Everything about Brown Alga totally explained
The
Phaeophyceae or
brown algae, (singular: alga) is a large group of mostly
marine multicellular
algae, including many
seaweeds of colder
Northern Hemisphere waters. They play an important role in marine environments both as food, and for the habitats they form. For instance
Macrocystis, a member of the
Laminariales or
kelps, may reach 60
m in length, and forms prominent underwater
forests. Another example is
Sargassum, which creates unique habitats in the tropical waters of the
Sargasso Sea. This is one of the few areas where a large biomass of brown algae may be found in
tropical waters. Many brown algae such as members of the order
Fucales are commonly found along rocky seashores. Some members of the division are used as food for humans.
Worldwide there are about 1500-2000 brown seaweed
species.
Brown algae belong to a very large group, the
Heterokontophyta, a eukaryotic group of organisms distinguished most prominently by having
chloroplasts surrounded by four membranes, suggesting an origin from a symbiotic relationship between a basal eukaryote and another eukaryotic organism. Most brown algae contain the pigment
fucoxanthin, which is responsible for the distinctive greenish-brown color that gives them their name. Brown algae are unique among heterokonts in developing into multicellular forms with
differentiated tissues, but they reproduce by means of
flagellate spores, which closely resemble other heterokont cells. Genetic studies show their closest relatives to be the
yellow-green algae.
Phaeophyta first appear in the
fossil record in the
Mesozoic, possibly as early as the
Jurassic. Their occurrence as fossils is rare due to their generally soft-bodied habit, and scientists continue to debate the identification of some finds. Other algae groups, such as the
red algae and
green algae have a number of
calcareous members, which are more likely to leave evidence in the
fossil record than the soft bodies of the brown algae.
Miocene fossils of a soft-bodied brown macro algae,
Julescrania, have been found well-preserved in
Monterey Formation diatomites, but few other certain fossils, particularly of older specimens are known in the fossil record.
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Taxonomy
This is a list of the
orders in the class Phaeophyceae:
A few species, such as
Botrydium stoloniferum, are placed
incertae sedis, or of uncertain position, as to order in this classification scheme.
Life cycle
The life cycle shows great variability from one group to another. However the life cycle of
Laminaria consists of the
diploid generation, that's the large plant well know to most people. It produces sporangia from specialised microscioic structures, these divide meiotically (
meiosis) before they're released. As they're
haploid there are equal numbers of male and female spores.
Adaptations
Brown algae have adapted to a wide variety of marine ecological niches including the tidal splash zone, rock pools, the whole intertidal zone and relatively deep near shore waters. However they're predominantly cool and cold water organisms that benefit from nutrients in up welling cold water currents and inflows from land;
Sargassum being an obvious exception to this generalisation.
Further Information
Get more info on 'Brown Alga'.
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