ZooSize: Crustacean zooplankton community size distributions across a worldwide set of freshwater lakes

The ZooSize project was formed by a sub-working group of the TTG called Traits & Tech during the GLEON 21.5 virtual meeting (19-10-2020 to 22-10-2020). A post-GLEON meeting (14-01-2021) with interested participants helped to frame the main objective of this study to further develop within the GLEON community.

• This project aims to get well represented individual crustacean zooplankton body length measurements for freshwater lakes across global lake thermal regions (Maberly et al., 2020 - Nature communications). The fundamental research question for this project is: how do size distributions of crustacean zooplankton communities differ across the globe?

To our knowledge, this question has never been answered before (Sprules & Barth, 2016 - Can. J. Fish. Aquat. Sci.), despite recent interesting published studies dealing with average body sizes (Beaver et al., 2020 - J. Plankton Res.; Havens et al. 2015 - Hydrobiologia), general aquatic community size spectra (Atkinson et al., 2021 - Limnol. Oceanogr.; Rossberg et al., 2019 - Nature communications), size diversity index (Sorf et al., 2014 - Hydrobiologia; Brucet et al., 2006 - Estuarine, Coastal and Shelf Science) and more site specific studies (Barth et al., 2019 - Can. J. Fish. Aquat.; Barbiero et al., 2019 - Journal of Great Lakes Research; de Eyto & Irvine, 2007 - Wiley-Blackwell).  

• Body size patterns in zooplankton communities have been linked to both bottom-up (e.g. nutrients and temperature; Daufresne et al., 2009 - PNAS; Sprules & Munawar, 1986 - Can. J. Fish. Aquat. Sci.) and top-down (e.g. fish; Brucet et al., 2017 - Freshwater Biology; Brucet et al., 2010 - Limnol. Oceanogr) drivers.  However, macroecological studies on crustacean zooplankton communities have been limited to testing only bottom-up effects (Beaver et al., 2020 - J. Plankton Res.; Havens et al. 2015 - Hydrobiologia; Pinto-Coelho et al., 2005 - Can. J. Fish. Aquat. Sci.). Elucidating macroecological patterns in zooplankton community size distributions will provide valuable insight into potential effects of climate change, exploitation and nutrient enrichment on zooplankton communities and consequently the ecosystem services that zooplankton provide (e.g. grazing control of phytoplankton, carbon sink and energy transfer to higher trophic levels).   

We hypothesise that zooplankton size distributions will vary across global thermal regions (i.e. temperature-size-rule) and productivity and planktivory gradients.  Interesting questions we would like to investigate are:

1. Do we find different patterns between tropical and temperate lakes? 
2. Do more nutrient rich lakes have more irregular size distributions and lower size diversity, due to strong top-down cascades, than low nutrient lakes? 
3. Are certain size distributions more resilient to perturbations? (i.e. trait redundancy = stability?) For example, do assemblages with high trait variance with the same function (i.e. grazing) control better algae development? (Gianuca et al., 2016 - Proceedings of the Royal Society B) 
4. Does the increased frequency of cyanobacteria blooms (Taranu et al., 2015 - Ecology Letters) affect zooplankton size distributions?
5. Is there an alternative measure to mean size that would have more ecological relevance?

• In this initial stage of the project we are interested in involving participants to contribute to a more extended literature review as well as narrow down the requirements for a potential data call, in line with the zooplankton as indicator group (ZIG) project.

Due to the nature of our aim, we need to target lakes from all thermal regions, get high quality data of individual zooplankton body size measurements as well as information on fish predation pressure, nutrient status, and temperature. For this reason, it may be better to carry out another specific data call (separate from the ZIG project) or consider analyzing targeted old samples with current technology (i.e. FlowCam, optical plankton counter, or any other available technology among interested participants).  The latter would aid in standardizing our dataset and control for variability that would be introduced by using different measurement methodologies.  

• To follow up on this project feel free to email the champions and/or join the GLEON Slack Channel #adhoc-ttg-traitsandtech. We will keep organising regular meetings (i.e. monthly); discussion open and project alive!
• For further information on past meetings discussions feel free to ask us the shared google drive link! Hope to keep working together!

New data call available in https://rosalieb.github.io/rosaliebruelweb/ZooSize.html Looking forward to working with you! Lauren, Rosalie and Maria