Cattoor, K., H. Rantala, D. Staples, J. Walsh, J. Hirsh & G. Montz. (2025). A Decade of Change: Crustacean Zooplankton Communities in Nine Minnesota Large Lakes. Minnesota Department of Natural Resources, St. Paul, Minnesota, USA , Special Publication 1. 92:1-118.

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Cattoor, K., H. Rantala, D. Staples, J. Walsh, J. Hirsh & G. Montz

2025

92:1-118.

Publication

Available for editors  

The purpose of this report is to summarize the zooplankton community in the nine largest walleye lakes in Minnesota (hereafter, Large Lakes). Standardized zooplankton sampling was conducted consistently in the Large Lakes since 2012. Since that time, aquatic invasive species (AIS) such as spiny waterflea (Bythotrephes cederströmii, synonym Bythotrephes longimanus) and/or zebra mussels (Dreissena polymorpha), made their way into all nine lakes. This report examines the impacts of those invasive species on zooplankton community structure and function, and we provide broad recommendations to the zooplankton monitoring program on the frequency and intensity of data collection for another decade. Highlights/Insights. —We observed major and progressive impacts of spiny waterflea and zebra mussel on native zooplankton biomass, community composition, and secondary production. These impacts varied among lakes based on which taxon/taxa invaded, characteristics of invasion (timing and magnitude), and the zooplankton assemblage. We found that the impacts of AIS varied, both between spiny waterflea and zebra mussels and among the four major groups of native zooplankton (small cladocerans, large Daphnia spp., calanoid copepods, and cyclopoid copepods). In all cases, however, AIS were related to declines in zooplankton population and community metrics. Additionally, declines in native zooplankton varied throughout the summer, and in the case of communities invaded by spiny waterflea, persisted even early in the season before the invasive predator was detected in our samples. Recommendations. —We determined appropriate sample efforts that are lake-specific (Table A.1). We also recommend limiting to 30 individual nauplii and copepodite measurements in each sample to improve efficiency. We will continue to refine and standardize protocols (whenever possible) so that the data continue to advance our understanding of AIS impacts to Minnesota waters. We recommend that monitoring of zooplankton continues in the Section of Fisheries Large Lakes program. The data are important for understanding impacts to food webs, serving as an indicator of system change. We further recommend that studies related to the effects of AIS on lake ecosystems and fisheries continue to be supported, beyond the work of the Large Lake program. Data and samples from this program have been used by researchers to quantify the impacts of zebra mussels and spiny waterflea on these lakes (Kerfoot et al. 2016; Rantala et al. 2022; Bethke et al. 2023). Additionally, there are many unexplored applications of zooplankton data that will increase understanding of these important ecosystems.

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