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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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Isotopic niche for each species and the entire community pre- and post-bloom.Stable isotope bi-plots illustrating the isotopic niche of the four species, M. affinis (black), M. arctia (red), M. balthica (green), P. femorata (blue) at three study sites (top stn Håldämman, mid stn Uttervik and bottom stn Mörkö) before and after the bloom, for both years (2009, left panels, and 2010, right panel). The dotted lines enclose convex hull area for each species and solid line shows the standard ellipse area, SEAc, for the entire community. Note the presence of M. affinis post-bloom at stn Mörkö 2009 inflates the niche area, since it was not found pre-bloom. Excluding M. affinis at this station in 2009 results in a reduced niche area (as in Fig 5, top panel).
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pone-0104460-g004: Isotopic niche for each species and the entire community pre- and post-bloom.Stable isotope bi-plots illustrating the isotopic niche of the four species, M. affinis (black), M. arctia (red), M. balthica (green), P. femorata (blue) at three study sites (top stn Håldämman, mid stn Uttervik and bottom stn Mörkö) before and after the bloom, for both years (2009, left panels, and 2010, right panel). The dotted lines enclose convex hull area for each species and solid line shows the standard ellipse area, SEAc, for the entire community. Note the presence of M. affinis post-bloom at stn Mörkö 2009 inflates the niche area, since it was not found pre-bloom. Excluding M. affinis at this station in 2009 results in a reduced niche area (as in Fig 5, top panel).

Mentions: For all species except P. femorata, the δ15N values became significantly depleted after the bloom (Figure 2, Table 3). The δ13C values were also significantly depleted after the bloom for M. balthica and the amphipods, but not for M. arctia (Figure 4, Table 3). In line with these observations, bloom was a significant explanatory variable in all winning models, with the exception of δ15N for P. femorata (Table 3).


Nitrogen fixed by cyanobacteria is utilized by deposit-feeders.

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

Isotopic niche for each species and the entire community pre- and post-bloom.Stable isotope bi-plots illustrating the isotopic niche of the four species, M. affinis (black), M. arctia (red), M. balthica (green), P. femorata (blue) at three study sites (top stn Håldämman, mid stn Uttervik and bottom stn Mörkö) before and after the bloom, for both years (2009, left panels, and 2010, right panel). The dotted lines enclose convex hull area for each species and solid line shows the standard ellipse area, SEAc, for the entire community. Note the presence of M. affinis post-bloom at stn Mörkö 2009 inflates the niche area, since it was not found pre-bloom. Excluding M. affinis at this station in 2009 results in a reduced niche area (as in Fig 5, top panel).
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4126700&req=5

pone-0104460-g004: Isotopic niche for each species and the entire community pre- and post-bloom.Stable isotope bi-plots illustrating the isotopic niche of the four species, M. affinis (black), M. arctia (red), M. balthica (green), P. femorata (blue) at three study sites (top stn Håldämman, mid stn Uttervik and bottom stn Mörkö) before and after the bloom, for both years (2009, left panels, and 2010, right panel). The dotted lines enclose convex hull area for each species and solid line shows the standard ellipse area, SEAc, for the entire community. Note the presence of M. affinis post-bloom at stn Mörkö 2009 inflates the niche area, since it was not found pre-bloom. Excluding M. affinis at this station in 2009 results in a reduced niche area (as in Fig 5, top panel).
Mentions: For all species except P. femorata, the δ15N values became significantly depleted after the bloom (Figure 2, Table 3). The δ13C values were also significantly depleted after the bloom for M. balthica and the amphipods, but not for M. arctia (Figure 4, Table 3). In line with these observations, bloom was a significant explanatory variable in all winning models, with the exception of δ15N for P. femorata (Table 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