Phytoplankton

Food webs and food chains often have one bottom part, most often Phytoplankton. The reason for this is because phytoplankton provide food for a wide range of marine life. Also known as micro-algae, these microscopic organisms contain chlorophyll and require sunlight to live. This is why phytoplankton are buoyant and reside in the top layer of the ocean where sunlight is still accessible.

Flagella of a Dinoflagellate

There are two main class of phytoplankton: dinoflagellates and diatoms. Dinoflagellates have flagella that extend to help with movement. Their main body is covered in a complex shell. Diatoms also have shells, but theirs are more rigid and have interlocking parts. Diatoms don't rely on flagella like dinoflagellates do to move, instead they rely on ocean currents. 

Phytoplankton blooms

One category of phytoplankton includes single-celled algae known as protists. These forms include diatoms. When these organisms bloom rapidly, the explode in population in response to changing season and also due to nitrogen, iron, and phosphorous. 

Diatoms

There is a type of phytoplankton known as photosynthetic bacteria. This abundant algae is "invisible but present in numbers of hundreds of thousands of cells per tablespoon of ocean water" (WHOI, "Phytoplankton"). These unknown organisms weren't found until the 1970's, and until then weren't found to be responsible for over half the ocean's productivity and abundance. 

Phytoplankton are a critical organism that generate about half of the atmosphere's oxygen, they transform and recycle elements needed by other organisms. However, their dense blooms can deplete oxygen in water, causing fish to suffocate. Overall, phytoplankton are very important to marine life's homeostasis.

Works Cited

"Phytoplankton." Woods Hole Oceanographic Institution. Web. 01 Mar. 2016.

"What Are Phytoplankton? : Feature Articles." What Are Phytoplankton? : Feature Articles. Web. 01 Mar. 2016.

"What Are Phytoplankton?" What Are Phytoplankton? Web. 01 Mar. 2016.