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.
Plankton can grow to depths of 120 meters if light is available!
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 species mainly found in the summer. It is a dinoflagellate.
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.
These phytoplankton are diatoms.
This is a common summer species
This is a winter species; it is also
Zooplankton, the animal form of plankton, includes protozoa, small crustaceans, jellyfish and worms. Protozoa are single celled organisms that can colonize; they can live in oceans, salt lakes, freshwater lakes, rivers and ponds and vary in size for two to seventy micrometers and even larger. Crustaceans are invertebrates that live in water as well as on land and can vary from microscopic to sixty centimeters. Zooplanktons main sustenance are bacteria and phytoplankton,making them the second link in the food chain (Vegas).
|Zooplankton feed off of Phytoplankton, making them the second link in the marine food chain. Zooplankton then get eaten by krill, fish and larger crustaceans. To find out more about the role zooplankton plays in our food chain, head over to page. picture from octopus.gma.org/onlocation/ zooplankton.gif|
In order for the zooplankton to have easy access to their food source, they need to be located near the phytoplankton. Because phytoplankton needs to have access to sunlight to photosynthesize, they must be near the surface of the water. Zoplankton also need iron in their diet. So, that is also where zooplankton can be found; the top 100 meters of the water to be exact. Just like phytoplankton, zooplankton can’t swim; instead they just float along with the currents, tides and and winds. The difference between the movement of phytoplankton and zooplankton is that zooplankton can often weight too much to just float along, like the phytoplankton, so they use spikes for weight distribution (Microsoft Encarta Encyclopedia).
Research has been done that could prove plankton itself is a good food source for humans. This idea can be credited to a Norwegian scientist and writer, Thor Hayerdahl, who traveled from Peru to Polynesia on a raft. During his trip he found that zooplankton made “good eating.” Further research has been done to prove plankton is a good source of protein and carbohydrates. (Vegas). Because it is plentiful, easy to harvest and cheap, it is a good possibility for the future.
|This is a variety of zooplankton. Can you find the copepod? (Hint: use the drawing above as a guide). picture courtesy of http://www.clas.ufl.edu/…/Oceanography/ images/zooplankton.jpg|