“Bloom and Bust” Behavior in Oceanic Plankton: Range-expansions are Rare and Short in Fossil Foraminifera

Abstract:

Oceanic plankton commonly have ocean wide, or even world-wide distributions, suggesting that suitable habitats are widespread. But how persistent are these populations of ocean-spanning species, and how do they change over time? We tested the persistence of globe-spanning ranges by studying both the timing and abundance changes of fossil plankton as they moved throughout the global ocean between 2-3 million years ago. We used a global network of deep-sea sediment cores to track the abundance and biogeographic movements of the planktonic foraminifera, Globorotalia truncatulinoides. Core chronology was established by comparing benthic δ¹⁸O for each site with the global chronology of Lisiecki and Raymo (2004). Globorotalia truncatulinoides evolved in the SW Pacific between 2.942-2.865 Ma, and subsequently dispersed into the tropical Atlantic by 2.528 Ma and then the tropical Pacific by 2.481 Ma. The species was always most abundant in the SW Pacific, whereas in the tropical oceans, foraminifer populations appeared for 20-100 kyr before dropping to such low numbers as to be undetectable. For example, in both the Caribbean and tropical western Atlantic, the species was only present for about 20 kyr and then vanished for nearly 500,000 years. In the tropical Pacific, G. truncatulinoides was sometimes absent for hundreds of thousands of years but periodically bloomed for ~40 kyr intervals before vanishing again. While the species was always present in the SW Pacific, the “Bloom and Bust” behavior of populations in the tropical oceans show that suitable habitats are rarely found there. These oceanic plankton were able to readily disperse into all the tropical and subtropical oceans, but only occasionally supported truly global populations.