Carbonate sediment production by marine fish: quantifying production across carbonate provinces and applications to global marine carbonate modelling

Lead Research Organisation: University of Exeter
Department Name: Geography


A major component of the marine-atmospheric carbon cycle is the precipitation and dissolution of calcium carbonate in seawater. Calcium carbonate is the mineral that makes up rocks such as limestone and chalk. Detailed knowledge of this component is important to our understanding of the global carbon cycle, and to the earth system as a whole. This proposal builds upon recent findings that represent a fundamental and previously unexpected change to our understanding of one aspect of marine carbon cycling, namely carbonate sediment production. Specifically, we have recently discovered an entirely new source of carbonate sediment derived from marine bony fish (like barracuda, flatfish and grouper, collectively known as 'teleosts'). All teleosts precipitate carbonates within their guts as a by-product of continuously drinking Ca- and Mg-rich seawater, excreting the ingested marine Ca and Mg as insoluble carbonate into the marine environment. Funded through a NERC small grant in 2008 (NE/G010617/1) we made a series of remarkable discoveries regarding the significance of these fish-derived carbonates within shallow tropical marine environments, and which have major implications for the field of carbonate sedimentology. Specifically, we showed that in that region fish produce and excrete, in very large amounts, a wide range of fine-grained (mostly <30 micron) precipitated calcium carbonates. This carbonate is in the form of both 'low' and 'high' Mg-calcite, and aragonite. Additionally, using site specific fish biomass and measured carbonate excretion rate data, we estimated that fish produce ~6.1 million kg of calcium carbonate sediment per year across the Bahamian archipelago, and that estimated contributions from fish to total carbonate mud production average ~14 % overall, and exceed 70 % in specific habitats. Finally, we made the crucial observation that the crystals produced by fish occur commonly in the finest sediment fractions of surface sediments from all sedimentary environments examined in the Bahamas, thus demonstrating that such material does indeed represent both a novel and quantitatively important source of marine carbonate sediment.

The above discoveries thus have direct application to conceptual ideas of how shallow marine carbonate factories function both today and in the past. Arising from this however are a series of fundamental questions about the wider global significance of this carbonate sediment source in different marine carbonate depositional environments:

Q1. Do fish produce similar types of fine-grained carbonate sediment (morphologically and compositionally) in different marine environments and what is the range in variability of these carbonate sediments across tropical to cool temperate environmental gradients?

Q2. How do rates of fish-derived carbonate sediment production derived from sites in The Bahamas compare to those in other tropical, subtropical and temperate regions, and can this be reliably predicted from temperature and body size?

Q3. How variable is the preservation (and dissolution) potential of the range of carbonate sedimentary phases produced by fish in different marine environments?

Q4. How do overall rates and phases of carbonate produced in different environments vary as a function of local fish community structure and abundance?

To address these questions we propose to collect data on the types and rates of carbonate sediment produced by fish across a latitudinal gradient (14o to 43oS) that spans tropical through to cool temperate marine environments (~30 to ~12oC), and to use this data: (i) to determine the dissolution/ preservation potential of fish-derived carbonate sediments (as a function of composition and morphology) across these environments; and (ii) to model, at regional and global scales, the volumes and phases of fish-derived sediment that are initially produced, and then either preserved or dissolved in different marine environments.

Planned Impact

This project will address a number of key questions directly arising from the novel data generated through a previous NERC small grant (NE/G010617/1), and which relate to the carbonate sedimentary processes that operate within neritic marine environments. Given: (1) the spatial significance of neritic (<200 m depth) marine environments (continental shelf, banks/bays, coral reef complexes), whose global extent is estimated at ~ 26 million km2; (2) that these environments produce between 40-4000 g of carbonate sediment/m2/yr; and 3) that this neritic sourced carbonate sediment accumulates both in-situ, but also that significant flux occurs to deeper water settings, an improved understanding of the functioning of the neritic marine carbonate cycle is of critical importance both from a marine carbonate cycling and marine geo-environmental perspective. This research has these issues at its heart, and thus there is a tremendous opportunity to develop an exchange of information between scientists from multiple disciplines and those involved in the study of marine carbonate sediment systems as a key component of the global carbon cycle.

The main stakeholders, in addition to academics in relevant disciplines, with an interest in the data generated by this research, will thus be: (1) In the UK at The Centre for Environment, Fisheries and Aquaculture Science (Cefas), and at the Met Office Hadley Climate Centre, Exeter. At Cefas, there is wide ranging interest in global marine fisheries and the impacts of environmental change on fish biomass, and the implications of this for marine systems generally. At the Met Office Hadley Centre, our work has direct relevance to work being conducted in the marine carbon cycle group, specifically because of its potential to contribute key data on the different phases of carbonate produced by fish in different marine environments. Specifically, the Met Office are interested in integrating the data we will generate into a new calcium carbonate module to inform the next-generation Earth System Model HadGEM3-ES. (2) Overseas in each of the marine stations we will visit (e.g., local marine resource managers, research staff at the various institutes, and local environmental and marine conservation organisations), all of whom have an active interest in the functioning and feedbacks that exist between ecological communities and the physical environment.

We will engage with these stakeholders through the following specific activities: (i) Workshops and PDRA placement with the Met Office Hadley Centre, primarily aimed at working with them to integrate the carbonate production and dissolution data into their Earth System Models; (ii) End of project conference/workshop to which we will invite key researchers and stakeholders both from the UK and internationally. Key organisations are likely to include: Cefas, Met Office Hadley Climate Centre, National Oceanographic Centre, Plymouth Marine Laboratory, and the Rosenstiel School of Marine and Atmospheric Science, Miami; (iii) Participation at the Exeter University - Met Office Carbon Cycle Forum where PI Perry will give a talk to discuss various aspects of carbonate production and carbonate cycling, but which fall outside of the immediate activities under (i) and (ii) above; (iv) Give research lectures during each of our overseas fieldtrips at the different marine labs and, at the Sydney and Brisbane labs, offer open public lectures; (v) Offer UK public lectures as part of the "City of Science" initiative in Exeter such as Café Scientifique; and (vi) Develop media-friendly articles for submission to popular science outlets (e.g. New Scientist, Planet Earth).
Description This project commenced in late 2013 and has involved a number of phases of fieldwork - both in Australia/New Zealand and, to support pilot experimental work, in the Bahamas. The project supported the collection of an extensive dataset on fish carbonates across a wide latitudinal range of sites in Australia and New Zealand. Analysis of this data has been exceptionally time consuming, but was completed by the end of the project. A number of papers from this project have now been published, including related to a spin -off side project. The grant also provided an opportunity to start to consider the relevance of fish carbonates in the context of other major sources of marine carbonate mud (through work in the Bahamas) and to undertake more detailed assessments of carbonate preservation potential over time - a body of work that was more appropriately carried out in a region where we could readily isolate key fish and their products ahead of experiment deployment.
Exploitation Route The main science applications will arise from improved understanding of the role of fish in nearshore carbonate production and cycling, with the wider body of research ultimately being used to improve global reef carbonate production models. Policy implications are, at this stage, unclear.
Sectors Environment

Description Leverhulme Trust grant
Amount £156,000 (GBP)
Funding ID RPG-2017-024 
Organisation The Leverhulme Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 12/2017 
End 11/2020