Insight into the role of cyanobacterial bloom in the trophic link between ciliates and predatory copepods

Joanna Kosiba,Wojciech Krztoń

doi:10.1007/s10750-021-04780-x

Abstract

An important group of protozooplankton, the ciliates, are a crucial component of aquatic food webs. They are the main grazers on bacteria and algae transferring carbon to higher levels of the food web (metazooplankton and fish fry). Changes in the quality and quantity of protozooplankton can modify the quality and quantity of metazooplankton, especially predatory copepods, causing changes in energy transfer and the matter cycle. Observable climate change is one of the most significant factors promoting the increase of cyanobacterial blooms. Therefore, the aim of this study was to find out how cyanobacterial blooms modify relationships between ciliates (prey) and copepods (predator), and to discover possible pathways of changes in freshwater food webs. We analysed the relationship between the biomass of predatory copepods and feeding guilds of ciliates (algivorous, bacterivorous, bacteri-algivorous). The relationship of predators biomass with algivorous and bacteri-algivorous ciliate biomasses, with a simultaneous lack of relationship with bacterivorous ciliate biomass, demonstrates that bacterial fixed carbon may be only partially contributing to the total energy passed through this link. Results demonstrated that the bloom enhanced the relationship between prey and predator. Larger and free-swimming ciliate species appear to play a greater role in energy transfer than smaller sedentary species.

Highlights

Zooplankton species, both proto- and metazooplankton, are directly or indirectly dependent on primary producers (Pace & Lovett, 2013), which in all waterbodies are phytoplankton
We found cyanobacterial blooms in all four waterbodies
Our results suggest that the ciliate–predatory copepod link in eutrophic aquatic ecosystems is a significant pathway of energy flow, functioning both under non-bloom and bloom periods

Summary

Introduction

Zooplankton species, both proto- and metazooplankton, are directly or indirectly dependent on primary producers (Pace & Lovett, 2013), which in all waterbodies are phytoplankton. One particular group included by ecologists as phytoplankton are cyanobacteria. Many species of cyanobacteria are capable of releasing cyanotoxins which can negatively affect other organisms or become concentrated via bioaccumulation, threatening aquatic and terrestrial organisms (Papadimitriou et al, 2010; Martins et al, 2011; Paldaviciene_ et al, 2015). It can be seen that one of the negative effects of cyanobacterial blooms is a decrease in biodiversity of water ecosystems, including in particular the zooplankton group (Kosiba et al, 2018) and changes in their functional groups (Krztonet al., 2019; Krzton & Kosiba, 2020)

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Conclusion