I am a Chilean young scientist with a background in Marine Biology (Bachelor's degree obtained in 2012) and Ecology (PhD completed in 2021). Throughout my doctoral studies, I acquired theoretical knowledge and technical skills in plankton ecology and diversity, which included participation in relevant courses and workshops. Under the guidance of experienced advisors, Dr. Peter von Dassow and Dra. Catharina Alves-de-Souza, I gained expertise in the identification and enumeration of functional planktonic types, such as coccolithophores, diatoms, and dinoflagellates. Additionally, I developed skills in linking these data with environmental conditions gathered during cruises.
My research also involved studying natural plankton assemblages to understand their responses to stressors, such as ocean acidification and nutrient scarcity. I received comprehensive training in statistics and scientific writing and participated in research cruises, honing my skills in fieldwork at sea. After comple
EDUCATION
Marine Biologist (Bachelor 2012) and Ecologist (PhD 2021)
Particulate inorganic carbon pools by coccolithophores in low-oxygen–low-pH waters off the Southeast Pacific margin Francisco Javier Díaz-Rosas, Cristian Antonio Vargas, Peter von Dassow Biogeosciences, 2025 A predicted consequence of ocean acidification is the decrease in coccolithophore-produced particulate inorganic carbon (PIC) pools. PIC is thought to enhance the sinking of particulate organic carbon (POC) to deeper waters, potentially influencing the depth of organic matter remineralization and subsurface O2 levels. To explore these potential feedbacks, we examined the relationships between PIC, coccolithophores, carbonate chemistry, and dissolved O2 in the Southeast Pacific open-ocean oxygen minimum zone – a region characterized by naturally low dissolved O2, low pH, and high pCO2 levels. Measurements of PIC and coccolithophore abundance from late spring 2015 and mid-summer 2018 revealed that coccolithophores, particularly Gephyrocapsa (Emiliania) huxleyi, were major contributors to PIC through the shedding of coccoliths. On average, about half of the PIC was attributed to reliably enumerated coccospheres and detached coccoliths, with significantly diminished pools below the euphotic zone. Temperature, O2, and pH emerged as key factors associated with PIC variability. PIC pools and PIC : POC ratios in both surface and subsurface waters in this naturally low-pH–low-O2 zone are lower than available data from most oceanic regions, with the exception of the Western Arctic. Our findings support the prediction that in upwelling regions with a shallow oxygen minimum zone, POC production is promoted by phytoplankton other than PIC-producing coccolithophores due to the injection of nutrient rich but low-pH water. This process decreases PIC : POC ratios, suggesting that the role of PIC in POC sedimentation might be decreased under such conditions. We emphasize that comparing PIC dynamics across diverse upwelling systems will be valuable for understanding how low-pH and low-O2 conditions influence POC fluxes mediated by coccolithophores.
Abundances and morphotypes of the coccolithophore Emiliania huxleyi in southern Patagonia compared to neighbouring oceans and Northern Hemisphere fjords Francisco Díaz-Rosas, Catharina Alves-de-Souza, Emilio Alarcón, Eduardo Menschel, Humberto E. González, Rodrigo Torres, Peter von Dassow Biogeosciences, 2021 Coccolithophores are potentially affected by ongoing ocean acidification, where rising CO2 lowers seawater pH and calcite saturation state (Ωcal). Southern Patagonian fjords and channels provide natural laboratories for studying these issues due to high variability in physical and chemical conditions. We surveyed coccolithophore assemblages in Patagonian fjords during late spring 2015 and early spring 2017. Surface Ωcal exhibited large variations driven mostly by freshwater inputs. High-Ωcal conditions (max. 3.6) occurred in the Archipelago Madre de Dios. Ωcal ranged from 2.0–2.6 in the western Strait of Magellan and 1.5–2.2 in the inner channel and was subsaturating (0.5) in Skyring Sound. Emiliania huxleyi was the only coccolithophore widely distributed in Patagonian fjords (> 96 % of total coccolithophores), only disappearing in the Skyring Sound, a semi-closed mesohaline system. Correspondence analysis associated higher E. huxleyi biomasses with lower diatom biomasses. The highest E. huxleyi abundances in Patagonia were in the lower range of those reported in Norwegian fjords. Predominant morphotypes were distinct from those previously documented in nearby oceans but similar to those of Norwegian fjords. Moderately calcified forms of E. huxleyi A morphotype were uniformly distributed throughout Patagonia fjords. The exceptional R/hyper-calcified coccoliths, associated with low Ωcal values in Chilean and Peruvian coastal upwellings, were a minor component associated with high Ωcal levels in Patagonia. Outlying mean index (OMI) niche analysis suggested that pH and Ωcal conditions explained most variation in the realized niches of E. huxleyi morphotypes. The moderately calcified A morphotype exhibited the widest niche breadth (generalist), while the R/hyper-calcified morphotype exhibited a more restricted realized niche (specialist). Nevertheless, when considering an expanded sampling domain, including nearby southeast Pacific coastal and offshore waters, even the R/hyper-calcified morphotype exhibited a higher niche breadth than other closely phylogenetically related coccolithophore species. The occurrence of E. huxleyi in naturally low pH–Ωcal environments indicates that its ecological response is plastic and capable of adaptation.
Impacts of reduced inorganic N:P ratio on three distinct plankton communities in the Humboldt upwelling system Kristian Spilling, Maria-Teresa Camarena-Gómez, Tobias Lipsewers, Alícia Martinez-Varela, Francisco Díaz-Rosas, Eeva Eronen-Rasimus, Nelson Silva, Peter von Dassow, Vivian Montecino Marine Biology, 2019 The ratio of inorganic nitrogen to phosphorus (NP) is projected to decrease in the Eastern Boundary Upwelling Systems (EBUS) due to warming of the surface waters. In an enclosure experiment, we employed two levels of inorganic NP ratios (10 and 5) for three distinct plankton communities collected along the coast of central Chile (33°S). The primary effect of the NP treatment was related to different concentrations of NO3, which directly influenced the biomass of phytoplankton. In addition, low inorganic NP ratio reduced the seston NP and Chl a-C ratios, and there were some effects on the plankton community composition, e.g., benefitting Synechococcus spp. in some communities. One of the communities was clearly top-down controlled and trophic transfer to grazers was up to 5.8% during the 12 day experiment. Overall, the initial, natural plankton community composition was more important for seston stoichiometry and trophic transfer than the manipulation of the inorganic NP ratio, highlighting the importance of plankton community structure for marine ecosystem functioning.
Over-calcified forms of the coccolithophore Emiliania huxley in high-CO2 waters are not preadapted to ocean acidification Peter von Dassow, Francisco Díaz-Rosas, El Mahdi Bendif, Juan-Diego Gaitán-Espitia, Daniella Mella-Flores, Sebastian Rokitta, Uwe John, Rodrigo Torres Biogeosciences, 2018 Marine multicellular organisms inhabiting waters with natural high fluctuations in pH appear more tolerant to acidification than conspecifics occurring in nearby stable waters, suggesting that environments of fluctuating pH hold genetic reservoirs for adaptation of key groups to ocean acidification (OA). The abundant and cosmopolitan calcifying phytoplankton Emiliania huxleyi exhibits a range of morphotypes with varying degrees of coccolith mineralization. We show that E. huxleyi populations in the naturally acidified upwelling waters of the eastern South Pacific, where pH drops below 7.8 as is predicted for the global surface ocean by the year 2100, are dominated by exceptionally over-calcified morphotypes whose distal coccolith shield can be almost solid calcite. Shifts in morphotype composition of E. huxleyi populations correlate with changes in carbonate system parameters. We tested if these correlations indicate that the hyper-calcified morphotype is adapted to OA. In experimental exposures to present-day vs. future pCO2 (400 vs. 1200 µatm), the over-calcified morphotypes showed the same growth inhibition (−29.1±6.3 %) as moderately calcified morphotypes isolated from non-acidified water (−30.7±8.8 %). Under the high-CO2–low-pH condition, production rates of particulate organic carbon (POC) increased, while production rates of particulate inorganic carbon (PIC) were maintained or decreased slightly (but not significantly), leading to lowered PIC ∕ POC ratios in all strains. There were no consistent correlations of response intensity with strain origin. The high-CO2–low-pH condition affected coccolith morphology equally or more strongly in over-calcified strains compared to moderately calcified strains. High-CO2–low-pH conditions appear not to directly select for exceptionally over-calcified morphotypes over other morphotypes, but perhaps indirectly by ecologically correlated factors. More generally, these results suggest that oceanic planktonic microorganisms, despite their rapid turnover and large population sizes, do not necessarily exhibit adaptations to naturally high-CO2 upwellings, and this ubiquitous coccolithophore may be near the limit of its capacity to adapt to ongoing ocean acidification.
Recent reticulate evolution in the ecologically dominant lineage of coccolithophores El Mahdi Bendif, Ian Probert, Francisco Díaz-Rosas, Daniela Thomas, Ger van den Engh, Jeremy R. Young, Peter von Dassow Frontiers in Microbiology, 2016 The coccolithophore family Noëlaerhabdaceae contains a number of taxa that are very abundant in modern oceans, including the cosmopolitan bloom-forming Emiliania huxleyi. Introgressive hybridization has been suggested to account for incongruences between nuclear, mitochondrial and plastidial phylogenies of morphospecies within this lineage, but the number of species cultured to date remains rather limited. Here, we present the characterization of 5 new Noëlaerhabdaceae culture strains isolated from samples collected in the south-east Pacific Ocean. These were analyzed morphologically using scanning electron microscopy and phylogenetically by sequencing 5 marker genes (nuclear 18S and 28S rDNA, plastidial tufA, and mitochondrial cox1 and cox3 genes). Morphologically, one of these strains corresponded to Gephyrocapsa ericsonii and the four others to Reticulofenestra parvula. Ribosomal gene sequences were near identical between these new strains, but divergent from G. oceanica, G. muellerae, and E. huxleyi. In contrast to the clear distinction in ribosomal phylogenies, sequences from other genomic compartments clustered with those of E. huxleyi strains with which they share an ecological range (i.e., warm temperate to tropical waters). These data provide strong support for the hypothesis of past (and potentially ongoing) introgressive hybridization within this ecologically important lineage and for the transfer of R. parvula to Gephyrocapsa. These results have important implications for understanding the role of hybridization in speciation in vast ocean meta-populations of phytoplankton.
Coexistence in a subtidal habitat in southern Chile: The effects of giant kelp Macrocystis pyrifera overgrowth on the slipper limpet Crepipatella fecunda Francisco J. Díaz, Sandra V. Pereda, Alejandro H. Buschmann Journal of the Marine Biological Association of the United Kingdom, 2015 In many coastal areas substrate is the limiting resource for benthic organisms. Some sessile species can be used as secondary substrate, reducing competition and increasing coexistence. In southern Chile, annual populations ofMacrocystis pyriferarecruit and grow on the shells ofCrepipatella fecunda.This study describes ecological interactions between the kelp and the slipper limpet over an annual cycle. The degree of kelp overgrowth was established by collecting sporophytes and throughin situsubmarine photography over a 10 month period (starting when kelp recruits became visible and ending when sporophytes were no longer present). Changes in the biochemical composition of the limpet tissue were also recorded by chemical analyses, to evaluate the potential effects (positive/neutral/negative) of kelp onC. fecundanutritional condition. The results indicate that both species coexist, although kelp overgrowth may cause a decrease in carbohydrates inC. fecundatissues, restricted to the period when the kelp forest reaches its maximum biomass. Individually, the short duration of the maximum overgrowth period and the size reached byC. fecundafemales (up to 65 mm shell length) may enable rapid limpet recovery, avoiding competitive exclusion. On a population level, theM. pyriferaannual cycle generates the needed ‘break’ forC. fecundapopulations, reducing the effects of kelp overgrowth. Thus, in the view of the neutral effect of kelp overgrowth, together with the positive effect ofC. fecundaonM. pyriferarecruitment described somewhere else, this ecological interaction can be categorized as commensalism.
