Patterns of phytoplankton size structure and productivity in contrasting open-ocean environments

Abstract

A total of 94 vertical profiles of size-fractionated chlorophyll a concentration and primary production rate were obtained along a meridional transect from the United Kingdom to the Falkland Islands (50°N to 50°S) during 4 cruises carried out in April and October 1996 and in April and October 1997. This data set allowed us to characterize the patterns of phytoplankton size-structure and productivity in temperate, oligotrophic, upwelling and equatorial regions. On average, picophytoplankton (0.2 to 2 µm) accounted for 56 and 71% of the total integrated carbon (C) fixation and autotrophic biomass, respectively. Enhanced biomass and productivity contributions by nano-and microplankton took place in the temperate regions and in the upwelling area off Mauritania. Small (< 2 µm in diameter) phytoplankton cells should not be regarded as a background, relatively invariant component of the microbial community, given that most of the latitudinal variability in total photoautotrophic biomass and production was driven by changes in the picophytoplankton. In temperate regions and in the upwelling area off Mauritania, small (< 2 µm) and large (> 2 µm) phytoplankton accounted for a proportion of total biomass that was similar to their shares of productivity. In the oligotrophic and equatorial regions, in contrast, large phytoplankton tended to account for a fraction of the total production that was significantly higher than their share of the biomass. We found that the equatorial upwelling causes an increase in phytoplankton biomass and productivity without altering the typical size structure found in less productive regions such as the subtropical gyres. In the oligotrophic ocean, significant changes in C fixation rates take place without accompanying variations in the magnitude of the phytoplankton standing stocks or the size structure of the microbial community.KEY WORDS: Size distribution · Phytoplankton · Chlorophyll · Primary production · Plankton food webs · Atlantic Ocean Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 216: [43][44][45][46][47][48][49][50][51][52][53][54][55][56] 2001 which determine the magnitude of different C pathways (i.e. size structure of primary production and coupling between production and grazing) are, in turn, under hydrodynamical control (Legendre & Rassoulzadegan 1996).Numerous studies have been carried out in which size-fractionated chlorophyll concentration and primary production are simultaneously quantified in particular geographical areas (see reviews in Tremblay & Legendre 1994, Legendre & Rassoulzadegan 1996. The majority of these observations, however, have been made in coastal and/or temperate environments, with relatively little attention given to tropical and subtropical open-ocean environments. In the tropical and subtropical Atlantic Ocean, only a few studies have dealt with the distribution of size-fractionated phytoplankton (i.e. Platt et al. 1983, Malone et al. 1993, Jochem & Zeitzschel 1993, and these have not c...

Size-fractionated phytoplankton biomass and production in the tropical Atlantic

“…A similar pattern has been previously reported for the Atlantic Ocean by Marañón et al (2001), Fernández et al (2003), Teira et al (2005), and Poulton et al (2006). These authors concluded that the observed mismatch was related, among other factors, to the higher photosynthetic efficiency of larger phytoplankton, and they pointed out that this discrepancy is greater in areas and seasons characterized by low nutrient availability and high irradiance levels (i.e.…”

“…the AMT programme, see Marañón et al, 2000;Marañón et al, 2001;Poulton et al, 2006), and was characterized by very low chl a in the NATR and SATL provinces (<0.1 mg m -3 ) and increased chl a at depth to form a basin scale subsurface chl a maximum. The highest chl a was recorded in the WTRA province at the DCM (0.8 mg m -3 ).…”

“…Marañón et al (2001) described the main patterns of size-fractionated chl a and carbon fixation in the Atlantic Ocean and showed a marked discrepancy between the relative contribution of picophytoplankton to total chl a and primary production, particularly in the oligotrophic gyres (see also Teira et al, 2005). In these ecological domains, the relative contribution of picophytoplankton to total carbon incorporation was lower than its relative contribution to total chl a.…”

“…Although many studies have focused on the sizefractionated chlorophyll a (chl a) and primary production in different marine environments (Tremblay and Legendre, 1994;Legendre and Rassoulzadegan, 1996), only a small fraction of the available size-fractionated phytoplankton information has been recorded from open ocean waters and over large spatial scales (Marañón et al, 2001;Pérez et al, 2006;Morán et al, 2004;Poulton et al, 2006). Marañón et al (2001) described the main patterns of size-fractionated chl a and carbon fixation in the Atlantic Ocean and showed a marked discrepancy between the relative contribution of picophytoplankton to total chl a and primary production, particularly in the oligotrophic gyres (see also Teira et al, 2005).…”

“…In addition, the size distribution of phytoplankton biomass and production should also be known, as it is a major biological factor governing the dynamics and function of the pelagic ecosystem, significantly influencing the rate of carbon export from the upper layers to the ocean's interior (Malone, 1980;Azam et al, 1983;Legendre and Le Fèvre, 1991;Tremblay and Legendre, 1994;Marañón et al, 2001).…”