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Unlock This CoursePhytoplankton are the tiny floating plants of the ocean that you can't see without a microscope. Despite their small size, they're absolutely vital to life on Earth. These microscopic organisms drift in the open ocean, using sunlight to make their own food through photosynthesis - just like plants on land. They form the foundation of nearly all marine food webs and produce over half of the oxygen we breathe!
The open ocean might look empty from the surface, but it's actually teeming with billions of these tiny organisms. They're so important that without them, most marine life would disappear and our planet's climate would be completely different.
Key Definitions:
Phytoplankton are like the grass of the ocean - they feed everything else! From tiny zooplankton to massive whales, most marine animals depend on phytoplankton either directly or indirectly. They're also climate heroes, absorbing carbon dioxide from the atmosphere and helping to regulate Earth's temperature.
There are thousands of different phytoplankton species, but they fall into several main groups. Each type has special features that help it survive in the open ocean's challenging conditions.
Diatoms are probably the most important phytoplankton in the ocean. They live inside beautiful glass-like shells called frustules, made of silica (the same material as glass). These shells come in amazing geometric patterns - some look like tiny pillboxes, others like delicate snowflakes.
Glass-like cell walls made of silica, arranged in two halves that fit together like a petri dish with a lid.
Thrive in cooler waters and areas rich in nutrients, especially where upwelling brings deep water to the surface.
Produce about 25% of all oxygen on Earth and form the base of food webs in polar and temperate oceans.
Unlike most phytoplankton that just drift with currents, dinoflagellates can actually swim! They have two whip-like tails called flagella that help them move through the water. Some can even hunt and eat other organisms as well as photosynthesise.
Many dinoflagellates can glow in the dark (bioluminescence). When disturbed, they create beautiful blue sparkles in the water. Some species can also form harmful algal blooms called "red tides" that can be toxic to marine life and humans.
These tiny organisms are covered in intricate chalk plates called coccoliths. They're incredibly small - you could fit 100 of them across the width of a human hair! Despite their size, they play a huge role in the ocean's chemistry.
The famous White Cliffs of Dover in England are made almost entirely from the remains of coccolithophores that lived millions of years ago. These tiny organisms literally built one of Britain's most iconic landmarks!
Cyanobacteria aren't true plants, but they photosynthesise just like other phytoplankton. They're some of the oldest life forms on Earth and were the first organisms to produce oxygen billions of years ago. In the open ocean, tiny cyanobacteria like Prochlorococcus are incredibly abundant.
Phytoplankton wear many hats in the ocean ecosystem. They're not just floating around aimlessly - they're working hard to keep our planet healthy and all ocean life fed.
As primary producers, phytoplankton convert sunlight into food energy that supports the entire marine food web. They're like underwater farms, constantly producing food that feeds everything from tiny copepods to enormous blue whales.
Transform solar energy into chemical energy through photosynthesis, creating the foundation of ocean food webs.
Support zooplankton, small fish and filter-feeding animals like krill, which then feed larger predators.
Produce 50-80% of Earth's oxygen and absorb massive amounts of carbon dioxide from the atmosphere.
Every second breath you take comes from phytoplankton! Through photosynthesis, they release oxygen as a waste product. The Amazon rainforest gets called "the lungs of the Earth," but phytoplankton actually produce much more oxygen than all land plants combined.
Phytoplankton are nature's carbon capture system. They absorb carbon dioxide from seawater (which comes from the atmosphere) and use it to build their bodies. When they die, some sink to the deep ocean, taking that carbon with them and storing it away from the atmosphere for hundreds or thousands of years.
Scientists estimate that phytoplankton remove about 2 billion tonnes of carbon from the atmosphere each year through the "biological pump." This process helps slow down climate change by reducing the amount of CO₂ in the air. In the Southern Ocean around Antarctica, massive blooms of diatoms are particularly important for carbon storage.
Phytoplankton don't grow everywhere equally. Like land plants, they need the right conditions to thrive. Understanding what controls their growth helps us predict where marine life will be most abundant.
Since phytoplankton photosynthesise, they need sunlight. They're mostly found in the euphotic zone - the top 100-200 metres of the ocean where enough light penetrates. Deeper than this, it's too dark for photosynthesis.
Just like garden plants need fertiliser, phytoplankton need nutrients to grow. The most important ones are nitrogen, phosphorus and silica (for diatoms). These nutrients often come from deep water that rises to the surface through upwelling.
Areas where deep, nutrient-rich water rises to the surface create some of the most productive regions in the ocean. The coasts of Peru, California and West Africa are famous upwelling zones that support huge phytoplankton blooms and rich fisheries.
Water temperature affects which types of phytoplankton can survive. Diatoms prefer cooler water, while some dinoflagellates like it warmer. Seasonal changes in temperature, light and nutrients cause phytoplankton blooms - massive population explosions that can turn the ocean green and feed countless marine animals.
Human activities are changing phytoplankton communities around the world. Some changes help them grow, while others harm them. Understanding these impacts is crucial for protecting ocean ecosystems.
As the ocean warms due to climate change, phytoplankton communities are shifting. Warmer water holds less nutrients and changes circulation patterns. Some species are moving towards the poles, while others are declining in abundance.
The ocean is becoming more acidic as it absorbs extra CO₂ from the atmosphere. This particularly affects coccolithophores and other phytoplankton that build shells or plates from calcium carbonate, as acid dissolves these structures.
Fertiliser runoff from farms can cause massive phytoplankton blooms near coasts. While this might sound good, these blooms can use up all the oxygen in the water when they die and decompose, creating "dead zones" where nothing can survive.
Every summer, fertiliser from farms along the Mississippi River creates a massive dead zone in the Gulf of Mexico. The extra nutrients cause huge phytoplankton blooms that consume all the oxygen when they decompose, killing fish, shrimp and other marine life across an area the size of Wales.
Scientists are working hard to understand how phytoplankton communities might change in the future and what this means for ocean ecosystems and our planet's climate. Protecting these tiny but mighty organisms is essential for maintaining healthy oceans and a stable climate.
Satellites can detect phytoplankton blooms from space by measuring ocean colour. Scientists also use research ships and underwater robots to study phytoplankton communities and track changes over time.