DOES THE ‘LILLIPUT EFFECT’ APPLY TO MARINE MICROPLANKTON? A MORPHOLOGICAL ANALYSIS OF SIZE AND SHAPE IN THE CALCAREOUS NANNOPLANKTON GENUS BRAARUDOSPHAERA FOLLOWING THE CRETACEOUS-PALEOGENE (K-PG) MASS EXTINCTION

The dwarfism of marine vertebrates and invertebrates following mass extinction events has been well documented in the fossil record (the ‘Lilliput effect’). However, except for the planktic foraminifera, little work has been conducted to determine whether these patterns are also observed in the marine microplankton. Because trends in the size of these organisms could greatly affect nutrient availability in the surface ocean, as well as the export efficiency of biogenic material to depth, examining changes in the size of microplankton is critical in our understanding of how marine ecosystems recovered following mass extinction events.

One group of microplankton, calcareous nannoplankton, are unicellular marine autotrophs which have been dominant primary producers since the late Triassic. These organisms were almost completely eradicated by the bolide impact at the Cretaceous Paleogene (K-Pg) boundary (~66 Ma), greatly altering trophic interactions and marine ecosystem structure. One of the only surviving nannoplankton taxa was Braarudosphaera, an enigmatic genus associated with high nutrient, coastal environments, which formed geographically restricted blooms during the K-Pg recovery interval. As one of the only nannoplankton taxa to range across the K-Pg boundary, this genus is ideal for testing whether these organisms also experienced dwarfism after the mass extinction event, and if so, how long it took for them to increase in size.

To address this problem, we have measured the size and shape of the pentagonal calcite plates (pentaliths) produced by Braarudosphaera at four K-Pg sites in the Gulf of Mexico and paleo-Tethyan Ocean. Using multivariate statistical techniques such as Principal Components Analysis (PCA), we aim to determine: (a) whether Braarudosphaera decreased in size after the mass extinction event, (b) whether Braarudosphaera increased in size during the K-Pg recovery interval (and if so how quickly), and (c) whether any observed patterns are local, regional, or global.