Environmentally induced functional shifts in phytoplankton and their potential consequences for ecosystem functioning

Abstract

Phytoplanktonic organisms are particularly sensitive to environmental change, and, as they represent a direct link between abiotic and biotic compartments within the marine food web, changes in the functional structure of phytoplankton communities can result in profound impacts on ecosystem functioning. Using a trait‐based approach, we examined changes in the functional structure of the southern North Sea phytoplankton over the past five decades in relation to environmental conditions. We identified a shift in functional structure between 1998 and 2004 which coincides with a pronounced increase in diatom and decrease in dinoflagellate abundances, and we provide a mechanistic explanation for this taxonomic change. Early in the 2000s, the phytoplankton functional structure shifted from slow growing, autumn blooming, mixotrophic organisms, towards earlier blooming and faster‐growing microalgae. Warming and decreasing dissolved phosphorus concentrations were linked to this rapid reorganization of the functional structure. We identified a potential link between this shift and dissolved nutrient concentrations, and we hypothesise that organisms blooming early and displaying high growth rates efficiently take up nutrients which then are no longer available to late bloomers. Moreover, we identified that the above‐mentioned functional change may have bottom‐up consequences, through a food quality‐driven negative influence on copepod abundances. Overall, our study highlights that, by altering the phytoplankton functional composition, global and regional changes may have profound long‐term impacts on coastal ecosystems, impacting both food‐web structure and biogeochemical cycles.

Reinterpreting two regime shifts in North Sea plankton communities through the lens of functional traits

“…Our approach shows that the functional composition of both phytoplankton and zooplankton across the whole North Sea changed more after the 1996–2003 regime shift than after the 1980s regime shift, confirming and broadening conclusions from more local studies (Di Pane et al, 2022). In previous works using different metrics of community composition and abundances, the two regime shifts have often been presented as events of similar importance (e.g., Alvarez‐Fernandez et al, 2012; Beaugrand et al, 2014), which might seem to contradict our results obtained with functional trait‐based approaches.…”

“…The composition of a community in functional traits (i.e., its functional composition) is now recognized as an important community metric because it can give important insights into the drivers of community composition (Mouillot et al, 2013) or into the relationship between the community composition and ecosystem functioning (van der Plas, 2019). Functional composition has also been applied successfully to study abrupt shift in communities (Di Pane et al, 2022; McLean et al, 2018). For marine plankton specifically, functional traits are increasingly documented and associated with databases making functional trait‐based approaches available (Litchman & Klausmeier, 2008; Litchman et al, 2013; Martini et al, 2021; Ostle et al, 2021).…”

“…For marine plankton specifically, functional traits are increasingly documented and associated with databases making functional trait‐based approaches available (Litchman & Klausmeier, 2008; Litchman et al, 2013; Martini et al, 2021; Ostle et al, 2021). Yet so far, the only long‐term functional insight on the change of plankton functional composition associated with the North Sea regime shifts is derived from a single coastal time series and focused on phytoplankton (Di Pane et al, 2022). An assessment at the scale of the whole North Sea and including zooplankton remains to be done.…”

Sequencing our way to more accurate community abundance

“…For example, Karlusich et al (2022) highlights the ecological importance of marine phytoplankton including, their position at the foundation of ocean ecosystems and roles in primary productivity and biogeochemical cycles (Field, Behrenfeld, Randerson, & Falkowski, 1998). Under future global change species sorting will potentially alter the composition of functional groups within marine microbial communities (Di Pane, Wiltshire, McLean, Boersma, & Meunier, 2022), which in turn feeds back into the biogeochemical cycles. It is therefore important to know how these communities will be composed in the future, and the consequences to ecosystem services they provide.…”

Sequencing our way to more accurate community abundance

“…For example, Pierella Karlusich et al ( 2022 ) highlight the ecological importance of marine phytoplankton, including their position at the foundation of ocean ecosystems and their roles in primary productivity and biogeochemical cycles (Field et al, 1998 ). Under future global change species sorting will potentially alter the composition of functional groups within marine microbial communities (Di Pane et al, 2022 ), which in turn feeds back into the biogeochemical cycles. It is therefore important to know how these communities will be composed in the future, and the consequences for the ecosystem services they provide.…”