A research indicates that plankton deviated from their diets of absorbing sunlight to eating bacteria in order to make it through the wreck that eliminated the dinosaurs 66 million years ago.
The UK and US researchers examined how fossils of the microscopic algae altered in the rock catalog from before and after the asteroid collision.
Prior to the asteroid collision, microorganisms like planktons obtained their energy via photosynthesis, however, due to the dust cloud from the impact, sunlight was blocked out.
The plankton that resisted the impact could also hunt and eat up bacterial prey — an ability proven by the holes in their shells for the ‘tails’ that let them swim.
‘This event came closest to wiping out all multicellular life on this planet, at least in the ocean,’ said paper author and earth scientist Andrew Ridgwell of the University of California, Riverside.
‘If you remove algae — which form the base of the food chain — everything else should die,’ he added.
‘We wanted to know how Earth’s oceans avoided that fate, and how our modern marine ecosystem re-evolved after such a catastrophe.’
Professor Ridgwell and team examined small fossils of algae that had been conserved in clay-rich residues for the last 66 million years.
Evolutionary computer models were used to simulate how the microorganisms would have functioned before and after the total extinction incident.
‘This blackout or shutdown of primary productivity would have been felt across all of Earth’s ecosystems,’ said paper author and palaeoceanographer Samantha Gibbs of the University of Southampton.
‘The Cretaceous–Paleogene (K–Pg) event is distinct from all other mass extinctions that have shaped the history of life.’
The difference appears ‘both in its rapidity — related to an instantaneous impact event — and its darkness kill mechanism, which shook the foundations of the food chains.’ she explained.
Prior to the K–Pg boundary, plankton skeletons — which was referred to as ‘coccospheres’ by scientists — discovered in the fossil catalog appeared apparently diverse to those conserved from after the catastrophe, the team said.
A big hole in the coccospheres from after the total extinction indicates that the microorganisms had flagella.
The existence of flagella indicates that the plankton had evolved the capacity to grasp food for energy in the lack of sunlight, the researchers said.
‘The only reason you need to move is to get your prey,’ noted Professor Ridgwell.
‘Those species that were lost at the mass extinction show no evidence of a mixotrophic lifestyle and were likely to be completely reliant on sunlight and photosynthesis,’ Dr Gibbs said.
‘Fossils following the K–Pg extinction show that mixotrophy dominated.’
‘Our model indicates this is because of the exceptional abundance of small prey cells — most likely surviving bacteria — and reduced numbers of larger ‘grazers’ in the post-extinction oceans.’
‘The results illustrate both the extreme adaptability of ocean plankton and their capacity to rapidly evolve,’ said Professor Ridgwell.
‘Yet also, for plants with a generation time of just a single day, that you are always only a year of darkness away from extinction.’
‘Mixotrophy was both the means of initial survival and then an advantage after the post-asteroid darkness lifted because of the abundant small pretty cells — likely survivor cyanobacteria.’
‘It is the ultimate Halloween story — when the lights go out, everyone starts eating each other,’ he quipped.