Geophysical exploration of an active pockmark field in the Bay of Concarneau, southern Brittany, and implications for resident suspension feeders

Baltzer, Agnès; Ehrhold, Axel; Rigolet, Carinne; Souron, Aurélie; Cordier, Céline; Clouet, Hélène; Dubois, Stanislas F.

doi:10.1007/s00367-014-0368-0

Cited by 25 publications

(32 citation statements)

References 52 publications

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“…about 2 pocks km −2 , or 500 pockmarks altogether, in the 179 km 2 of the inner Oslo fjord, Norway) (Webb et al 2009c) or higher densities of about 200 pocks km −2 in Belfast Bay (United Kingdom) (Hovland & Judd 1988, Kelley et al 1994. To our knowledge, the highest densities of pockmarks found to date are those discovered in muddy sediments of South Brittany (France), where up to 2500 pocks km −2 were recorded (Baltzer et al 2014).…”

Section: Introductionmentioning

confidence: 75%

“…1A−C). Several thousand pockmarks have recently been mapped in this area of 36 km 2 (Baltzer et al 2014). This bay resembles many coastal embayments in Brittany be cause it is sheltered by a succession of rocky islets and is characterized by soft-bottom substrates, spanning from mud to muddy sand, with depths ranging from 15 to 35 m (Ehrhold et al 2006).…”

Section: Study Sitementioning

confidence: 99%

“…In the Bay of Concarneau (South Brittany, France), recent investigations using sonar and seismic profiles have indicated the presence of a large pockmark field covering a well-delimited area of 36 km 2 in water depths ranging between 20 and 40 m (Baltzer et al 2014). While pockmark densities here vary from less than 1000 to 2500 km −2 , their sizes range from less than 1 to about 35 m, with depths rarely exceeding 2 m. The pockmark field is located above a palaeovalley system and is restricted to a muddy benthic habitat engineered by the amphipod species Haploops nirae (Ehrhold et al 2006, Baltzer et al 2014. H. nirae (hereafter referred to as Haploops) is a gregarious tubiculous organism that builds extensive mats in shallow muddy habitats.…”

Section: Introductionmentioning

confidence: 99%

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Role of pockmarks in diversity and species assemblages of coastal macrobenthic communities

Dubois¹,

Dérian²,

Caisey³

et al. 2015

Mar. Ecol. Prog. Ser.

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We used existing bathymetric data to study the macrofauna of a geophysical pockmark field restricted to a benthic habitat engineered by the tubiculous amphipod Haploops nirae in South Brittany (France). Stations inside and outside pockmarks of different morphometric characteristics (location, size, depression depth) were sampled for macrofauna and environmental parameters (sediment characteristics, organic matter, chl a, hydrogen sulfide and methane concentrations). Diversity indices showed higher species richness inside pockmarks, especially for species with medium to high abundances. Most sediment cores showed low methane but high hydrogen sulfide concentrations. We hypothesised that after eruption, the remaining residual methane from pockmark sediments is oxidised by seawater sulfate and accounts for the high sulfide concentrations found at increasing depth in our samples and the low methane concentrations. We found no relationship between sediment profiles and morphometric features of the pockmarks. Macrofauna assemblages inside vs. outside pockmarks appeared to be different. Pockmarks appear to increase connectivity among habitats and heterogeneity within habitats, thereby creating local hotspots that allow the settlement of species that cannot otherwise develop in Haploops tube mats. Multivariate analyses distinguished 4 groups of pockmarks and control stations. We assumed that deeper pockmarks were created more recently than shallow pockmarks and that each pockmark is at a different stage of evolution, hence explaining the large variability in the characteristics of pockmark groups. This explains why previous investigations have found contradictory results when comparing macrofauna species diversity and composition between areas inside and outside pockmarks. Finally, we propose and discuss a successional stage model for pockmarks.

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Section: Introductionmentioning

confidence: 75%

Section: Study Sitementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Role of pockmarks in diversity and species assemblages of coastal macrobenthic communities

Dubois¹,

Dérian²,

Caisey³

et al. 2015

Mar. Ecol. Prog. Ser.

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“…The two main habitats engineered by H. nirae (termed hereafter “ Haploops habitats”) in the northeastern Atlantic are located on the Brittany coast, in the Bay of Concarneau and the Bay of Vilaine (Ehrhold, Hamon, & Guillaumont, ; Glémarec, Le Bris, & Le Guellec, ; Rigolet, ). Opportunistic video surveys revealed continuous expansion of the two Haploops habitats over the last two decades (Baltzer et al., ; Ehrhold et al., ). To explain the ecological succession of these habitats, it was suggested that Haploops colonization of surrounding habitats is facilitated by the presence of the tubiculous polychaete Maldane glebifex (Glémarec et al., ), which is associated with the Amphiura filiformis sandy‐mud habitat.…”

Section: Introductionmentioning

confidence: 99%

Functional roles of an engineer species for coastal benthic invertebrates and demersal fish

Chaalali

Brind’Amour

Dubois

et al. 2017

Ecology and Evolution

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Through their tissues or activities, engineer species create, modify, or maintain habitats and alter the distribution and abundance of many plants and animals. This study investigates key ecological functions performed by an engineer species that colonizes coastal ecosystems. The gregarious tubiculous amphipod Haploops nirae is used as a biological model. According to previous studies, the habitat engineered by H. nirae (i.e., Haploops habitat) could provide food and natural shelter for several benthic species such as benthic diatoms belonging to the gender Navicula, the micrograzer Geitodoris planata, or the bivalve Polititapes virgineus. Using data from scientific surveys conducted in two bays, this study explored whether (1) the Haploops sandy‐mud community modifies invertebrate and ichthyologic community structure (diversity and biomass); (2) H. nirae creates a preferential feeding ground; and (3) this habitat serves as a refuge for juvenile fish. Available Benthic Energy Coefficients, coupled with more traditional diversity indices, indicated higher energy available in Haploops habitat than in two nearby habitats (i.e., Sternaspis scutata and Amphiura filiformis/Owenia fusiformis habitats). The use of isotopic functional indices (IFIs) indicated (1) a higher functional richness in the Haploops habitat, related to greater diversity in food sources and longer food chains; and (2) a higher functional divergence, associated with greater consumption of a secondary food source. At the invertebrate‐prey level, IFIs indicated little specialization and little trophic redundancy in the engineered habitat, as expected for homogenous habitats. Our results partly support empirical knowledge about engineered versus nonengineered habitats and also add new perspectives on habitat use by fish and invertebrate species. Our analyses validated the refuge‐area hypothesis for a few fish species. Although unique benthic prey assemblages are associated with Haploops habitat, the hypothesis that it is a preferential feeding area was not verified. However, specialist feeding behavior was observed for predators, which calls for further investigation.

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“…1). Although the initial pockmark craters are thought to be formed during seismic events (Baltzer et al, 2014), pockmarks could be activated when the tidal pressure would be high enough during spring tides, leading to the formation of plumes in the water column.…”

Section: Triggering and Control Mechanismsmentioning

confidence: 99%

Geological fluid flow in sedimentary basins

Migeon

2017

Bull. Soc. géol. Fr.

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Geophysical exploration of an active pockmark field in the Bay of Concarneau, southern Brittany, and implications for resident suspension feeders

Cited by 25 publications

References 52 publications

Role of pockmarks in diversity and species assemblages of coastal macrobenthic communities

Role of pockmarks in diversity and species assemblages of coastal macrobenthic communities

Functional roles of an engineer species for coastal benthic invertebrates and demersal fish

Geological fluid flow in sedimentary basins

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