

  • Floating: plants that float on the water surface (e.g. water lilies or duckweed)

• Role in food webs:

  • They provide habitat and food for various aquatic organisms

  • They capture solar energy and convert it into biomass through photosynthesis

  • They contribute to oxygen production and nutrient cycling

Energy flow in aquatic food webs

• Producers: phytoplankton and macrophytes capture energy from sunlight through photosynthesis

• Primary consumers: zooplankton, small fish and some invertebrates and birds feed on primary producers

• Secondary consumers: larger fish and birds consume primary consumers

• Tertiary consumers: top predators like sharks and birds of prey eat secondary consumers

• Decomposers: aquatic bacteria and fungi break down dead organisms, recycling nutrients back into the ecosystem