q-bio.PE · Populations and Evolution stat.AP · Applications

In 2010–2014, Lake Monona lost as much May–September water clarity as Lake Mendota with 1–2% of its spiny water flea density; a Mendota-only clarity loss appeared only in 2015–2022

Question: Walsh et al. (2016, PNAS) reported that the invasive spiny water flea (Bythotrephes longimanus) decreased water clarity in Lake Mendota (Wisconsin, USA) by almost 1 m after 2009. Did lakes with few or no spiny water fleas have the same clarity loss? Approach: We used North Temperate Lakes LTER data (1995–2025) for a before–after–control–impact (BACI) test. Mendota is the impact lake. Lake Monona (downstream, spiny water flea density 1–2% of Mendota in 2009–2014) and Fish Lake (no surface connection, almost no spiny water fleas) are the controls. The response is the mean May–September Secchi depth. Periods: before 1995–2008, outbreak 2010–2014, later 2015–2022. We used year-bootstrap intervals, HAC tests, a short baseline and pre-trend checks. Results: In 2010–2014, Mendota clarity decreased by 0.75 m (95% interval −1.25 to −0.29) and Monona clarity decreased by 0.79 m (−1.07 to −0.53). The Mendota-minus-Monona BACI change was +0.04 m (−0.48 to +0.52); with Fish Lake as the control it was +0.25 m (−0.27 to +0.78). Daphnia changes in 2010–2014 were also the same in both lakes: D. mendotae increased by about 1.5 log10 units and total spring Daphnia did not change. In 2015–2022, Monona clarity returned to its earlier level but Mendota clarity did not. This gave a Mendota-specific change of −0.70 m (−1.31 to −0.08) and of −1.65 m in May–June. In Mendota, years with more spiny water fleas did not have less D. pulicaria. Conclusion: These data do not support the attribution of the whole 2010–2014 Mendota clarity loss to the spiny water flea. A Mendota-specific deficit occurred only from 2015, and its cause is not identified. Limitations: There are two or three lakes and 5–8 after-years. Monona receives Mendota water. Fish Lake and the Mendota–Monona difference have pre-trends; if the Mendota–Monona pre-trend had continued, the 2010–2014 Mendota-specific change would be −0.42 m. We also found and corrected a units error: all 2024 zooplankton lengths in NTL package 90 revision 37 are in micrometres. Code, unchanged source files and derived tables are included.

invasive species · Bythotrephes longimanus · spiny water flea · Daphnia pulicaria · water clarity · Secchi depth · Lake Mendota · Lake Monona · BACI · trophic cascade · North Temperate Lakes LTER · ecosystem services · zooplankton · eutrophic lakes

Admitted 2026-11-09 08:15 UTC11 citing publications

References

challengesdoi:10.1073/pnas.1600366113
We test its attribution of the post-2009 Lake Mendota clarity loss to the spiny water flea against control lakes; the 2010–2014 loss also occurred in Lake Monona.
doi:10.1002/ecs2.1628
Timing of the 2009 spiny water flea outbreak in Lake Mendota.
doi:10.1002/lno.10582
Spiny water flea reversal of the Mendota trophic cascade; context for Daphnia changes.
doi:10.1038/s42003-022-04355-z
Zebra mussel invasion and clarity in Lake Mendota.
doi:10.1002/lol2.10364
Other ecosystem effects in Lake Mendota after the invasion.
usesdoi:10.6073/pasta/5a246c865599c842060eec14844b3d9a
NTL-LTER zooplankton, Madison lakes (knb-lter-ntl.90.37).
usesdoi:10.6073/pasta/5eeda84205dc2a73213da0dad4a54624
Madison lakes zooplankton 1976-1994 (knb-lter-ntl.262.4).
usesdoi:10.6073/pasta/4c5b055143e8b7a5de695f4514e18142
NTL-LTER Secchi depth (knb-lter-ntl.31.32).
usesdoi:10.6073/pasta/4bbf44033e97cab9a9dedcd35323dfb3
Mendota Microbial Observatory Secchi 2012-2025 (knb-lter-ntl.416.3).
usesdoi:10.6073/pasta/da59b1093236ceb67d2cf220b17e5658
Chlorophyll, Madison lakes (knb-lter-ntl.38.30).
usesdoi:10.6073/pasta/ffa652bb3cb1a2c82c674c3e5354a5b2
Chemical limnology, total phosphorus (knb-lter-ntl.1.65).
usesdoi:10.6073/pasta/6a95bee73799927cbafbf87393be7038
Ice duration, Madison lakes (knb-lter-ntl.33.40).
usesdoi:10.6073/pasta/88fbbf7755442b1e16673460d799fb5b
Madison daily weather (knb-lter-ntl.20.38).
usesdoi:10.6073/pasta/e40fea55fdc5ccb364c2541d32647150
Dedicated spiny water flea sampling 2009-2014 (knb-lter-ntl.342.2).
usesdoi:10.6073/pasta/4a5e212d2ef75527e33058e0f3bf699c
Southern lakes spiny water flea 2016-2025 (knb-lter-ntl.431.2).

Cited by

11 publications

Public catalog entries on Sciscape.

usesThe Mendota–Monona spring clarity peak gap increased by 15 days in selected 1996–2019 surveys
We reuse its retained original Secchi and ice source files. Its seasonal mean-depth comparison motivates a new paired date metric. We do not reuse its code or derived results.
usesAutumn Daphnia density fell relative to May–June density in sampled Lake Mendota years, 2010–2024 versus 1995–2008
We reuse its retained source file and provenance. We add autumn-to-spring density estimates, later years and coverage and date checks.
usesThe clearest 28-day May–July Secchi depth fell in Mendota relative to Monona from 1996–2008 to 2015–2019
We reused its retained unchanged Secchi source files and followed its later-period clarity finding with a moving-window test. We wrote new analysis code.
usesPaired summer surveys did not show a clear change in the Daphnia length difference between Mendota and Monona, 2001–2008 to 2011–2018
We reuse its retained original source files and retrieval record. Its notes identify the 2024 length scale change and the Monona coverage gap.
usesSpring Daphnia density gave no clear gain in linear summer clarity forecasts for Mendota and Monona in 2005–2018
We reuse its retained unchanged NTL-LTER source files and source provenance. All summaries and forecast code here are new.
usesThe sampled clarity peak moved later relative to the Daphnia count peak in Mendota than in Monona in matched 1996–2018 surveys
Its retained collection supplied unchanged source files. Its fixed size-weight rule is used as a sensitivity index.
usesSampled spring Secchi maxima fell in Mendota relative to Monona from 1995–2008 to 2015–2022
We reuse its fixed source archive and period definitions. We test spring timing and sampled maxima with new code. This follows its monthly clarity result and is not an independent data replication.
usesThe forecast gain from ice-off dates was uncertain for sampled Daphnia peaks at two Wisconsin lakes in 2007–2024
We reuse its unchanged retained source files and provenance records. Our response is peak date, rather than water clarity.
usesObserved spring clarity peaks fell in Lake Mendota relative to Lake Monona from 1996–2008 to 2015–2019
We reuse its retained original NTL-LTER source snapshot and fixed period choices. We test a timing explanation with new seasonal peak and ice-relative indices.
usesRecorded Daphnia lengths within taxa offset the size decrease from species replacement in sampled Mendota and Monona springs, 1995–2024
We reuse its retained unchanged source files and its reported 2024 length-unit correction. Its species replacement results motivate this direct length partition.
usesEqual monthly sample counts preserve the observed Mendota–Monona peak clarity deficit in 2015–2019 and 2022
We reuse its retained NTL source snapshot and fixed period choices. We wrote a new analysis.