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More, smaller bacteria in response to ocean's warming?

Morán XA, Alonso-Sáez L, Nogueira E, Ducklow HW, González N, López-Urrutia Á, Díaz-Pérez L, Calvo-Díaz A, Arandia-Gorostidi N, Huete-Stauffer TM - Proc. Biol. Sci. (2015)

Bottom Line: Over this relatively short period, we also found that bacterioplankton cells were significantly smaller, a trend that is consistent with the hypothesized temperature-driven decrease in body size.Temperature manipulation experiments in 2012 confirmed a direct effect of warming on bacterial size.The increasing prevalence of these typically oligotrophic taxa may severely impact marine food webs and carbon fluxes by an overall decrease in the efficiency of the biological pump.

View Article: PubMed Central - PubMed

Affiliation: Red Sea Research Center, Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Xixón, Asturies 33212, Spain xelu.moran@kaust.edu.sa.

ABSTRACT
Heterotrophic bacteria play a major role in organic matter cycling in the ocean. Although the high abundances and relatively fast growth rates of coastal surface bacterioplankton make them suitable sentinels of global change, past analyses have largely overlooked this functional group. Here, time series analysis of a decade of monthly observations in temperate Atlantic coastal waters revealed strong seasonal patterns in the abundance, size and biomass of the ubiquitous flow-cytometric groups of low (LNA) and high nucleic acid (HNA) content bacteria. Over this relatively short period, we also found that bacterioplankton cells were significantly smaller, a trend that is consistent with the hypothesized temperature-driven decrease in body size. Although decadal cell shrinking was observed for both groups, it was only LNA cells that were strongly coherent, with ecological theories linking temperature, abundance and individual size on both the seasonal and interannual scale. We explain this finding because, relative to their HNA counterparts, marine LNA bacteria are less diverse, dominated by members of the SAR11 clade. Temperature manipulation experiments in 2012 confirmed a direct effect of warming on bacterial size. Concurrent with rising temperatures in spring, significant decadal trends of increasing standing stocks (3% per year) accompanied by decreasing mean cell size (-1% per year) suggest a major shift in community structure, with a larger contribution of LNA bacteria to total biomass. The increasing prevalence of these typically oligotrophic taxa may severely impact marine food webs and carbon fluxes by an overall decrease in the efficiency of the biological pump.

No MeSH data available.


Related in: MedlinePlus

Seasonal variations of temperature and bacterioplankton. Monthly mean ± s.e. values of (a) temperature, and (b–d) total, LNA and HNA (b) bacterial abundance, (c) bacterial size, (d) bacterial biomass and (e) per cent contribution of LNA bacteria to total biomass in the upper mixed layer of the study site for the April 2002–March 2012 period. Fitted curves represent statistically significant seasonality detailed in table 1.
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RSPB20150371F1: Seasonal variations of temperature and bacterioplankton. Monthly mean ± s.e. values of (a) temperature, and (b–d) total, LNA and HNA (b) bacterial abundance, (c) bacterial size, (d) bacterial biomass and (e) per cent contribution of LNA bacteria to total biomass in the upper mixed layer of the study site for the April 2002–March 2012 period. Fitted curves represent statistically significant seasonality detailed in table 1.

Mentions: Temperature displayed a marked seasonality (figure 1a), with the 12-month periodic component explaining 80% of total variance (table 1). HNA bacteria had no persistent cyclical components, whereas LNA bacteria showed a statistically significant annual cycle explaining 25% of total variance (figure 1b and table 1). The spring and autumn peaks in total bacterial abundance (approx. 106 cells ml−1; figure 1b) and biomass (approx. 16 µg C l−1; figure 1d) were characterized by a different relative contribution of both groups, resulting in a strong seasonality of the percentage contribution of LNA cells to bacterial biomass (figure 1e). Earlier work had already shown a very strong seasonal signal of the percentage of HNA cell abundance, with approximately 40% minima in summer and maxima more than 80% around April [17], which is definitely confirmed with this larger dataset. However, little was known about the temporal variability in HNA and LNA bacterial cell size, and no prior attempt had been made at relating their seasonal and long-term patterns to temperature. Bacterial cell size had significant seasonal components for LNA and total bacteria (figure 1c and table 1), with maxima and minima lagged by roughly one month because of the marked summer peak in HNA cell size. For LNA bacteria, seasonal patterns of abundance and size were roughly opposite, and pooled LNA cell abundance and size were negatively correlated (r = −0.33, p < 0.001, n = 114). LNA cell size was also negatively correlated with temperature (r = −0.19, p = 0.044, n = 114). Other variables concurrently measured and potentially relevant for bacteria include total chlorophyll (size-fractionated also since 2003), inorganic nutrient concentrations and stratification index. Briefly, marked stratification from June to October was accompanied by strong nutrient limitation, resulting in low chlorophyll and picophytoplankton dominance. Chlorophyll usually peaked around March–May, with greater contributions of the larger size-fractions. The variance decomposition of these ancillary variables is shown in electronic supplementary material, table S1.Table 1.


More, smaller bacteria in response to ocean's warming?

Morán XA, Alonso-Sáez L, Nogueira E, Ducklow HW, González N, López-Urrutia Á, Díaz-Pérez L, Calvo-Díaz A, Arandia-Gorostidi N, Huete-Stauffer TM - Proc. Biol. Sci. (2015)

Seasonal variations of temperature and bacterioplankton. Monthly mean ± s.e. values of (a) temperature, and (b–d) total, LNA and HNA (b) bacterial abundance, (c) bacterial size, (d) bacterial biomass and (e) per cent contribution of LNA bacteria to total biomass in the upper mixed layer of the study site for the April 2002–March 2012 period. Fitted curves represent statistically significant seasonality detailed in table 1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4590472&req=5

RSPB20150371F1: Seasonal variations of temperature and bacterioplankton. Monthly mean ± s.e. values of (a) temperature, and (b–d) total, LNA and HNA (b) bacterial abundance, (c) bacterial size, (d) bacterial biomass and (e) per cent contribution of LNA bacteria to total biomass in the upper mixed layer of the study site for the April 2002–March 2012 period. Fitted curves represent statistically significant seasonality detailed in table 1.
Mentions: Temperature displayed a marked seasonality (figure 1a), with the 12-month periodic component explaining 80% of total variance (table 1). HNA bacteria had no persistent cyclical components, whereas LNA bacteria showed a statistically significant annual cycle explaining 25% of total variance (figure 1b and table 1). The spring and autumn peaks in total bacterial abundance (approx. 106 cells ml−1; figure 1b) and biomass (approx. 16 µg C l−1; figure 1d) were characterized by a different relative contribution of both groups, resulting in a strong seasonality of the percentage contribution of LNA cells to bacterial biomass (figure 1e). Earlier work had already shown a very strong seasonal signal of the percentage of HNA cell abundance, with approximately 40% minima in summer and maxima more than 80% around April [17], which is definitely confirmed with this larger dataset. However, little was known about the temporal variability in HNA and LNA bacterial cell size, and no prior attempt had been made at relating their seasonal and long-term patterns to temperature. Bacterial cell size had significant seasonal components for LNA and total bacteria (figure 1c and table 1), with maxima and minima lagged by roughly one month because of the marked summer peak in HNA cell size. For LNA bacteria, seasonal patterns of abundance and size were roughly opposite, and pooled LNA cell abundance and size were negatively correlated (r = −0.33, p < 0.001, n = 114). LNA cell size was also negatively correlated with temperature (r = −0.19, p = 0.044, n = 114). Other variables concurrently measured and potentially relevant for bacteria include total chlorophyll (size-fractionated also since 2003), inorganic nutrient concentrations and stratification index. Briefly, marked stratification from June to October was accompanied by strong nutrient limitation, resulting in low chlorophyll and picophytoplankton dominance. Chlorophyll usually peaked around March–May, with greater contributions of the larger size-fractions. The variance decomposition of these ancillary variables is shown in electronic supplementary material, table S1.Table 1.

Bottom Line: Over this relatively short period, we also found that bacterioplankton cells were significantly smaller, a trend that is consistent with the hypothesized temperature-driven decrease in body size.Temperature manipulation experiments in 2012 confirmed a direct effect of warming on bacterial size.The increasing prevalence of these typically oligotrophic taxa may severely impact marine food webs and carbon fluxes by an overall decrease in the efficiency of the biological pump.

View Article: PubMed Central - PubMed

Affiliation: Red Sea Research Center, Division of Biological and Environmental Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia Instituto Español de Oceanografía, Centro Oceanográfico de Xixón, Xixón, Asturies 33212, Spain xelu.moran@kaust.edu.sa.

ABSTRACT
Heterotrophic bacteria play a major role in organic matter cycling in the ocean. Although the high abundances and relatively fast growth rates of coastal surface bacterioplankton make them suitable sentinels of global change, past analyses have largely overlooked this functional group. Here, time series analysis of a decade of monthly observations in temperate Atlantic coastal waters revealed strong seasonal patterns in the abundance, size and biomass of the ubiquitous flow-cytometric groups of low (LNA) and high nucleic acid (HNA) content bacteria. Over this relatively short period, we also found that bacterioplankton cells were significantly smaller, a trend that is consistent with the hypothesized temperature-driven decrease in body size. Although decadal cell shrinking was observed for both groups, it was only LNA cells that were strongly coherent, with ecological theories linking temperature, abundance and individual size on both the seasonal and interannual scale. We explain this finding because, relative to their HNA counterparts, marine LNA bacteria are less diverse, dominated by members of the SAR11 clade. Temperature manipulation experiments in 2012 confirmed a direct effect of warming on bacterial size. Concurrent with rising temperatures in spring, significant decadal trends of increasing standing stocks (3% per year) accompanied by decreasing mean cell size (-1% per year) suggest a major shift in community structure, with a larger contribution of LNA bacteria to total biomass. The increasing prevalence of these typically oligotrophic taxa may severely impact marine food webs and carbon fluxes by an overall decrease in the efficiency of the biological pump.

No MeSH data available.


Related in: MedlinePlus