The seasonal succession of optimal diatom traits

Abstract

Diatoms are a successful taxon of primary producers in the world's oceans with significant impact both on biogeochemical cycles and the structure of marine food webs. We present a trait-based model that captures key physical characteristics of diatoms: a silica exoskeleton and a large centric vacuole. We examine how these unique features contribute to the success of diatoms compared to similar-sized, nonvacuolated, shell-less phytoplankton with identical photosynthetic and nutrient uptake machinery. Our predicted seasonal succession of optimal diatom traits and growth rates are consistent with observed annual time series. The respective environmental conditions where the diatom attributes of shell and vacuole confer an advantage over nonvacuolated, shell-less phytoplankton are typical during the transition phases of seasonal cycles-during the early phase when vacuolation provides an advantage in terms of light affinity and protection against protist grazers and late phase when specific nutrient affinity and protection from metazoan grazers are of benefit. Although the model reproduces high light and nutrient affinities as well as observed seasonal patterns of diatom dominance, it fails to predict the high growth rates generally observed in diatoms compared to other phytoplankton taxa. This exposes a conundrum in our mechanistic understanding of phytoplankton trade-offs; namely, if the high growth rate of diatoms is independent of their physical attributes (shell and/or vacuole), why has it not been exploited by nondiatom taxa?

Linking plankton size spectra and community composition to carbon export and its efficiency

“…Gelatinous zooplankton can also largely contribute to carbon export (Luo et al, 2020). Both gelatinous zooplankton and diatoms need different parametrizations relative to their carbon mass, size, and sinking (Kiørboe, 2013; Hansen & Visser, 2019; Cadier et al, 2020), and therefore have not been included in the model.…”

Subsurface Chlorophyll-a Maxima in the Southern Ocean

“…Interestingly, Southern Ocean large diatoms have been observed to increase their buoyancy under bloom conditions, iron addition and decreased light, leading to reduced downward carbon export (Waite et al, 1992;Fisher and Harrison, 1996;Waite and Nodder, 2001;Acuña et al, 2010). Diatoms efficiently use nutrients, due to their ability to take up nutrients rapidly and maintain large nutrient reserves (Lomas and Glibert, 2000;Litchman et al, 2006;Villareal, 2013, 2018;Hansen and Visser, 2019). This coupled with adaptions to low-light environments -including optimized photosystems and photonic crystals that enhance light harvesting -allows large diatoms to be active producers in the pycnocline which receives pulses of nutrients via internal waves (Holligan et al, 1985;Kemp and Villareal, 2013;Strzepek et al, 2019;Goessling et al, 2020).…”

Latitudinal Variation in Plankton Traits and Ecosystem Function

“…This is because investing in phagotrophy appears cheaper than investing in two other traits that would incur more costs than benefits. The model could in principle be extended with traits representing vacuole formation and developing a silica frustule, together with related trade-offs in terms of extra metabolic costs and silica dependence, and benefits from resource acquisition, reduction in predation pressure, and buoyancy regulation (Hansen & Visser, 2019). We expect that these traits would provide more benefit 10.1029/2020GB006564 Global Biogeochemical Cycles than phagotrophy during spring at high latitudes and allow big vacuolated cells covered with silica frustule (diatoms) to dominate during spring in high latitudes (Cadier et al, 2019).…”