(MPA) Marine Plants & Algae Lesson

Marine Plants and Algae

Just like terrestrial organisms, marine organisms exist within complex food webs. The foundation for these food webs is the producers. Producers are organisms that are capable of producing organic compounds from inorganic compounds. In other words, the are the organisms that can make their own food. In marine ecosystems, the producers are phytoplankton, algae, grasses, mangroves, and chemoautotrophs.

Phytoplankton

Phytoplanktona are small unicellular plants that live in the ocean. Examples of phytoplankton are diatom and dinoflagellate. These organisms are the basis of the marine food chain. Diatoms and dinoflagellates take in inorganic material and produce organic material (food) and oxygen. In fact, 75% – 85 % of the organic matter and 80% of the oxygen found in the ocean is produced by phytoplankton! Phytoplankton are most productive where there is the most sunlight. Typically the temperate zones have the greatest oceanic productivity.

Diatoms

Diatoms are single celled yellow-green algae. The name for these organisms comes from the Greek word diatom which means "cut in two." This is because these organisms have a cell wall made up from silica with one half of the shell fitting over the other half like a lid over a box. Diatoms have different shapes, lines, and markings on their shells which distinguish them from one type and another. Their shape also allows them to float at the top of the water column to receive maximum sunlight. Some diatoms even use droplets of oil to help them stay afloat. Diatoms are also probably the single most important food source in the ocean. Diatoms are eaten by zooplankton, oysters, and clams.

Dinoflagellates

Dinoflagellates are both animal and plant like. They are like animals because they have flagella which allow them to swim like simple animals. But they are also like plants because they perform photosynthesis. Dinoflagellates are the number two producer in the marine environment. However, dinoflagellates can also cause environmental concerns. Two species of dinoflagellates, Gonyaulax and Gymnodinium are responsible for a condition known as red tide. Red tide is a surge of these dinoflagellates that may cause fish and shellfish kills. This surge may sometimes cause the water to look red giving this condition its characteristic name. At night this surge may also cause the water to glow in the dark. This is because some dinoflagellates are bioluminescent, which means they can produce their own light.

Algae are known as a species of nonvascular plants. They are nonvascular because they do not have roots, stems, leaves, or flowers. Algae can also be found as unicellular or multi-cellular organisms. There are several different types of algae found in the ocean. These different types of algae are distinguished by their methods of reproduction and location. For the sake of brevity, we will discuss benthic and pelagic algae. In fact, you have already learned about pelagic algae. Pelagic algae are phytoplankton! Remember, phytoplankton is free-floating unattached plants – specifically algae.

Benthic Algae

Benthic algae are divided into four major groups:  blue-green algae, green algae, red algae and brown algae. These divisions are characterized by their dominant colors and specific biochemistry.

Blue green algae is sometimes referred to as cyanobacteria because they are prokaryotic – meaning they have no membrane around their nucleus. However, these cells contain chlorophyll and are photosynthetic. Blue-green algae are found almost anywhere light and water is present, including fresh water.

Green algae are pretty uncommon in the ocean. Only 13 % of green algae are marine, but the green alga that is found in the ocean is large enough to be seen without a microscope. Green algae are most easily seen on the shore as grassy green filament.

There are more species of red algae than of brown and green algae combined. Red algae are red for more than good looks. The red pigments actually collect light under low conditions which allows them to grow at greater ocean depths. Red algae are also used commercially as food, for laboratory use and for cosmetics.

 

 

 

 

Brown algae are probably the most familiar form of algae. Brown algae is usually found as large seaweeds such as rockweed and kelp. Rockweed are the large slippery brown seaweeds that are found in dense beds along our coasts. They contain air bladders which help the plants float and stay close to the sun for light. Kelp is usually found in warmer waters and can be found in giant forests along the coast of California. On our coast, the kelp is much smaller. Kelp also has many commercial uses including dietary and medicinal uses.

 

 

 

 

Marine Grass

Marine grasses are true flowering plants with strong roots, stems leaves and flowers. On the coast of Georgia we would find Eelgrass and Turtle grass. These grasses are wholly submerged and provide a nursery ground for many invertebrates and fish. Eel grass, Zostera marina grows in sandy flats and inlets just below the low tide line. Turtle grass, Thalassia testidinum is the most abundant marine grass in the tropical waters of the West Atlantic. Turtle grass can grow in sand, mud, and broken shells in areas of clear calm water. Both grasses provide a habitat and food source for their particular environments.

Mangroves

Unlike marine grasses, mangroves grow only partially submerged in the salt water. They are however true flowering plants. They grow where its roots are flooded at high tide and use the roots and leaves to filter the salt from the water. Mangroves are not found in Georgia; they are limited to coastal Florida. But it is still important to include them in our study of marine plants. In Florida, there are three types of mangroves, the Red Mangrove, Black Mangrove and White mangrove. Each type of mangrove lives in a different environment and employs different adaptations to deal with the salinity of the environment.

Chemoautotrophs

Unlike the other producers discussed in this unit, chemoautotrophs do not use sunlight as an energy source. Chemoautotrophs are unique in the fact that they use energy from chemicals to make organic compounds. Most chemoautotrophs are bacteria or archaea that live in extreme or hostile environments. In the ocean, chemoautotrophs live near deep ocean vents and use the hydrogen, sulfur, methane, ammonia, or hydrogen sulfide available to make food. Because the sunlight does not reach the ocean floor, photoautotrophs, producers that use light, can not live deep within the ocean, so chemoautotrophs are the foundation for the food chain in the ocean depths.

Productivity

Because marine producers are the foundation for the oceanic food web, it is important to consider factors that may limit producer productivity. Photoautotrophs require water, carbon dioxide, inorganic nutrients, and sunlight. Chemoautotrophs require water, carbon dioxide and inorganic nutrients. Obviously, water is not a limiting factor in the ocean and because carbon dioxide is highly soluble in water, there are large amounts of CO2. So the greatest limiting factors for productivity are inorganic nutrients and sunlight. Upwellings are important to maintaining productivity as they cycle inorganic nutrients throughout the water. Sunlight is generally available, but only to certain depths. Most of the sunlight penetrates through the sunlit zone which only extends about 100 meters. After that point, very little photosynthesis takes place.

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