Life cycle focus Fucus is a genus of brown algae found in the intertidal zones of rocky seashores almost throughout the ...
Life cycle focus
Fucus is a genus of brown algae found in the intertidal zones of rocky seashores
almost throughout the world.
Description and life cycle
The thallus is perennial with an
irregular or disc-shaped holdfast or with haptera. The erect portion of the thallus is dichotomous or subpinnately
branched, flattened and with a distinct midrib. Gas-filled pneumatocysts (air-vesicles) are
present in pairs in some species, one on either side of the midrib. The erect
portion of the thallus bears cryptostomata and caecostomata (sterile surface
cavities). The base of the thallus is stipe-like due to
abrasion of the tissue lateral to the midrib and it is attached to the rock by
a holdfast. The gametangia develop in conceptacles embedded in receptaclesin the apices of the
final branches. They may be monoecious or dioecious.
These algae have a relatively simple life
cycle and produce only one type of thallus which grows to a
maximum size of 2 m. Fertile cavities, the conceptacles, containing the
reproductive cells are immersed in the receptacles near the ends of the
branches. After meiosis oogonia and antheridia are produced and
released, fertilisation follows and the zygote develops directly
into the diploid plant. It may be considered to be analogous to the life cycle
of the flowering plant, but in
algae the oogonia are released and fertilised in the sea while in flowering plants the ovules are fertilised while
attached to the parent plant and then released as aseed.
Distribution and ecology
Species of Fucus are recorded almost worldwide. They are
dominant on the shores of the British Isles,[5] the northeastern
coast of North America and California.
In the British Isles these larger brown
algae occur on sheltered shores in fairly well defined zones along the shore
from high-water mark to below low water mark. On the more exposed shores not
all of these species can be found and on very exposed shores few, if any,
occur. Pelvetia canaliculata forms a zone at the
top of the shore. Just below this Fucus spiralis, Fucus vesiculosus andFucus serratus and Laminaria form clear zones, one
below the other, along the shore down to low water mark. On sheltered shores Ascophyllum
nodosum usually forms a broad
and dominating zone along the shore at the mid-littoral. On very exposed
shores few if, any plants, of these species can be found. Other brown algae can
be found at the low-littoral such as Himanthalia,Laminaria
saxatilis and Alaria esculenta. Small green
and red algae and animals occur, protected under these large brown algae.
Uses
In Scotland and Norway, up until the mid 19th
century, several seaweed species from Fucus and other genera were harvested,
dried, burned to ash, and further processed to become "kelp", which was a type of soda ash that was less costly
in Britain than the barilla imported from Spain.
It has an alkali content of about
2.5%–5% that was mainly sodium carbonate (Na2CO3);
alkali is essential to soapmaking, glassmaking, and other industries. The
seaweed was also used as fertilizer for crop land in the same areas in which it
was harvested. The purest barilla had a sodium carbonate concentration of about
30%.
In 2005, it was announced that bacteria grown on Fucus have the ability to attack and kill
the MRSA superbacterium
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