Biomanipulation in lakes

2. Introduction
Human impact on aquatic ecosystems, particularly in the form of eutrophication, has been one of
the major environmental concerns for aquatic ecosystems in recent decades.
The subsidization of nutrients, particularly phosphorus, to inland waters of surrounding landscapes
leads to increased Primary production and facilitates the formation of cyanobacterial blooms during
the hot summer months.
These cyanobacterial blooms, often caused by different genera of cyanobacteria such as
Microcystis spp. and Anabaena spp. often have the potential to produce a variety of toxins such as
microcystins and anatoxin-a, posing a serious threat to humans and aquatic animals’ organisms.

3. Cont.…
To counter these changes, the researchers Significant efforts have been made by interest groups to
find ways to restore reservoirs and lakes to their former Condition .
Several restoration measures have been proposed both in the watersheds and in the lakes
themselves.
Measures in the catchment area are mainly focused on reducing the external nutrient load on the
lakes.
For example by building buffer zones around watercourses in agricultural areas, reducing point
sources and building wetlands to capture nutrients before they reach the lake.

4. Cont.….
 The term " Biomanipulation " was coined by Shapiro et al. (1975). Also called top-down feeding, it involves the
manipulation of components of the trophic cascade (Paine, 1980; Carpenter et al., 1985).
 The premise of Biomanipulation, as elucidated by Shapiro (1980) and Carpenter et al. (1985, 1987), is that apex
predators, such as piscivorous fish, can influence the abundance of planktivorous fish, which in turn influence the
abundance, size structure, and productivity of zooplankton and phytoplankton.
 The key to Biomanipulation success is the addition of piscivorous fish, which should theoretically reduce the
number of planktivorous fish, which in turn promotes population development of large Daphnia species and a
decline in phytoplankton populations.
 Observations of fish-zooplankton- phytoplankton relationships and successful manipulation of all or part of the
trophic cascade in enclosures, ponds and lakes provided evidence that the principle is fundamentally valid.

5. Biomanipulation
 Biomanipulation is further explained as a management practice adopted by humans to
improve degraded water bodies.
 Following this term, the water quality of lakes is improved by using the biomanipulation
technique.
PURPOSE OF BIOMANIPULATION
 The key purpose of this technique is to decrease the high concentration of toxic
phytoplankton in the water bodies that cause eutrophication.
 The growth of phytoplankton is controlled by introducing zooplanktons that eventually
improve water quality and nutrient cycling.

7. Biomanipulation in lakes
The basic goal of biomanipulation as a tool in water quality management is greater water clarity due
to increased grazing losses of phytoplankton.
This is usually achieved by promotion of Daphnia biomass and an increase in their body size
 In lakes, trophic cascades are used to improve water quality through biomanipulation, a
management practice in which humans intentionally remove whole species from ecosystems.
 The goal of biomanipulation is to reduce the concentration of harmful phytoplankton, such as toxic
blue-green algae.

8. Cont.….
The stocking of game fish (or their protection from harvest using special regulations)
triggers a trophic cascade with decreases in the biomass of smaller-bodied fish,
increases in the biomass of herbivorous zooplankton, and decreases in the biomass
of harmful phytoplankton.
 In some cases, plankton-eating fish have been removed directly by lake managers.
In addition, the removal of bottom-feeding fish from shallow lakes leads to increases
in rooted vegetation and increased water clarity as the rooted plants stabilize the
sediments

9. • Trophic cascade hypothesis viewed according to HSS (Hairston, N.G et al 1960

10. • ADVANTAGES OF BIOMANIPULATION
• Natural Process Introduced by Humans
• Reduces Turbidity