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Nitrogen fixed by cyanobacteria is utilized by deposit-feeders.

Karlson AM, Gorokhova E, Elmgren R - PLoS ONE (2014)

Bottom Line: We also expected the settled cyanobacteria with their associated microheterotrophic community and relatively high nitrogen content to increase the isotopic niche area, trophic diversity and dietary divergence between individuals (estimated as the nearest neighbour distance) in the benthic fauna after the bloom.The three surface-feeding species (Monoporeia affinis, Macoma balthica and Marenzelleria arctia) showed significantly lower δ(15)N values after the bloom, while the sub-surface feeder Pontoporeia femorata did not.The effect of the bloom on isotopic niche varied greatly between stations; populations which increased niche area after the bloom had better body condition than populations with reduced niche, regardless of species.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Environmental Science, Stockholm University, Stockholm, Sweden.

ABSTRACT
Benthic communities below the photic zone depend for food on allochthonous organic matter derived from seasonal phytoplankton blooms. In the Baltic Sea, the spring diatom bloom is considered the most important input of organic matter, whereas the contribution of the summer bloom dominated by diazotrophic cyanobacteria is less understood. The possible increase in cyanobacteria blooms as a consequence of eutrophication and climate change calls for evaluation of cyanobacteria effects on benthic community functioning and productivity. Here, we examine utilization of cyanobacterial nitrogen by deposit-feeding benthic macrofauna following a cyanobacteria bloom at three stations during two consecutive years and link these changes to isotopic niche and variations in body condition (assayed as C:N ratio) of the animals. Since nitrogen-fixing cyanobacteria have δ(15)N close to -2‰, we expected the δ(15)N in the deposit-feeders to decrease after the bloom if their assimilation of cyanobacteria-derived nitrogen was substantial. We also expected the settled cyanobacteria with their associated microheterotrophic community and relatively high nitrogen content to increase the isotopic niche area, trophic diversity and dietary divergence between individuals (estimated as the nearest neighbour distance) in the benthic fauna after the bloom. The three surface-feeding species (Monoporeia affinis, Macoma balthica and Marenzelleria arctia) showed significantly lower δ(15)N values after the bloom, while the sub-surface feeder Pontoporeia femorata did not. The effect of the bloom on isotopic niche varied greatly between stations; populations which increased niche area after the bloom had better body condition than populations with reduced niche, regardless of species. Thus, cyanobacterial nitrogen is efficiently integrated into the benthic food webs in the Baltic, with likely consequences for their functioning, secondary production, transfer efficiency, trophic interactions, and intra- and interspecific competition.

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Carbon and nitrogen content pre- and post-bloom.Carbon and nitrogen (%) in the test species (left to right: Mac - M. balthica, Mz - M. arctia, Mon - M. affinis and Pon - P. femorata) before (white) and after (grey) the bloom. Values are median with 25 and 75% percentiles as well as 95% CI (n = 6 for Mac and Mz, n = 5 for Mon and n = 3 for Pon).
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pone-0104460-g003: Carbon and nitrogen content pre- and post-bloom.Carbon and nitrogen (%) in the test species (left to right: Mac - M. balthica, Mz - M. arctia, Mon - M. affinis and Pon - P. femorata) before (white) and after (grey) the bloom. Values are median with 25 and 75% percentiles as well as 95% CI (n = 6 for Mac and Mz, n = 5 for Mon and n = 3 for Pon).

Mentions: Macrofaunal body condition, indicated by the C:N ratio, changed over the season (Figure 2). In M. affinis, both individual weight and lower C:N ratio were lower after the bloom (Paired t-tests, biomass: t = 2.66, p = 0.057, C:N ratio t = 4.60, p = 0.01). In the other species, no change in the individual weight from the pre-bloom to the post-bloom were observed (M. balthica p = 0.82, M. arctia p = 0.53), but their C:N ratios declined (M. balthica, t = 3.41, p = 0.02, M. arctia, t = 2.11, p = 0.09). The small sample size for P. femorata precluded meaningful comparisons. Nitrogen content (%) increased after the bloom for the surface-feeding species (M. balthica and M. arctia: Z = 2.20, p = 0.028, n = 6, M. affinis Z = 2.02, p = 0.043, n = 5), with no change in C% (M. balthica Z = 1.15, p = 0.25, M. arctia Z = 0.94, p = 0.35, M. affinis Z = 1.75, p = 0.08). The carbon and nitrogen content for each species and period are shown in Figure 3.


Nitrogen fixed by cyanobacteria is utilized by deposit-feeders.

Karlson AM, Gorokhova E, Elmgren R - PLoS ONE (2014)

Carbon and nitrogen content pre- and post-bloom.Carbon and nitrogen (%) in the test species (left to right: Mac - M. balthica, Mz - M. arctia, Mon - M. affinis and Pon - P. femorata) before (white) and after (grey) the bloom. Values are median with 25 and 75% percentiles as well as 95% CI (n = 6 for Mac and Mz, n = 5 for Mon and n = 3 for Pon).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4126700&req=5

pone-0104460-g003: Carbon and nitrogen content pre- and post-bloom.Carbon and nitrogen (%) in the test species (left to right: Mac - M. balthica, Mz - M. arctia, Mon - M. affinis and Pon - P. femorata) before (white) and after (grey) the bloom. Values are median with 25 and 75% percentiles as well as 95% CI (n = 6 for Mac and Mz, n = 5 for Mon and n = 3 for Pon).
Mentions: Macrofaunal body condition, indicated by the C:N ratio, changed over the season (Figure 2). In M. affinis, both individual weight and lower C:N ratio were lower after the bloom (Paired t-tests, biomass: t = 2.66, p = 0.057, C:N ratio t = 4.60, p = 0.01). In the other species, no change in the individual weight from the pre-bloom to the post-bloom were observed (M. balthica p = 0.82, M. arctia p = 0.53), but their C:N ratios declined (M. balthica, t = 3.41, p = 0.02, M. arctia, t = 2.11, p = 0.09). The small sample size for P. femorata precluded meaningful comparisons. Nitrogen content (%) increased after the bloom for the surface-feeding species (M. balthica and M. arctia: Z = 2.20, p = 0.028, n = 6, M. affinis Z = 2.02, p = 0.043, n = 5), with no change in C% (M. balthica Z = 1.15, p = 0.25, M. arctia Z = 0.94, p = 0.35, M. affinis Z = 1.75, p = 0.08). The carbon and nitrogen content for each species and period are shown in Figure 3.

Bottom Line: We also expected the settled cyanobacteria with their associated microheterotrophic community and relatively high nitrogen content to increase the isotopic niche area, trophic diversity and dietary divergence between individuals (estimated as the nearest neighbour distance) in the benthic fauna after the bloom.The three surface-feeding species (Monoporeia affinis, Macoma balthica and Marenzelleria arctia) showed significantly lower δ(15)N values after the bloom, while the sub-surface feeder Pontoporeia femorata did not.The effect of the bloom on isotopic niche varied greatly between stations; populations which increased niche area after the bloom had better body condition than populations with reduced niche, regardless of species.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Environmental Science, Stockholm University, Stockholm, Sweden.

ABSTRACT
Benthic communities below the photic zone depend for food on allochthonous organic matter derived from seasonal phytoplankton blooms. In the Baltic Sea, the spring diatom bloom is considered the most important input of organic matter, whereas the contribution of the summer bloom dominated by diazotrophic cyanobacteria is less understood. The possible increase in cyanobacteria blooms as a consequence of eutrophication and climate change calls for evaluation of cyanobacteria effects on benthic community functioning and productivity. Here, we examine utilization of cyanobacterial nitrogen by deposit-feeding benthic macrofauna following a cyanobacteria bloom at three stations during two consecutive years and link these changes to isotopic niche and variations in body condition (assayed as C:N ratio) of the animals. Since nitrogen-fixing cyanobacteria have δ(15)N close to -2‰, we expected the δ(15)N in the deposit-feeders to decrease after the bloom if their assimilation of cyanobacteria-derived nitrogen was substantial. We also expected the settled cyanobacteria with their associated microheterotrophic community and relatively high nitrogen content to increase the isotopic niche area, trophic diversity and dietary divergence between individuals (estimated as the nearest neighbour distance) in the benthic fauna after the bloom. The three surface-feeding species (Monoporeia affinis, Macoma balthica and Marenzelleria arctia) showed significantly lower δ(15)N values after the bloom, while the sub-surface feeder Pontoporeia femorata did not. The effect of the bloom on isotopic niche varied greatly between stations; populations which increased niche area after the bloom had better body condition than populations with reduced niche, regardless of species. Thus, cyanobacterial nitrogen is efficiently integrated into the benthic food webs in the Baltic, with likely consequences for their functioning, secondary production, transfer efficiency, trophic interactions, and intra- and interspecific competition.

Show MeSH
Related in: MedlinePlus