Do mixotrophic protists make oligotrophic oceanic gyres sustainable ecosystems?
Lead Research Organisation:
NATIONAL OCEANOGRAPHY CENTRE
Department Name: Science and Technology
Abstract
The aim of the proposal is to explain the functioning of the oligotrophic oceanic gyres, the Earth's largest ecosystems, which profoundly affect global biogeochemistry and climate. Compared to complex biogeochemical dynamics of C and N with their multiple inorganic pools that do not allow their complete microbial budgets to be accurately determined experimentally, a phosphate (P) budget in surface waters, particularly in the P depleted North Atlantic gyre, is easier to quantify because inorganic P has only one dissolved form in which it is taken up by microbes. The project proposes to experimentally test and to numerically model a new concept of a simplest ecosystem i.e. that: mixotrophic protists control the two dominant bacterioplankton populations, Prochlorococcus cyanobacteria and the SAR11 clade, competing for depleted inorganic P. Using a combination of outlined laboratory and oceanic cruise experiments the following hypotheses will be addressed (i) mixotrophic protists rather than heterotrophic protists dominate bacterial phagotrophy in oligotrophic waters; (ii) mixotrophic protists and not phototrophic protists or cyanobacteria dominate primary production in oligotrophic waters; (iii) protist phagotrophy rather than bacterioplankton senescent death / viral lysis dominate nutrient recycling in oligotrophic waters; (iv) an oligotrophic ecosystem controlled by mixotrophic protists is sustainable in terms of P recycling and C budget. The above hypotheses will be tested by employing and further developing methodology that combines multiple labelling of microorganisms with isotopic tracers and flow cytometric sorting, in combination with nutrient bioassay experiments.
Publications
Hartmann M
(2009)
Assessing amino acid uptake by phototrophic nanoflagellates in nonaxenic cultures using flow cytometric sorting.
in FEMS microbiology letters
Grob C
(2015)
Cell-specific CO2 fixation rates of two distinct groups of plastidic protists in the Atlantic Ocean remain unchanged after nutrient addition.
in Environmental microbiology reports
Gómez-Pereira PR
(2013)
Comparable light stimulation of organic nutrient uptake by SAR11 and Prochlorococcus in the North Atlantic subtropical gyre.
in The ISME journal
Hartmann M
(2011)
Comparison of phosphate uptake rates by the smallest plastidic and aplastidic protists in the North Atlantic subtropical gyre.
in FEMS microbiology ecology
Hartmann M
(2014)
Efficient CO2 fixation by surface Prochlorococcus in the Atlantic Ocean.
in The ISME journal
Mojtahid M
(2011)
Grazing of intertidal benthic foraminifera on bacteria: Assessment using pulse-chase radiotracing
in Journal of Experimental Marine Biology and Ecology
Aldridge D
(2014)
Growth and survival of Neoceratium hexacanthum and Neoceratium candelabrum under simulated nutrient-depleted conditions
in Journal of Plankton Research
Zubkov MV
(2008)
High bacterivory by the smallest phytoplankton in the North Atlantic Ocean.
in Nature
Hartmann M
(2013)
In situ interactions between photosynthetic picoeukaryotes and bacterioplankton in the Atlantic Ocean: evidence for mixotrophy.
in Environmental microbiology reports
Grob C
(2011)
Invariable biomass-specific primary production of taxonomically discrete picoeukaryote groups across the Atlantic Ocean.
in Environmental microbiology
Description | Oligotrophic subtropical gyres are the largest oceanic ecosystems, covering >40% of the Earth's surface. Unicellular cyanobacteria and the smallest algae (plastidic protists) dominate CO2 fixation in these ecosystems, competing for dissolved inorganic nutrients. Here we present direct evidence from the surface mixed layer of the subtropical gyres and adjacent equatorial and temperate regions of the Atlantic Ocean, collected on three Atlantic Meridional Transect cruises on consecutive years, that bacterioplankton are fed on by plastidic and aplastidic protists at comparable rates. Rates of bacterivory were similar in the light and dark. Furthermore, because of their higher abundance, it is the plastidic protists, rather than the aplastidic forms, that control bacterivory in these waters. These findings change our basic understanding of food web function in the open ocean, because plastidic protists should now be considered as the main bacterivores as well as the main CO2 fixers in the oligotrophic gyres. |
Exploitation Route | Through publications and data archived at BODC |
Sectors | Education,Environment |