Notes on Marine Microorganisms

Marine microorganisms (or marine microbes) are very small and simple. They are generally primary producers in marine environments.

Virus

• Considered nonliving because they are not composed of cell
• Virus consist of a nucleic acid protected by a capsid
• Capsid is an outer protein coat
• Viruses are small ranging from about 20 to 200 nanometers
• Viruses are parasites and they reproduce and develop only when they infect a living host cell
• In the seawater, viruses are common in deep-sea sediments
• Viruses can be sometimes responsible for diseases that affect marine organisms
• Viruses infect marine organisms such as bacteria and phytoplankton
• Viral infections can cause cells to lyse
• Some types of viruses
• Lysogenic viruses
• Retroviruses
• Bacteriophages

Bacteria

• Bacteria are unicellular and prokaryotic
• Some of the significant roles of bacteria
• Bacteria can be autotrophs and a source of food
• Cyanobacteria are photosynthetic bacteria
• Also known as blue-green algae
• Bacteria can be nitrogen fixers
• Some bacteria are components of detritus (dead organic matter particles)
• Decay bacteria break down dead organic matter and waste products, and they release the nutrient to the environment
• Some bacteria can produce blooms
• Some bacteria cause disease

Archaea

• Small, unicellular, prokaryotic cells
• However, evidence suggests that archaea are more closely related eukaryotes than bacteria
• Archaea live in extreme environments
• For example, they can be found in hydrothermal vents, very deep water, deep ocean basins (very salty environment)
• Some can also be found in not extreme environments, such as on sponges or even fishes
• Archaea can be autotrophs or heterotrophs

Diatoms

• Eukaryotic
• Unicellular
• The cell walls, or the shell, of diatoms contain silica.
• They are primary producers
• Some planktonic diatoms produce domoic acid, which is a toxin that accumulates in shellfish and certain fishes.

Dinoflagellates

• Eukaryotic
• Unicellular
• They have two flagella, and one of those flagella is wrapped around a groove located in the middle of the cell.
• Important contributions to the marine environment:
• They can perform photosynthesis (primary producers)
• They can sometimes form blooms, causing red tides and releasing toxic substances
• They can produce light, or bioluminescence
• A group of dinoflagellates called zooxanthellae form symbiotic relationships with other organisms such as corals.
• Some are parasites of marine animals and even seaweeds

Cryptophytes

• These are unicellular algae that are important primary producers.
• They are characterized by having two flagella and lacking a skeleton
• Other types of unicellular algae in the marine environment include silicoflagellates and coccolithophorids.

Foraminiferans

• Eukaryotic protozoans
• Unicellular
• Foraminiferans have shells containing calcium carbonate, which can be calcareous components of coral reefs and sandy beaches. It can also be components of calcareous sediments of the ocean floor.

Radiolarians

• Eukaryotic protozoans
• Unicellular
• These marine microorganisms have shells containing silica, which helps form siliceous sediments found on the ocean floor. 

Ciliates

• Eukaryotic protozoans that contain cilia used for feeding and movement
• Unicellular
• They can be found on the skins of fishes, the intestines of sea urchins, on seaweeds and in the bottom sediments.
• Planktonic ciliates are important for helping to facilitate the movement of energy from dissolved organic matter to bigger plankton organisms.

Fungi

• Fungi are eukaryotic
• Unicellular or multicellular
• They are heterotrophs
• They lack the structures chloroplast and chlorophyll, which prevents them from performing photosynthesis.
• They do have, however, cell walls.
• They are  mostly bottom-dwelling organisms
• They are very important for decomposing dropped mangrove leaves
• Some are parasites of fishes, sponges and seaweeds
• Some marine fungi are being researched in medicine
• Some fungi can live in symbiotic relationships with algae to form lichens.

Click here to learn more about fungi

End of Marine Microorganisms Notes

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