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.
There are two broad categories of phytoplankton:
and
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
What plankton are likely to be found in Greenwich Bay?
..........
These are the ten most common phytoplankton in
Narragansett Bay:
Skeletonema costatum (diatom)
Leptocylindrus minimus (diatom)
Species of the genus Gymnodinium (Gymnodinium spp.)
(dinoflagellate)
Asterionella glacialis (diatom)
Thalassiosira spp. (diatom)
Thalassiosira nordenskioldii (diatom)
Nitzschia closterium (diatom)
Rhizoselenia delicatula (diatom)
Leptocylindrus danicus (diatom)
Thalassionema nitzschoides (diatom)
