Size-specific growth and grazing rates for picophytoplankton in coastal and oceanic regions of the eastern Pacific

Estimates of growth and grazing mortality rates for different size classes and taxa of natural picophytoplankton assemblages were measured in mixed-layer experiments conducted in 3 regions of the eastern Pacific: the California Current Ecosystem, Costa Rica Dome, and equatorial Pacific. Contrary to expectation, size-dependent rates for cells between 0.45 and 4.0 μm in diameter showed no systematic trends with cell size both in and among regions. For all size classes, mean ± SD growth rates ranged from .0.70 ± 0.17 to 0.83 ± 0.13 d-1 and grazing rates between .0.07 ± 0.13 and 1.17 ± 0.10 d-1. Taxon-specific growth rates for Prochlorococcus ranged from 0.17 ± 0.12 to 0.59 ± 0.01 d -1, for Synechococcus from 0.68 ± 0.03 to 0.97 ± 0.04 d-1, for picoeukaryotes from 0.46 ± 0.13 to 1.03 ± 0.06 d-1, and for all cells combined between 0.45 ± 0.03 and 0.65 ± 0.02 d-1. For grazing, Prochlorococcus rates ranged between 0.02 ± 0.12 and 0.66 ± 0.02 d-1, Synechococcus rates between 0.24 ± 0.08 and 0.92 ± 0.05 d-1, for picoeukaryotes between 0.19 ± 0.10 and 0.78 ± 0.09 d-1, and for all cells between 0.16 ± 0.05 and 0.75 ± 0.02 d -1. When comparing rates among taxa, only Prochlorococcus had consistently lower rates than Synechococcocus in all regions. No other trends were apparent. Temperature relationships based on the Metabolic Theory of Ecology were able to explain more of the variability among grazing rates than among growth rates for each taxon considered. © 2014 Inter-Research

Size-specific growth and grazing rates for picophytoplankton in coastal and oceanic regions of the eastern Pacific

Estimates of growth and grazing mortality rates for different size classes and taxa of natural picophytoplankton assemblages were measured in mixed-layer experiments conducted in 3 regions of the eastern Pacific: the California Current Ecosystem, Costa Rica Dome, and equatorial Pacific. Contrary to expectation, size-dependent rates for cells between 0.45 and 4.0 μm in diameter showed no systematic trends with cell size both in and among regions. For all size classes, mean ± SD growth rates ranged from .0.70 ± 0.17 to 0.83 ± 0.13 d-1 and grazing rates between .0.07 ± 0.13 and 1.17 ± 0.10 d-1. Taxon-specific growth rates for Prochlorococcus ranged from 0.17 ± 0.12 to 0.59 ± 0.01 d -1, for Synechococcus from 0.68 ± 0.03 to 0.97 ± 0.04 d-1, for picoeukaryotes from 0.46 ± 0.13 to 1.03 ± 0.06 d-1, and for all cells combined between 0.45 ± 0.03 and 0.65 ± 0.02 d-1. For grazing, Prochlorococcus rates ranged between 0.02 ± 0.12 and 0.66 ± 0.02 d-1, Synechococcus rates between 0.24 ± 0.08 and 0.92 ± 0.05 d-1, for picoeukaryotes between 0.19 ± 0.10 and 0.78 ± 0.09 d-1, and for all cells between 0.16 ± 0.05 and 0.75 ± 0.02 d -1. When comparing rates among taxa, only Prochlorococcus had consistently lower rates than Synechococcocus in all regions. No other trends were apparent. Temperature relationships based on the Metabolic Theory of Ecology were able to explain more of the variability among grazing rates than among growth rates for each taxon considered. © 2014 Inter-Research

Size-specific growth and grazing rates for picophytoplankton in coastal and oceanic regions of the eastern Pacific

Estimates of growth and grazing mortality rates for different size classes and taxa of natural picophytoplankton assemblages were measured in mixed-layer experiments conducted in 3 regions of the eastern Pacific: the California Current Ecosystem, Costa Rica Dome, and equatorial Pacific. Contrary to expectation, size-dependent rates for cells between 0.45 and 4.0 μm in diameter showed no systematic trends with cell size both in and among regions. For all size classes, mean ± SD growth rates ranged from .0.70 ± 0.17 to 0.83 ± 0.13 d and grazing rates between .0.07 ± 0.13 and 1.17 ± 0.10 d . Taxon-specific growth rates for Prochlorococcus ranged from 0.17 ± 0.12 to 0.59 ± 0.01 d , for Synechococcus from 0.68 ± 0.03 to 0.97 ± 0.04 d , for picoeukaryotes from 0.46 ± 0.13 to 1.03 ± 0.06 d , and for all cells combined between 0.45 ± 0.03 and 0.65 ± 0.02 d . For grazing, Prochlorococcus rates ranged between 0.02 ± 0.12 and 0.66 ± 0.02 d , Synechococcus rates between 0.24 ± 0.08 and 0.92 ± 0.05 d , for picoeukaryotes between 0.19 ± 0.10 and 0.78 ± 0.09 d , and for all cells between 0.16 ± 0.05 and 0.75 ± 0.02 d . When comparing rates among taxa, only Prochlorococcus had consistently lower rates than Synechococcocus in all regions. No other trends were apparent. Temperature relationships based on the Metabolic Theory of Ecology were able to explain more of the variability among grazing rates than among growth rates for each taxon considered. © 2014 Inter-Research. -1 -1 -1 -1 -1 -1 -1 -1 -1 -

Temporal and spatial patterns of microbial community biomass and composition in the Southern California Current Ecosystem

As part of the California Current Ecosystem Long Term Ecological Research (CCE-LTER) Program, samples for epifluorescence microscopy and flow cytometry (FCM) were collected at ten 'cardinal' stations on the California Cooperative Oceanic Fisheries Investigations (CalCOFI) grid during 25 quarterly cruises from 2004 to 2010 to investigate the biomass, composition and size-structure of microbial communities within the southern CCE. Based on our results, we divided the region into offshore, and inshore northern and southern zones. Mixed-layer phytoplankton communities in the offshore had lower biomass (16±2μgCL-1; all errors represent the 95% confidence interval), smaller size-class cells and biomass was more stable over seasonal cycles. Offshore phytoplankton biomass peaked during the winter months. Mixed-layer phytoplankton communities in the northern and southern inshore zones had higher biomass (78±22 and 32±9μgCL-1, respectively), larger size-class cells and stronger seasonal biomass patterns. Inshore communities were often dominated by micro-size (20-200μm) diatoms; however, autotrophic dinoflagellates dominated during late 2005 to early 2006, corresponding to a year of delayed upwelling in the northern CCE. Biomass trends in mid and deep euphotic zone samples were similar to those seen in the mixed-layer, but with declining biomass with depth, especially for larger size classes in the inshore regions. Mixed-layer ratios of autotrophic carbon to chlorophyll a (AC:Chl a) had a mean value of 51.5±5.3. Variability of nitracline depth, bin-averaged AC:Chl a in the mixed-layer ranged from 40 to 80 and from 22 to 35 for the deep euphotic zone, both with significant positive relationships to nitracline depth. Total living microbial carbon, including auto- and heterotrophs, consistently comprised about half of particulate organic carbon (POC)

Fine spatial structure of genetically distinct picocyanobacterial populations across environmental gradients in the Costa Rica Dome

We investigated the spatial variability of picocyanobacterial community structure across the Costa Rica Dome (CRD), an offshore upwelling system characterized by high seasonal abundance of Synechococcus spp. We constructed clone libraries of the rpoC1 gene to survey picocyanobacterial diversity and developed specific real-time quantitative polymerase chain reaction assays to assess the distribution of genetically distinct Synechococcus (SYN) and Prochlorococcus (PRO) populations across vertical and horizontal physicochemical gradients. Flow cytometry data showed that cell abundances for both SYN and PRO were highest near the dome center. Phylogenetic analysis of rpoC1 sequences revealed a remarkably high and distinctive picocyanobacterial diversity (FLU1-3, CRD1, Clade II, XV, XVI) that included "novel" SYN and PRO genotypes. Furthermore, genetically different populations exhibited vertical and horizontal spatial partitioning. Abundances of distinct SYN genotypes peaked at subsequent depth horizons, leading to a fine vertical structure with at least three populations stacked within the upper 30-40 m at the dome. Clade II and FLU1A peaked in surface waters, while maximum concentrations of CRD1, FLU1B, and Clade XVI occurred in the upper and lower thermocline, respectively. Horizontally, Clade II abundance in surface waters remained high across the entire region, while SYN genotypes CRD1 and FLU1A increased with shoaling of the thermo- and nutricline toward the center of the dome to become the dominant genotypes of the SYN assemblage in the dome. Below the mixed layer, Clade XVI and PRO genotype FLU2, virtually absent outside the dome, became abundant components of the picocyanobacterial assemblage. Despite their phylogenetic relatedness, FLU1A and FLU1B subclades followed different distributional patterns, suggesting ecological significance of the microdiversity within the clade. The unprecedented fine vertical structure demonstrated for SYN genotypes is driven by sharp physicochemical gradients (e.g., density, nutrient, oxygen, and trace metals) created by the dome and the presence of a shallow oxycline that enhances habitat diversification. © 2014, by the Association for the Sciences of Limnology and Oceanography, Inc

Fine spatial structure of genetically distinct picocyanobacterial populations across environmental gradients in the Costa Rica Dome

We investigated the spatial variability of picocyanobacterial community structure across the Costa Rica Dome (CRD), an offshore upwelling system characterized by high seasonal abundance of Synechococcus spp. We constructed clone libraries of the rpoC1 gene to survey picocyanobacterial diversity and developed specific real-time quantitative polymerase chain reaction assays to assess the distribution of genetically distinct Synechococcus (SYN) and Prochlorococcus (PRO) populations across vertical and horizontal physicochemical gradients. Flow cytometry data showed that cell abundances for both SYN and PRO were highest near the dome center. Phylogenetic analysis of rpoC1 sequences revealed a remarkably high and distinctive picocyanobacterial diversity (FLU1-3, CRD1, Clade II, XV, XVI) that included "novel" SYN and PRO genotypes. Furthermore, genetically different populations exhibited vertical and horizontal spatial partitioning. Abundances of distinct SYN genotypes peaked at subsequent depth horizons, leading to a fine vertical structure with at least three populations stacked within the upper 30-40 m at the dome. Clade II and FLU1A peaked in surface waters, while maximum concentrations of CRD1, FLU1B, and Clade XVI occurred in the upper and lower thermocline, respectively. Horizontally, Clade II abundance in surface waters remained high across the entire region, while SYN genotypes CRD1 and FLU1A increased with shoaling of the thermo- and nutricline toward the center of the dome to become the dominant genotypes of the SYN assemblage in the dome. Below the mixed layer, Clade XVI and PRO genotype FLU2, virtually absent outside the dome, became abundant components of the picocyanobacterial assemblage. Despite their phylogenetic relatedness, FLU1A and FLU1B subclades followed different distributional patterns, suggesting ecological significance of the microdiversity within the clade. The unprecedented fine vertical structure demonstrated for SYN genotypes is driven by sharp physicochemical gradients (e.g., density, nutrient, oxygen, and trace metals) created by the dome and the presence of a shallow oxycline that enhances habitat diversification. © 2014, by the Association for the Sciences of Limnology and Oceanography, Inc

Fine spatial structure of genetically distinct picocyanobacterial populations across environmental gradients in the Costa Rica Dome

We investigated the spatial variability of picocyanobacterial community structure across the Costa Rica Dome (CRD), an offshore upwelling system characterized by high seasonal abundance of Synechococcus spp. We constructed clone libraries of the rpoC1 gene to survey picocyanobacterial diversity and developed specific real-time quantitative polymerase chain reaction assays to assess the distribution of genetically distinct Synechococcus (SYN) and Prochlorococcus (PRO) populations across vertical and horizontal physicochemical gradients. Flow cytometry data showed that cell abundances for both SYN and PRO were highest near the dome center. Phylogenetic analysis of rpoC1 sequences revealed a remarkably high and distinctive picocyanobacterial diversity (FLU1-3, CRD1, Clade II, XV, XVI) that included "novel" SYN and PRO genotypes. Furthermore, genetically different populations exhibited vertical and horizontal spatial partitioning. Abundances of distinct SYN genotypes peaked at subsequent depth horizons, leading to a fine vertical structure with at least three populations stacked within the upper 30-40 m at the dome. Clade II and FLU1A peaked in surface waters, while maximum concentrations of CRD1, FLU1B, and Clade XVI occurred in the upper and lower thermocline, respectively. Horizontally, Clade II abundance in surface waters remained high across the entire region, while SYN genotypes CRD1 and FLU1A increased with shoaling of the thermo- and nutricline toward the center of the dome to become the dominant genotypes of the SYN assemblage in the dome. Below the mixed layer, Clade XVI and PRO genotype FLU2, virtually absent outside the dome, became abundant components of the picocyanobacterial assemblage. Despite their phylogenetic relatedness, FLU1A and FLU1B subclades followed different distributional patterns, suggesting ecological significance of the microdiversity within the clade. The unprecedented fine vertical structure demonstrated for SYN genotypes is driven by sharp physicochemical gradients (e.g., density, nutrient, oxygen, and trace metals) created by the dome and the presence of a shallow oxycline that enhances habitat diversification. © 2014, by the Association for the Sciences of Limnology and Oceanography, Inc

Seasonal dynamics of phytoplankton in the Antarctic Polar Front region at 170°W

Phytoplankton dynamics in the region of 55-70degreesS, 170degreesW were investigated using Sea-viewing Wide Field-of-View Sensor satellite imagery, shipboard sampling and experimental rate assessments during austral spring and summer, 1997-1998. We used image-analysis microscopy to characterize community biomass and composition, and dilution experiments to estimate growth and microzooplankton grazing rates. Iron concentrations were determined by flow-injection analysis. The phytoplankton increase began slowly with the onset of stratification at the Polar Front (PF) (60-61degreesS) in early November. Seasonally enhanced levels of chlorophyll were found as far north as 58degreesS, but mixed-layer phytoplankton standing stock was highest, approaching 200 mg C m(-3), in the region between the receding ice edge and a strong silicate gradient, which migrated from similar to62degreesS to 65degreesS during the study period. The most southern stations sampled on four cruises were characterized by small pennate diatoms and Phaeocystis. From the PF to the Southern Antarctic circumpolar current front (similar to65degreesS), this ice margin assemblage was seasonally replaced by a community dominated by large diatoms. The large diatom community developed only in waters where measured iron concentrations were initially high (greater than or equal to0.2 nM), and crashed when dissolved silicate was depleted to low levels. Phytoplankton growth rates were highest (0.5-0.6 d(-1)) between the PF and silicate front (60degreesS and 63degreesS) in December. In January, growth rates were lowest (0.1 d(-1)) near the PF, and the highest rates (0.34.4 d(-1)) were found in experiments between 64.8degreesS and 67.8degreesS. Phytoplankton production estimates were highest south of the PF through December and January, averaging 2.2-2.4 mmol C m(-3) d(-1) and reaching levels of 5 mmol cm(-3) d(-1) (64.8degreesS and 67.8degreesS in January). Microzooplankton grazers consumed 54-95% of production for experiments conducted on four AESOPS cruises. They were less efficient in balancing growth rates during the time of highest phytoplankton growth and increase in December, and most efficient in February-March, after the large diatom bloom had collapsed. The diatom bloom region in the present study is in an upwelling zone for Antarctic circumpolar deep water with high iron content. This may explain why this marginal ice zone differs from others where blooms have not been observed. (C) 2002 Published by Elsevier Science Ltd