A size‐structured food‐web model for the global ocean

Abstract

We present a model of diverse phytoplankton and zooplankton populations embedded in a global ocean circulation model. Physiological and ecological traits of the organisms are constrained by relationships with cell size. The model qualitatively reproduces global distributions of nutrients, biomass, and primary productivity, and captures the power‐law relationship between cell size and numerical density, which has realistic slopes of between −1.3 and −0.8. We use the model to explore the global structure of marine ecosystems, highlighting the importance of both nutrient and grazer controls. The model suggests that zooplankton : phytoplankton (Z : P) biomass ratios may vary from an order of 0.1 in the oligotrophic gyres to an order of 10 in upwelling and high‐latitude regions. Global estimates of the strength of bottom‐up and top‐down controls within plankton size classes suggest that these large‐scale gradients in Z : P ratios are driven by a shift from strong bottom‐up, nutrient limitation in the oligotrophic gyres to the dominance of top‐down, grazing controls in more productive regions.

Obtaining Phytoplankton Diversity from Ocean Color: A Scientific Roadmap for Future Development

“…This classification is the closest to ocean color PT products as defined above. Though less common, models can also group phytoplankton in terms of size: the model of Ward et al (2012) includes 25 size classes of phytoplankton. The advantage of such an approach is that it can use empirical allometric relationships of key growth parameters (e.g., maximum growth rates).…”

Phytoplankton community structure in relation to vertical stratification along a north‐south gradient in the Northeast Atlantic Ocean

“…Cell size is an important feature to consider from an ecological point of view, as it affects numerous functional characteristics of phytoplankton (Litchman et al 2007). Important advances have therefore been made by models that predict phytoplankton community composition from the size structure of the constituent species (Armstrong 1994;Baird and Suthers 2007;Ward et al 2012). This matches our data, where we find clear differences in the biogeographical distributions of picocyanobacteria (0.6-1 lm), picoeukaryotic phytoplankton (1-2 lm), small nanoeukaryotic phytoplankton (Nano I; 6-8 lm) and larger nanoeukaryotes (Nano II & III; 8-9 lm).…”

Modelling the plankton groups of the deep, peri-alpine Lake Bourget

“…Since long, phytoplankton cell size has been recognized to be an important aspect in determining the ecophysiology of phytoplankton (e.g., Finkel et al, 2010;Litchman et al, 2010, and references therein), and cell size has been increasingly used as a`master trait' (Litchman et al, 2010) in theoretical modelling studies (e.g., Grover, 1991;Armstrong, 1994;Litchman et al, 2009;Kerimoglu et al, 2012, submitted), although the integration of size concept in realistic ecosystem models attempting to reproduce mesocosm or eld observations at relevant ecological time scales has been gaining momentum only recently (but see, e.g., Ward et al, 2012;Wirtz, 2013;Terseleer et al, 2014). Following many decades of dichotomous classi cation of planktonic organisms as`autotrophs' and`heterotrophs' (Flynn et al, 2012), importance of mixotrophy in ecosystem functioning has been increasingly recognized (Mitra et al, 2014, and references therein).…”