“Seaweeds” are a group of photoautotrophic, multi-cellular algae occurring in marine environments. Basically, they are simple organisms that can perform photosynthesis.
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| Algae usually have the following characteristics: |
- Algae are non-vascular plants, they lack true roots, stems or leaves.
- Algae are flowerless.
- Algae are seedless.
- The reproductive structures of algae are not protected by any particular tissue. Most algae have cells that serve to reproduce by the means of gametes or spores.
- Algae do not have embryos.
- All cells contain chlorophyll a.
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Using chlorophyll a all algae perform photosynthesis for energy. In addition, different types of algae contain a great variety of accessory pigments in different forms and quantities, such as chlorophyll b, chlorophyll c, chlorophyll d, β-carotene, phycocyanins, phycoerythrin, fucoxanthin and lutein. Different combinations and concentrations of accessory pigments are the reason why algae have so many different colors.
As algae are non-vascular organisms, they do not have true roots, stems and leaves. Many kinds of algae have differentiated cells, yet the differentiation is not complete. Their root-like holdfasts help the algae attach themselves to the substrate and algae mainly absorb nutrients or exchanging substances from the environment. Algae are seedless and flowerless, their reproductive gamets or spores, termed gametangia or sporangia, are unicellular produced from either uni- or multi-cellular algae.
Generally speaking, seaweeds can be divided into two categories: microalgae and macroalgae. |
- Microalgae are unicellular algae not visible to the naked eye. They are considered phytoplankton and can be found anywhere in the oceans where there is light. Some types of microalgae have flagella to move around in the water. There is a great variety of microalgae. The most common ones include diatoms and dinoflagellates. Microalgae play an important role in the food web in the marine environments.
- Macroalgae refer to multicellular algae found in littoral or infralittoral zones. They have rhizoids to attach themselves to rocks. Their structures are more complex and they appear in a variety of colors and forms. Some algae, such as Macrocystis can grow up to 60 meters in height, making it the largest alga in the world.
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| For the sake of differentiation，microalgae are referred to as phytoplankton while macroalgae usually visible to the naked eye along most coastal areas are referred to as “seaweeds.” The latter can be divided into the four following phyla:blue-green algae、green algae、brown algae and red algae. |
