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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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Change in faunal isotope and elemental composition during summer.Temporal trends in δ15N, δ13C, C:N ratio and individual weight (top to bottom panels) for each species and station (solid line = stn Uttervik, broken line =  stn Mörkö and dotted =  stn Håldämman). The peak of the bloom is indicated by the grey bar. The pre-bloom samples were taken 7 and 1 weeks before the peak of the bloom and the post-bloom samples were taken 6 and 11 weeks after the bloom. Data are transformed to z-scores and pooled for 2009 and 2010. Error bars are 95% CI (n∼20 for each sampling occasion; see also Table 1).
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pone-0104460-g002: Change in faunal isotope and elemental composition during summer.Temporal trends in δ15N, δ13C, C:N ratio and individual weight (top to bottom panels) for each species and station (solid line = stn Uttervik, broken line =  stn Mörkö and dotted =  stn Håldämman). The peak of the bloom is indicated by the grey bar. The pre-bloom samples were taken 7 and 1 weeks before the peak of the bloom and the post-bloom samples were taken 6 and 11 weeks after the bloom. Data are transformed to z-scores and pooled for 2009 and 2010. Error bars are 95% CI (n∼20 for each sampling occasion; see also Table 1).

Mentions: Macrofauna was sampled with a benthic sled, set to collect the top 1–2 cm of sediment, which was sieved through a 1 mm mesh to retain the macrofauna. The two most abundant species, the Baltic clam Macoma balthica and the non-indigenous spionid polychaete Marenzelleria cf. arctia[37], were found at all stations on all sampling occasions. The amphipod Monoporeia affinis was less abundant and absent from stn Mörkö in May and July 2009. The amphipod Pontoporeia femorata was never found at stn Uttervik and absent from stn Håldämman in May and July 2009. On each sampling event ∼10 individuals of each species of approximately 2 mg dry weight (shell-free for M. balthica) were collected for isotope analyses. Due to the unbalanced sampling design and the different timing of the bloom between years and stations, we pooled the two pre-bloom sampling occasions and those after the bloom (in 2009) in the statistical analyses (Table 1, but see Figure 2). This simplified comparisons among stations and between years and facilitated the statistical niche analysis, which requires relatively large sample size.


Nitrogen fixed by cyanobacteria is utilized by deposit-feeders.

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

Change in faunal isotope and elemental composition during summer.Temporal trends in δ15N, δ13C, C:N ratio and individual weight (top to bottom panels) for each species and station (solid line = stn Uttervik, broken line =  stn Mörkö and dotted =  stn Håldämman). The peak of the bloom is indicated by the grey bar. The pre-bloom samples were taken 7 and 1 weeks before the peak of the bloom and the post-bloom samples were taken 6 and 11 weeks after the bloom. Data are transformed to z-scores and pooled for 2009 and 2010. Error bars are 95% CI (n∼20 for each sampling occasion; see also Table 1).
© Copyright Policy
Related In: Results  -  Collection

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

pone-0104460-g002: Change in faunal isotope and elemental composition during summer.Temporal trends in δ15N, δ13C, C:N ratio and individual weight (top to bottom panels) for each species and station (solid line = stn Uttervik, broken line =  stn Mörkö and dotted =  stn Håldämman). The peak of the bloom is indicated by the grey bar. The pre-bloom samples were taken 7 and 1 weeks before the peak of the bloom and the post-bloom samples were taken 6 and 11 weeks after the bloom. Data are transformed to z-scores and pooled for 2009 and 2010. Error bars are 95% CI (n∼20 for each sampling occasion; see also Table 1).
Mentions: Macrofauna was sampled with a benthic sled, set to collect the top 1–2 cm of sediment, which was sieved through a 1 mm mesh to retain the macrofauna. The two most abundant species, the Baltic clam Macoma balthica and the non-indigenous spionid polychaete Marenzelleria cf. arctia[37], were found at all stations on all sampling occasions. The amphipod Monoporeia affinis was less abundant and absent from stn Mörkö in May and July 2009. The amphipod Pontoporeia femorata was never found at stn Uttervik and absent from stn Håldämman in May and July 2009. On each sampling event ∼10 individuals of each species of approximately 2 mg dry weight (shell-free for M. balthica) were collected for isotope analyses. Due to the unbalanced sampling design and the different timing of the bloom between years and stations, we pooled the two pre-bloom sampling occasions and those after the bloom (in 2009) in the statistical analyses (Table 1, but see Figure 2). This simplified comparisons among stations and between years and facilitated the statistical niche analysis, which requires relatively large sample size.

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