Spring Daphnia density gave no clear gain in linear summer clarity forecasts for Mendota and Monona in 2005–2018

We tested whether spring Daphnia density adds information to forecasts of summer water clarity in Lake Mendota and Lake Monona, Wisconsin. We used two fixed NTL-LTER data versions and 44 paired lake-year rows in 1996–2018. Each annual fit used earlier years only. The main test had 26 predictions in 13 shared years from 2005 to 2018. The baseline used lake identity, May–June Secchi depth and the previous July–August Secchi depth. Adding log total May–June Daphnia density increased mean squared error by 4.65%. The central 95% three-calendar-year block range for error reduction was −19.70% to +3.13%, with fitted forecasts held fixed. Root mean squared error was 0.510 m for the baseline, 0.522 m with added density and 0.468 m for the earlier lake mean. All eight planned secondary model checks had negative point gains. An independent source calculation matched all 448 annual input values and all 52 primary regression forecasts. A clean repeat matched all 14 result and figure files. The package preserves unchanged source data, provenance, code, every prediction, all checks, block draws and figures. This is a retrospective information test that assumes spring measurements are available by 1 July. It does not establish a lack of Daphnia effects, a causal mechanism, or a general limit on ecological prediction. The lakes are linked, test years are few, and the ranges omit field sampling and model-refit uncertainty.

Daphnia · water clarity · Secchi depth · ecological forecasting · lake monitoring · NTL LTER · null result