Which outcome would indicate a successful biomanipulation aimed at reducing algal blooms in a eutrophic lake?

Which outcome would indicate a successful biomanipulation aimed at reducing algal blooms in a eutrophic lake?

• A. Increased phytoplankton biomass.
• B. Decreased water clarity.
• C. Reduced zooplankton grazing.
• D. Greater water clarity and reduced algal blooms due to enhanced zooplankton grazing.

Answer: (D)

Biomanipulation works by strengthening top-down control in the lake food web so zooplankton graze more on phytoplankton and curb blooms. When grazing pressure from zooplankton increases, phytoplankton biomass drops, water becomes clearer, and algal blooms decline. That map of change—clearer water and fewer blooms due to enhanced zooplankton grazing—best shows the intended outcome. If phytoplankton biomass rose, water would stay murky; if zooplankton grazing were reduced, blooms would likely worsen. So the described improvement in clarity driven by grazing is the clearest sign of success.

Biomanipulation works by strengthening top-down control in the lake food web so zooplankton graze more on phytoplankton and curb blooms. When grazing pressure from zooplankton increases, phytoplankton biomass drops, water becomes clearer, and algal blooms decline. That map of change—clearer water and fewer blooms due to enhanced zooplankton grazing—best shows the intended outcome. If phytoplankton biomass rose, water would stay murky; if zooplankton grazing were reduced, blooms would likely worsen. So the described improvement in clarity driven by grazing is the clearest sign of success.