Page 295 - Algae

278 Algae: Anatomy, Biochemistry, and Biotechnology

South Africa, Porphyra is in demand for abalone feed and recommendations have been made for
the management of the wild population of the macroalgae. Pacific dulse (Palmaria mollis) has been
found to be a valuable food for the red abalone, Haliotis rufescens, and development of land-based
cultivation has been undertaken with a view to producing commercial quantities of the macroalgae.
The green macroalgae, Ulva lactuca, has been fed to Haliotis tuberculata and Haliotis discus.
Feeding trials showed that abalone growth is greatly improved by high protein content, and this
is attained by culturing the macroalgae with high levels of ammonia present.

FERTILIZERS
There is a long history of coastal people using macroalgae, especially the large brown macroalgae,
to fertilize nearby land. Wet macroalgae is heavy, so it was not usually carried very far inland,
although on the west coast of Ireland enthusiasm was such that it was transported several kilometres
from the shore. Generally drift macroalgae or beach-washed macroalgae is collected, although in
Scotland farmers sometimes cut Ascophyllum exposed at low tide. In Cornwall (U.K.), the practice
was to mix the macroalgae with sand, let it rot, and then dig it in. For over a few hundred kilometres
of the coast line around Brittany (France), the beach-cast, brown macroalgae is regularly collected
by farmers and used on fields up to a kilometre inland. Similar practices can be reported for many
countries around the world. For example, in a more tropical climate like the Philippines, large quan-
tities of Sargassum have been collected, used wet locally, but also sun-dried and transported to
other areas. In Puerto Madryn (Argentina), large quantities of green macroalgae are cast ashore
every summer and interfere with recreational uses of beaches. Part of this algal mass has been com-
posted and then used in trials for growing tomato plants in various types of soil. In all cases, the
addition of the compost increased water holding capacity and plant growth, so composting simul-
taneously solved environmental pollution problems and produced a useful organic fertilizer.
Macroalgae meal is dried, milled macroalgae, and again it is usually based on the brown macro-
algae because they are the most readily available in large quantities. Species of Ascophyllum, Eck-
lonia, and Fucus are the common ones. They are sold as soil additives and function as both fertilizer
and soil conditioner. They have a suitable content of nitrogen and potassium, but are much lower in
phosphorus than traditional animal manures and the typical N : P : K ratios in chemical fertilizers.
The large amounts of insoluble carbohydrates in brown macroalgae act as soil conditioners
(improve aeration and soil structure, especially in clay soils) and have good moisture retention
properties. Their effectiveness as fertilizers is also sometimes attributed to the trace elements
they contain, but the actual contribution they make is very small compared with normal plant
requirements. A company in Ireland that produces milled macroalgae for the alginate industry is
developing applications for macroalgae meal in Mediterranean fruit and vegetable cultivation.
“Afrikelp” is another example of a commercially available dried macroalgae, sold as a fertilizer
and soil conditioner; it is based on the brown macroalgae Ecklonia maxima that is washed up on
the beaches of the west coast of Africa and Namibia. Like all brown macroalgae, Ascophyllum con-
tains alginate, a carbohydrate composed of long chains. When calcium is added to alginate, it forms
strong gels. By composting the dried, powdered Ascophyllum under controlled conditions for 11–
12 days, the alginate chains are broken into smaller chains and these chains still form gels with
calcium but they are weaker. The composted product is a dark brown, granular material containing
20–25% water and it can be easily stored and used in this form. Steep slopes are difficult to culti-
vate with conventional equipment and are likely to suffer soil loss by runoff. Spraying such slopes
with composted Ascophyllum, clay, fertilizer, seed, mulch, and water has given good results, even
on bare rock. Plants quickly grow and topsoil forms after a few years. The spray is thixotropic, that
is, it is fluid when a force is applied to spread it but it sets to a weak gel when standing for a time and
sticks to the sloping surface. It holds any soil in place and retains enough moisture to allow the
seeds to germinate. Composted Ascophyllum has been used after the construction of roads in a
number of countries, and has found other uses as well.