Phytoplankton are microscopic sea creatures that stand at the bottom of the marine food chain produce oxygen, are a food source and may also be involved in rainfall.

The name of planet Earth is indeed given thanks to its dry portion of land, but if we look at the globe we know it is actually covered mainly in water. Oceans and seas cover 72 percent of the planet attributing to fertile and varied ecosystems, with only a small proportion being investigated. The basis for all life in the sea is phytoplankton (from Greek phyto = plant; plankton = tiny sea creatures) and micro-algae, a diverse group of single-celled organisms capable of performing photosynthesis. Phytoplankton are responsible for a significant portion of the oxygen we breathe, but its main role is for the existence of life at sea.

Although phytoplankton is not defined as a "plant", it is still able to perform photosynthesis. This remarkable process harnesses the sun's energy to use carbon dioxide (CO2) and water to form sugars - the basis for most food chains on Earth.

Food chains within the sea can be very short. Krill, for example, directly feed on the tiny phytoplankton and in turn are eaten by blue whales, which can reach a length of 30 meters. The individual phytoplankton cannot be seen without the aid of a microscope, but sometimes they form in such huge concentrations creating a giant-sized patch of hundreds of kilometers that can even be identified from space.

Spectacular shapes. Phytoplankton in bloom as seen from space. | Source: Wikipedia

The main product of photosynthesis is sugar, used in the construction of the cell, but it also has an important byproduct - atmospheric oxygen (O2). It is thought that the primary source of oxygen in the air is from plants on land, but a thorough examination reveals that half of the oxygen in the atmosphere actually comes from the sea, for which phytoplankton are primarily responsible. Thus phytoplankton allows the existence of life in the oceans, and out of them: as the main food producers in the oceans they are the solid basis for the marine food chain, and as oxygen producers they are contributing to life at sea and on land.

Phytoplankton can also affect climate. In the 80s, investigators hypothesized that the volatile molecules released by some of the phytoplankton species affect the formation of clouds over the sea. For example, some types of phytoplankton emit sulfur-based materials, apparently protecting them from aquatic viruses. These materials also attract their predators, however a scientific explanation has not yet been assigned to this mechanism. The researchers claim that these volatile substances can serve as nuclei that assist in condensation of water molecules, eventually developing into rain clouds. This hypothesis is controversial for which there is no definitive evidence.

Understanding the enormous significance of phytoplankton to life on Earth in recent years prompted many studies aimed at investigating whether climate change due to human activity may be harmful to phytoplankton populations. One example of this is the increase in acidity of water. Burning fuels like oil and coal releases huge quantities of carbon dioxide into the atmosphere, amounting to about nine billion tonnes per year. Much of it dissolves in the oceans lending to an increase in the acidity of the water. Many phytoplankton have limestone skeletons, which are highly sensitive to changes in water acidity, and studies have shown that a slight change in acidity may lead to a decrease in this type of phytoplankton species.

Other studies show that phytoplankton actually have great flexibility and easily adapt to changing environmental conditions. An example is the November 2015 study from the University of Exeter in England that showed the phytoplankton were able to adapt within 45 days to water with an increasing temperature.

In light of the dominant influence of phytoplankton in the oceans as well as life outside the ocean, and as the basis of many food chains, they should be given proper attention in any scenario that examines the human impact on climate change. Studies show these changes really can have very negative consequences on populations of phytoplankton, which will in turn affect all ecosystems that depend on them. On the other hand, the flexibility and their ability to survive, even under less favorable conditions, seems to leave enough room for hope.


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