Seaweed refers to several species of macroscopic, multi-cellular, marine algae. Macroalgae, which are found in the Divisions Chlorophyta, Phaeophyta and Rhodophyta are commonly called seaweeds because of their size, multicellular construction, and attachment to firm substrata.
The three major divisions of seaweeds contain taxa that have more fundamental (e.g. cytological, chemical, life histories) differences among each other .
The differences between divisions of seaweeds are evident when comparing the photosynthetic pigments, reserve foods, cell wall, mitosis, flagellar construction, morphology, and life histories.
- Seweeds probably evolved in the late Precambrian, about 900 to 600 million years ago.
- The biodiversity of algae is large but difficult to determine, because of the limited biogeographic inventories world-wide (Norton et al. 1996)
- Bold and Wynne (1985) noted that the morphological diversity and cytology of algae make them difficult to clearly define.
Seaweeds are colonial members of the Kingdom Protista, usually connect to a substratum , take up nutrients from the surrounding water, and don’t have the extensive support structures or other adaptations needed for life in air.
A seaweed usually occur as an individual or thallus, consisting of holdfast, stipe and blade.
Seaweeds live in seawater which is much denser than air. Seaweeds therefore, don’t have nearly the degree of support tissue found in terrestrial plants.
Of the total ocean surface only in 2% along the narrow fringes of the continents (coastal areas) marine algal vegetation (aside from phytoplankton and negligible number of flowering plants, called “sea grasses”) occurs.
Seaweed and their occurrence
Seaweed growth beyond the continental shelves are limited by light and lack of rocky substratum. Their growth and distribution are further affected by light, temperature, strong waves, water circulation/current.
The growth and distribution factors mentioned above are also applicable for phytoplankton.
Kelps (Brown large seaweeds)
Vertical section of ocean floor, a coast and seaweeds in a rock pool, SMI
Structure of ocean floor, rocky or sandy, tides, temperature, transparency and nutrient status of the seawater and biological factors like zoo-, bacterioand virio-plankton all interact in any part of a water body affecting growth and distribution of algae.
Rock pools and intertidal zone harbor a good number of submerged seaweeds.
Occurrence of submerged seaweeds depend on the compensation depth which varies with transparency, lowest (5 meter) near the shore to 200 meter in the continental shelf (if rocky substrata present) to about 300 meter in the pelagic or oceanic waters, up to which phytoplankton grow.
Effects of Environment
Effects of oceanic currents and temperature on seaweed distribution
Temperature in the ocean water is extremely variable, over 30º C in the equatorial region and gradually decrease to 0º C towards poles.
Kelps preferably grow in cooler waters of both the hemispheres, e.g. Macrocyatis pyrifera grows from 26º N lat. on the west coast of Pacific to 60º N and then to south along the west coast of North America but exceeding 33º N lat. (where oceanic currents from north carry cooler waters towards equator). Similar is the case with several spp. of Laminaria in the north Atlantic, M. integrifolia along Pasific coast of South America.
Coralline seaweeds also show distinct latitudinal separation, Arctic (Clathromorphum), Pantropic (Lithoporella) and Antarctic (Pseudolithophyllum)
Effects of surf and waves on Seaweed distribution
Fucas vesiculosus can not grow on exposed coasts (with surf and waves) but happily on sheltered coasts. Fucas inflatus grows on exposed coasts but not on sheltered coast.
Fucas spiralis grows on both the environments but prefers surf environment.
Why seaweeds are valuable to cultivate?
Food and nutrition
China consumes more than 70 species; Japan, over 20 species
Alginic acid, or alginate, is extracted from brown algaeSeaweeds are valuable…
Algae-based fuels hold great promise, directly related to the potential to produce more biomass per unit area in a year than any other form of biomass. Algae-based bio-fuels is estimated to occur by 2025.
For centuries, seaweed has been used as a fertilizer;Seaweeds are valuable…
Sewage can be treated with algae, reducing the use of large amounts of toxic chemicals that would otherwise be needed.
Common Edible Seaweeds
Red algae (Rhodophyta)
- Callophyllis sp. (Carola)
- Mastocarpus stellatus
- Palmaria palmata
- Eucheuma spinosum
- Eucheuma cottonii
- Gelidiella acerosa
- Gracilaria edulis
- Gracilaria corticata
- Chondrus crispus
- Porphyra tenera
- Porphyra yezoensis
- Porphyra haitanensis
- Porphyra purpurea
- Porphyra cordata
Brown algae (Phaeophyceae)
- (Laminariales) Kelp
- (Eisenia bicyclis) Arame
- (Alaria esculenta) Badderlocks
- (Durvillaea antarctica) Cochayuyo
- (Ecklonia cava)
- (Saccharina japonica) Kombu
- (Laminaria digitata) Oarweed
- (Saccharina latissima) Sugar kelp
- (Undaria pinnatifida) & (Undaria undarioides) Wakame
- (Fucus vesiculosus) Bladderwrack
- (Pelvetia canaliculata) Channelled wrack
- (Sargassum fusiforme) Hijiki or Hiziki
- (Sargassum echinocarpum) Limu Kala
- (Fucus spiralis) Spiral wrack
- (Himanthalia elongata) Thongweed
- (Cladosiphon okamuranus) Mozuku
- (Chlorella sp.) Chlorella
- (Ulva intestinalis) Gutweed
- (Caulerpa lentillifera) Sea grapes or green caviar
- (various species of the genus Ulva) Sea lettuce
- Monostroma grevillei
- Codium tomentosum
- Prasiola calophylla
- Cladophora rupestris