Do deep chlorophyll layers have bottom-up effects on zooplankton communities?

Session: 32. - Long-Term Monitoring: Achievements, Challenges, and Solutions

Annie Scofield, Cornell University, [email protected]
James Watkins, Cornell University, [email protected]
Kayden Nasworthy, Cornell University, [email protected]
Lars Rudstam, Cornell University Bio Field Station, Dept. of Natural Resources, [email protected]

Abstract

Although epilimnetic chlorophyll is typically used as an indicator of algal resource availability to zooplankton, deep chlorophyll layers (DCLs) are also important contributors to primary production in oligotrophic lakes such as the Laurentian Great Lakes. DCL chlorophyll concentrations can exhibit trends that differ from epilimnetic chlorophyll because DCLs are affected by water clarity, as well as by changing nutrient dynamics. The depth and temperature at which DCLs form have implications for zooplankton, and we hypothesize that deeper/colder DCLs are associated with shifts in zooplankton community structure toward calanoid copepod species and Mysis, which are adapted to cold temperatures. In lakes where the DCL occurs within the thermocline, such as Lake Ontario, migrating zooplankton including Daphnia can take advantage of DCL resources. However, the DCL is likely inaccessible to metalimnetic-epilimnetic migrators in the upper lakes, where DCLs have shifted deeper and often occur below the thermocline. In recent decades, there have been continued declines in zooplankton biomass in Lakes Huron and Michigan and changes to zooplankton community structure across the Great Lakes. In this research, we explore the potential bottom-up effects of DCLs using evidence from long-term monitoring data, zooplankton feeding experiments, field gut fluorescence data, and diel vertical migration studies.

1. Keyword
zooplankton

2. Keyword
productivity

3. Keyword
migrations

4. Additional Keyword
deep chlorophyll layers

5. Additional Keyword
bottom-up effects