Prochlorophytes as secondary prey for heterotrophic nanoflagellates in the deep chlorophyll maximum layer of the (sub)tropical North Atlantic (original) (raw)
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Journal of Plankton Research, 1997
Phytoplankton <2-3 \im in diameter, or autotrophic picoplankton, can constitute the majority of the biomass and productivity of photosynthetic organisms in marine and freshwater systems. Indirect evidence has indicated that mortality of autotrophic picoplankton occurs principally at night in the open ocean, but continuously in coastal water, lie predominant view of the fate of autotrophic picoplankton production in the ocean is that they are consumed by heterotrophic nanoflagellates. A possible mechanism to explain these observations is that grazing of heterotrophic nanoflagellates on autotrophic picoplankton is inhibited by ultraviolet radiation (UV), at least in clear open-ocean environments. A series of laboratory experiments was conducted to examine the effects of UV radiation on the grazing impact of two heterotrophic nanoflagellates on Synechococcus spp., a commonly occurring genus of autotrophic picoplankton. The two nanoflagellates used were Paraphysomonas bandaiensis and Paraphysomonas imperforata. For both nanoflagellates, there was an inverse relationship between the grazing mortality of Synechococcus and UV irradiance. The grazing mortality of Synechococcus was reduced less with P.imperforata than with P.bandaiensis. In some experiments, the effect of UV on the grazing impact of the nanoflagellate populations was caused in part by UV-related reductions in nanoflagellate survival. However, UV reduced the grazing impact of nanoflagellates primarily by reducing the rates of consumption of Synechococcus by individual nanoflagellates, to a degree directly related to UV irradiance. The results suggest that UV radiation may be an important selection factor in clear open-ocean water, and that in order to predict the effect of increasing UV radiation on marine microbial plankton communities, we must consider interactions between trophic levels as well as effects on single trophic levels.
Microbial Ecology, 2009
We investigated seasonal variation of grazing impact of the pigmented nanoflagellates (PNF) with different sizes upon Synechococcus in the subtropical western Pacific coastal waters using grazing experiments with fluorescently labeled Synechococcus (FLS). For total PNF, conspicuous seasonal variations of ingestion rates on Synechococcus were found, and a functional response was observed. To further investigate the impact of different size groups, we separated the PNF into four categories (<3, 3-5, 5-10, and >10 μm). Our results indicated that the smallest PNF (<3 μm PNF) did not ingest FLS and was considered autotrophic. PNF of 3-5 μm in size made up most of the PNF community; however, their ingestion on Synechococcus was too low (0.1-1.9Syn PNF −1 h −1) to support their growth, and they had to depend on other prey or photosynthesis to survive. The ingestion rate of the 3-5 μm group exhibited no significant seasonal variation; by contrast, the ingestion rates of 5-10 and >10 μm PNFs showed significant seasonal variation. During the warm season, 3-5 μm PNF were responsible for the grazing of 12% of Synechococcus production, 5-10 μm PNF for 48%, and >10 μm PNF for 2%. Taken together, our results demonstrate that the PNF of 3-10 μm consumed most Synechococcus during the warm season and exhibited a significant functional response to the increase in prey concentration.
Aquatic Microbial Ecology, 1997
An intensive 5 wk study was conducted to investigate the role of protists, especially heterotrophic nanoflagellates (HNF), in microbial food webs during the summer phytoplankton bloom in the epilimnion and metalimnion of the eutrophic h m o v reservoir (South Bohemia. Czech Republic). On average, protists consumed -90 % of bacterial production in both layers. The community composition of HNF and the relative importance of different HNF groups as picoplankton consumers were determined. Small HNF ( < 8 pm), as chryson~onads, bodonlds and choanoflagellates, usually accounted for <30% of total HNF biomass but numerically dominated the community in both layers They consumed most of (-70 to 85 %) the bacterioplankton as well as autotrophic picoplankton (APP, exclusively cyanobacteria) production in the reservoir, with the rest consumed by ciliates. Both ciliates and HNF had higher clearance rates on APP than on bactena and their grazing was likely responsible for a sharp decrease in APP abundance (from 3-4 X 105 to <2 X 103 ml-') and a very constant size structure of bacterioplankton in which short rods in the size class of 0.4 to 0.8 pm constituted 55 to 80':') of the total bacterial biomass in both layers. The proportion of HNF to total picoplankton biomass in the epilimnion indicated that the picoplankton biomass was sufficiently high to support HNF growth for most of the study. Uptake of picoplankton by less numerous, but larger, HNF (kathablepharids, Goniomonas sp., and Streptomonas sp.) was negligible, while their biomass, especially in the metalimnion, exceeded that of smal.1 HNF and the total biomass of picoplankton. This suggested that food items other than picoplankton were consumed to meet their carbon requirements. Analyzing potential bottom-up and top-down factors controlling HNF numbers and biomass, we dld not find a tight relationsh~p between HNF and the concentration of baclerid dnd chlorophyll. Variab~iity of HNF abundance and biomass in the epilimnion could largely be explained by cladocerans or by pooled abundances of all potential crustacean consumers of HNF. In the metalimnion, the mean cell volume of HNF was positively linked to chlorophyll but negatively to the abundance of Cyclopidae and to the pooled abundances of Ceriodaphnia quadrangula and Diaphanosoma brachyurum.
About Pigmented Nanoflagellates and the Importance of Mixotrophy in a Coastal Upwelling System
Frontiers in Marine Science, 2020
Mixotrophy, understood as food ingestion and photosynthesis occurring in the same organism, is a nutrition mode relatively common in marine protists. Among these, pigmented nanoflagellates 2-20 µm in size (PNF) are now known to be responsible for a significant part of consumption of bacteria in the open ocean. However, knowledge about the importance of the mixotrophic nutrition of these organisms in coastal upwelling systems, where autotrophy prevails, is very limited. Here we compile the limited available information about mixotrophy of PNF in coastal upwelling systems, focusing on the NW Iberian upwelling, to show that this type of nutrition is relevant in these productive systems and to urge for further studies. Several indirect approaches allow inferring that mixotrophy is significant for PNF in the NW Iberian upwelling, with heterotrophy supplying approximately seventy-five percent of the total carbon requirements in this plankton group. This new insight has major implications for our view of marine food webs in coastal upwelling regions, and must be taken into account to improve biogeochemical models of the transfer of matter and energy in these marine areas.
Journal of Geophysical Research, 2005
1] Heterotrophic nanoflagellates and ciliates and their herbivorous activity were studied within the framework of the Programme Océan Multidisciplinaire Méso Echelle (POMME) in the northeastern Atlantic between 16°-22°W and 38°-45°N during winter, spring, and late summer/autumn 2001. Ciliate ingestion rates of Synechococcus and eukaryotic algae were measured using fluorescently labeled prey. Heterotrophic nanoflagellate ingestion rates of Synechococcus and Prochlorococcus were also estimated. Heterotrophic nanoflagellate and ciliate standing stock within the surface layer (0-100 m) showed seasonal variation, with maximal values in spring (866 mg C m À2 and 637 mg C m À2 , respectively). Oligotrichs dominated the ciliate assemblages, except at one site visited during spring, where a tintinnid bloom was observed. Ingestion of photosynthetic cells less than 10 mm in size was positively correlated (r = 0.7, p < 0.05, n = 12) with primary production and accounted for 2-94% of this. Phytoplankton consumption reflected differences in the evolution of the phytoplankton bloom and in the structure of the microbial food web, both associated with the strong mesoscale hydrodynamic variability of the study area. In that context it is worthy to note that when tintinnids reached high abundances locally (1260 cells L À1 ), their impact as phytoplankton grazers was important and reached 69% of primary production. Generally, heterotrophic nanoflagellates and ciliates were relatively more important in determining the fate of phytogenic carbon during spring. Another interesting feature of primary production consumption was that during the autumn, when Prochlorococcus dominated the phytoplankton community, the protozoan grazing activity was ineffective in regulating the fate of primary producers. Citation: Karayanni, H., U. Christaki, F. Van Wambeke, M. Denis, and T. Moutin (2005), Influence of ciliated protozoa and heterotrophic nanoflagellates on the fate of primary production in the northeast Atlantic Ocean,
Limnology and Oceanography, 1999
Theory suggests that variation in the attractive solvation force associated with cell-surface hydrophobicity can significantly affect contact rates among small cells in aqueous environments and consequently may influence rates and selective impacts of marine nanoflagellate grazers feeding on picoplankton assemblages. To investigate this hypothesis, we assayed the natural range in hydrophobic characteristics of subtropical picoplankton from the oligotrophic subtropical Pacific (Station Aloha, 22Њ45ЈN, 158ЊW) and mesotrophic Kaneohe Bay, Hawaii, using hydrophobic interaction chromatography (HIC) in conjunction with analytical flow cytometry. Variability in a relative index of cell-surface hydrophobicity (HIC index) for heterotrophic bacteria, Prochlorococcus and Synechococcus, exhibited some consistent spatial patterns. The HIC index for Prochlorococcus at Station Aloha varied about threefold, being consistently more hydrophobic in the upper 80 m of the water column and dropping abruptly below this depth. Heterotrophic bacteria were more hydrophobic near the surface and decreased slightly, but steadily, with increasing depth. The hydrophobicity of heterotrophic bacteria steadily increased along a Kaneohe Bay transect extending from oligotrophic to mesotrophic conditions. In experiments involving nanoflagellates grazing on laboratory cultures of Prochlorococcus, cell cultures exhibiting the highest HIC indices were grazed upon at the highest rates. An additional experiment involving mixtures of Prochlorococcus cells exhibiting high and low hydrophobicities showed that the average hydrophobicity of the uningested prey mixture was driven progressively toward lower hydrophobicity as the more hydrophobic cells were selectively removed through time. If these laboratory grazing results hold in nature, the rate at which picoplankton cells are cleared from suspension by nanoflagellates could vary by as much as twofold due solely to natural variation in cell surface hydrophobicity.
Microbial Ecology, 2002
We compared the characteristics of ingestion of Prochlorococcus and Synechococcus by the marine heterotrophic nano¯agellate Pseudobodo sp. and by a mixed nano¯agellate culture (around 3 lm in size) obtained from an open sea oligotrophic area. Maximum ingestion rate on Synechococcus (2.7 Syn¯agellate )1 h )1 ) was reached at concentrations of 5´10 5 Syn mL )1 and decreased between 6´10 5 and 1.5´10 6 Syn mL )1 . In order to validate laboratory data, one set of data on Synechococcus grazing was obtained during a ®eld study in the oligotrophic northeastern Mediterranean Sea. Ingestion rates by heterotrophic nano¯agellates were related to Synechococcus abundance in the water, and the feeding rate showed a clear diel rhythm with consumption being highest during the night, declining during the day hours, and being lowest at dusk. Ingestion rates on Prochlorococcus increased linearly for the whole range of prey density used (i.e., from 1´10 3 to 3´10 6 Proc mL )1 ), with maximum ingestion of 6.7 Proc¯agellate )1 h )1 . However, for prey concentrations in the range of 10 3 ±l0 5 , which are usually encountered in aquatic systems, ingestion rates were signi®cantly less than on Synechococcus. In our experiments, both Prochlorococcus and Synechococcus proved to be poor food items for support of nano¯agellate growth.
Microbial plankton abundance and heterotrophic activity across the Central Atlantic Ocean
Progress in Oceanography, 2008
The role of microorganisms in the transfer of carbon of marine systems is very important in open oligotrophic oceans. Here, we analyze the picoplankton structure, the heterotrophic bacterioplankton activity, and the predator-prey relationships between heterotrophic bacteria and nanoflagellates during two large scale cruises in the Central Atlantic Ocean ($29°N to $40°S). Latitud cruises were performed in 1995 between March-April and October-November. During both cruises we crossed the regions of different trophic statuses; where we measured different biological variables both at the surface and at the deep chlorophyll maximum (DCM). The concentration of chlorophyll a varied between 0.1 and 0.8 mg m À3 , the abundance of heterotrophic bacteria varied between <1.0 Â 10 5 and >1.0 Â 10 6 cells ml À1 , and that of heterotrophic nanoflagellates between <100 and >1.0 Â 10 4 cells ml À1. The production of heterotrophic bacteria varied more than three orders of magnitude between <0.01 and 24 lgC L À1 d À1 ; and the growth rates were in the range <0.01-2.1 d À1. In the Latitud-II cruise, Prochlorococcus ranged between <10 3 and >3 Â 10 5 cells ml À1 , Synechococcus between <100 and >1.0 Â 10 4 cells ml À1 , and picoeukaryotes between <100 and >10 4 cells ml À1. Two empirical models were used to learn more about the relationship between heterotrophic bacteria and nanoflagellates. Most bacterial production was ingested when this production was low, the heterotrophic nanoflagellates could be controlled by preys during Latitud-I cruise at the DCM, and by predators in the surface and in the Latitud-II cruise. Our results were placed in context with others about the structure and function of auto-and heterotrophic picoplankton and heterotrophic nanoplankton in the Central Atlantic Ocean.