Article by Gavin W. Maneveldt
Department of Biodiversity & Conservation Biology,
University of the Western Cape
T
he fourth part of our series on common intertidal seaweeds of the Cape Peninsula looks at
the red seaweeds, which form by far the largest group of seaweeds on the Peninsula, dominating the mid to lower intertidal area. Like the brown
seaweeds, many of the reds are fleshy and bulky and
generally occur lower down the shore because they are
less tolerant of salinity and temperature extremes than
some of the common green seaweeds.
Red seaweeds appear red because they possess pigments known as phycobilins that absorb blue and
green light, and reflect red light. Although they are
commonly called red seaweeds, some may appear
black, blue, yellow and even green. This is especially
true for intertidal reds, the red pigments of which may
become masked by the chlorophyll and other pigments
present in them. As blue light penetrates water to a
greater depth than any other light, the phycobilins present in red seaweeds allow these seaweeds to photosynthesize and survive at great depths – some as deep
as 250 m.
The red seaweeds common to the Cape Peninsula include Porphyra species, Hildenbrandia lecanellierii,
Aeodes orbitosa, Gelidium pristoides, Gigartina polycarpa, Sarcothalia stiriata, Nothogenia erinacea and
Hypnea spicifera.
Purple laver, Porphyra, looking much like wrinkled cellophane,
are common high on the shore.
Porphyra species, or purple laver,
are extremely thin (only one cell
thick), flat, membranous seaweeds.
These seaweeds look like sheets of
wrinkled cellophane when dry – all
crumpled and folded. They vary in
colour from yellow to purple to almost black. Porphyra are abundant
high on the shore where desiccation stress is at its greatest, and not
many other species can survive.
They have remarkable recovery capabilities and can survive dehydration for several days.