Algal games: The vertical distribution of phytoplankton in poorly mixed water columns

Abstract

Phytoplankton often face the dilemma of living in contrasting gradients of two essential resources: light that is supplied from above and nutrients that are often supplied from below. In poorly mixed water columns, algae can be heterogeneously distributed, with thin layers of biomass found on the surface, at depth, or on the sediment surface. Here, we show that these patterns can result from intraspecific competition for light and nutrients. First, we present numerical solutions of a reaction-diffusion-taxis model of phytoplankton, nutrients, and light. We argue that motile phytoplankton can form a thin layer under poorly mixed conditions. We then analyze a related game theoretical model that treats the depth of a thin layer of phytoplankton as the strategy. The evolutionarily stable strategy is the depth at which the phytoplankton are equally limited by both resources, as long as the layer is restricted to the water column. The layer becomes shallower with an increase in the nutrient supply and deeper with an increase in the light supply. For low nutrient levels, low background attenuation, and shallow water columns, a benthic layer occurs; for intermediate nutrient levels in deep water columns, a deep chlorophyll maximum occurs; and for high nutrient levels, a surface scum occurs. These general patterns are in agreement with field observations. Thus, this model can explain many patterns of algal distribution found in poorly mixed aquatic ecosystems.

Importance of climate change-physical forcing on the increase of cyanobacterial blooms in a small, stratified lake

“…In stratified lakes with low external nutrient sources, CYAN growth occurs in the deep part of the lakes where P is more abundant, given sufficient light availability. This hypothesis is supported both by existing empirical data on deep phytoplankton maxima, and by models of maximum algal growth in relation to vertical light and nutrient availability (Fee, 1976;Klausmeier and Litchman, 2001).…”

A deep chlorophyll maximum nourishes benthic filter feeders in the coastal zone of a large clear lake

“…At the two shallowest stations, maximum Chl a fluorescence was found at the height measured closest to the lake bottom. These patterns are predicted to occur as a consequence of high water clarity combined with a supply of nutrients from the lake bottom (Klausmeier and Litchman 2001). At some time following offshore stratification, the DCM receded in the shallowest depths.…”

“…Dense subsurface aggregations of viable phytoplankton are predicted to arise in waters with a pycnocline, a gradient of nutrient concentration supplied from depth, and sufficient water-column transparency to support photosynthesis at depth (Klausmeier and Litchman 2001;Hickman et al 2009). These dense aggregations of phytoplankton can be manifest as deep chlorophyll maxima (DCMs), a phenomenon that is observed widely, reported from all the world's oceans (Cullen 1982;Huisman et al 2006), from coastal shelves (Hickman et al 2009), as well as from transparent stratified lakes of a wide range of sizes and geographic distribution (Camacho et al 2003;Burnett et al 2006;Pannard et al 2011).…”

Artificial mixing to control cyanobacterial blooms: a review

“…This can be described by the following set of partial differential equations (Klausmeier and Litchman 2001;Huisman et al 2004):…”