Benthic ecology of pockmarks in the Inner Oslofjord, Norway

Webb, Karen E.; Barnes, David K. A.; Gray, John S.

doi:10.3354/meps08079

Cited by 17 publications

(21 citation statements)

References 38 publications

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“…For macrofauna on the other hand, there is literature available describing communities inside and outside pockmarks. In brief, bioturbating macrofaunal species in sediment communities were found to be significantly different inside and outside of pockmarks at several locations in the Oslofjord suggesting that pockmarks influence the distribution of macrofaunal species [11]. Bioturbators can both redistribute particles and/or ventilate the sediments by moving water in or out of the burrows, which could affect both redox gradients and availability of microbial resources (e.g.…”

Section: Introductionmentioning

confidence: 99%

Linking Geology and Microbiology: Inactive Pockmarks Affect Sediment Microbial Community Structure

2014

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Pockmarks are geological features that are found on the bottom of lakes and oceans all over the globe. Some are active, seeping oil or methane, while others are inactive. Active pockmarks are well studied since they harbor specialized microbial communities that proliferate on the seeping compounds. Such communities are not found in inactive pockmarks. Interestingly, inactive pockmarks are known to have different macrofaunal communities compared to the surrounding sediments. It is undetermined what the microbial composition of inactive pockmarks is and if it shows a similar pattern as the macrofauna. The Norwegian Oslofjord contains many inactive pockmarks and they are well suited to study the influence of these geological features on the microbial community in the sediment. Here we present a detailed analysis of the microbial communities found in three inactive pockmarks and two control samples at two core depth intervals. The communities were analyzed using high-throughput amplicon sequencing of the 16S rRNA V3 region. Microbial communities of surface pockmark sediments were indistinguishable from communities found in the surrounding seabed. In contrast, pockmark communities at 40 cm sediment depth had a significantly different community structure from normal sediments at the same depth. Statistical analysis of chemical variables indicated significant differences in the concentrations of total carbon and non-particulate organic carbon between 40 cm pockmarks and reference sample sediments. We discuss these results in comparison with the taxonomic classification of the OTUs identified in our samples. Our results indicate that microbial communities at the sediment surface are affected by the water column, while the deeper (40 cm) sediment communities are affected by local conditions within the sediment.

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Section: Introductionmentioning

confidence: 99%

Linking Geology and Microbiology: Inactive Pockmarks Affect Sediment Microbial Community Structure

2014

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“…Soft sediment environments have previously been considered to have low topographic structure (Pethick 1984). However, features such as pockmarks and iceberg scours are now being recognized as important in structuring soft sediment environments (Webb et al 2009). Pockmarks are craters formed in the seafloor, presumably by the expulsion of fluids from the sediments.…”

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confidence: 99%

Pockmarks: Refuges for marine benthic biodiversity

Webb

Barnes

Plankea

2009

Limnology & Oceanography

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Pockmarks are one of the most obvious and abundant structural features of the North Sea seabed, yet their influence on fauna is virtually unknown. We report the distribution of benthic megafaunal assemblages in and around four ''pockmark complexes'' in the North Sea to determine the structure of megafaunal communities inside pockmarks and whether these ubiquitous topographical features acted as refuges against trawling and other disturbances. The study focuses on the large central pockmarks in each of the pockmark complexes. These large pockmarks had depths of around 10 m and diameters of 160-235 m. Remotely operated vehicle video transects showed that megafauna increased in abundance, species richness, and diversity from outside (background seabed) toward the center of the pockmarks. The number of taxa present in the center of pockmarks was approximately double those of similar surrounding areas, and the centers had almost an order of magnitude more individuals than outside. Carbonate rocks were found in the centers of all the pockmarks and may be indicative of their formation (past methane seeps). These rocks also provide novel habitat to fauna: a complex hard substrate for colonization and shelter in an otherwise homogeneous soft sediment environment. Habitat enrichment and morphological protection are suggested to be the main reasons for the increased faunal abundance and species richness. Indeed, despite fishing data showing the area to be intensively disturbed, large slow-growing (old) and vulnerable species, such as gorgonian corals, were found in the center of the pockmarks. Pockmarks may offer important refuges from trawling activity.

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“…One of these genera, the bivalve mollusc Thyasira sp., was found in low abundances at St 20 and 40. This genus, is known to predominantly utilise sulphur-oxidising bacteria for obtaining nutrition, therefore, its presence may indicate the presence of gas seeps at these locations (Dando et al, 1991, Webb et al, 2009a, Wildish et al, 2008. It must be noted, however, that this genus also occurs in organic-rich sediments (Dando et al, 1991) and may also explain its presence in Dunmanus Bay.…”

Section: Pockmarks and Benthic Communitiesmentioning

confidence: 90%

“…Communities of polychaetes and echinoderms have previously been observed in a North Sea pockmark (Dando et al, 1991), though the species composition differs in that there are few Amphiura sp. This composition is not specific to pockmarked regions; Oslo fjord, for example, is also dominated by polychaetes and bivalve molluscs (Webb et al, 2009a), but this is more representative of the regional biota than pockmark. The polychaete and echinoderm mix of infauna in Dunmanus Bay is similar to Killary Harbour, also in the west of Ireland, (Keegan and Mercer, 1986), particularly with regard to the Amphiura brittle star community, though A. filiformis dominates A. chiajei in Dunmanus Bay.…”

Section: Pockmarks and Benthic Communitiesmentioning

confidence: 98%

Occurrence, characteristics and formation mechanisms of methane generated micro-pockmarks in Dunmanus Bay, Ireland

Szpak

Monteys

O’Reilly

et al. 2015

Continental Shelf Research

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a b s t r a c tA small gas pockmark field in Dunmanus Bay, SW Ireland was surveyed and ground-truthed to assess its activity, geomorphology, explore its formation mechanisms and to investigate its potential influence on the benthic community. The field consisted of 121 circular, shallow units ranging from 5 to 17 m in diameter and not exceeding 1 m in relief. Sub-bottom profiles revealed broad acoustic signatures typical of shallow gas accumulation in the subsurface in addition to vertically elongated signals of ascending bubbles captured in the echo sounder data. The pockmarks show strong correlation with the depth of sub-surface gas fronts. However methane concentrations in the water column and directly above the features were close to typical marine, background values and did not exceed 15 nM. This suggests a very mild, periodic venting scenario. Sediment core samples revealed permeable sandy layers with slightly elevated methane concentrations indicative of stratified, diffusive flow. Pore-water sulphate and chloride data show no sign of pore water freshening and thus suggest that methane gas is the sole fluid responsible for formation of these pockmarks. Benthic infauna distributions showed reduced diversity in pockmarked regions, primarily influenced by the sediment composition. Few species utilising chemosymbiotic associations were identified, and there was little indication of a community influenced by methane venting in Dunmanus Bay.

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Benthic ecology of pockmarks in the Inner Oslofjord, Norway

Cited by 17 publications

References 38 publications

Linking Geology and Microbiology: Inactive Pockmarks Affect Sediment Microbial Community Structure

Linking Geology and Microbiology: Inactive Pockmarks Affect Sediment Microbial Community Structure

Pockmarks: Refuges for marine benthic biodiversity

Occurrence, characteristics and formation mechanisms of methane generated micro-pockmarks in Dunmanus Bay, Ireland

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