Flora and Fauna of the Ocean: A Survey of Marine Life

The ocean hosts an estimated 2.2 million species (91% undescribed). Life spans microscopic to massive, surface to hadal trench.

Ocean Flora (Primary Producers & Habitat Formers)

• Phytoplankton: Diatoms, dinoflagellates, cyanobacteria. Base of food web; 50% global O₂ production.
• Macroalgae (Seaweeds): Green (Chlorophyta), Brown (Phaeophyceae — kelp, Sargassum), Red (Rhodophyta). Forests, beds, drift.
• Seagrasses: Flowering plants (angiosperms) — 72 species. Meadows: nurseries, carbon sinks, stabilizers.
• Mangroves: Salt-tolerant trees (70 spp.). Tropical coasts. Nurseries, storm buffers, blue carbon.
• Corals: Cnidarians + zooxanthellae. Reef builders (25% marine spp. on <1% ocean floor).

Ocean Fauna (Consumers & Engineers)

• Zooplankton: Copepods, krill, larval forms. Primary consumers; biological pump.
• Fish (34,000+ spp.): Jawless (lampreys), cartilaginous (sharks, rays), bony (teleosts). All habitats.
• Marine Mammals: Cetaceans (whales, dolphins), pinnipeds (seals, sea lions), sirenians (manatees), mustelids (otters), polar bear.
• Sea Turtles: 7 species. Long-distance migrants.
• Cephalopods: Squid, octopus, cuttlefish, nautilus. Intelligent, rapid adaptation.
• Crustaceans: Crabs, lobsters, shrimp, krill, barnacles, copepods. Exoskeletons, diverse niches.
• Mollusks: Bivalves (clams, oysters), gastropods (snails, nudibranchs), cephalopods, chitons.
• Echinoderms: Sea stars, urchins, cucumbers, crinoids, brittle stars. Pentaradial, water vascular system.
• Cnidarians (non-coral): Jellies, anemones, hydroids, siphonophores.
• Sponges (Porifera): Basal animals; filter feeders, reef framework.
• Worms: Polychaetes, nematodes, flatworms, ribbon worms — abundant, diverse.

Vertical Zonation

• Epipelagic (0–200 m): Light, photosynthesis, highest biomass.
• Mesopelagic (200–1,000 m): Twilight; diel vertical migration (largest animal migration).
• Bathypelagic (1,000–4,000 m): Dark, cold, high pressure; "marine snow" feeders.
• Abyssopelagic (4,000–6,000 m): Abyssal plains; deposit feeders.
• Hadal (>6,000 m): Trenches; extremophiles.

Ocean life is interconnected, vertically and horizontally. Removing one group cascades through the web. We are part of that web.