Phytoplankton 

Plankton is a general term for both phytoplankton and zooplankton, which are passively floating and some weakly swimming animal-like and plant-like organisms that are moved with the currents. Phytoplankton are the plant-like division of planktonic organisms. Phytoplankton are the energy for all of life in the underworld. This is because most phytoplankton photosynthesize, changing light energy from the sun into energy that all non-photosynthesizing organisms (including us) can use. Phytoplankton are at the bottom of the food chain in the aquatic ecosystem. In most cases they are eaten by very small animal-like organisms called zooplankton.

Zooplankton are animal-like division of plankton and are heterotrophic. Invertebrate and fish larvae make up the biggest type of zooplankton. Zooplankton are consumed by yet larger animals, who are consumed by yet larger animals. However, sometimes large animals directly depend on these thin plankton. For example, the filter-feeding whale feeds on these microscopic organisms as its only food source!!

Most phytoplankton are autotrophic, meaning they photosynthesize and create their own food source (although some can be heterotrophic, which means they must consume autotrophic organisms for energy.) Phytoplankton are considered "plant-like" instead of considered plants because while they can photosynthesize, they are usually single-celled, meaning they are not as structurally complex as plants.

The phytoplankton you will view on this page are very small. This cube is about one cubic centimeter, which can contain hundreds of thousands of phytoplankton during a bloom.

While phytoplankton are one-celled organisms, they are extremely diverse in size, shape and color, which makes them interesting to view through a microscope. The same species of phytoplankton can actually look different depending upon the perspective you are viewing the organism from. Both of the organism below are diatoms of the same species from different points of view! The picture on the left is the frontal view, or the valve view, while the photograph on the right shows a side view of the diatom, or the girdle view.

All the phytoplankton you will view on this page were found in the Rhode River estuary, a tributary of the Chesapeake Bay. Water samples collected from the area were preserved in order to identify and photograph the organisms. This is necessary because live phytoplankton can be slightly mobile, making them hard to see! The preservative kills and stains the organisms. It also highlights the living cells in the sample. The sample is cleared of the stain as much as possible before viewing. The background color you see in these photographs is actually a result of the color-enhanced film used to photograph the cells.

In field samples, much of what you view though a microscope field is detritus, which can include parts of dead organisms, particulate matter, animal feces and broken seagrass particles. See if you can identify the phytoplankton being photographed in each of the following pictures.

Phytoplankton of the Rhode River Estuary

Different species are found in different seasons mainly due to changes in salinity, nutrients, light and temperature which accompany the changing seasons.

This is a diatom that is usually present in the Rhode River estuary in the summer. Diatoms are single-celled phytoplankton that can be found in both marine and fresh waters. This species is larger than most other diatoms.    

  

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