Diazotrophic cyanobacteria in planktonic food webs

Sanna Suikkanen,Laura Uusitalo,Sirpa Lehtinen,Maiju Lehtiniemi,Pirkko Kauppila,Katja Mäkinen,Harri Kuosa

doi:10.1016/j.fooweb.2021.e00202

Sanna Suikkanen, Laura Uusitalo + Show 5 more

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https://doi.org/10.1016/j.fooweb.2021.e00202

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Journal: Food Webs	Publication Date: Jun 1, 2021
Citations: 9	License type: cc-by

Affiliation: Finnish Environment Institute, University of Turku

Abstract

Blooms of cyanobacteria are recurrent phenomena in coastal estuaries. Their maximum abundance coincides with the productive period of zooplankton and pelagic fish. Experimental studies indicate that diazotrophic, i.e. dinitrogen (N2)-fixing cyanobacterial (taxonomic order Nostocales) blooms affect zooplankton, as well as other phytoplankton. We used multidecadal monitoring data from one archipelago station (1992–2013) and ten open sea stations (1979–2013) in the Baltic Sea to explore the potential bottom-up connections between diazotrophic and non-diazotrophic cyanobacteria and phyto- and zooplankton in natural plankton communities. Random forest regression, combined with linear regression analysis showed that the biomass of cyanobacteria (both diazotrophic and non-diazotrophic) was barely connected to any of the phytoplankton and zooplankton variables examined. Instead, physico-chemical variables (salinity, temperature, total phosphorus), as well as spatial and temporal variability seemed to have more significant connections to both phytoplankton and zooplankton variables. Zooplankton variables were also connected to the biomass of phytoplankton groups other than cyanobacteria (such as chrysophytes, cryptophytes and prymnesiophytes), and phytoplankton variables had connections with the biomass of different zooplankton groups, especially copepods. Overall, negative relationships between cyanobacteria and other plankton taxa were scarcer than expected based on previous experimental studies.

Highlights

Primary production of organic matter is the basis of secondary pro duction in aquatic systems
Random forest analysis revealed a connection between Nostocales biomass and the biomass of the autotrophic phytoplankton community
Since growth of autotrophic phytoplankton communities is usually N-limited during summer in the study area, the results may indicate that the atmospheric N2 fixed by diazotrophic cyanobacteria was transferred through the food web to coexisting primary producers and supported the increase of other autotrophic phytoplankton biomass

Summary

Introduction

Primary production of organic matter is the basis of secondary pro duction in aquatic systems. Though phytoplankton consists of micro scopic cells, which are visible only by their exceptional growth as ‘blooms’, their communities are a mixture of tens or hundreds of species. These communities include numerous species of prokaryotic cyano bacteria, which are members of the phytoplankton community since they participate in the pelagic primary production to the autotrophic planktonic microalgae. In addition to different sizes, phyto plankton species hold a number of functional traits (Barton et al, 2013), including defense systems against herbivory, which may decrease the usability of primary production by zooplankton (Van Donk et al, 2011)

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