New study finds no evidence of daily vertical migration in planktic foraminifera

PhD student Ulrike Baranowski on FS Meteor Expedition M140 sampling plankton nets

New study finds no evidence of daily vertical migration in planktic foraminifera 

Birmingham PhD student Ulrike Baranowski is a co-author on a new paper resolving a century old controversy about whether or not the microscopic marine plankton, foraminifera migrate daily through the water column. This work has implications for the accuracy of palaeoenvironmental reconstructions made from these organisms.

Many organisms from plankton to fish migrate vertically through the water column every day, moving towards the surface of the ocean at dawn and descending with dusk in order to escape predation. This phenomena is known as diurnal vertical migration (DVM) and can occur on the scale of metres to hundreds of metres. Planktic foraminifera can not ‘swim’ but may be able to regulate their buoyancy and it’s been suspected since the early 1900s that they may undergo DVM. This is potentially problematic as planktic foraminifera are one of the dominant recorders of surface ocean conditions used in paleoceanographic studies and DVM may introduce significant noise to past surface ocean reconstructions. 

In Autumn 2017, Birmingham PhD student Ulrike Baranowski was part of a team of scientists on board the FS Meteor Expedition M140 “FORAMFLUX”  to the subtropical Atlantic Ocean that aimed to uncover some of the secrets of modern planktic foraminiferal ecology. During the expedition, intense sampling of planktic foraminifera species abundances from multiple depth-segregated plankton net tows were conducted in a small area of the ocean over a 26 hour period. This work, led by the MARUM in Germany, found that all of the planktic foraminifera species sampled maintained relatively consistent depth habitats over the 26 hour period, rejecting the hypothesis that DVM exists in planktic foraminifera. This is good news for studies looking to characterise the calcification depths of species necessary to interpret geochemical proxies in palaeoceanography.

These findings were published this month in a paper led by Julie Meilland at the MARUM, and includes Ulrike Baranowski as a co-author. Find the paper at - doi.org/10.1093/plankt/fbz002/10.1093/plankt/fbz002