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: Larger 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.