Light and growth in marine phytoplankton: allometric, taxonomic, and environmental variation

Abstract

Light-dependent growth of phytoplankton is a fundamental process in marine ecosystems, but we lack a comprehensive view of how light utilization traits vary across genotypes and species, and how this variation is structured by cell size, taxonomy, and environmental gradients. Here, we compile 308 growth-irradiance experiments performed on 119 species of marine phytoplankton from all major functional groups, and characterize growth-irradiance relationships in terms of the initial slope of the growth-irradiance curve (a), the optimal irradiance above which growth declines (I opt ), and the maximum growth rate (l max ). We find that a declines with increasing cell size, although cell size appears to be a weak constraint on this trait. There are significant differences across taxa in a and l max , with dinoflagellates, raphidophytes, and diazotrophs having the lowest values for both traits, and Phaeocystis spp. and diatoms having relatively high values. I opt does not vary among taxonomic groups, and all traits exhibit large variation within most groups. Open-ocean isolates tend to have higher a, lower I opt , and lower l max than coastal isolates, implying adaptation to low light and low productivity. The three traits are correlated across species such that a and I opt are negatively related while l max is positively correlated with both of these traits. There is some evidence that high a carries a cost of high N demand even when nitrogen (not light) is limiting. The results elucidate contrasting light-related ecological strategies across phytoplankton and should help improve the parameterization of major functional groups in biogeochemical models.

Influence of light and nutrients on the vertical distribution of marine phytoplankton groups in the deep chlorophyll maximum

“…The studies on which this work is based correspond to the most representative seasonal periods of the NW Mediterranean (Latasa et al 2010), a small but representative area for temperate oceans with deep winter mixing and a typical spring bloom (D'Ortenzio and Ribera d'Alcalà 2009), and to the summer conditions in the NE Atlantic (Cabello 2015), where a typical temperate DCM corresponding to a deep biomass maximum occurs. Models incorporating the traits of phytoplankton groups are usually based on laboratory studies of individual species (Gregg et al 2003, Litchman et al 2006, Schwaderer et al 2011, Edwards et al 2015). Here we have used a procedure different from what is habitually assumed as a traitbased approach.…”

Microbial community structure in the western tropical South Pacific

“…The lack of variability of PPE abundance maxima relative to PAR, along with the decoupling of PPE maxima from the nitracline at LDB, suggest PPE abundances to be primarily controlled by light levels rather than by the availability of dissolved nutrients. However, it is difficult to consider these factors independently, with the increased chlorophyll concentrations required at low light levels likely increasing nitrogen requirements on shadeadapted organisms (Edwards et al, 2015).…”

Microbial community structure in the Western Tropical South Pacific

“…While some general in situ trends are apparent-for example the predominance of Synechococcus and P PE in nutrient rich waters and the predominance of Prochlorococcus in nutrient depleted regions-spatial and temporal variability provide significant challenges to the generalization of these patterns at a global level (Fuhrman, 2009). And while there are accounts of microbial community structure in oligotrophic regions of the North Atlantic (Partensky et al, 1996) and North Pa-10 cific (Campbell and Vaulot, 1993;Karl, 1999), as well as for the Mediterranean (Denis et al, 2010) and Arabian Seas (Campbell et al, 1998), the South Pacific remains less well documented.…”

“…The lack of variability of PPE abundance maxima relative to PAR, along with the decoupling of PPE maxima from the nitracline at LDB, suggest PPE abundances to be primarily controlled by light levels rather than by the availability of dissolved nutrients. However, it is difficult to consider 25 these factors independently with the increased chlorophyll concentrations required at low light levels likely increasing nitrogen requirements on shade-adapted organisms (Edwards et al, 2015).…”