the direct consumption of algae by members of western society. If this use
spreads, as it now appears to be doing, it will enhance the status of microbial
protein sources and make their introduction to subsistence economies far
easier. In Trujillo, Peru, site of the German algae project, ready acceptance
of the algal product by the local population has already been achieved.
Unfortunately, in the case of both Spirulina and the German Scenedesmus, the
price of the algal product is higher than any other protein food. Certainly
for Spirulina, this is an anomoly that will eventually correct itself. The
important point is that direct consumption of algae by man represents
ecologically sound use of agricultural resources.

 In spite of the fact that some 90% of the food value is lost in moving
to a higher trophic level, the most promising avenue for introducing algae
into industrial and developing economies is as an animal feed. Algae meal can
be substituted for soybean meal in the diets of poultry (Shelef et al. 1977,
Loncoln and Hill 1980) swine (Hintz and Heitman 1967, Lee 1980, Lincoln and
Hall 1980) and ruminants (Hintz et al. 1966).

 A problem we have encountered is the sensitivity of poultry to blue-green
algal toxins, notably of Synechocystis, to which swine are relatively immune
(Lincoln and Carmichael 1980).

 Another problem has been the high phosphate ash content of algae meal
flocculated with ferric and aluminum salts. This ash appears to interfere
with digestion, particularly in swine, and precludes the use of high dietary
levels of algae meal (Loncoln and Hall 1980). The problem was solved by using
a polyelectrolyte flocculant which can bring the ash content down to the
acceptable range of 8 to 16%, but at considerable trade-off in cost (Lincoln
1980). This trade-off is hard to measure since polymer costs may differ by
a factor of ten or more, and effectiveness varies even more. Continued research
in this area is definitely needed, since manufacturers can give no realistic
evaluation of their product for algae flocculation, and the number of such
compounds is in the hundreds. Because information on molecular structure
of commercial flocculating agents is proprietary and generally unavailable,
assays are at best superficial. They are nevertheless needed. From the field
studies we have conducted and the limited information at hand, the branched
chain, low molecular weight polyamines appear among the most effective algal
flocculants.

 Another area in which research is needed is the feeding of algae to
aquatic organisms. Alum-flocculated algae have been fed to the common carp
(Cyprinus carpio) in large amounts with no indication of adverse effects due
to ash content (Sandbank and Hepher 1978, Meske and Pfeffer 1978). An optimum
level of 80% algae gave better growth than commercial trout rations.

 The direct feeding of suspended algae without harvesting appears to be
possible with filter feeders such as molluscs (Ryther et al 1972) and plank-
tivorous fish like Tilapia and silver carp (Hypothalmichthys molitrix)
(Edwards 1979, Zweig et al. 1979, Maddox et al. 1978). The key question with
regard to these and other filter feeding fish is just how well they are able
to capture cells in the 4 to 5 micron range and convert them to flesh.