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Seaweed is a loose colloquial term encompassing macroscopic, multicellular, benthic marine algae. The term includes some members of the red, brown and green algae. Seaweeds can also be classified by use (as food, medicine, fertilizer, industrial, etc.).
Taxonomy A seaweed may belong to one of several groups of multicellular algae: the red algae, green algae, and brown algae. As these three groups are not thought to have a common multicellular ancestor, the seaweeds are a paraphyletic group. In addition, some tuft-forming bluegreen algae (Cyanobacteria) are sometimes considered as seaweeds—"seaweed" is a colloquial term and lacks a formal definition.
Structure Seaweeds' appearance somewhat resembles non-arboreal terrestrial plants.
- thallus: the algal body
- lamina: a flattened structure that is somewhat leaf-like
- sorus: spore cluster
- on Fucus, air bladders: float-assist organ (on blade)
- on kelp, floats: float-assist organ (between lamina and stipe)
- stipe: a stem-like structure, may be absent
- holdfast: specialized basal structure providing attachment to a surface, often a rock or another alga.
- haptera: finger-like extensions of holdfast anchoring to benthic substrate
The stipe and blade are collectively known as the frond.
EcologyThe ecology of seaweeds is dominated by two specific environmental requirements. These are the presence of seawater (or at least brackish water) and the presence of light sufficient to drive photosynthesis
. A very common requirement is also to have a firm point of attachment. As a result, seaweeds are most commonly found in the littoral zone and within that zone more frequently on rocky shores than on sand or shingle. The ecological niches utilised by seaweeds are wide ranging. At the highest level are those that inhabit the zone that is only wetted by the tops of sea spray, the deepest living are those that are attached to the seabed under several meters of water. In some parts of the world, the area colonized by littoral seaweeds can extend for several miles away from the shore. The limiting factor in such cases is the availability of sufficient sun-light to support photosynthesis. The deepest living seaweeds are the various kelps.
In addition to the familiar seashore seaweeds, a number of species have adapted to a fully planktonic niche and are free-floating, often with the assistance of gas filled sacs. Sargassum is one of the better known examples of this type of seaweed.
A number of species have adapted to the specialised environment of tidal rock pools. In this niche seaweeds are able to withstand rapidly changing temperature and salinity and even occasional drying.
Uses Seaweed has a variety of purposes, for which it is farmed,[url= www.sunstar.com.ph/static/dav/2008/06/19/bus/seaweed.farmers.get.better.prices.if.united.jica.html ] or foraged from the wild.
Food
Copyright Citations
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