Plankton are the organisms that drift with the currents rather than swim against them. Some are plants, some are animals, and most are microscopic. Together they form the first link in the marine food web and influence where larger animals choose to feed.
01
What plankton are
Plankton is a collective word for organisms that live in the water column and drift with the currents. The name comes from a Greek word meaning wanderer or drifter. It is not a single species or group but a category defined by behaviour: if an organism cannot swim strongly enough to move against the current, it is plankton.
The category includes tiny plants, tiny animals, the larvae of larger animals, and single-celled organisms. Some plankton are larger, such as jellyfish, which also drift. The word covers a wide range of life, from microscopic cells to creatures visible to the naked eye.
Plankton are found in all the world's seas, including the warm waters of the Maldives. They are most abundant in the upper layers of the ocean, where sunlight reaches, because the plant-like forms need light to grow.
02
Phytoplankton, the plant-like drifters
Phytoplankton are the plant-like plankton. They contain chlorophyll and photosynthesise, using sunlight and dissolved nutrients to grow. They include diatoms, dinoflagellates and other single-celled groups. Like land plants, they take up carbon dioxide and release oxygen.
Because they need light, phytoplankton are concentrated near the surface. Their growth depends on nutrients, which are often scarce in the clear surface waters of tropical seas. When nutrients are available, they can multiply quickly, forming blooms.
Phytoplankton are thought to produce a substantial share of the oxygen in the atmosphere, though estimates vary. They also form the base of the marine food web, since they are the primary producers that other organisms feed on.
03
Zooplankton, the animal drifters
Zooplankton are the animal plankton. Some feed directly on phytoplankton; others eat smaller zooplankton. The group includes tiny crustaceans such as copepods, krill and the larvae of fish, crabs and other animals. Many are grazers, cropping the phytoplankton that grow in sunlit water.
Zooplankton often migrate vertically, rising towards the surface at night to feed and sinking deeper by day, possibly to avoid predators. This daily movement is one of the largest migrations on the planet by biomass, though it is invisible from the surface.
Some zooplankton are the young stages of animals that will later settle on the reef or swim in open water. Fish larvae, for example, drift as plankton before they are strong enough to swim.
- Phytoplankton: plant-like, photosynthesise, need light and nutrients.
- Zooplankton: animal-like, feed on phytoplankton and on each other.
- Meroplankton: the temporary plankton, such as fish larvae and crab larvae.
04
The base of the food web
Plankton form the first link in the marine food web. Phytoplankton are eaten by zooplankton, which are in turn eaten by small fish, which are eaten by larger fish, and so on up to sharks, tuna and dolphins. Not every chain follows the same path, but the base is plankton.
For filter feeders, plankton is the direct food source. Manta rays, whale sharks and some other large animals strain plankton from the water. The presence of plankton-rich water can therefore attract these animals, though other factors such as temperature and currents also play a part.
In the Maldives, the link between plankton and larger animals is often noticed when manta rays gather to feed. The exact timing and location of these gatherings vary, and local dive centres can advise on current conditions.
05
Blooms, currents and upwelling
Plankton blooms occur when conditions allow rapid growth. This usually means a supply of nutrients and enough light. In the open ocean, nutrients often come from deeper water through upwelling, where currents bring cold, nutrient-rich water to the surface. Blooms can also follow mixing caused by storms or currents.
In atoll waters, currents and eddies can concentrate plankton. Where currents meet, or where water flows over a reef, plankton may gather. These concentrations can attract fish and other predators.
Blooms are not always visible, but they can affect water clarity. Nutrient-rich water may support more plankton, and this can reduce visibility for divers and snorkellers. The effect varies with the type of plankton and the amount of suspended material.
06
Oxygen and the wider picture
Phytoplankton release oxygen as a by-product of photosynthesis. A significant share of the oxygen produced on Earth is thought to come from marine phytoplankton, though estimates vary. This oxygen enters the atmosphere and the water, supporting life in the sea and on land.
Plankton also play a part in the carbon cycle. As they grow, they take up carbon dioxide. When they die or are eaten, some of that carbon can sink to the deeper ocean, where it may be stored for long periods. This process is part of what is called the biological carbon pump.
The exact scale of these processes is an active area of research, and figures are often revised. What is clear is that plankton are central to how the ocean works, from the air above the islands to the fish on the reef.
FAQ
Questions people ask
What are plankton and why do they matter in the Maldives?+
Plankton are drifting organisms, including plant-like phytoplankton and animal-like zooplankton. They form the base of the marine food web. In the Maldives, plankton-rich water can attract filter feeders such as manta rays and whale sharks, though other factors also influence where these animals gather. Local dive centres can advise on current conditions.
Are phytoplankton and zooplankton different?+
Yes. Phytoplankton are plant-like and photosynthesise, using sunlight and nutrients to grow. Zooplankton are animal-like and feed on phytoplankton or on other zooplankton. Both drift with the currents. Together they form the first two levels of the marine food web, supporting larger animals.
How does plankton support manta rays and whale sharks?+
Manta rays and whale sharks are filter feeders. They strain plankton from the water as they swim. Plankton-rich water can therefore attract them, but the exact link varies with species, season and currents. The Maldives has sites where these animals are seen regularly, and dive centres can advise on the best times.
Do plankton blooms affect water visibility in the Maldives?+
They can. Blooms may increase the amount of suspended material in the water, and nutrient-rich water can reduce clarity. The effect depends on the type of plankton and the amount present. Visibility can change quickly, so it is worth asking the dive centre or guesthouse about current conditions before a dive or snorkel trip.
What causes plankton blooms?+
Blooms occur when conditions allow rapid growth, usually a supply of nutrients and enough light. In the open ocean, nutrients often come from upwelling, where deeper water rises to the surface. Currents and eddies can also concentrate plankton. The timing and location of blooms vary and are not easily predicted.
Do plankton produce oxygen?+
Phytoplankton release oxygen as a by-product of photosynthesis. A significant share of the oxygen produced on Earth is thought to come from marine phytoplankton, though estimates vary. This oxygen enters the atmosphere and the water, supporting life in the sea and on land.
Can plankton be seen while snorkelling or diving in the Maldives?+
Most plankton are microscopic and not visible individually. However, large concentrations can make the water look cloudy or greenish. Some plankton, such as jellyfish, are visible. Snorkellers and divers may notice changes in water clarity. The effect varies with the type and amount of plankton present.
Is plankton the same as bioluminescence?+
No. Bioluminescence is the emission of light by living organisms, and some plankton are bioluminescent. Plankton is a broader category of drifting organisms. The two topics overlap where bioluminescent plankton occur, but plankton itself is not defined by light production. The Maldives has sites where bioluminescence can be seen.
How does plankton fit into the food web in Maldivian waters?+
Plankton form the base of the food web. Phytoplankton are eaten by zooplankton, which are eaten by small fish, and so on up to larger predators. Filter feeders such as manta rays and whale sharks feed directly on plankton. The exact links vary, but plankton underpin the productivity of the reef and open ocean.
