Phytoplankton size diversity and ecosystem function relationships across oceanic regions

Abstract

Trait diversity, a key component of biodiversity, mediates many essential ecosystem functions and services. However, the mechanisms behind such relationships at large spatial scales are not fully understood. Here we adopt the functional biogeography approach to investigate how the size composition of phytoplankton communities relates to primary production and export production along a broad latitudinal gradient. Using in situ phytoplankton size distribution data and a trait-based model, we find an increase in the average phytoplankton size, size diversity, primary production and export when moving from low to high latitudes. Our analysis indicates that the interplay between spatio-temporal heterogeneities in environmental conditions and a trade-off between the high affinity for nutrients of smaller cells and the ability to avoid predation by larger cells are the main mechanisms driving the observed patterns. Our results also suggest that variations in size diversity alone do not directly lead to changes in primary production and export. The trade-off thus introduces a feedback that influences the relationship between size diversity and ecosystem functions. These findings support the importance of environmentally mediated trade-offs as crucial mechanisms shaping biodiversity and ecosystem function relationships at large spatial scales.

Scaling‐up biodiversity‐ecosystem functioning research

“…We need stronger links between the scaling theory, spatially explicit models of species networks that link functional diversity to (a)synchronous patterns of biomass variation that characterise the change in selection and complementarity effects of diversity on ecosystem processes in space and time. A new generation of networked experiments, surveys and remote-sensing observations are needed to inform global ecosystem models that incorporate BEF knowledge (Enquist et al 2003;Ward et al 2012;Harfoot et al 2014;Asner & Martin 2016;Lausch et al 2016;Acevedo-Trejos et al 2018;Schweiger et al 2018;Tr eguer et al 2018). These connections must be understood if BEF research is to foster progress towards the UN's Sustainable Development Goals and our efforts to manage biodiversity for the many benefits ecosystems provide people from local to global scales (Dee et al 2017;Isbell et al 2018).…”

“…Future theory and empirical research could assess three predictors of interspecific synchrony. The first is forcing caused by fluxes in energy which varies considerably across scales on land and in the oceans (Carrara & V azquez 2010;Vogt et al 2011;Acevedo-Trejos et al 2018) and is known to be synchronising when driven by strong periodic cycles (Blauw et al 2018), disturbances (Keitt 2008) and autocorrelated random fluctuations (Petchey et al 1997). This environmental variation engenders different compensatory responses among species or functional groups at different scales, reflecting variation in seasonal and interannual phenology (Thackeray et al 2010;Lasky et al 2016) and asynchronous population fluctuations across trophic levels (Fontaine & Gonzalez 2005;Keitt & Fischer 2006;Vasseur & Gaedke 2007;Loreau & de Mazancourt 2008;Fauchald et al 2011;Vasseur et al 2014;Sheppard et al 2019).…”

Size fractionation, chemotaxonomic groups and bio-optical properties of phytoplankton along a transect from the Mediterranean Sea to the SW Atlantic Ocean

“…Gibb et al (2000) sampled the Atlantic Ocean between 50°N and 50°S and, based on HPLC analyses, recorded a dominance of PSCs to PPCs from 50-30°N, to the north of the start of our survey, to 35-45°S. Acevedo-Trejos et al (2018) used in situ data and traitbased modelling to find an increase of average phytoplankton size and other parameters when moving from low to high latitudes.…”

Abrupt declines in marine phytoplankton production driven by warming and biodiversity loss in a microcosm experiment

“…Analyses have demonstrated positive associations between ecosystem production and community‐level diversity in cell size (Acevedo‐Trejos et al . ), as well as complex interactions between production and traits linked to grazing and nutrient uptake (Prowe et al . ,b; Cermeño et al .…”

“…Models suggest that the unimodality could be due to stronger top-down control by grazers at extreme levels of ecosystem productionthe so-called 'kill the winner hypothesis' (Vallina et al 2014). Analyses have demonstrated positive associations between ecosystem production and communitylevel diversity in cell size (Acevedo-Trejos et al 2018), as well as complex interactions between production and traits linked to grazing and nutrient uptake (Prowe et al 2012a,b;Cermeño et al 2016;Hodapp et al 2016). In freshwater ecosystems, primary production and resource use efficiency have been found to be log-linearly related to taxonomic richness (Ptacnik et al 2008, Striebel et al 2009).…”