Wednesday, August 8, 2007

PS 55-200: Do lake ecosystem characteristics make the difference? Diel horizontal migration of zooplankton in a kettle lake (Sites Lake, OH)

Patricia A. Saunders, Jamie Yost, Angela Lowell, Justin Nussbaum, and Brian Speer. Ashland University

Sites Lake, OH (40o46.9’N, 82o23.0’W) is a small, deep kettle lake (area = 2.6 ha, Zmax > 11 m).  It has relatively large littoral areas (~20-30% of open water area) located on two opposing sides of the basin.  The lake is eutrophic, and the hypolimnion becomes anoxic relatively early in the growing season.  Macrophyte genera include Nuphar and Myriophyllum, as well as several less abundant species of floating-leaved and submerged aquatic plants.  We have been investigating the possibility that pelagic zooplankton use littoral areas as predation refugia.  This hypothesis has been suggested by other researchers who found evidence for diel horizontal migration (DHM) by zooplankton of shallow, unstratified lakes with relatively abundant aquatic macrophytes.  Those studies observed DHM instead of the more typical predator-avoidance behavior of diel vertical migration (DVM).  A preliminary study in Sites Lake found clear and strong support for DHM by Daphnia parvula, a small daphnid (< 1.5 mm).  The present study was designed to answer three basic questions: (1) can DHM behavior occur along with DVM in a stratified lake?, (2) do other zooplankton species exhibit either behavior?, and (3) is DHM behavior correlated with body size?  At the central station, we used a 30-L Schindler-Patalas trap to sample multiple depths at 6-hour intervals on 20-21 October 2005.  Enumeration of these samples included calanoid copepods and dominant cladoceran species.  Results showed that there was no evidence for DVM of zooplankton in Sites Lake.  Two larger cladocerans, Daphnia and Diaphanosoma, were migrating horizontally.  Larger Daphnia (0.5-1.1 mm) were approximately 80% of the nighttime increase in population size.  We conclude that (i) conditions in this small, stratifying lake are favorable to DHM behavior, rather than DVM, and (ii) differences in migration behavior among species and within species are consistent with the predation refugia hypothesis.

See more of PS 55 - Trophic dynamics
See more of Contributed Oral and Poster Abstracts

See more of The ESA/SER Joint Meeting (August 5 -- August 10, 2007)