Marine Algae are generally known as Seaweeds. Seaweeds need sunlight for its growth, like any other photosynthetic plants. Most of the seaweeds grow in shallow waters around shores or reefs as the sunlight penetrates depths greater than 15meters. Most of the seaweeds which filter dead particles from the water provide food for small creatures.
Seaweeds have no leaves, flowers, roots or seeds. The body of the seaweed plant is called thallus. It is divided into a holdfast or hapteron, a stalk or stipe and a frond. The stalk may be millimeters long and sometimes it may be many meters long. If the seaweeds is taken out of the water, it cannot be able to support themselves.
Life cycle of Seaweed:
At the tip of fronds, separate male and female reproductive patches called receptacles are developed.
Conceptacles are embedded in receptacles and it contains the sex organs namely antheridia (male) and oogonia (female).
The sex organ oogonia split to release female sex cells. Male sex cells swim into the water through pores.
The Male sex cells are attracted to a female cell to fertilize it by means of chemicals.
Brown Seaweeds include the kelps, gulfweed and wracks. They are tough and slippery plants. These brown seaweeds can survive for a long time out of water.
Green Seaweeds are small to medium sized plants which are usually very thin having soft fronds. Ten percent of the green algae are seaweeds.
Red Seaweeds are small to medium sized plants. Some of the red seaweeds are made rigid by a chalky secretion. The Red seaweeds get their red color from a pigment called phycoerythrin.
Giant Kelp Seaweed
Giant Kelp seaweed lives in much deeper water than other seaweeds and can grow more than 60 meters long. It is attached to the seabed and each plant produces a long stipe that can grow more than a meter in one day to reach the light.