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Phytoplankton
Phytoplankton
are one-celled, microscopic plants that float at the surface of the water.
They may resemble disks, spiky balls, or chains. Life in Greenwich Bay
depends on these tiny plants to make large contributions to the bay's
food and oxygen supply.
In Narragansett Bay as a whole, phytoplankton are the most important primary
producers, using the sun's energy to produce organic matter. These miscroscopic
phytoplankton are far simpler structurally than larger plants, and their
life cycle is short. Populations may double in a day and entire communities
rise and fall each year. The ever-changing abundance and species composition
of the bay's phytoplankton follow a more or less regular annual pattern
directly related to the abundance of nutrients, temperature, and the effects
of grazing by zooplankton, benthic animals, and fish.
Phytoplankton are either diatoms or dinoflagellates.
Diatoms
Diatoms have glasslike shells made of the element silica. When the days begin to get longer at the end of December, diatoms begin to increase and mutiply. They carry out photosynthesis to convert the sun's energy into a form that they can use. By spring, there are billions of diatoms in the water. There may be 16, 000 in one milliliter. Diatoms come in a wide variety of shapes and sizes; the plankton shown in the photograph above are all diatoms.
Dinoflagellates
The dinoflagellates
actually have some characteristics of both plants and animals. They are
able to move (although they are not strong swimmers) using a whip-like
appendage called a flagellum (see picture of Gymnodinium below).
Like diatoms, dinoflagellates make their own food through photosynthesis,
but some species have also been known to eat other plankton! Some types
of dinoflagellates produce a toxin. This can make people sick if they
eat clams that have eaten the plankton. A very fast and lage increase,
called a bloom of dinoflagellates, can result in a phenomenon call red
tide. During this time, there is a danger of people becoming sick from
eating shellfish contaminated by the toxin these plankton produce.
More
on dinoflagellates
These are some of the common phytoplankton in Narragansett Bay:
