Can warm climate-related structure of littoral predator assemblies weaken the clear water state in shallow lakes?

Authors

  • MARIANA MEERHOFF,

    1. Department of Freshwater Ecology, National Environmental Research Institute, University of Aarhus, Vejlsøvej 25, 8600 Silkeborg, Denmark,
    2. Department of Biological Sciences, University of Aarhus, Ole Worms Allé, Building 135, 8000 Aarhus, Denmark,
    3. Departamento de Ecología, Facultad de Ciencias, Universidad de la República, Iguá 4225, CP 11400, Montevideo, Uruguay,
    4. Grupo de Investigación en Ecología Básica y Aplicada, Asociación Civil I + D, Iguá 4225, CP 11400, Montevideo, Uruguay,
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  • JUAN M. CLEMENTE,

    1. Departamento de Ecología, Facultad de Ciencias, Universidad de la República, Iguá 4225, CP 11400, Montevideo, Uruguay,
    2. Grupo de Investigación en Ecología Básica y Aplicada, Asociación Civil I + D, Iguá 4225, CP 11400, Montevideo, Uruguay,
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  • FRANCO TEIXEIRA De MELLO,

    1. Departamento de Ecología, Facultad de Ciencias, Universidad de la República, Iguá 4225, CP 11400, Montevideo, Uruguay,
    2. Grupo de Investigación en Ecología Básica y Aplicada, Asociación Civil I + D, Iguá 4225, CP 11400, Montevideo, Uruguay,
    3. Grupo de Investigación en Ecotoxicología y Química Ambiental, Facultad de Ciencias, Universidad de la República, Iguá 4225, CP 11400, Montevideo, Uruguay
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  • CARLOS IGLESIAS,

    1. Departamento de Ecología, Facultad de Ciencias, Universidad de la República, Iguá 4225, CP 11400, Montevideo, Uruguay,
    2. Grupo de Investigación en Ecología Básica y Aplicada, Asociación Civil I + D, Iguá 4225, CP 11400, Montevideo, Uruguay,
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  • ASGER R. PEDERSEN,

    1. Department of Freshwater Ecology, National Environmental Research Institute, University of Aarhus, Vejlsøvej 25, 8600 Silkeborg, Denmark,
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  • ERIK JEPPESEN

    1. Department of Freshwater Ecology, National Environmental Research Institute, University of Aarhus, Vejlsøvej 25, 8600 Silkeborg, Denmark,
    2. Department of Biological Sciences, University of Aarhus, Ole Worms Allé, Building 135, 8000 Aarhus, Denmark,
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Mariana Meerhoff, Department of Freshwater Ecology, National Environmental Research Institute, University of Aarhus, Vejlsøvej 25, 8600 Silkeborg, Denmark, fax +45 89201414, e-mail: mm@dmu.dk, merluz@fcien.edu.uy

Abstract

Shallow lakes, the most abundant lake type in the world, are very sensitive to climatic changes. The structure and functioning of shallow lakes are greatly impacted by submerged plants, and these may be affected by climate warming in various, contrasting, ways.

Following a space-for-time substitution approach, we aimed to analyse the role of aquatic (submerged and free-floating) plants in shallow lakes under warm climates. We introduced artificial submerged and free-floating plant beds in five comparable lakes located in the temperate zone (Denmark, 55–57 °N) and in the subtropical zone (Uruguay, 30–35 °S), with the aim to study the structure and dynamics of the main associated communities.

Regardless of differences in environmental variables, such as area, water transparency and nutrient status, we found consistent patterns in littoral community dynamics and structure (i.e. densities and composition of fish, zooplankton, macroinvertebrates, and periphyton) within, but substantial differences between, the two regions. Subtropical fish communities within the macrophyte beds exhibited higher diversity, higher density, smaller size, lower relative abundance of potentially piscivores, and a preference for submerged plants, compared with otherwise similar temperate lakes. By contrast, macroinvertebrates and cladocerans had higher taxon richness and densities, and periphyton higher biomass, in the temperate lakes. Several indicators suggest that the fish predation pressure was much stronger among the plants in the subtropical lakes. The antipredator behaviour of cladocerans also differed significantly between climate zones. Submerged and free-floating plants exerted different effects on the spatial distribution of the main communities, the effects differing between the climate zones. In the temperate lakes, submerged plants promoted trophic interactions with potentially positive cascading effects on water transparency, in contrast to the free-floating plants, and in strong contrast to the findings in the subtropical lakes.

The higher impact of fish may result in higher sensitivity of warm lakes to external changes (e.g. increase in nutrient loading or water level changes). The current process of warming, particularly in temperate lakes, may entail an increased sensitivity to eutrophication, and a threat to the high diversity, clear water state.

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