Assessing phytoplankton community composition in the Atlantic Ocean from in situ and satellite observations

The Atlantic Meridional Transect (AMT) program (www.amt-uk.org) provides the perfect opportunity to observe the phytoplankton community size structure over a long latitudinal transect 50oN to 50oS, thereby covering the most important latitude-related basin-scale environmental gradients of the Atlantic Ocean. This work presents cell abundance data of phytoplankton taxa recently collected during cruises AMT28 and 29 (in 2018 and 2019, respectively) using flow cytometer and microscope observations, as well as the pigment composition of the community, to assess the abundance and spatial distribution of taxonomic groups across the Atlantic. The community size structure showed a clear consistency between cruises at large spatial scale, with a dominance of picoplanktonic Cyanobacteria in oceanic gyres, an increase in all groups in the equatorial upwelling region, and high biomass of microplankton size class at higher latitudes. Phytoplankton carbon biomass for oceanographic provinces, ranged from median values of 10 to 47 mg Carbon m-3, for the oligotrophic gyres, and South Atlantic (45°S-50oS), respectively. Satellite images of total chlorophyll a (as a proxy for phytoplankton biomass) as well as the relative contribution of the three phytoplankton size classes were produced for both cruises, and despite the small number of matchups, statistically agreed well with in situ size classes estimated as carbon biomass, constituting the first attempt in the literature to match satellite size classes with in situ data derived from cell abundance. The comparison of community structure between recent cruises (2019, 2018, 2015) and earlier ones (1995-1998) indicates a decrease in the number of diatom-bloom forming species, and an increase in Dinoflagellates, whereas nitrogen-fixing Trichodesmium abundance in tropical Atlantic remains constant. Within the recent period, a relative increase in the median values of picoplankton fraction was seen in SATL region, counterbalanced by a decrease in both nano- and microplankton fractions. Additionally, this study includes a database of species identified by microscopy, which had been interrupted for 20 years, providing a basis for long-term series of phytoplankton species

Aspects of the grazing behaviour of the marine dinoflagellate Oxyrrhis marina, Dujardin

The feeding biology and aspects of the grazing behaviour of the dinoflagellate Oxyrrhis marina were studied in a variety of laboratory-based experiments. Video studies on the mode of prey capture revealed that it involved primary capture via Oxyrrhis' transverse flagellum. Further entanglement in the transverse flagellum brought the prey close to the body where trichocysts were ejected to hold the prey while it was phagocytosed. Phagocytosis occurred all over the flagellar and of the body, not being limited to the sulcal region. Capture and ingestion time was dependent on the size of prey, large (20&mu;m) particles taking longer to capture and ingest than small (1&mu;m) particles. Grazing studies were carried out a wide range of autotrophs in batch culture. Food selection experiments identified the ability of Oxyrrhis to discriminate between live prey and inert spheres of the same size, but only after most of the spheres had first been ingested, indicating a form of learning process. Grazing in mixed autotroph populations also indicated selection for a certain autotroph, the cryptomonad Rhodomonas sp. being grazed more heavily than the prasinophyte Tetraselmis suecica and the diatom Phaeodactylum tricornutum. The grazing ability of Oxyrrhis was affected by its nutritional history. Oxyrrhis prefed with T.suecica or Pyramimonas obovata grazed and grew less well than Oxyrrhis prefed with Dunaliella tertiolecta, Rhodomonas sp. or Hemiselmis rufescens. Food quality, in terms of nitrogen available was not found to affect Oxyrrhis growth efficiency but was found to influence growth. The total carbon available was important, both in terms of Oxyrrhis growth and growth efficiency. At low prey biovolumes (&#60; 60x106&mu;m^3 ml^-1) the increase in Oxyrrhis biovolume due to grazing was greater than the biovolume of prey available, indicating that osmotrophy might play a significant role in Oxyrrhis nutrition.</p

High spatial resolution global ocean metagenomes from Bio-GO-SHIP repeat hydrography transects.

Detailed descriptions of microbial communities have lagged far behind physical and chemical measurements in the marine environment. Here, we present 971 globally distributed surface ocean metagenomes collected at high spatio-temporal resolution. Our low-cost metagenomic sequencing protocol produced 3.65 terabases of data, where the median number of base pairs per sample was 3.41 billion. The median distance between sampling stations was 26 km. The metagenomic libraries described here were collected as a part of a biological initiative for the Global Ocean Ship-based Hydrographic Investigations Program, or "Bio-GO-SHIP." One of the primary aims of GO-SHIP is to produce high spatial and vertical resolution measurements of key state variables to directly quantify climate change impacts on ocean environments. By similarly collecting marine metagenomes at high spatiotemporal resolution, we expect that this dataset will help answer questions about the link between microbial communities and biogeochemical fluxes in a changing ocean