Why are phytoplankton critical to life on earth

The more that scientists like Corradino understand how to protect these critical marine species, the more likely it is that their research will help creatures further up the food chain survive threats such as climate change. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

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Marine ecosystems contain a diverse array of living organisms and abiotic processes. From massive marine mammals like whales to the tiny krill that form the bottom of the food chain, all life in the ocean is interconnected. While the ocean seems vast and unending, it is, in fact, finite; as the climate continues to change, we are learning more about those limits. Explore these resources to teach students about marine organisms, their relationship with one another, and with their environment.

Students explore major marine ecosystems by locating them on maps. Students use marine examples to learn about energy transfer through food chains and food webs. They discuss how food webs can illustrate the health and resilience of an ecosystem.

The marine ecosystem is made up of a complicated series interconnected energy producers—like plants and photoplankton—and consumers—from plant-eaters to meat-eaters, both great and small. Some of this carbon is carried to the deep ocean when phytoplankton die, and some is transferred to different layers of the ocean as phytoplankton are eaten by other creatures, which themselves reproduce, generate waste, and die.

Phytoplankton are responsible for most of the transfer of carbon dioxide from the atmosphere to the ocean. Carbon dioxide is consumed during photosynthesis, and the carbon is incorporated in the phytoplankton, just as carbon is stored in the wood and leaves of a tree. Most of the carbon is returned to near-surface waters when phytoplankton are eaten or decompose, but some falls into the ocean depths. Even small changes in the growth of phytoplankton may affect atmospheric carbon dioxide concentrations, which would feed back to global surface temperatures.

Phytoplankton form the base of the aquatic food web. Phytoplankton samples can be taken directly from the water at permanent observation stations or from ships. Sampling devices include hoses and flasks to collect water samples, and sometimes, plankton are collected on filters dragged through the water behind a ship. Marine biologists use plankton nets to sample phytoplankton directly from the ocean.

Samples may be sealed and put on ice and transported for laboratory analysis, where researchers may be able to identify the phytoplankton collected down to the genus or even species level through microscopic investigation or genetic analysis. Although samples taken from the ocean are necessary for some studies, satellites are pivotal for global-scale studies of phytoplankton and their role in climate change.

Individual phytoplankton are tiny, but when they bloom by the billions, the high concentrations of chlorophyll and other light-catching pigments change the way the surface reflects light.

In natural-color satellite images top , phytoplankton appear as colorful swirls. Scientists use these observations to estimate chlorophyll concentration bottom in the water. These images show a bloom near Kamchatka on June 2, The water may turn greenish, reddish, or brownish. The chalky scales that cover coccolithophores color the water milky white or bright blue.

Scientists use these changes in ocean color to estimate chlorophyll concentration and the biomass of phytoplankton in the ocean. Phytoplankton thrive along coastlines and continental shelves, along the equator in the Pacific and Atlantic Oceans, and in high-latitude areas.

Winds play a strong role in the distribution of phytoplankton because they drive currents that cause deep water, loaded with nutrients, to be pulled up to the surface. These upwelling zones, including one along the equator maintained by the convergence of the easterly trade winds, and others along the western coasts of several continents, are among the most productive ocean ecosystems.

By contrast, phytoplankton are scarce in remote ocean gyres due to nutrient limitations. Phytoplankton are most abundant yellow, high chlorophyll in high latitudes and in upwelling zones along the equator and near coastlines. They are scarce in remote oceans dark blue , where nutrient levels are low. This map shows the average chlorophyll concentration in the global oceans from July —May View animation: small 5 MB large 18 MB.

Like plants on land, phytoplankton growth varies seasonally. In high latitudes, blooms peak in the spring and summer, when sunlight increases and the relentless mixing of the water by winter storms subsides. Recent research suggests the vigorous winter mixing sets the stage for explosive spring growth by bringing nutrients up from deeper waters into the sunlit layers at the surface and separating phytoplankton from their zooplankton predators. In the subtropical oceans, by contrast, phytoplankton populations drop off in summer.

As surface waters warm up through the summer, they become very buoyant. With warm, buoyant water on top and cold, dense water below, the water column doesn't mix easily. Phytoplankton use up the nutrients available, and growth falls off until winter storms kick-start mixing. In lower-latitude areas, including the Arabian Sea and the waters around Indonesia, seasonal blooms are often linked to monsoon-related changes in winds.

As the winds reverse direction offshore versus onshore , they alternately enhance or suppress upwelling, which changes nutrient concentrations. In the equatorial upwelling zone, there is very little seasonal change in phytoplankton productivity. In spring and summer, phytoplankton bloom at high latitudes and decline in subtropical latitudes. These maps show average chlorophyll concentration in May — left and November — right in the Pacific Ocean.

ENSO cycles are significant changes from typical sea surface temperatures, wind patterns, and rainfall in the Pacific Ocean along the equator. Compared to the ENSO-related changes in the productivity in the tropical Pacific, year-to-year differences in productivity in mid- and high latitudes are small. Because phytoplankton are so crucial to ocean biology and climate, any change in their productivity could have a significant influence on biodiversity, fisheries and the human food supply, and the pace of global warming.

Many models of ocean chemistry and biology predict that as the ocean surface warms in response to increasing atmospheric greenhouse gases, phytoplankton productivity will decline.

Productivity is expected to drop because as the surface waters warm, the water column becomes increasingly stratified ; there is less vertical mixing to recycle nutrients from deep waters back to the surface. Between late and mid, satellites observed that warmer-than-average temperatures red line led to below-average chlorophyll concentrations blue line in these areas.

There were 45 billion tonnes of new phytoplankton each year, 45 times more than their own mass at any given time. The phytoplankton would therefore have had to reproduce themselves entirely, on average, 45 times a year, or roughly once a week.

In contrast, the world's land plants have a total biomass of billion tonnes, much of it wood. The same calculations showed that the world's land plants reproduce themselves entirely once every ten years.

Phytoplankton have no roots, trunks or leaves. So what was happening to all the organic matter they were absorbing? Biologists considered two scenarios. In the first, all the phytoplankton in the sunlit top metres of the ocean would be consumed in that layer by heterotrophs, animals and certain microorganisms that break down the phytoplankton's organic matter to obtain energy and nutrients to build their own tissues. This process would produce carbon dioxide. The carbon dioxide would be instantly available to be taken up by other phytoplankton, which would use it and the Sun's energy to grow.

In this situation, carbon dioxide levels in the sunlit top layer of the ocean would be in a steady state, and none of the gas would be pumped to the deep ocean. In a second scenario, the dead bodies of phytoplankton and some of the faecal material and bodies of the heterotrophs would sink slowly below the top metres of the ocean.

In the dark, cold waters below, scavengers and microorganisms would break down all this organic matter into its chemical constituents. Because those cold, deep waters rarely mix with the warm upper waters floating above, carbon dioxide and other simple nutrients would be stored in the deep ocean.

A slow cycle of deep-ocean circulation would return this carbon dioxide-rich water to the surface centuries later, returning carbon dioxide to the atmosphere.

In this scenario, the upper layer would act as a biological pump, sending carbon dioxide to the deep sea for hundreds of years. In fact, both scenarios are occurring. Once there, about 0. When conditions are right in Earth's crust, the fossil phytoplankton are turned into oil over a period of several million years.

We have been using oil from fossil phytoplankton to fuel our cars and heat our homes for more than a century. Each year, we burn oil that took a million years to produce. This practice, along with our habit of burning fossil land plants in the form of coal, has pushed the atmospheric level of carbon dioxide to more than parts per million p.

The phytoplankton are still protecting us, however: if the phytoplankton in the upper ocean stopped pumping carbon down to the deep sea tomorrow, atmospheric levels of carbon dioxide would eventually rise by another p. Ominously, global warming has begun to slow down this phytoplankton-driven pump.

In a study I worked on that was led by Michael Behrenfeld, now at Oregon State University, researchers cross-checked satellite measurements of ocean chlorophyll with global climate measurements between and As the climate warmed between and , we found that the upper layer of the ocean got warmer. Water becomes less dense as it warms and is more likely to float without mixing with the cold, nutrient-rich waters below.

The warm top layer of these stratified waters therefore contained reduced nutrients, reduced phytoplankton growth, and diminished pumping to the deep sea. As our climate warms, we concluded, we can expect lower ocean carbon fixation in much of the world's oceans 4. If that happens, it will alter ecosystems, diminish fisheries, and leave more carbon dioxide in the atmosphere. In a slightly more encouraging vein, carbon fixation could accelerate at high latitudes, such as the North Pacific, as its frigid waters warm.

Phytoplankton are clearly essential for the global cycling of carbon and other elements, but they are not the only microorganisms in the sea.

How many other microorganisms are there in the oceans, and how are they making a living? For many years, no one knew how to address these questions. For scientists to study micro-organisms in depth, they needed to grow them in laboratory cultures, but they could culture only a very small fraction of the microorganisms they could see when they placed a drop of sea water under a microscope.

All that began to change in the s, when marine microbiologists started using molecular biology techniques to survey the ocean's microbial biodiversity. They isolated bulk DNA from all the microbes in various samples of sea water. Then they used a technique called the polymerase chain reaction that allowed them to study all the samples of the gene that produced 16S ribosomal RNA, which every microorganism uses to manufacture proteins.

Each variant 16S rRNA gene present indicated a different species of microorganism. These analyses typically revealed hundreds of microbial species in each sample of sea water. In the early s, biologists ramped up the biodiversity search using methods adapted from the human genome project.

By then, molecular biologists had developed powerful techniques and computational methods that let them clone, sequence and analyse DNA thousands of times faster than before. Craig Venter, a molecular biologist and entrepreneur who had founded Celera Genomics, had helped developed one of those methods, called shotgun sequencing. In shotgun sequencing, an organism's DNA is broken randomly into many small segments and sequenced.

Then a computer program finds regions of sequence overlap between the segments and uses them to stitch the segments together to reconstruct the original DNA sequence. Not long after his team from Celera Genomics reported the first human genome sequence in , Venter, an avid sailor, turned his attention to the sea. He sailed a research vessel to the Sargasso Sea, a well-studied area of the Atlantic Ocean off the coast of Bermuda, where his team collected hundreds of litres of sea water.

They filtered the microbes out, isolated their DNA en masse , and began shotgun sequencing them on an almost industrial scale. By determining the nucleotide sequence of more than 1. In other words, there were more than 47, species in just that one small area, and the microbial biodiversity in the open ocean was immense 5. What's more, the Sargasso Sea is one of the ocean's least biologically active areas.

Veter's study opened a door to large-scale genomics of the ocean itself, and by microbiologists had identified 20 million genes. This work has already found previously undiscovered forms of metabolism and new types of microorganisms. Many of these genes are essential for the survival of the microorganisms, but about 1, genes are especially important.

Some of these genes encode the proteins used in photosynthesis, which supplies the oxygen that keeps our atmosphere breathable and converts carbon dioxide to organic matter. Other genes encode enzymes that burn the organic matter with oxygen to create energy, returning the carbon dioxide and completing the cycle.

Some encode enzymes that convert elemental nitrogen from the air to ammonia, which organisms can use to build tissues.

Others encode enzymes that oxidize the nitrogen in the ammonia in several steps, regenerating the nitrogen. The enzymes encoded by these 1, genes do more than keep their organisms alive. Importantly, they oxidize and reduce the most abundant elements in organisms — hydrogen, nitrogen, sulphur, oxygen, carbon and phosphorus — allowing planetary-scale cycling that maintains an environment suitable to life as we know it.

The more we learn, the more questions we have. Some of the questions are in the realm of basic biology. What evolutionary processes maintained such an extraordinary diversity of microbial species? Have microorganisms that play key biogeochemical roles gone undiscovered? How did these essential reactions evolve, and when did they become ubiquitous enough to influence the land, the oceans and the atmosphere worldwide?

Then there are the practical questions. As humanity pumps nitrogen into the oceans and carbon into the atmosphere, causing dead zones and disrupting the climate, how long can phytoplankton keep cleaning up our mess? Can we enlist phytoplankton genes to make hydrocarbons so we no longer have to drill for oil? Can we use other genes to help us harvest energy from the Sun?