Plant Life in the Open Ocean: Phytoplankton, Kelp, Sargassum, and Coral

Plant Life in the Open Ocean: Phytoplankton, Kelp, Sargassum, and Coral

The open ocean (pelagic zone) hosts diverse photosynthetic organisms, though true plants are limited to seagrasses (coastal). Key groups:

• Phytoplankton: Microscopic algae (diatoms, dinoflagellates, cyanobacteria); base of marine food web; produce ~50% of Earth's oxygen.
• Kelp (Phaeophyceae): Large brown algae; form underwater forests in cold, nutrient-rich temperate waters; up to 60 m tall.
• Sargassum: Pelagic brown algae; floats in vast mats in the Sargasso Sea (North Atlantic gyre); unique habitat for turtles, fish, crabs, eels.
• Corals (Anthozoa): Animals, not plants, but host symbiotic algae (zooxanthellae); build reefs in clear, shallow, tropical waters; biodiversity hotspots.

These organisms drive ocean productivity, carbon cycling, and habitat formation.