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Characterisation of the nematode community of a low-activity cold seep in the recently ice-shelf free Larsen B area, Eastern Antarctic Peninsula.

Hauquier F, Ingels J, Gutt J, Raes M, Vanreusel A - PLoS ONE (2011)

Bottom Line: The nematode community at the Larsen B seep site differed significantly from other Antarctic sites in terms of dominant genera, diversity and abundance.The recent ice-shelf collapse and enhanced food input from surface phytoplankton blooms were responsible for the shift from oligotrophic pre-collapse conditions to a phytodetritus-based community with high densities and low diversity.The parthenogenetic reproduction of the highly dominant Halomonhystera species is rather unusual for marine nematodes and may be responsible for the successful colonisation by this single species.

View Article: PubMed Central - PubMed

Affiliation: Marine Biology Section, Ghent University, Ghent, Belgium. freija.hauquier@ugent.be

ABSTRACT

Background: Recent climate-induced ice-shelf disintegration in the Larsen A (1995) and B (2002) areas along the Eastern Antarctic Peninsula formed a unique opportunity to assess sub-ice-shelf benthic community structure and led to the discovery of unexplored habitats, including a low-activity methane seep beneath the former Larsen B ice shelf. Since both limited particle sedimentation under previously permanent ice coverage and reduced cold-seep activity are likely to influence benthic meiofauna communities, we characterised the nematode assemblage of this low-activity cold seep and compared it with other, now seasonally ice-free, Larsen A and B stations and other Antarctic shelf areas (Weddell Sea and Drake Passage), as well as cold-seep ecosystems world-wide.

Principal findings: The nematode community at the Larsen B seep site differed significantly from other Antarctic sites in terms of dominant genera, diversity and abundance. Densities in the seep samples were high (>2000 individuals per 10 cm(2)) and showed below-surface maxima at a sediment depth of 2-3 cm in three out of four replicates. All samples were dominated by one species of the family Monhysteridae, which was identified as a Halomonhystera species that comprised between 80 and 86% of the total community. The combination of high densities, deeper density maxima and dominance of one species is shared by many cold-seep ecosystems world-wide and suggested a possible dependence upon a chemosynthetic food source. Yet stable (13)C isotopic signals (ranging between -21.97±0.86‰ and -24.85±1.89‰) were indicative of a phytoplankton-derived food source.

Conclusion: The recent ice-shelf collapse and enhanced food input from surface phytoplankton blooms were responsible for the shift from oligotrophic pre-collapse conditions to a phytodetritus-based community with high densities and low diversity. The parthenogenetic reproduction of the highly dominant Halomonhystera species is rather unusual for marine nematodes and may be responsible for the successful colonisation by this single species.

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A. Nematode densities in comparison with other Larsen and Weddell Sea stations.Average nematode densities (in ind/10 cm2, bars) and chlorophyll a concentrations (µg/g, dots) for the different Larsen stations and reference areas. Bars represent standard errors. Note that for the reference stations, pigment data are not shown because they were expressed in µg/cm3 and hence could not be compared. B. Nematode densities (ind/10 cm2) for the different stations relative to their depth (0–1000 m). The position of the Larsen B_Seep station is marked with an asterisk*.
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pone-0022240-g004: A. Nematode densities in comparison with other Larsen and Weddell Sea stations.Average nematode densities (in ind/10 cm2, bars) and chlorophyll a concentrations (µg/g, dots) for the different Larsen stations and reference areas. Bars represent standard errors. Note that for the reference stations, pigment data are not shown because they were expressed in µg/cm3 and hence could not be compared. B. Nematode densities (ind/10 cm2) for the different stations relative to their depth (0–1000 m). The position of the Larsen B_Seep station is marked with an asterisk*.

Mentions: Although CPE values were low in the Larsen region, average meiofauna density at Larsen B_Seep was within the higher range found at other seasonally ice-free shelf locations in the Weddell, Scotia and Ross Seas [40], [43], [48] (see Fig 4A & B). At B_Seep, densities varied substantially between the different replicates (Table 4) but such microscale variation could be ascribed to small-scale differences in microtopography and physical structure of the habitat, as well as patchiness of food availability in the sediments [40], [42], [49]. Since nematode densities at B_Seep were higher compared to shallower Larsen stations and reference stations in the Weddell Sea (Fig 4B), they do not seem to conform to the general pattern of decrease in abundance with water depth. Highest nematode densities and CPE concentrations at B_Seep within the Larsen area could indicate that higher nematode densities are a consequence of this elevated food input. However, when put in a broader geographical context, higher densities at B_Seep relative to Weddell Sea regions of similar depth cannot simply be explained by assuming higher food input in the Larsen B_Seep area.


Characterisation of the nematode community of a low-activity cold seep in the recently ice-shelf free Larsen B area, Eastern Antarctic Peninsula.

Hauquier F, Ingels J, Gutt J, Raes M, Vanreusel A - PLoS ONE (2011)

A. Nematode densities in comparison with other Larsen and Weddell Sea stations.Average nematode densities (in ind/10 cm2, bars) and chlorophyll a concentrations (µg/g, dots) for the different Larsen stations and reference areas. Bars represent standard errors. Note that for the reference stations, pigment data are not shown because they were expressed in µg/cm3 and hence could not be compared. B. Nematode densities (ind/10 cm2) for the different stations relative to their depth (0–1000 m). The position of the Larsen B_Seep station is marked with an asterisk*.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3140504&req=5

pone-0022240-g004: A. Nematode densities in comparison with other Larsen and Weddell Sea stations.Average nematode densities (in ind/10 cm2, bars) and chlorophyll a concentrations (µg/g, dots) for the different Larsen stations and reference areas. Bars represent standard errors. Note that for the reference stations, pigment data are not shown because they were expressed in µg/cm3 and hence could not be compared. B. Nematode densities (ind/10 cm2) for the different stations relative to their depth (0–1000 m). The position of the Larsen B_Seep station is marked with an asterisk*.
Mentions: Although CPE values were low in the Larsen region, average meiofauna density at Larsen B_Seep was within the higher range found at other seasonally ice-free shelf locations in the Weddell, Scotia and Ross Seas [40], [43], [48] (see Fig 4A & B). At B_Seep, densities varied substantially between the different replicates (Table 4) but such microscale variation could be ascribed to small-scale differences in microtopography and physical structure of the habitat, as well as patchiness of food availability in the sediments [40], [42], [49]. Since nematode densities at B_Seep were higher compared to shallower Larsen stations and reference stations in the Weddell Sea (Fig 4B), they do not seem to conform to the general pattern of decrease in abundance with water depth. Highest nematode densities and CPE concentrations at B_Seep within the Larsen area could indicate that higher nematode densities are a consequence of this elevated food input. However, when put in a broader geographical context, higher densities at B_Seep relative to Weddell Sea regions of similar depth cannot simply be explained by assuming higher food input in the Larsen B_Seep area.

Bottom Line: The nematode community at the Larsen B seep site differed significantly from other Antarctic sites in terms of dominant genera, diversity and abundance.The recent ice-shelf collapse and enhanced food input from surface phytoplankton blooms were responsible for the shift from oligotrophic pre-collapse conditions to a phytodetritus-based community with high densities and low diversity.The parthenogenetic reproduction of the highly dominant Halomonhystera species is rather unusual for marine nematodes and may be responsible for the successful colonisation by this single species.

View Article: PubMed Central - PubMed

Affiliation: Marine Biology Section, Ghent University, Ghent, Belgium. freija.hauquier@ugent.be

ABSTRACT

Background: Recent climate-induced ice-shelf disintegration in the Larsen A (1995) and B (2002) areas along the Eastern Antarctic Peninsula formed a unique opportunity to assess sub-ice-shelf benthic community structure and led to the discovery of unexplored habitats, including a low-activity methane seep beneath the former Larsen B ice shelf. Since both limited particle sedimentation under previously permanent ice coverage and reduced cold-seep activity are likely to influence benthic meiofauna communities, we characterised the nematode assemblage of this low-activity cold seep and compared it with other, now seasonally ice-free, Larsen A and B stations and other Antarctic shelf areas (Weddell Sea and Drake Passage), as well as cold-seep ecosystems world-wide.

Principal findings: The nematode community at the Larsen B seep site differed significantly from other Antarctic sites in terms of dominant genera, diversity and abundance. Densities in the seep samples were high (>2000 individuals per 10 cm(2)) and showed below-surface maxima at a sediment depth of 2-3 cm in three out of four replicates. All samples were dominated by one species of the family Monhysteridae, which was identified as a Halomonhystera species that comprised between 80 and 86% of the total community. The combination of high densities, deeper density maxima and dominance of one species is shared by many cold-seep ecosystems world-wide and suggested a possible dependence upon a chemosynthetic food source. Yet stable (13)C isotopic signals (ranging between -21.97±0.86‰ and -24.85±1.89‰) were indicative of a phytoplankton-derived food source.

Conclusion: The recent ice-shelf collapse and enhanced food input from surface phytoplankton blooms were responsible for the shift from oligotrophic pre-collapse conditions to a phytodetritus-based community with high densities and low diversity. The parthenogenetic reproduction of the highly dominant Halomonhystera species is rather unusual for marine nematodes and may be responsible for the successful colonisation by this single species.

Show MeSH
Related in: MedlinePlus