4.3A Phytoplankton and macrophhytes Notes

Phytoplankton

1. Phytoplankton are microscopic, photosynthetic organisms suspended in the upper, sunlit layers of oceans, seas, and freshwater bodies (the euphotic zone).
2. They are autotrophic, meaning they use sunlight, carbon dioxide, and dissolved nutrients to produce organic compounds through photosynthesis.
3. Although they make up only ~1% of global plant biomass, they perform nearly 50% of global photosynthesis and are responsible for half of Earth’s oxygen production.
4. Belong to diverse groups including:
   1. Diatoms: single-celled algae with silica shells.
   2. Dinoflagellates: some bioluminescent, others symbiotic or toxic.
   3. Cyanobacteria (blue-green algae): photosynthetic bacteria, not true algae.

Ecological and Global Importance of Phytoplankton

1. Form the base of marine food webs, feeding zooplankton, fish larvae, and filter feeders.
2. Influence global climate regulation by removing CO₂ from the atmosphere.
3. Support commercial fisheries indirectly through higher trophic levels.
4. Cause seasonal blooms, visible from space, which drive oceanic productivity patterns.

Phytoplankton in Food Webs

1. Producers: Capture sunlight to create organic matter.
2. Primary consumers (zooplankton): Feed on phytoplankton.
3. Secondary consumers: Small fish and crustaceans feeding on zooplankton.
4. Tertiary consumers: Lar[Image]ger fish, seabirds, and marine mammals.
5. Decomposers: Bacteria recycle organic material back into nutrients for producers.

Macrophytes

1. Macrophytes are large aquatic plants visible to the naked eye, found in both freshwater and marine environments.
2. Unlike microscopic phytoplankton, macrophytes are rooted or floating, with structures similar to terrestrial plants.
3. They play a vital role in oxygen production, habitat formation, and water purification.

Types of Macrophytes

1. Emergent Plants: Grow with roots in water but leaves above the surface (e.g., cattails, reeds).
2. Submerged Plants: Grow entirely underwater (e.g., eelgrass, pondweed).
3. Floating Plants: Float on the water's surface (e.g., water lilies, duckweed).

Ecological Roles of Macrophytes

1. Primary Production: Convert solar energy into organic biomass for herbivores.
2. Habitat and Shelter: Support invertebrates, fish, and microbial communities.
3. Nutrient Cycling: Absorb nitrates and phosphates, reducing eutrophication.
4. Sediment Stabilization: Reduce erosion by slowing water velocity.
5. Water Purification: Trap pollutants and heavy metals through uptake.

Energy Flow in Aquatic Food Webs

1. Producers: Phytoplankton and macrophytes harness solar energy.
2. Primary Consumers: Zooplankton, small fish, and filter-feeding invertebrates.
3. Secondary Consumers: Larger fish, amphibians, and aquatic birds.
4. Tertiary Consumers: Apex predators such as sharks, seals, or raptors.
5. Decomposers: Bacteria and fungi recycle organic matter, releasing nutrients for reuse.