Investigating the effects of multiple predators and hypolimnetic hypoxia on zooplankton migration behavior
Conference Year
January 2021
Abstract
Zooplankton are an essential bridge between trophic levels in aquatic food webs; they consume primary producers and serve as prey for many intermediate and higher-level predators. Zooplankton often exhibit diel vertical migration (DVM), whereby they spend the day in deeper waters (hypolimnion) to avoid visual predators and then migrate to surface waters (epilimnion) at night to feed under reduced predation risk. Zooplankton can alter their DVM behavior in lakes depending on predator densities – in particular, invertebrate predators such as Chaoborus larvae and fish predators such as roach (Rutilus rutilus). They also will change their DVM behavior in the presence of low dissolved oxygen (DO) conditions (hypoxia) in the hypolimnion of lakes, altering the extent/magnitude of their migration behavior to avoid the hypoxic hypolimnia. We studied how zooplankton biomass, density, and DVM behavior change along a gradient of Chaoborus density, roach density, and hypolimnetic DO. As part of an EU AQUACOSM funded study at the PLANAQUA experimental lake platform in northern France, we sampled 16 experimental lake systems. Paired night and day zooplankton samples were taken from the epilimnion (0-2 meters depth) and the hypolimnion (2-3 meters depth) of each lake (max depth = 3 m), in addition to temperature, DO, and phytoplankton profiles. Zooplankton and Chaoborus larvae were counted, measured, and identified with a dissecting microscope to estimate biomass and density in each depth stratum, day and night, in each lake. We expected that zooplankton biomass and density would decrease with increasing roach and Chaoborus larvae density and decreasing hypolimnetic DO because of increased overlap between fish and zooplankton due to unfavorable hypolimnetic DO conditions. We also expected increasing magnitude of DVM with increasing roach density due to heightened predation pressure in the epilimnion during the day, but decreasing magnitude of DVM with increasing Chaoborus density and with decreasing hypolimnetic DO due to heightened predation pressure by Chaoborus in the epilimnion at night and constant unfavorable conditions in the hypolimnion. However, our preliminary results show no significant relationships between total pelagic zooplankton biomass/density or DVM behavior and roach density, Chaoborus density, and DO concentration in the hypolimnion. Climate change and other anthropogenic stressors are changing aquatic community composition and DO conditions in lakes; understanding how these factors influence zooplankton populations may shed light on how aquatic ecosystems respond to climate change.
Primary Faculty Mentor Name
Jason Stockwell
Faculty/Staff Collaborators
Rosaura Chapina, Jonathan Doubek, Sadye Goldfarb, Jonathan Rickwood, Heather Wander, Jason D. Stockwell
Status
Undergraduate
Student College
Rubenstein School of Environmental and Natural Resources
Program/Major
Environmental Sciences
Primary Research Category
Biological Sciences
Investigating the effects of multiple predators and hypolimnetic hypoxia on zooplankton migration behavior
Zooplankton are an essential bridge between trophic levels in aquatic food webs; they consume primary producers and serve as prey for many intermediate and higher-level predators. Zooplankton often exhibit diel vertical migration (DVM), whereby they spend the day in deeper waters (hypolimnion) to avoid visual predators and then migrate to surface waters (epilimnion) at night to feed under reduced predation risk. Zooplankton can alter their DVM behavior in lakes depending on predator densities – in particular, invertebrate predators such as Chaoborus larvae and fish predators such as roach (Rutilus rutilus). They also will change their DVM behavior in the presence of low dissolved oxygen (DO) conditions (hypoxia) in the hypolimnion of lakes, altering the extent/magnitude of their migration behavior to avoid the hypoxic hypolimnia. We studied how zooplankton biomass, density, and DVM behavior change along a gradient of Chaoborus density, roach density, and hypolimnetic DO. As part of an EU AQUACOSM funded study at the PLANAQUA experimental lake platform in northern France, we sampled 16 experimental lake systems. Paired night and day zooplankton samples were taken from the epilimnion (0-2 meters depth) and the hypolimnion (2-3 meters depth) of each lake (max depth = 3 m), in addition to temperature, DO, and phytoplankton profiles. Zooplankton and Chaoborus larvae were counted, measured, and identified with a dissecting microscope to estimate biomass and density in each depth stratum, day and night, in each lake. We expected that zooplankton biomass and density would decrease with increasing roach and Chaoborus larvae density and decreasing hypolimnetic DO because of increased overlap between fish and zooplankton due to unfavorable hypolimnetic DO conditions. We also expected increasing magnitude of DVM with increasing roach density due to heightened predation pressure in the epilimnion during the day, but decreasing magnitude of DVM with increasing Chaoborus density and with decreasing hypolimnetic DO due to heightened predation pressure by Chaoborus in the epilimnion at night and constant unfavorable conditions in the hypolimnion. However, our preliminary results show no significant relationships between total pelagic zooplankton biomass/density or DVM behavior and roach density, Chaoborus density, and DO concentration in the hypolimnion. Climate change and other anthropogenic stressors are changing aquatic community composition and DO conditions in lakes; understanding how these factors influence zooplankton populations may shed light on how aquatic ecosystems respond to climate change.