Zooplankton as indicators of lake trophic status: Novel universal metrics from 224 temperate lakes
Maciej Karpowicz, Natalia Kuczyńska‐Kippen, Łukasz Sługocki, Robert Czerniawski, Elżbieta Bogacka‐Kapusta, Jolanta Ejsmont‐Karabin
Abstract
• Robust zooplankton indicators developed from 223 lakes and 462 communities. • Six structural metrics reliably indicate trophic status across regions. • Metalimnion data improves indicator performance in stratified temperate lakes. • New index combines sensitive, practical metrics for lake monitoring (TSI zoo ) • Body size of zooplankton and rotifer abundance respond clearly to eutrophication. Identifying effective indicators of eutrophication, one of the most pressing threats to freshwater ecosystems, remains a challenge. Zooplankton, as a key link in pelagic food webs and highly sensitive to environmental change, offers promise but is rarely included in lake monitoring. We analyzed a large dataset of 462 zooplankton communities from 224 lowland lakes in Poland, covering a wide trophic gradient and including both epilimnion and metalimnion layers, to develop robust and broadly applicable zooplankton indicators of trophic status (TSI ZOO ). Thirty-seven structural and functional zooplankton parameters were tested against Carlson’s Trophic State Index. Six key metrics emerged: rotifer abundance, mean zooplankton size, Cyclopoida biomass, the proportion of Cladocera and Calanoida biomass, the Cyclopoida to Calanoida abundance ratio, and the proportion of Cyclopoida biomass, all showing consistent and ecologically meaningful relationships with trophic status. These indicators reflected clear community shifts from large-bodied cladocerans and calanoids in oligotrophic lakes to small-bodied rotifers and cyclopoids in hypertrophic systems. In stratified lakes, zooplankton structure in the metalimnion corresponded more strongly to trophic conditions than in the epilimnion, and the best results were obtained when data from both layers were combined. Our multimetric TSI ZOO performed comparably or better than existing zooplankton-based indices, while relying only on main taxonomic groups, which makes it practical for routine monitoring. These findings highlight the potential of zooplankton-based indicators as ecologically meaningful and accessible tools for lake assessment, supporting their broader inclusion in monitoring programs.