Planktonic food web structure and trophic transfer efficiency along a productivity gradient in the tropical and subtropical Atlantic Ocean

Abstract

Oligotrophic and productive areas of the ocean differ in plankton community composition and biomass transfer efficiency. Here, we describe the plankton community along a latitudinal transect in the tropical and subtropical Atlantic Ocean. Prochlorococcus dominated the autotrophic community at the surface and mixed layer of oligotrophic stations, replaced by phototrophic picoeukaryotes and Synechococcus in productive waters. Depth-integrated biomass of microzooplankton was higher than mesozooplankton at oligotrophic stations, showing similar biomasses in productive waters. Dinoflagellates dominated in oligotrophic waters but ciliates dominated upwelling regions. In oligotrophic areas, microzooplankton consumed ca. 80% of the production, but ca. 66% in upwelling zones. Differences in microzooplankton and phytoplankton communities explain microzooplankton diel feeding rhythms: higher grazing rates during daylight in oligotrophic areas and diffuse grazing patterns in productive waters. Oligotrophic areas were more efficient at recycling and using nutrients through phytoplankton, while the energy transfer efficiency from nutrients to mesozooplankton appeared more efficient in productive waters. Our results support the classic paradigm of a shorter food web, and more efficient energy transfer towards upper food web levels in productive regions, but a microbially dominated, and very efficient, food web in oligotrophic regions. Remarkably, both models of food web exist under very high microzooplankton herbivory.

Zooplankton and Micronekton Active Flux Across the Tropical and Subtropical Atlantic Ocean

“…Stukel et al (2018) explained the energy transfer from the characteristic small phytoplankton (cyanobacteria) of these physical structures to zooplankton due to the role of protists as an important intermediate trophic level in these upwelling systems. Armengol et al (2019) during our cruise observed the Guinea Dome dominated by small cells (picoeukaryotes and Synechococcus), not showing a high microzooplankton biomass compared to other productive stations, but displaying relatively high autotroph growth rates at the surface layer. In any case, oceanic domes are physical structures promoting an important role of the pelagic fauna in the biological pump.…”

“…In the Guinea Dome, lateral transport should also be important as we sampled in the area affected by the westward motion of the cyclonic structure, probably transporting the highly productive coastal upwelled waters. In this sense, Armengol et al (2019) showed a filament-like structure affecting station 8 in their surface map of primary production during the same oceanographic cruise (see their Figure 5). Whatever the effect of zooplankton or lateral advection, in areas of high primary production large organisms are favored (e.g., Frost, 1974), as constant energy fuels their longer lives, therefore, promoting a large biomass.…”

“…The section carried out covered the tropical and subtropical Atlantic Ocean from the very oligotrophic, high stratified waters off Brazil (Figure 2A) to the meso-and eutrophic waters off the Northwest African upwelling. Descriptions of the physical scenario were published elsewhere (Olivar et al, 2017;Armengol et al, 2019). In short, we moved from the South Equatorial Counter Current (SECC, stations 1-3) observing there a deep thermocline and high salinity (Figure 2B).…”

The planktonic protist interactome: where do we stand after a century of research?

“…Dinoflagellates also include species that can form harmful algal blooms (HABs) [51], producing toxins that can have devastating effects on fisheries and aquaculture, making the research on their ecology and life cycles a priority [52]. Other heterotrophic dinoflagellates and ciliates are among the most important microzooplankton predators in the ocean, consuming between 60 and 80% of the primary production every day at a global scale [53][54][55][56]. Although the SAR supergroup dominated PIDA, our comparison of the SAR records with the Tara Oceans data [45] revealed that there are several SAR lineages, which are abundant and diverse in the marine realm, that were underrepresented when it comes to characterization of their ecological roles as interactors in aquatic environments, such as Labyrinthulomycetes and MAST (Stramenopiles), Syndiniales (MALV II; Alveolata), Acantharia, Polycystinea, and Cercozoa (Rhizaria).…”

Plankton Community Changes From Warm to Cold Winters in the Oligotrophic Subtropical Ocean

“…The microbial loop controls most of the flow of energy and matter in subtropical gyres (Pomeroy, 1974;Azam et al, 1983;Longhurst, 1998). Picophytoplankton accounts for a large proportion of the primary productivity (Li et al, 1983), which is mostly consumed by nano-and micrograzers (Calbet and Landry, 2004;Armengol et al, 2019). Micrograzers control more than 80% of primary production in the CanCS (Arístegui et al, 2001;Marañón et al, 2007), and microzooplankton grazing has been pointed out as the principal mechanism limiting the phytoplankton growth both in artificial iron injections (Landry et al, 2000a,b;de Baar et al, 2005;Boyd et al, 2007;Henjes et al, 2007) and in dust addition experiments (Herut et al, 2005;Marañón et al, 2010).…”