Phytoplankton - A Critical Link in a Big Chain

Last week, Reef Brief covered the global phenomenon of red tides. Red tides are composed of dinoflagellates, which are a type of phytoplankton (or plant) found in the sea. Most people have probably seen phytoplankton without even knowing it, witnessing the bioluminescent qualities that some of these tiny organisms have, shimmering in the water at night. These plants, however, have a much greater role in the sea and are considered critical to all life on Earth. Among other things, these tiny organisms (0.02 inches in diameter) greatly contribute to the food chain and are responsible for generating large amounts of oxygen through photosynthesis.

    Phytoplankton are tiny, drifting, plantlike organisms that are found throughout the world's oceans, but mostly along coasts. These tiny organisms come in every shape imaginable, but only under a microscope can the diversity and intricacy of phytoplankton truly be appreciated. Interestingly enough, some phytoplankton, known as diatoms, contain silica in their cell walls, which is the substance from which glass is formed.

Reef Brief is a weekly column published in the San Pedro Sun
    Aside from this fact, phytoplankton are responsible for producing the food that is consumed by an abundance of life in the sea. The general rule of the ocean food chain is that plants produce and animals consume, thus plants, such as phytoplankton, are the first link of the food chain. As the primary producers of the food chain, phytoplankton must be produced in great quantity_some estimate that between 200 and 250 billion metric tons are produced annually! An example of the role phytoplankton play in the ocean food chain is that zooplankton consume phytoplankton, then bivalves (mussels) consume the zooplankton, and cod consume the bivalves, and finally a top consumer, such as a killer whale, eats the cod.

    So, we know that phytoplankton produces food for many animals of the sea; but how is it produced? Four essential ingredients are necessary for phytoplankton to grow: water, sunlight, nutrients and carbon dioxide. When these factors are in balance, phytoplankton is able to thrive. Often because these tiny organisms are dependent on specific conditions to grow, they are used as an indicator for environmental problems. For example, in an area where pollutants are present, phytoplankton will likely be absent. Another important role that phytoplankton play in the environment is their ability to use photosynthesis to remove carbon dioxide from seawater and consequently release oxygen. Thus, the sea can absorb a lot of the carbon dioxide produced in the atmosphere, caused from activities such as deforestation and burning of fossil fuels. The reason why this is so important is that carbon dioxide is considered a green house gas, contributing to global warming, so the less we have in the atmosphere, the better. In addition, when phytoplankton (which is composed of carbon) dies, it also helps to control carbon dioxide levels in the atmosphere by sinking to the ocean bottom and being covered by other material. Thus, this harmful gas has no way of returning to the atmosphere.

    Phytoplankton may be microscopic in size, but they are certainly enormous in the roles they play throughout the ocean ecosystem.

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