Phytoplankton play key roles in both marine and freshwater ecosystems and exhibit an incredible diversity in cell morphology. Central to this studentship is asking the related questions:
- Does cell morphology link to a species’ ecological function or the role they play in biogeochemical processes?
- Does form follow function in aquatic environments?
- Does diversity matter in aquatic biogeochemistry?
Predicting ecosystem responses to environmental change on regional and global scales requires a mechanistic, or functional, understanding of the ecological and biogeochemical role of individual species. The development of functional, rather than taxonomic, classifications of phytoplankton has led to major improvements in our ability to assess, understand and predict the function and metabolism of both marine and freshwater ecosystems. However, the development of these functional classifications differs between marine and freshwater systems; in marine systems functional groups relate to biogeochemical roles (e.g. Le Quere et al., 2005), whereas in freshwater systems functional groups relate to responses to environmental variability (e.g. Reynolds et al., 2002, 2014). In these schemes, only a few exemplar species are used to fully represent phytoplankton functional types, which can lead to an oversimplification of their ecologies or functions. In many ways, the unique characteristics of individual species are lost in these interpretations and there is the potential for the loss of key ecological and biogeochemical information (e.g. Kemp & Villereal, 2018).
A major development in our understanding of the ecology of phytoplankton has been the recent focus on ecological traits’ species characteristics such as cell size, motility, life-history, and cellular physiology. Traits often link a species’ cell morphology to its ecological interactions and biogeochemical role. For example, cell size dictates resource acquisition, competition and fate, while cell silica-content in diatoms relates to their propensity for grazing, sinking and their role in carbon cycling (e.g. Fragoso et al., 2018).
What we propose here is an amalgamation of marine and freshwater functional ecology with species-specific traits related to the role of phytoplankton in the global carbon cycle. We want to build a bridge of understanding between marine and freshwater phytoplankton ecology, drawing on their different strengths, to provide insights into how individual species respond to environmental change combined with how this then influences key aquatic biogeochemical processes. Our primary focus is on carbon cycling – linking together species’ ecological traits and functional roles in regulating carbon fixation (primary production), carbon cycling (respiration, organic matter release), carbon export (sinking) and the transfer of organic matter between trophic levels (grazing losses).
The central aim of this studentship is to examine how species traits link to their ecology and biogeochemical role(s), with a specific interest in how aquatic systems cycle carbon.
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Fig 1. Freshwater and marine phytoplankton exist in a huge diversity of cell shape and morphology – how does this diversity in form relate to their ecological and biogeochemical function? (Image sources: Carvalho, L; Widdicombe, C.)