Assessment of the lake biomanipulation mediated by piscivorous rainbow trout and herbivorous daphnids using a self-organizing map: A case study in Lake Shirakaba, Japan

• This study aims to evaluate biomanipulation based on zooplankton communities and ambient conditions.
• A self-organizing map was used to pattern an ecosystem aspect in Lake Shirakaba.
• Data clusters delineate serial changes of zooplankton communities during pre-, intermediate and post-biomanipulation.

This paper focuses on assessing a lake biomanipulation and introduces self-organizing maps (SOMs) as an analytical tool. In 2000, the biomanipulation using herbivorous plankters (Daphnia galeata) and piscivorous fish (Oncorhynchus mykiss) was implemented to improve water quality in Lake Shirakaba, Japan. We aimed to identify the relationships among dominant zooplankton and environmental conditions during the study period (pre-: 1997–1999, intermediate-: 2000–2002, and post-biomanipulation: 2003–2006, sampled between May and October on the biweekly basis, N = 122). From the SOM, the limnological characteristics of the lake were categorized into five features. The results accommodated that the newly introduced non-native grazers, D. galeata, were well stabilized by introducing O. mykiss which helped D. galeata survive away from predation pressure of Hypomesus transpacificus nipponensis. The interplay and relationship between variables projected by the SOM were also supported by the previous research and evidences in compliance with competitions and predations. Hence the results manifest that a regime shift of zooplankton communities in this lake has occurred since the biomanipulation. Furthermore, the present study highlights the applicability of contemporaneous introduction of both top-down cascade regulators (i.e. D. galeata and O. mykiss) as an alternative choice for the successful biomanipulation.