Pyramimonas is a green micro-algae, that is a type of  phytoplankton.

Phytoplankton refers to the autotrophic component of the plankton that drifts in the water column.

 Most phytoplankton are too small to be individually seen with the unaided eye. However, when present in high numbers, their presence may appear as discoloration of the water (the color of which may vary with the phytoplankton present).This is certainly the case in the high intertidal tide pools at Race Rocks

The intense green color of the pools, swirly coloration of the water and a frothy covering early in the day indicate high photosynthetic capability. These plankton have an interesting response to changing salinity referred to in the video above.

Phytoplankton, like other plants, obtain energy through photosynthesis, and so must live in the well-lit surface layer (termed the euphotic zone) of an ocean, sea, or lake. Through photosynthesis, phytoplankton (and terrestrial plants) are responsible for much of the oxygen present in the Earth's atmosphere.

 Phytoplankton is consumed by microscopic animals called zooplankton (these are the second level in the food chain).
Zooplankton is consumed by Crustaceans (the third level in the food chain).
Fish that eat crustaceans could constitute the fourth trophic level, while seals consuming the fishes are the fifth.

A major reference work on this species may be found at :

http://megasun.bch.umontreal.ca/protists/pyram/appearance.html