Marine life
What are plankton and phytoplankton? The Pacific's invisible engine
Almost everything you see on a marine expedition — from sardines to whales — depends, somewhere along the chain, on organisms too small to see with the naked eye.
What is plankton?
Plankton includes all organisms that float or swim weakly in the water, without enough strength to move against currents. According to NOAA, it is mainly divided into two large groups: phytoplankton, microscopic plant-like organisms that photosynthesize, and zooplankton, animal-like organisms ranging from copepods and krill to fish and crab larvae.
Phytoplankton, an oxygen factory
Phytoplankton is not just food — it also produces oxygen. NOAA estimates that roughly half of the oxygen produced on the planet comes from the ocean, much of it thanks to these microscopic organisms.
The base of the Pacific food chain
Zooplankton feeds mainly on phytoplankton, and in turn becomes food for small fish such as sardines. Those fish support larger predators — sea lions, marlin, seabirds — in phenomena like the sardine run off Baja California Sur. NOAA notes that a shift in the timing or amount of available phytoplankton can quickly affect zooplankton, and from there, the whole chain.
Why there is so much life off Baja California Sur
The Pacific coast of the peninsula benefits from coastal upwelling: winds and currents that push cold, deep, nutrient-rich water up to the surface. Those conditions favor phytoplankton growth, which in turn supports everything that follows in the chain.
Invisible but essential
Next time a trip shows you a school of sardines, a bait ball, or even a feeding whale, it is worth remembering that the scene began long before, with organisms you can never actually see from the boat.
References to keep exploring
- NOAA, National Ocean Service · What is Plankton?
- NOAA, National Ocean Service · What is Phytoplankton?
- NOAA, National Ocean Service · How much oxygen comes from the ocean?
Sources accessed on November 8, 2026. Editorial text by Con Gorra Expeditions.
