Biomanipulation at Rice Lake, Ontario, Canada

ABSTRACT

The potential for using biomanipulation to reduce algal standing stocks and improve water clarity was investigated during 1988 and 1989 at Rice Lake, Ontario, Canada. During both study years, fish bioenergetics simulations showed that for a short period in the spring food consumption by young-of-the-year (YOY) yellow perch could account for almost all of the Daphnia (primarily Daphnia galeata mendotae) population losses that were calculated from a secondary production model applied to daphnids. However, during summer, YOY perch densities decreased and YOY perch community consumption rates became much lower than Daphnia production rates. This was associated with an order of magnitude increase in Daphnia biomass. Despite these dramatic summer increases in daphnid biomasses, chlorophyte and cyanophyte biovolumes and chlorophyll a concentrations increased more than five fold, and Secchi depths decreased from spring values greater than 2 m to summer values less than 1 m. Through both summers, increased algal biomasses were associated with increased total phosphorus concentrations and with late spring die-backs of the extensive macrophyte beds (primarily Potamogeton crispus) that developed during early spring. These data suggest that at Rice Lake algal production and biomass are strongly influenced by bottom-up factors, and it is unlikely that top-down biomanipulations offish populations could stimulate additional Daphnia biomass or lead to improvement of water clarity.

Key Words:

• Daphnia
• biomanipulation
• YOY yellow perch
• bottom-up
• top-down
• bioenergetics
• secondary production