Marine phytoplankton consist of the microscopic algae that live in suspension in the surface waters of oceans. Most of them are single-celled organisms, but some form chains of several or many cells. Like terrestrial plants, phytoplankton organisms have the green pigment chlorophyll a, which is essential to photosynthesis. Phytoplankton can only be observed by means of a microscope; most of them are just a few micrometers (thousands of millimeters) in size.
Phytoplankton organisms are not all identical. They include numerous groups that are characterized by a variety of shapes and sizes, and play different roles in marine ecosystems. For example:
These organisms possess flagella and, more importantly, they are covered with microscopic plates made of limestone (calcite). When coccolithophores die, they shed their small calcite plates, which sink into the deep ocean when incorporated into heavier particles. They accumulate on the ocean floor for millions of years and form limestone, which is actually chalk!
Take a piece of chalk and put it in an acidic solution (lemon juice or vinegar): you should observe effervescence when chalk dissociates into carbon dioxide (CO2) and calcium (Ca). It is limestone!
As for terrestrial plants, phytoplankton organisms synthesize their own organic matter by utilizing sunlight, mineral substances (nutrients), carbon dioxide (CO2) dissolved in water, and water itself. This process is known as photosynthesis, and phytoplankton organisms are said to be "photo-autotrophic". On the opposite, animals are "heterotrophic". They use the organic matter of other organisms to make their own organic matter.
On land, plant growth is often water-limited. In the oceans, phytoplankton growth is more frequently light-limited. For this reason phytoplankton organisms develop preferentially in the surface layer of the oceans, where light is available. Nutrients are abundant in deep waters, from where they must be brought up to the surface by different physical mechanisms before being consumed by phytoplankton. In brief, phytoplankton find optimal growth conditions in surface waters when these are sufficiently sunlit and nutrient-rich.
Phytoplankton organisms form the basis of the food web (or trophic web) in the ocean, like plants in meadows and forests on land. The (photo)synthesis of organic matter by phytoplankton is called "primary production". This organic matter is consumed by zooplankton, which serve in turn as food for fish or marine mammals or shellfishes.
Through photosynthesis, phytoplankton produce large amounts of oxygen (O2), which dissolves in seawater. As the ocean continuously exchange gases with the atmosphere, part of the oxygen dissolved in seawater is released into the atmosphere. Hence, at least 50% of the oxygen we breathe come from phytoplankton organisms!
To build their own organic matter via photosynthesis, phytoplankton use atmospheric CO2 that is dissolved in seawater. This contributes to the "sequestration" of CO2 in the deep ocean, a process called by oceanographers "biological carbon pump". Globally on earth, marine phytoplankton organisms fix the same amount of CO2 as terrestrial plants. Hence, marine phytoplankton are as important to Planet Earth as meadows and forests. Without phytoplankton, the increase in temperature caused by human activities (greenhouse effect) would be much larger than it is today and the functioning of ecosystems, including human societies, would be strongly affected!
Some phytoplankton species are toxic, and may develop into large numbers under special circumstances. As shellfishes filter seawater, they may retain cells of toxic phytoplankton. For this reason, the marketing of mussels or oysters is sometimes forbidden, to prevents us from food poisoning caused by the accumulation of toxins in shellfishes.
Click on the image to start a quizz or game...
Quizz phytoplankton 
Memory phytoplankton
Marine phytoplankton consist of the microscopic algae that live in suspension in the surface waters of oceans. Most of them are single-celled organisms, but some form chains of several or many cells. Like terrestrial plants, phytoplankton organisms have the green pigment chlorophyll a, which is essential to photosynthesis. Phytoplankton can only be observed by means of a microscope; most of them are just a few micrometers (thousands of millimeters) in size.
Phytoplankton organisms are not all identical. They include numerous groups that are characterized by a variety of shapes and sizes, and play different roles in marine ecosystems. For example:
These organisms possess flagella and, more importantly, they are covered with microscopic plates made of limestone (calcite). When coccolithophores die, they shed their small calcite plates, which sink into the deep ocean when incorporated into heavier particles. They accumulate on the ocean floor for millions of years and form limestone, which is actually chalk!
Take a piece of chalk and put it in an acidic solution (lemon juice or vinegar): you should observe effervescence when chalk dissociates into carbon dioxide (CO2) and calcium (Ca). It is limestone!
As for terrestrial plants, phytoplankton organisms synthesize their own organic matter by utilizing sunlight, mineral substances (nutrients), carbon dioxide (CO2) dissolved in water, and water itself. This process is known as photosynthesis, and phytoplankton organisms are said to be "photo-autotrophic". On the opposite, animals are "heterotrophic". They use the organic matter of other organisms to make their own organic matter.
On land, plant growth is often water-limited. In the oceans, phytoplankton growth is more frequently light-limited. For this reason phytoplankton organisms develop preferentially in the surface layer of the oceans, where light is available. Nutrients are abundant in deep waters, from where they must be brought up to the surface by different physical mechanisms before being consumed by phytoplankton. In brief, phytoplankton find optimal growth conditions in surface waters when these are sufficiently sunlit and nutrient-rich.
Phytoplankton organisms form the basis of the food web (or trophic web) in the ocean, like plants in meadows and forests on land. The (photo)synthesis of organic matter by phytoplankton is called "primary production". This organic matter is consumed by zooplankton, which serve in turn as food for fish or marine mammals or shellfishes.
Through photosynthesis, phytoplankton produce large amounts of oxygen (O2), which dissolves in seawater. As the ocean continuously exchange gases with the atmosphere, part of the oxygen dissolved in seawater is released into the atmosphere. Hence, at least 50% of the oxygen we breathe come from phytoplankton organisms!
To build their own organic matter via photosynthesis, phytoplankton use atmospheric CO2 that is dissolved in seawater. This contributes to the "sequestration" of CO2 in the deep ocean, a process called by oceanographers "biological carbon pump". Globally on earth, marine phytoplankton organisms fix the same amount of CO2 as terrestrial plants. Hence, marine phytoplankton are as important to Planet Earth as meadows and forests. Without phytoplankton, the increase in temperature caused by human activities (greenhouse effect) would be much larger than it is today and the functioning of ecosystems, including human societies, would be strongly affected!
Some phytoplankton species are toxic, and may develop into large numbers under special circumstances. As shellfishes filter seawater, they may retain cells of toxic phytoplankton. For this reason, the marketing of mussels or oysters is sometimes forbidden, to prevents us from food poisoning caused by the accumulation of toxins in shellfishes.
Click on the image to start a quizz or game...
Quizz phytoplankton Memory phytoplankton
