Cell Size Decrease and Altered Size Structure of Phytoplankton Constrain Ecosystem Functioning in the Middle Danube Rive
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Cell Size Decrease and Altered Size Structure of Phytoplankton Constrain Ecosystem Functioning in the Middle Danube River Over Multiple Decades Andra´s Abonyi,1,3* Keve Tihame´r Kiss,2 Andra´s Hidas,2,4 Ga´bor Borics,2,5 ´ cs2,6 Ga´bor Va´rbı´ro´,2,5 and E´va A 1 Centre for Ecological Research, Institute of Ecology and Botany, Alkotma´ny u 2-4, Va´cra´to´t 2163, Hungary; 2Centre for Ecological Research, Danube Research Institute, Karolina u 29, Budapest 1113, Hungary; 3WasserCluster Lunz, Biologische Station GmbH, Dr. Carl Kupelwieser Promenade 5, 3293 Lunz am See, Austria; 4Doctoral School of Environmental Sciences, Eo¨tvo¨s Lora´nd University, Pa´zma´ny Pe´ter se´ta´ny 1/A, Budapest 1117, Hungary; 5Centre for Ecological Research, GINOP Sustainable Ecosystems Group, Hungarian Academy of Sciences, Klebelsberg Kuno u 3, Tihany 8237, Hungary; 6Faculty of Water Sciences, National University of Public Service, Bajcsy-Zsilinszky u 12-14, Baja 6500, Hungary
ABSTRACT Reduced body size is among the universal ecological responses to global warming. Our knowledge on how altered body size affects ecosystem functioning in ectothermic aquatic organisms is still limited. We analysed trends in the cell size structure of phytoplankton in the middle Danube River over a 34year period at multiple levels: (1) average cell size of assemblages (ACS), (2) within the centric diatom community and (3) in the dominant centric diatom taxon: Stephanodiscus. We asked whether global warming and human impacts affected the average cell size of phytoplankton. Also, whether the altered size structure affected how chlorophyll-a, as
Received 25 July 2019; accepted 13 November 2019 Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-019-00467-6) contains supplementary material, which is available to authorized users. Author’s contributions KTK and E´A´ collected samples; AA formulated the idea and measured size of centric diatoms from stored samples; AH and VG built the database; AA performed statistical analyses; AA, GB, E´A´ and KTK contributed to interpreting results; AA wrote the manuscript, and then, all authors contributed to revisions substantially. *Corresponding author; e-mail: [email protected]
an ecosystem functioning measure, relates to the ACS of phytoplankton. The cell size of phytoplankton decreased significantly at all organisation levels, and the assemblages became more dispersed in cell size over time. Environmental variables related to global warming and human impacts affected the ACS of phytoplankton significantly. The relationship between chlorophyll-a and the ACS of phytoplankton shifted from negative linear to broad and then narrow hump shape over time. Longer water residence time, warming and decline in nutrients and suspended solids decrease the ACS of phytoplankton in the middle Danube and expectedly in other large rivers. Our results suggest that cell size decrease in phytoplankton, especially of centric diatoms, constrains planktic algal biomass production in la
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