Palaeobaselines for assessing ecosystem health: what is ‘natural’ anyway?

Background to the project

Natural ecosystems are fundamentally changing due to the expanding footprint of human activity, this is leading to deteriorations in ecosystem health. The expanding global population will exacerbate these pressures, which are now undermining the functioning of ecosystems and our access to the ‘ecosystem services’ on which we depend (e.g., our food supply, flood and storm defences, recreation and climate regulation).

 

Attempts to manage the impacts of human activities are constrained by a lack of information on the state of the system and how it relates to the pressures imposed, the ‘pressure-state’ relationship. A key factor in defining this relationship is establishing a ‘reference state’ that requires information on the pre-impact state of ecosystems often referred to as ‘ecological baselines’. However, the data used within management frameworks are rarely ‘true’ baselines because they span only the last few decades and so do not describe a state prior to human pressures. Additionally, they are subject to bias from the ‘shifting baseline’ phenomena, e.g. whereby the temporally-limited knowledge-base of the observer, continually shifts and so does not reflect the ‘natural’ state. These problems can be circumnavigated by the inclusion of baselines that predate human activities.

 

Using fossil and extant foraminifera (calcified, single celled marine protists; figured above) we will construct baselines for marine ecosystem health. Ecological quality status assessments within the European Water Framework and Marine Strategy Framework Directives employ a range of indices including the Azti Marine Biotic Index (AMBI; Borja et al. 2011), which are used to assess ecosystem health based on seafloor macroinvertebrates. Foram-AMBI, a modification of AMBI which uses foraminifera, has been suggested as a valuable addition to this toolkit. Being highly sensitive to their environment both populations and communities of foraminifera can respond quickly to environmental change (e.g., the presence of organic pollution, desalination discharges, oil spills, and heavy metal pollution) by altering their characteristics (e.g., changes in test morphology, composition, thickness, and morphology) and behaviour (e.g., living habit, feeding mode and life history), makes them useful for assessing ecosystem health (O’Brien et al. 2021). At present the application of foram-AMBI is limited by a lack of data for calibration, specifically the need for robust ecological baselines spanning a range of different environments and regions.

 

Project Objectives

By delving deeper into the past, this project will provide more realistic information on what is ‘natural’ or ‘normal’ for marine ecosystems using foraminifera from unique pristine marine ecosystems (that have experienced minimal human impacts) and fossil assemblages that predate human activities. These data can be used to construct baselines and inform management targets. The scope of existing baselines are temporally constrained and do not capture the full range of potential impacts nor ecological responses. The foraminifera underwent major changes across a number of palaeoenvironmental events including the early Toarcian mass extinction (183 million years ago), the Palaeocene–Eocene Thermal Maximum (65 million years ago) and so have the potential to describe the full range of conditions including future climate scenarios. These events for instance describe a similar magnitude of CO2emissions and warming as expected under the IPCC (Intergovernmental Panel on Climate Change) scenarios for 2100.

 

Using both present-day pristine environments (e.g., in Antarctica and sparsely populated regions of Australia) and the fossil record this project will determine exactly what is ‘normal’ for foraminifera assemblages. The utility of the microfossil record to provide baselines of marine ecosystem structure and function prior to human activities will also be assessed, with the objective of developing baselines that can be applied across regions and environments.

 

Comparisons of foram-AMBI with AMBI assessments on macroinvertebrates (e.g. Borja et al. 2011) and macrofossil assemblages (e.g., Caswell et al. 2019) will enable a more complete description of ecosystem change and will allow cross-validation between micro- and macrofossil datasets that have differing preservational bias (higher for the smaller and more numerous microfossils). By combining palaeo-baselines with existing present-day baselines from pristine environments our ability to describe the full range of ‘normal’ ecosystem states and future responses will be considerably improved.

 

Further reading

Borja, Á., et al., 2011. Marine Pollution Bulletin 62, 889–904. LINK

Borja, Á., Dauer, D.M., Grémare, A., 2012. Ecological Indicators 12, 1–7. LINK

Caswell, B. A., Frid, C. L. J., Borja, A. 2019. Marine Pollution Bulletin 140, 472–484. LINK

Frid, C. L. J., Caswell, B. A. 2017. Marine Pollution. Oxford University Press. LINK

O’Brien, P. A., Asteman, I. P., Bouchet, V. M. 2021. Water, 13, 1–33. LINK