DOI: 10.5061/dryad.xd2547dgn
title: Regime shifts in a shallow lake: Consequences for taxonomic and functional diversity, and ecosystem multifunctionality

description: Under increasing nutrient loading, shallow lakes may shift from a state of
 clear water dominated by submerged macrophytes to a turbid state dominated
 by phytoplankton or a shaded state dominated by floating macrophytes. How
 such regime shifts mediate the relationship between taxonomic and
 functional diversity and lake multifunctionality is poorly understood. We
 employed a detailed database describing a shallow lake over a 12-year
 period during which the lake has displayed all the three states (clear,
 turbid, and shaded) to investigate how species richness, functional
 diversity of fish and zooplankton, ecosystem multifunctionality, and five
 individual ecosystem functions (nitrogen and phosphorus concentrations,
 standing fish biomass, algae production, and light availability) differ
 among states. We also evaluated how the relationship between biodiversity
 (species richness and functional diversity) and multifunctionality is
 affected by regime shifts. We showed that species richness and the
 functional diversity of fish and zooplankton were highest during the clear
 state. The clear state also maintained the highest values of
 multifunctionality as well as standing fish biomass production, algae
 production, and light availability, whereas the turbid and shaded states
 had higher nutrient concentrations. Functional diversity was the best
 predictor of multifunctionality. The relationship between functional
 diversity and multifunctionality was strongly positive during the clear
 state, but such relationship became flatter after the shift to the turbid
 or shaded state. Our findings illustrate that focusing on functional
 traits may provide a more mechanistic understanding of how regime shifts
 affect biodiversity and the consequences for ecosystem functioning. Regime
 shifts towards a turbid or shaded state negatively affect the taxonomic
 and functional diversity of fish and zooplankton, which in turn impairs
 the multifunctionality of shallow lakes.
description: The
 research was conducted in Lake Osmar, a shallow lake (1.1 m average depth)
 located in the Upper Parana floodplain (22 º46´27. 53" S and 53º 19´
 57. 95"), Brazil (Figs. S1 and S2). This region has a tropical
 climate with a mean annual temperature of 22 °C (mean minimum and maximum
 temperatures of 10.3 and 33.6 °C, respectively) and a mean annual
 precipitation of 1500 mm. The data used for the analysis originate from a
 long-term ecological research project (PELD-Sitio PIAP) and include 12
 years (2005 to 2016). <b>Fish and zooplankton
 sampling</b> The sampling
 campaigns were explicitly designed to assess the taxonomic and functional
 diversity of fish and zooplankton, as well as ecosystem
 multifunctionality, during the three alternative states. During the 12
 years, four annual samples (summer, fall, winter, and spring) were
 collected, except in 2014 when only sampling campaigns were conducted,
 resulting in 48 sampling campaigns in total. Fish were caught using 20 m
 long seines with a mesh size of 0.5 cm in the littoral and middle zones of
 the lake for a 24 h period. As the lake is shallow, our sampling always
 included all lake compartments (i.e., sediment, the pelagic and littoral
 zones). Zooplankton were sampled in the subsurface of the pelagic zone
 using a motorized pump and a plankton net (68 µm), filtering 600 L water
 per sample. The samples were preserved in 4% formaldehyde solution and
 buffered with calcium carbonate. To identify and enumerate
 (ind.m<sup>-3</sup>) organisms, the samples were analyzed in
 optical microscope under 100 magnification. The abundance of individuals
 was estimated by analyzing minimum three subsamples, equivalent to 10% of
 the total sample, in a Sedgewick-Rafter chamber.