Biology of Giant Kelp
Morphology
Giant Kelp (or Macrocystis) has the distinction of being
the largest marine plant (and seaweed) in the world; with the
largest attached plant recorded being 65m long. The kelp plant
has a root-like holdfast that fixes to rocky surfaces;
a long slender stalk or stipe; and long, leaf-like blades
or fronds, that are the major site of photosynthetic activity.
The
kelp plant is supported in the water by gas-filled bladders on
each frond called pneumatocysts. The holdfast is cone-shaped
and can grow up to 60 cm in diameter in large plants.
Diagram of
Kelp Morphology
Reproduction
Giant Kelp have an unusual life history - a hetermorphic alternation
of generations - comprising a diploid (2n) sporophyte generation
(which forms the large leafy plants), which produces spores that
develop into the microscopic haploid (n) gametophyte generation
(comprising male and female gametophytes). These microscopic plants
on the seafloor fertilise to give rise to the leafy sporophyte.
Kelp Life Cycle
The
spores are found in sori located on the blades, within special
blades called sporophylls, located at the base of the plant
(branching off the stipes just above the holdfast). A single adult
plant can produce many sporophylls, each sporophyll containing
billions of spores.
Kelp sprophyll
(Photo by: John Heine)
