Plant Life in the Indian Ocean: Seagrasses, Mangroves, Corals, Algae

The Indian Ocean hosts diverse **marine primary producers** across coastal and pelagic zones.

1. Seagrasses (Flowering Plants)

• Halophila ovalis, Halodule uninervis, Thalassia hemprichii, Syringodium isoetifolium.
• Shallow, sheltered sediments; nursery grounds, carbon sinks (blue carbon), dugong/turtle food.

2. Mangroves (Woody Halophytes)

• Rhizophora mucronata, Bruguiera gymnorhiza, Ceriops tagal.
• Intertidal zones; prop roots stabilise coast, filter runoff, nursery habitat.
• Sundarbans (Ganges-Brahmaputra delta) = world's largest mangrove forest.

3. Corals (Animals with Symbiotic Algae)

• Reef-builders: Acropora, Porites, Favia, Favites spp.
• Symbiotic zooxanthellae (dinoflagellates) provide photosynthate.
• High diversity in Coral Triangle (SE Asia), Chagos, Red Sea, Madagascar.

4. Macroalgae (Seaweeds)

• Sargassum: Pelagic mats (Sargasso Sea analogue in IO? — limited; mostly coastal).
• Turbinaria, Padina, Dictyota (brown); Caulerpa, Halimeda (green); Gracillaria, Hypnea (red).
• Food, habitat, agar/carrageenan source.

5. Microalgae (Phytoplankton)

• Diatoms (siliceous frustules) — dominant in upwelling zones (Arabian Sea, Somali Current).
• Dinoflagellates, Cyanobacteria (Trichodesmium) — N₂ fixation.
• Base of food web; oxygen production; carbon pump.

Biogeographic Zones

• Western IO: Upwelling-driven productivity (monsoon).
• Eastern IO: Coral Triangle spillover, high endemism.
• Southern IO: Subtropical convergence, deep chlorophyll max.

These primary producers underpin one of Earth's most productive and threatened marine realms.