Phytoplankton across Tropical and Subtropical Regions of the Atlantic, Indian and Pacific Oceans

Abstract

We examine the large-scale distribution patterns of the nano- and microphytoplankton collected from 145 oceanic stations, at 3 m depth, the 20% light level and the depth of the subsurface chlorophyll maximum, during the Malaspina-2010 Expedition (December 2010-July 2011), which covered 15 biogeographical provinces across the Atlantic, Indian and Pacific oceans, between 35°N and 40°S. In general, the water column was stratified, the surface layers were nutrient-poor and the nano- and microplankton (hereafter phytoplankton, for simplicity, although it included also heterotrophic protists) community was dominated by dinoflagellates, other flagellates and coccolithophores, while the contribution of diatoms was only important in zones with shallow nutriclines such as the equatorial upwelling regions. We applied a principal component analysis to the correlation matrix among the abundances (after logarithmic transform) of the 76 most frequent taxa to synthesize the information contained in the phytoplankton data set. The main trends of variability identified consisted of: 1) A contrast between the community composition of the upper and the lower parts of the euphotic zone, expressed respectively by positive or negative scores of the first principal component, which was positively correlated with taxa such as the dinoflagellates Oxytoxum minutum and Scrippsiella spp., and the coccolithophores Discosphaera tubifera and Syracosphaera pulchra (HOL and HET), and negatively correlated with taxa like Ophiaster hydroideus (coccolithophore) and several diatoms, 2) a general abundance gradient between phytoplankton-rich regions with high abundances of dinoflagellate, coccolithophore and ciliate taxa, and phytoplankton-poor regions (second principal component), 3) differences in dominant phytoplankton and ciliate taxa among the Atlantic, the Indian and the Pacific oceans (third principal component) and 4) the occurrence of a diatom-dominated assemblage (the fourth principal component assemblage), including several pennate taxa, Planktoniella sol, Hemiaulus hauckii and Pseudo-nitzschia spp., in the divergence regions. Our findings indicate that consistent assemblages of co-occurring phytoplankton taxa can be identified and that their distribution is best explained by a combination in different degrees of both environmental and historical influences.

Trophic Diversity of Plankton in the Epipelagic and Mesopelagic Layers of the Tropical and Equatorial Atlantic Determined with Stable Isotopes

“…The observed changes in stable isotope composition of seston and plankton are consistent with the differences in productivity and likely in the phytoplankton composition between these zones The enrichment in heavy carbon isotopes (that is, less negative δ 13 C values) found in seston and zooplankton in zone 1 is indicative of the dominance of diatoms [14], also characteristically associated with phytoplankton blooms induced by the upwelling [24]. In contrast, low δ 13 C values of the same compartments in the tropical and equatorial zones agree with the dominance of picophytoplankton and other non-diatom phytoplankton groups in these waters [36]. For instance, δ 13 C values for seston fractions dominated by picophytoplankton (0.7-2 µm) were 2-3‰ lower than those dominated by diatoms (2-64 µm) in the western Mediterranean [37] Nitrogen sources may also vary between zones, even when the observed δ 15 N values for seston in the epipelagic layer suggest otherwise.…”

Higher contribution of globally rare bacterial taxa reflects environmental transitions across the surface ocean

“…Hence, higher annual chlorophyll values might reflect a greater diversity of microbial niches (e.g., different phytoplankton blooms along the year) that allow the coexistence and/or the sequential establishment of specialist taxa unable to thrive in more oligotrophic conditions, some of which may be currently present as remnants of past proliferations (Comte, Berga, Severin, Logue, & Lindstrom, ). Interestingly, only a few logistic OTUs (seven to 19 OTUs per area, Supporting Information Figure ) became abundant in these more productive sites, reflecting local selection of taxa rather than massive immigration events (i.e., mass effects, Niño‐García, Ruiz‐González, & Giorgio, ), even though upward transport of deeper ocean communities can happen in some of these areas (Estrada et al, ). Along these lines, the differences between the two LG subclusters are also illustrative.…”

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

“…Among those of other scientists, the studies by Marta Estrada have explored the distribution of diatoms, dinoflagellates, coccolithophores and other phytoplankton groups and species in relation to physical structures such as fronts (Estrada and Salat 1989, Estrada 1991, Estrada et al 1999, upwelling mesoscale heterogeneities (Estrada 1978) and the deep chlorophyll maximum (DCM) layer (Estrada 1985). In a very rough summary of those extensive works, Estrada and collaborators showed that diatoms dominated high biomass situations and occasional high chlorophyll patches in the DCM layer (Estrada 1991), whereas dinoflagellates, including heterotrophic forms because of the methodological limitation of light microscopy, showed a preference for the upper euphotic layers (Estrada 1985, 1991, Estrada et al 2016, and coccolithophores were abundant occasionally in areas of relative fertility (Estrada 1985, Estrada and Salat 1989, Estrada et al 1999. Cullen et al (2002) included picoplankton (small cells which are part of the microbial loop) and Mouriño-Carballido et al (2016) distinguished the position of Prochlorococcus, Synechococcus and photosynthetic picoeukaryotes in a plane of nutrient concentrations and mixing similar to Margalef's mandala.…”