Intraspecific size variation in planktonic foraminifera cannot be consistently predicted by the environment

Abstract

The size structure of plankton communities is an important determinant of their functions in marine ecosystems. However, few studies have quantified how organism size varies within species across biogeographical scales. Here, we investigate how planktonic foraminifera, a ubiquitous zooplankton group, vary in size across the tropical and subtropical oceans of the world. Using a recently digitized museum collection, we measured shell area of 3,799 individuals of nine extant species in 53 seafloor sediments. We first analyzed potential size biases in the collection. Then, for each site, we obtained corresponding local values of mean annual sea‐surface temperature (SST), net primary productivity (NPP), and relative abundance of each species. Given former studies, we expected species to reach largest shell sizes under optimal environmental conditions. In contrast, we observe that species differ in how much their size variation is explained by SST, NPP, and/or relative abundance. While some species have predictable size variation given these variables ( Trilobatus sacculifer, Globigerinoides conglobatus, Globigerinella siphonifera, Pulleniatina obliquiloculata, Globorotalia truncatulinoides ), other species show no relationships between size and the studied covariates ( Globigerinoides ruber , Neogloboquadrina dutertrei , Globorotalia menardii, Globoconella inflata ). By incorporating intraspecific variation and sampling broader geographical ranges compared to previous studies, we conclude that shell size variation in planktonic foraminifera species cannot be consistently predicted by the environment. Our results caution against the general use of size as a proxy for planktonic foraminifera environmental optima. More generally, our work highlights the utility of natural history collections and the importance of studying intraspecific variation when interpreting macroecological patterns.

Environmental Controls of Size Distribution of Modern Planktonic Foraminifera in the Tropical Indian Ocean

“…We chose size 95/5 because, compared to mean and maximum size, it is less sensitive to single outliers (Rillo et al, 2020;Schmidt, Renaud, et al, 2004). To validate our size spectra, we compared our size 95/5 data with published measurements reported for the TIO from core-top samples (Rillo et al, 2019(Rillo et al, , 2020. We also compared the relative abundances of the species recorded in this study with those reported for the closest sites to our core locations in the ForCenS Database, which compiles planktonic foraminifera assemblages from core-top sediments (Siccha & Kucera, 2017).…”

Determinants of Planktonic Foraminifera Calcite Flux: Implications for the Prediction of Intra‐ and Inter‐Annual Pelagic Carbonate Budgets

“…Sea-surface temperature data used in Figure 2 were taken from the National Centers for Environmental Information AVHRR Analysis and annual sea-surface temperature data used in Figure 3 were obtained from Locarnini et al (2019). Data used in the compilation of annual mean shell fluxes of planktonic foraminifera were taken from Jonkers and Kucera (2015) and from the time series listed in Table 2; morphometric data used in Figure 9b were taken from Rillo et al (2019). All data sources are cited in the references.…”

“…Evidently, the importance of shell flux as a predictor for planktonic foraminifera calcite flux depends on the ratio of variance in the shell flux over variance in the shell mass, specifically shell size. The prediction of inter-annual changes in the calcite flux at sites where the shell flux varies little, for example, at tropical Jonkers and Kucera (2015) and from time series listed in Table 2 and size data from Rillo et al, (2019;Figure 3). Boxes show the interquartile range and whiskers the maximum and minimum values.…”

“…Intra-and inter-annual (light and dark green) variability in (a): shell flux and (b): shell size of the most dominant species at Cape Blanc compared to the global range of annual mean flux and size (brown) of those species. Flux data taken fromJonkers and Kucera (2015) and from time series listed in Table2and size data fromRillo et al, (2019; Figure 3). Boxes show the interquartile range and whiskers the maximum and minimum values.…”

Towards a Fleet of Robots for Orientation, Imaging, and Morphometric Analyses of Planktonic Foraminifera

“…Equally important is the geographic mapping of an intraspecific variation of morphospecies, as shown in Brown (2007), Mary and Knappertsbusch (2015), or recently in Rillo (2019) and Rillo et al (2020). By doing both-mapping geographically and through time-the immigration of ecophenotypic variants of a species from an adjacent niche or a remote regional habitat can be disentangled from overlapping morphotypes within the same lineage.…”