BOTTOM-UP DRIVEN DIEL VERTICAL MIGRATION: SIZE AND SPECIES MATTERS

Diel vertical migration (DVM) of zooplankton in lakes and oceans is primarily thought to be driven by a top-down process of visual planktivory in illuminated surface waters. During the day zooplankton move to deep, dark depths to avoid predators and then ascend at night to feed on algae that thrive in surface waters. Different patterns occur where invertebrate predation can cause reverse DVM, but this still is a top-down process. Less work has examined how bottom-up forces such as productivity in surface waters and across depths affect DVM. Our study examined how lake trophic status and chlorophyll depth distributions drive zooplankton DVM. Six Wisconsin lakes varying in trophic status from oligotrophic (2 µg/L chlorophyll) to meso-eutrophic (> 10 µg/L) were sampled during mid-day and moonless nights. Replicate Schindler trap samples of zooplankton were collected from surface to bottom and basic limnological profiles of temperature, dissolved oxygen, chlorophyll and light flux were obtained. Zooplankton were enumerated by depth and Daphnia body sizes were measured. Both typical and reverse DVM were observed, and patterns differed based on species and on size, with greater migration amplitude for larger Daphnia. Migration amplitude was also greater in lakes with more chlorophyll a. Lakes with deep chlorophyll layers showed DVM different than expected by top-down driven processes. Overall, trophic status and chlorophyll depth profile patterns are underappreciated factors affecting zooplankton DVM.

Primary Presenter: Bart De Stasio, Lawrence University (destasib@lawrence.edu)

Authors:

Bart De Stasio, Lawrence University  (destasib@lawrence.edu)

Bennett McAfee, University of Wisconsin-Madison  (bennettjmcafee@gmail.com)

Maria Jankowski, Lawrence University  (maria.c.jankowski@gmail.com)

Mira Johnson, Lawrence University  (mira.m.johnson@lawrence.edu)

Laurice Lavajo, Lawrence University  (lavajoreese@gmail.com)

Eleanor Meng, Lawrence University  (eleanor.meng@lawrence.edu)

Mackenzie Petty, Lawrence University  (mackenzie.r.petty@lawrence.edu)

Brynn Schroeder, Lawrence University  (eliese.19.schroeder@gmail.com)

Gretchen Gerrish, University of Wisconsin-Madison  (ggerrish@wisc.edu)