pathogens, including
to waterhyacinth.
There are other
`or control of H.
(Freeman, Charudattan, and
1980) and
sporotrichoides for control of milfoil, M.
(Andrews and
Hecht 1981).
Neither is operational.
The application of insects and/or plant pathogens may produce a reduc-
tion of plant biomass slowly, and control may be long-lasting.
Few
negative
side effects are expected.
Research is continuing with this type of
biological control.
Biomanipulation
Biomanipulation is a term coined by Shapiro, La Marra, and Lynch (1975)
and Shapiro
although one of the first observations that algal blooms
were absent in ponds with a certain type of fish community was made by Caird
Biomanipulation includes some potentially effective but currently
(1945).
experimental procedures to control algal biomass.
Among them is the
tion or management of food webs to control fish species that recycle nutrients
during browsing and feeding, or that promote algal growth through thkir
activities on microscopic animals (zooplankton) which graze on algae.
These procedures may be difficult to implement in large reservoirs without
continual management due to the frequent introduction of undesirable fish spe-
it
cies, and because fish management is difficult in such habitats.
appears that food web manipulation can improve eutrophic systems.
manipulation is combined with control of nutrient loading, major declines in
Fish
stocking
programs
algal abundance can be expected (Benndorf 1987).
should be initiated with regard for problems of algal biomass, as well as
sports
fishing.
This means that the addition of gizzard or threadfin shad as
should be undertaken with great caution.
forage for game fish, for example,
These fish preferentially consume the species of zooplankton which are the
major grazers of some species of algae.
Reservoir manipulations such as an
occasional extreme
can provide an ideal opportunity to restructure
the fish community.
Figure 14 illustrates the open-water food chain or web (Shapiro et al.
1982).
zooplanktivorous fish (e.g., gizzard shad, alewives, perch,
Briefly,
and small sunfish) graze on the largest species of zooplankton.
These
are the most efficient grazers of algae, and their absence eliminates
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