01 Aug 2023
 | 01 Aug 2023
Status: this preprint is currently under review for the journal BG.

Killing the predator: impacts of top predator mortality on global-ocean ecosystem structure

David Talmy, Eric Carr, Harshana Rajakaruna, Selina Vage, and Anne Willem-Omta

Abstract. Recent metanalyses suggest that microzooplankton biomass density scales linearly with phytoplankton biomass density, suggesting a simple, general rule may underpin trophic structure in the global ocean. Here, we use a set of highly simplified food-web models, solved within a global general circulation model, to examine the core drivers of linear predator-prey scaling. We examine a parallel food-chain model which assumes microzooplankton grazers feed on distinct size-classes of phytoplankton, and contrast this with a diamond food-web model allowing shared microzooplankton predation on a range of phytoplankton size classes. Within these two contrasting model structures, we also evaluate the impact of fixed vs. density-dependent microzooplankton mortality. We find that the observed relationship between microzooplankton predators and prey can be reproduced with density-dependent mortality on the top predator, regardless of choices made about plankton food-web structure. Our findings point to the importance of parameterizing mortality of the top predator for models to recapitulate trophic structure in the global ocean.

David Talmy et al.

Status: open (extended)

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David Talmy et al.

David Talmy et al.


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Short summary
The structure of plankton communities is central to global cycles of carbon, nitrogen, and other elements. This study explored the sensitivity of different assumptions about top predator mortality in ecosystem models with contrasting food web structures. In the context of environmental data, we find support for models assuming density-dependent mortality of the top predator, irrespective of assumed food web structure.