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The balance between the uptake of CO2 during phytoplankton photosynthesis and the production of CO2 during bacterial, zooplankton and phytoplankton respiration influences how much carbon can be stored in the ocean and hence how much remains in the atmosphere to affect climate.


Yet, despite its crucial role, our knowledge of the respiration of component plankton groups such as bacteria, is severely limited because we do not have a method which can differentiate the respiration of one group from that of the rest of the community.


The recent development of a much more sensitive method (reduction of the tetrazolium salt INT) which can produce results in minutes and does not involve disruption of the plankton foodweb, is a major step forward and has revealed previously unknown variability in plankton respiration. Unexpectedly, the results also suggest that the proportion of respiration attributable to the bacterial size class is consistently low, even in communities where bacteria are the most numerous plankton.


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Tetrazolium salt INT

This has profound implications for our understanding of the amount of CO2 produced by different plankton groups, and poses two new questions - which size class contributes most to plankton respiration if not the bacterial size class, and what influences the variability in respiration if not the type of plankton present.

Marine scientists including ourselves have excitedly started to use the new INT technique, but it has not been thoroughly tested for all plankton communities. In fact, recent data suggest that the method can sometimes underestimate respiration because not all plankton can take up INT and sometimes overestimate respiration because compounds not associated with respiration can affect the INT. Thus while this method could potentially enable a critical improvement in our understanding and thus prediction of CO2 cycling in the ocean, these new intriguing results cannot be confirmed until a comprehensive test of the method has been completed.


This is what we will do.

The main deliverable of the project


REMAIN has a holistic approach and will quantify plankton respiration and INT reduction during laboratory experiments and also from an oceanographic cruise as part of the Atlantic Meridional Transect (AMT) project. 


Apportionment of plankton respiration to plankton size classes - is of benefit to marine scientists who aim to predict how a changing climate will affect plankton production of CO2, policy makers interested in how much carbon can be stored in the ocean, and potentially commercial companies interested in the development of a fluorescent probe for cell respiration applications in the medical or water quality arenas.


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