Invasive Bighead Carp Mediate Organic Matter Exchanges within and Between Ecosystems

Bighead carp can greatly deplete plankton and other pools of organic matter from the water column.  Due to inefficiencies of converting food into tissue, egested materials are shunted to benthic habitats where benthic insects may utilize these resources.  Bighead carp may indirectly influence cross-boundary exchanges of organic matter if benthic insects emerge in large numbers.  We conducted an additive experiment to evaluate these direct and indirect effects of juvenile bighead carp.  Ponds (0.04 ha.) were stocked with native fish communities (control, n=5) and native plus juvenile bighead carp (treatment, n=5).  Bighead carp reduced zooplankton production by 123%, and indirectly increased chlorophyll-a.  Bighead carp also reduced filamentous algae by 90% when compared to controls.  Two families of shiners experienced reduced growth, survival, and production. Consumption of pelagic resources by bighead carp resulted in increased secondary production and high rates of egestion.  In turn, flux of adult Chironomidae midges increased by three times in ponds with bighead carp.  In contrast, bighead carp reduced the emergence of adult Chaoboridae midges by five times.  Our experiment indicated that bighead carp greatly mediate the exchange of organic matter within and between ecosystems, and their impacts extend beyond the confines of the aquatic environment.