Green
seaweeds are part of a large group called Division Chlorophyta,
which includes all green algae. Only about 10% of green
algae are marine species, most live in freshwater. Green
algae are more closely related to the green vascular land plants
than any other group of algae. They have the same photosynthetic
system as vascular plants, which is dominated by the pigments chlorophyll
a and b. The chlorophyll pigments are what give this group of algae
their beautiful green colouration. Chlorophyll a and b absorb red
light, which is available in shallow waters, but absent in deeper
water. Thus, green seaweeds are most commonly found in the shallow
intertidal zone. There are more species of green algae found in
warm tropical oceans than in cooler temperate seas. The structure
of green seaweeds ranges from single-celled forms to multi-cellular
sheets, and branched filaments.
Some common species of green algae such as Ulva (sea lettuce),
and Enteromorpha (green string lettuce) are used as food
products.
Codium fragile - dead man's fingers
This gorgeous green seaweed has several
common names, including dead man's fingers, felty fingers, and the
sea staghorn. Felty fingers is an especially good name for this
seaweed because it has a spongy, felt-like texture, and it looks
like a bunch of fingers!
Codium fragile is found attached to rocks in the
mid to low intertidal, and subtidal zones of open coastal
areas. Its natural range extends along the pacific coast from Alaska
to Mexico, and along the coast of Japan. This shapely seaweed has
also been introduced to Mediterranean and North Atlantic coastal
waters. Codium fragile is dark green, has a branched form,
and can grow up to 30 centimetres in height/length. It is dichotomously
branched, which means that at each fork two equal branches are produced
opposite each other, forming a Y shape. The branches are cylindrical
and about 6 millimetres in diameter. The holdfast of this charming
seaweed is a wide, spongelike cushion of tissue. An interesting
and peculiar characteristic of codium fragile is that the
entire plant body is made up of one very long cell!! These unusual
long cells are called coenocytic, and have more than one nucleus,
but do not have cell walls separating them.
A species of sea slug called Alesia can steal the chloroplasts
from felty fingers and hold them in a special gland within their
body. The chloroplasts continue to photosynthesize within the slug,
and produce a slime that the sneaky sea slug uses to lubricate its
path.
Ulva - sea lettuce
Members
of this group of gorgeous green seaweeds are found on all the world's
coasts. The common name sea lettuce is often used when referring
to this group of algae. On the coasts of the Pacific Northwest there
are 8 species of Ulva, which share similar traits and appearances.
They can be seen growing on rocks in protected waters in the mid
to low intertidal zone.
Ulva plants have a small discoid holdfast that attaches
them to the rocks. The stipe of Ulva is very small and leads to
the larger blades. The blades are very thin, only 2 cells thick,
and are often ruffled or torn. The flat blades are usually less
than 30 centimetres long, but are often irregular in shape, and
may be broader than they are long. The plants are light to medium
emerald green in colour and often cover large areas in the intertidal
zone.
Sometimes the edges of the blades of Ulva are pale white
in colour in contrast to the rest of the green blade. When Ulva
becomes fertile the cells along the edges of the blades are converted
into reproductive cells containing spores or gametes. After the
contents of these cells are released, the edge of the blade appears
white. Ulva is an isomorphic seaweed, meaning that the
sporophyte and gametophye phases of the life cycle are have a similar
appearance.
Ulva is edible and can be used in salads, soups, and numerous
other dishes.
1 comments:
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