EFFECTS OF WHITE PERCH INTRODUCTIONS ON FOOD WEB DYNAMICS: COMBINING PALEOLIMNOLOGICAL AND WHOLE-LAKE BIOMANIPULATION APPROACHES

EFFECTS OF WHITE PERCH INTRODUCTIONS ON FOOD WEB DYNAMICS: COMBINING PALEOLIMNOLOGICAL AND

WHOLE-LAKE BIOMANIPULATION APPROACHES

By Kristin Elizabeth Ditzler

Thesis Advisors: Dr. Jasmine Saros and Dr. Kevin Simon

An Abstract of the Thesis Presented

in Partial Fulfillment of the Requirements for the Degree of

Master of Science

(in Ecology and Environmental Science)

August, 2010

Fish introduction to lakes may result in changes in zooplankton and algal communities via cascading interactions in food webs.  Food-web cascades occur when impacts from the upper levels of the food web cause corresponding changes in lower levels.  Cascading influences of fish typically result from strong predation by planktivorous fish on zooplankton, resulting in reduced grazing on algae.  In some cases, these cascading effects can lead to substantial increases in algal abundance, or algal blooms, which cause aesthetic and water quality problems.  This type of cascading influence of an introduced fish is thought to have contributed to the reduced water quality in East Pond, a shallow, productive lake in the Belgrade Chain of Lakes in central Maine.  Between 1920 and 1950, white perch (Morone americana) were introduced to East Pond.  Since this time there has been an increase in the frequency of noxious algal blooms and a decrease in water clarity.  To address this, the Maine Department of Environmental Protection has implemented a lake remediation project in which white perch (Morone americana) are being removed from the lake.  Results from the fish removal in East Pond were paired with paleolimnological techniques, using lake sediment fossil records to study long term changes to the lake ecosystem, in three additional Maine lakes before and after known dates of white perch introduction. 

Counter to predictions that suggest white perch are strictly planktivorous fish (feed on zooplankton and may reduce grazing pressure on algae), results from both removal and introduction of white perch suggest that they function primarily as a piscivorous fish (prey on planktivorous fish).  However, cascading effects to the algal community were only observed in the paleolimnological analyses of less productive lakes.  In these systems, results suggest that white perch introduction led to larger zooplankton, decreased algal production, and in some cases increased water transparency.  These results are counter to recent predictions that suggest cascading food web effects will increase with increasing productivity.  This study highlights the importance of food-web interactions in structuring the lake plankton community and the utility of combining experimental and paleolimnological approaches to study complex interactions in lakes.