The correspondence of morphological and geochemical trait dynamics in shifting plankton communities

Abstract

Humans are changing the Earth. What is unknown is how biotic communities and ecosystems will react to this change on both short and long timescales. The fossil record can provide us with a means of investigating ecosystem responses to long-term climatic fluctuations which can act as baselines for future anthropogenic induced change. How we utilize the fossil record is therefore of critical Importance. The high spatial and temporal resolution of the planktonic foraminifera fossil record provides an ideal system to investigate ecosystem responses to climatic fluctuations at multiple scales and levels. The primary objective of this thesis is to measure and understand the relationship between planktonic foraminifera and their environment, to enable a more biologically informative assessment of the fossil record. I created a diversity record of planktonic foraminifera through the Middle Eocene Climatic Optimum comprising of 22,800 individuals classified to three taxonomic levels and investigated the responses of these assemblages using effective diversity: a novel approach for Palaeogene and deep-time systems (Chapter 2). The results from this study show that analytical size fraction choice is a key determinant of diversity signals in deep-time and furthermore it is small species that maintain ecological function during transient climatic events. I then investigated a key component of these assemblages, Subbotina, using individual morphological and geochemical measurements to link their traits to the environment and assess their persistence through the climatic fluctuations of the Middle Eocene (Chapter 3). I found that longevity of Subbotina is a result of morphological and geochemical trait plasticity resulting in a wide ecological niche which in turn allowed for continued persistence and dominance through the Middle Eocene whilst other groups faltered. Next, I explored the relationship between geochemistry and morphology within a relatively recent system to understand the relationship between geochemistry, size, and genetically identified species (Chapter 4). The results showed that fine resolution geochemical analyses can be used to unpick the drivers of intraindividual variability. However, more work is needed to understand the drivers of geochemistry at the individual level which is possible using the methods I advocate and explore in this thesis. Together, these discoveries expand our understanding of how planktonic foraminifera communities are linked to their environment and demonstrate that by using the appropriate analytical approaches we can investigate this relationship in a more biologically meaningful way. Future studies on planktonic foraminifera will require the application of traitbased approaches through the integration of geochemistry, morphology, and diversity measurements to further our understanding of how past communities responded to climatic perturbations with an aim to inform our understanding of biotic responses to current and future anthropogenic change

More information

Identifiers

ORCID for Lorna Kearns: orcid.org/0000-0001-9740-7410

ORCID for Thomas Ezard: orcid.org/0000-0001-8305-6605

Catalogue record

Export record