The genetic isolation of planktonic foraminifera in the North Pacific gyre and adjacent marginal seas

Abstract

Gaining insight into the speciation processes prevailing in the modern open ocean requires a comprehensive understanding of the spatial dynamics of the planktonic species that inhabit it, calibrated against time. The high-resolution fossil record of the planktonic foraminifera not only provides such insight but also plays a crucial role in the study of past climate. Both rely on understanding how species relate to the current physical and ecological character of the oceanic water masses they inhabit. Within global single cell barcoding and metabarcoding studies of planktonic foraminifera, the North Pacific subtropical and subpolar gyres remain under-sampled, with the capacity to harbour unrecognised ecologically distinct cryptic species. Targeting this issue, Globigerina bulloides specimens were collected during 12 cruises and near shore sampling campaigns throughout the Northern Pacific and marginal seas. Using standard molecular approaches, 406 specimens were genetically characterised and combined with 42 publicly available sequences to provide a fully comprehensive overview of G. bulloides diversity throughout the North Pacific. Of ten globally recognised genotypes, six (Ia, Ic, Id, IIa, IId, IIf) inhabit the water masses south of the Subpolar Front, with only a single genotype (IIe) inhabiting the vast Subpolar gyre and marginal seas. Genetic isolation was found to prevail throughout both the western subtropical waters (Types Ic and Id) and subpolar waters (Type IIe) of the North Pacific together with the North and South Pacific eastern boundary currents (Type IId). Unlike the Atlantic, bipolarity does not occur between the North Pacific and the Southern Ocean subpolar/polar pelagic biomes.