Zooplankton perform daily migrations between surface pelagic waters, where they feed at night, and deeper waters (diel vertical migration, DVM) or littoral areas (diel horizontal migration, DHM), where they hide from visual predators during the day. We hypothesized that 1) in systems with hypoxic hypolimnia, DVM decreases and is replaced by higher DHM, and that 2) DVM and DHM are more extensive in lakes with higher fish predation pressure. Through the AQUACOSM Transnational Access program, we sampled zooplankton in 16 experimental ponds (30 m x 15 m x 3 m) at the National Experimental Platform in Aquatic Ecology (PLANAQUA) at the CEREEP-Ecotron ÎledeFrance facility in France. The ponds were manipulated with fish and nutrient treatments (2 levels each) in a 2 x 2 factorial design. We sampled zooplankton in the epilimnion, hypolimnion, and littoral zone of each pond near noon and midnight to characterize migrations. We found that crustacean DVM decreased and DHM was not impacted by lower hypolimnetic dissolved oxygen, partially supporting our first hypothesis. Our second hypothesis was not supported - as planktivore abundance increased, crustacean DVM decreased and DHM was not impacted. Some rotifer genera exhibited weak migration patterns. We discuss trophic and behavioral cascades among crustaceans, rotifers, and Chaoborus in response to gradients of fish planktivory and oxygen. These findings contribute to the body of knowledge regarding impacts of global changes and other pressures on zooplankton community dynamics and aquatic ecosystem function.

Primary Presenter: Anna Schmidt, University of Vermont (anna.schmidt@uvm.edu)

Authors:

Anna Schmidt, University of Vermont  (anna.schmidt@uvm.edu)

Isabel Anderson, University of Vermont  (isabel.anderson@uvm.edu)

Rosalie Bruel, OFB, Pôle R&D ECLA  (rosaliebruel@gmail.com)

Rosaura Chapina, University of Vermont  (rosaura.chapina@uvm.edu)

Jonathan Doubek, Lake Superior State University  (jdoubek@lssu.edu)

Sarah Fiorini, CEREEP-Ecotron ÎledeFrance  (sarah.fiorini@ens.fr)

Sadye Goldfarb, University of Vermont  (skgoldfarb@gmail.com)

Gérard Lacroix, CEREEP-Ecotron ÎledeFrance  (gerard.lacroix@bio.ens.psl.eu)

Heather Wander, Virginia Tech  (hwander@vt.edu)

Jason Stockwell, University of Vermont  (jason.stockwell@uvm.edu)