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

Abstract

Summary: Ecological traits of phytoplankton are being incorporated into models to better understand the dynamics of marine ecosystems and to predict their response to global change. We have compared the distribution of major phytoplankton groups in two different systems: in surface waters of the NW Mediterranean during key ecological periods, and in the DCM (deep chlorophyll maximum) formed in summer in the temperate NE Atlantic. This comparison disentangled the influence of light and nutrients on the relative position of diatoms, dinoflagellates, prymnesiophytes, pelagophytes, chlorophytes, Synechococcus and Prochlorococcus in these environments. Three clusters formed according to their affinity for nutrients: diatoms, chlorophytes and dinoflagellates as the most eutrophic groups; Synechococcus, pelagophytes and prymnesiophytes as mesotrophic groups; and Prochlorococcus as an oligotrophic group. In terms of irradiance, the phytoplankton groups did not cluster clearly. Comparing the nutrient and light preferences of the groups with their distribution in the DCM, dinoflagellates and chlorophytes appear as the most stressed, i.e. their position was most distant from their optimal light and nutrient conditions. Diatoms stayed in deeper than optimal irradiance layers, probably to meet their high nutrient requirements. On the opposite side, low nutrient requirements allowed Prochlorococcus to remain in the uppermost part of the DCM layer. The slight sub-optimal position of Synechococcus and prymnesiophytes with regard to their nutrient requirements suggests that their need for high irradiance plays a significant role in their location within the DCM. Finally, pelagophytes remained in deep layers without an apparent need for the high nutrient concentrations at those depths.Keywords: marine phytoplankton groups; ecological traits; irradiance; nutrients; deep chlorophyll maximum.Influencia de la luz y los nutrientes en la distribución vertical de grupos de fitoplancton marino en el máximo profundo de clorofila Resumen: Las características ecológicas del fitoplancton se están incorporando en modelos con el fin de comprender mejor la dinámica de los ecosistemas marinos y para predecir su respuesta al cambio global. En este trabajo, hemos comparado la distribución de los principales grupos del fitoplancton en dos sistemas diferentes: en las aguas superficiales del Mediterrá-neo noroccidental durante períodos ecológicos clave, y en el Máximo Profundo de Clorofila (MPC) que se forma en verano en el Atlántico NE templado. Esta comparación permitió diferenciar la influencia de la luz y los nutrientes en la posición relativa de diatomeas, dinoflagelados, primnesiofitas, pelagofitas, clorofitas, Synechococcus y Prochlorococcus en estos ambientes. Se pudieron diferenciar tres agrupaciones de acuerdo con su afinidad por los nutrientes: diatomeas, clorofitas y dinoflagelados como los grupos más eutróficos; Synechococcus, pelagofitas y primnesiofitas como grupos mesotróficos; y Prochlorococcus como el grupo más oligotrófico. En térm...

Bio-optical characterization of subsurface chlorophyll maxima in the Mediterranean Sea from a Biogeochemical-Argo float database

“…2) showed a robust relationship (R 2 = 0.86 and slope = 0.97, N = 162). The nitracline that separates upper nitrate-depleted waters from lower repleted waters corresponds, in this paper, to the depth at which [NO − 3 ] is 1 µM smaller than the median [NO − 3 ] value in the first 10 m of the water column (Lavigne et al, 2013). The diffusive vertical supply of nitrates to the euphotic zone is not only influenced by the depth of the nitracline from the sunlit surface layer but also by the slope of the nitracline.…”

“…10b). The seasonal MLD deepening almost never reached the nitracline, thus limiting the nitrate supply to the upper layer of the water column (Dugdale and Wilkerson, 1988;Lavigne et al, 2013;Pasqueron de Fommervault et al, 2015a), hence leading to relatively low surface primary production in this area (Krom et al, 1991;Psarra et al, 2000;Bricaud et al, 2002;Siokou-Frangou et al, 2010). The SCM is a permanent feature in this region, settling below the isolume 0.3 mol quanta m −2 d −1 and far above the nitracline (Fig.…”

Subsurface Chlorophyll-a Maxima in the Southern Ocean

“…Below the SCM, growth is limited by light, and by nutrients above the SCM. At the SCM community shifts can occur due to low rates of mixing as different phytoplankton groups respond differently to changing light, nutrient availability and disproportionate grazing pressures (Strom, 2001;Cullen, 2015;McKie-Krisberg et al, 2015;Latasa et al, 2016Latasa et al, , 2017. Despite these shifts, the community is dominated by picoplankton through the water column (Furuya, 1990;Estrada et al, 2016;Latasa et al, 2017).…”

Oceanic response to the consecutive Hurricanes Dorian and Humberto (2019) in the Sargasso Sea

“…The formation and persistence of the DCM is governed by biophysical processes accounting for both bottom-up and top-down controls (Cullen, 2015;Moeller et al, 2019). However, given that light and nutrient availability are primary factors governing phytoplankton abundance and distribution, they have also been recognized as relevant drivers of phytoplankton communities in the DCM (Latasa et al, 2016). It has been reported that turbulence (like the one induced by storms) can enlarge the phytoplankton density above the DCM (Liccardo et al, 2013) leading to a shoaling of the DCM.…”