Drivers of global pre‐industrial patterns of species turnover in planktonic foraminifera

Abstract

Anthropogenic climate change is altering global biogeographical patterns. However, it remains difficult to quantify how bioregions are changing because pre‐industrial records of species distributions are rare. Marine microfossils, such as planktonic foraminifera, are preserved in seafloor sediments and allow the quantification of bioregions in the past. Using a recently compiled data set of pre‐industrial species composition of planktonic foraminifera in 3802 worldwide seafloor sediments, we employed multivariate and statistical model‐based approaches to study spatial turnover in order to 1) quantify planktonic foraminifera bioregions and 2) understand the environmental drivers of species turnover. Four latitudinally banded bioregions emerge from the global assemblage data. The polar and temperate bioregions are bi‐hemispheric, supporting the idea that planktonic foraminifera species are not limited by dispersal. The equatorial bioregion shows complex longitudinal patterns and overlaps in sea surface temperature (SST) range with the tropical bioregion. Compositional‐turnover models (Bayesian bootstrap generalised dissimilarity models) identify SST as the strongest driver of species turnover. The turnover rate is constant across most of the SST gradient, showing no SST threshold values with rapid shifts in species composition, but decelerates above 25°C, suggesting SST is less predictive of species composition in warmer waters. Other environmental predictors affect species turnover non‐linearly, and their importance differs across regions. In the Pacific ocean, net primary productivity below 500 mgC m−2 day−1 drives fast compositional change. Water depth values below 3000 m (which affect calcareous microfossil preservation) increasingly drive changes in species composition among death assemblages in the Pacific and Indian oceans. Together, our results suggest that the dynamics of planktonic foraminifera bioregions are expected to be highly responsive to climate change; however, at lower latitudes, environmental drivers other than SST may affect these dynamics.

Regional and local environment drive biogeographic patterns in intertidal microorganisms

“…Among few exceptions conducted for marine microorganisms, Holman et al (2021) found that protists and bacteria followed biogeographic structure consistent with metazoans along the coastline of South Africa. Rillo et al (2022) showed that marine planktonic foraminifera are not limited by dispersal among bioregions. These opposing findings call for more research about marine microorganism biogeography and its underlying drivers.…”

Modeling drivers of biodiversity change emphasizes the need for multivariate assessments and rescaled targeting for management

“…The resulting graphs would have shown the contribution of differences in environmental variables to turnover and made interpreting results difficult. Instead, GDM relates changes in temporal turnover to gradients in environmental variables using monotonic I-spline functions (Rillo et al, 2022). In the resulting plots, the maximum height of each curve displays how much overall turnover is explained by each environmental variable.…”

Ocean kinetic energy and photosynthetic biomass are important drivers of planktonic foraminifera diversity in the Atlantic Ocean

“…However, geographic variability of simple community parameters of a planktonic group has been found to be stable enough in time and space, to reflect the spatial characteristics that approach biogeographical distributions (Angel, 1991). Previous studies, focused on free floating unicellular plankton organisms, including foraminifera, have been used to understand the drivers behind species diversity distribution (Rutherford et al, 1999;Hillebrand and Azovsky, 2001;Martiny et al, 2006;Cermeño and Falkowski, 2009;Rodrıǵuez-Ramos et al, 2015;Fenton et al, 2016;Rillo et al, 2022).…”

“…Previous works studying the ForCenS database were all unanimous that temperature is the main driver of foraminifera community changes and respective biodiversity (e.g. Morey et al, 2005;Fenton et al, 2016;Rillo et al, 2022). However, differences arise in terms of the other drivers that were found to be important, mostly according to the environmental datasets used.…”