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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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Cross-species overlap in isotopic niche pre- and post-bloom.Isotopic niche overlap defined as an area common for the two populations in relation to the total isotopic space occupied by these populations (proportion; left y-axis) and total community niche (arbitrary units; right y-axis) calculated using pre-bloom and post-bloom datasets for each station and year (see also Fig. 4 for raw data). The grey bars show the overlap estimate for each pair of species whose niches were found to overlap, white bars are the total community niche, and pie charts on the top of the gray bars show overlapping proportions of the isotopic niche for each population in question. Datasets that have no overlap during the study period are not included.
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pone-0104460-g006: Cross-species overlap in isotopic niche pre- and post-bloom.Isotopic niche overlap defined as an area common for the two populations in relation to the total isotopic space occupied by these populations (proportion; left y-axis) and total community niche (arbitrary units; right y-axis) calculated using pre-bloom and post-bloom datasets for each station and year (see also Fig. 4 for raw data). The grey bars show the overlap estimate for each pair of species whose niches were found to overlap, white bars are the total community niche, and pie charts on the top of the gray bars show overlapping proportions of the isotopic niche for each population in question. Datasets that have no overlap during the study period are not included.

Mentions: The isotope niche of M. arctia was distinct from the other species (Figure 4), but overlapped slightly (∼4% of the total niche area) with M. balthica on one occasion, after the 2010 bloom at stn Mörkö. For species that were found at a station before and after the bloom, the amount of overlap correlated negatively with the SEAc (Spearman R = −0.88, t = −5.28, p<0.01, n = 10). As such, post-bloom overlaps were recorded at stations that showed a decreasing or unchanged SEAc after the bloom, but not where the SEAc increased (Figure 6). At the stations with no cross-species overlap (stns Uttervik 2009 and Håldämman 2009) SEAc also increased considerably after the bloom (112 and 32% increase, respectively). Moreover, stns Uttervik and Håldämman showed increased dN range (56–19% and 6–9% increase) and MNND (25–34% and 37–100% increase) in 2009 and 2010 respectively, whereas stn Mörkö had nearly unchanged dN range, 29 and 39% reduction in SEAc and 9 and 29% lower MNND after the bloom in 2009 and 2010, respectively.


Nitrogen fixed by cyanobacteria is utilized by deposit-feeders.

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

Cross-species overlap in isotopic niche pre- and post-bloom.Isotopic niche overlap defined as an area common for the two populations in relation to the total isotopic space occupied by these populations (proportion; left y-axis) and total community niche (arbitrary units; right y-axis) calculated using pre-bloom and post-bloom datasets for each station and year (see also Fig. 4 for raw data). The grey bars show the overlap estimate for each pair of species whose niches were found to overlap, white bars are the total community niche, and pie charts on the top of the gray bars show overlapping proportions of the isotopic niche for each population in question. Datasets that have no overlap during the study period are not included.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0104460-g006: Cross-species overlap in isotopic niche pre- and post-bloom.Isotopic niche overlap defined as an area common for the two populations in relation to the total isotopic space occupied by these populations (proportion; left y-axis) and total community niche (arbitrary units; right y-axis) calculated using pre-bloom and post-bloom datasets for each station and year (see also Fig. 4 for raw data). The grey bars show the overlap estimate for each pair of species whose niches were found to overlap, white bars are the total community niche, and pie charts on the top of the gray bars show overlapping proportions of the isotopic niche for each population in question. Datasets that have no overlap during the study period are not included.
Mentions: The isotope niche of M. arctia was distinct from the other species (Figure 4), but overlapped slightly (∼4% of the total niche area) with M. balthica on one occasion, after the 2010 bloom at stn Mörkö. For species that were found at a station before and after the bloom, the amount of overlap correlated negatively with the SEAc (Spearman R = −0.88, t = −5.28, p<0.01, n = 10). As such, post-bloom overlaps were recorded at stations that showed a decreasing or unchanged SEAc after the bloom, but not where the SEAc increased (Figure 6). At the stations with no cross-species overlap (stns Uttervik 2009 and Håldämman 2009) SEAc also increased considerably after the bloom (112 and 32% increase, respectively). Moreover, stns Uttervik and Håldämman showed increased dN range (56–19% and 6–9% increase) and MNND (25–34% and 37–100% increase) in 2009 and 2010 respectively, whereas stn Mörkö had nearly unchanged dN range, 29 and 39% reduction in SEAc and 9 and 29% lower MNND after the bloom in 2009 and 2010, respectively.

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