Through an experimental approach we investigate the role of mucus secretion in postlarvae of Pectinaria koreni (tubicolous polychaete) on their ability to drift within the benthic boundary layer or ...to stay at the water-substratum interface. Fall velocity measurements were conducted with either living or dead postlarvae which were allowed to sink into a 2 m long Plexiglas cylindrical chamber. Five groups of increasing size-classes were tested ranging from the very first benthic stage (1 mm < Tube^sub length^ < 2 mm: membranous tube present accounting for more than 75% of the total tube length) to older stages (6 mm < Tube^sub length^ < 10 mm: membranous tube absent). We used these results to propose the first estimates of dispersal distances by several post-larval stages secreting mucus or sinking passively through the water column. Experiments were carried out in the HYCOBENTHOS flume to determine values of critical shear velocity (u ^sub *c^) inducing bedload transport and further resuspension of postlarvae of increasing sizes. The influence of mucus secretion by recruits on their ability to stay or quit a 'suitable' substratum was investigated by using either living or dead individuals. Results showed that: (a) the ability to secrete mucus rapidly is limited to the younger stages; (b) fall velocity of postlarvae is drastically lowered by mucus secretion (5 orders of magnitude) and is higher for the older stages; (c) dead recruits behave similarly to 'passive' recruits; (d) horizontal distances of drift dispersal may be considerable (up to 800 m for a single 22 min trip); (e) mucus secretion may be used by the postlarvae to anchor themselves to the substratum. Cost-benefit of using the mucus secretion as a tool for recruitment and the related spatial scales are discussed.PUBLICATION ABSTRACT
Recolonisation patterns of soft-bottom macrofauna on defaunated Cu-spiked sediments were studied in a field experiment at 63 m depth in the Oslofjord, Norway. Field experiments studying colonisation ...patterns of contaminated sediments are ecologically relevant since settling and metamorphosis of pelagic larvae are generally considered the most critical phases in the development of marine benthic assemblages. Total faunal abundance and the density of the polychaetes
Pectinaria koreni and
Prionospio cirrifera decreased significantly at sediment Cu-concentrations of 300 mg kg
−1. Also the polychaetes
Pseudopolydora paucibranchiata, Capitella capitata, Chaetozone setosa, Harmothoe spp., the bivalve
Thyasira sarsi and the brittlestar
Ophiura affinis were significantly negative correlated to increased sediment Cu-content. Although these species were affected negatively, most of the 116 taxa within the experimental trays showed no response over the entire range of Cu sediment concentrations. Most field studies on recolonisation have been performed in the intertidal or shallow subtidal. These environments are often dominated by robust organisms while animals living in deeper waters are more sensitive to disturbance. The experimental system developed could easily be used at depths between 20 and 100 m to study effects of toxic compounds separately or as mixtures, or colonisation and succession processes of uncontaminated sediments in general.
Benthic macrofauna communities were sampled with their 'undisturbed' sediments from 2 soft-bottom sites on the Swedish west coast. At one of the sites the top sediment had a positive redox potential ...(Expt 1) and at the other the sediment was comparatively more reduced close to the surface (Expt 2). The benthic communities at these 2 sites were each exposed to 3 treatments of oxygen concentrations: (1) normoxia (>8.0 mg l−1, >90% oxygen saturation), (2) moderate hypoxia (∼1.0 mg l−1, 12% oxygen saturation) and (3) severe hypoxia (∼0.5 mg l−1, 6% oxygen saturation). Redox potential profiles in the sediments showed a significant increase with time under normoxic conditions, whereas they showed an overall decline with time in moderate and severe hypoxia. The number of individuals and species at the 2 field sites did not differ significantly from corresponding numbers in the experimental normoxia (laboratory control) at the end of those experiments. In Expt 1 survival of the number of individuals was reduced in severe hypoxia compared to in moderate hypoxia and normoxia. The number of species was significantly reduced between all treatments. In Expt 2 community abundance and the number of species were significantly reduced in moderate and severe hypoxia compared to normoxia. Behaviour of dominant species is described: in general they left their position in the sediment (for Pectinaria koreni with their tubes) and occurred at the sediment surface in the moderate and severe hypoxic treatments. Comparison of the results of Expt 1 with those of Expt 2 suggests that the comparatively more reduced sediment in Expt 2 resulted in a greater negative response, implying the significance of sediment conditions for benthic macrofauna response to hypoxia.
According to a recent demographic survey, the population structure of Pectinaria koreni might fit a source–sink metapopulation model at least at a regional scale. Spatial and temporal genetic ...structure of the populations present in the Baie de Seine (eastern Baie de Seine and Baie des Veys) was assessed using four highly polymorphic microsatellite loci which have revealed strong intra-locality genetic diversity. In the eastern Baie de Seine, both temporal (1994–1996) and spatial (1994) genetic differentiation were relatively low but significantly different from zero despite a 15-day dispersing larval stage. Such structures may be explained by the settlement of larvae from different gene pools and differing recruitment histories among sites within the eastern Baie de Seine. At a larger scale, similar levels of spatial differentiation were observed in 1999 between the eastern Baie de Seine and the Baie des Veys. The lack of any significant differences in gene diversity and allelic richness rules out a source–sink functioning at the scale of our study. The present paper provides further knowledge on the population dynamics of a univoltine species and its persistence in a highly dispersive environment via a shifting spatial mosaic.
The spatial distribution and temporal variations of the Abra alba-Pectinaria koreni community from the eastern part of the Bay of Seine were investigated through four winter surveys (1986, 1987, 1988 ...and 1991). A grid of 40–67 stations was sampled each year using a Hamon grab (0·25 m-2) for macrofauna collection and sediment analysis. The fauna was dominated by polychaetes and in a lower part by molluscs and echinoderms. Although species richness with ~100 species collected during each survey was high, total density and biomass (±SE) resulted principally from about ten dominant species, and varied between 846·9 ±163·5 and 1135·3 ±186·7 ind m-2 and 23·52 ±4·41 and 27·48 ±4·45 g m-2respectively. The dominant species were patchily distributed and exhibited weak spatio-temporal fluctuations except the two bivalves A. alba and Cultellus pellucidus. Factorial correspondence analysis (FCA) of the distribution of main species among stations and automatic hierarchical classification identified five faunal assemblages which were relatively stable in space and time. The temporal stability of the community could be generated by processes of larval retention near parental population, and sediment stabilization induced by the low abundance of deposit feeders and the high densities of the tube-dwelling polychaete Owenia fusiformis. While the sediment variables were a poor indicator of the spatial structure of the community, the salinity gradient off the Seine Estuary and post-settlement processes (e.g. food limitation and postlarval drifting) have been proposed to explain it. Comparison with an earlier survey (i.e. 1971) suggested a degree of long-term persistence of the community structure in qualitative and quantitative terms.
Earlier papers dealing with the anatomy of the central nervous system of ampharetids, pectinariids and terebellids were studied. On this basis a re‐investigation appeared necessary: statements in the ...literature about the structure of the brain and the innervation of the appendages of the anterior end were incomplete and contradictory. In the present paper, the brain, the circum‐oesophageal connectives and the innervation of, inter alia, the tentacular membrane (including the dorsal ridge), the buccal tentacles, the alimentary canal, the nuchal organs and the branchiae (when present) of Amphicteis gunneri, Anobothrus gracilis, Melinna cf. cristata, Pectinaria auricoma, P. belgica, P. koreni, Petta pusilla, Pista cristata, Eupolymnia nebulosa, Thelepus cincinnatus and Polycirrus medusa are described. The results are summarized in schematic diagrams and compared with each other and with the central nervous system of other polychaetes. It is concluded that the ampharetids, the pectinariids and the terebellids bear no antennae and no palps and that their buccal tentacles belong to the alimentary canal. It is emphasized that all attempts to range their cephalic nervous system into previously proposed common and general schemes of ‘the polychaete nervous system’ seem totally fruitless.
A new retiolitid genus Cometograptus, restricted to the lundgreni Biozone (Late Wenlock), is characterized by a combination of primitive features such as strong transverse rods and ancora sleeve ...lists with seams facing out, with advanced features such as a long sicula, central, free nema and pustulose bandages. Cometograptus links two Subfamilies of the Family Retiolitidae. The Subfamily Retiolitinae is divided into redefined lineages: Pseudoretiolites, Retiolites, Paraplectograptus, whereas the Subfamily Plectograptinae is divisible into the Sokolovograptus (questionable), Gothograptus, Spinograptus, Plectograptus lineages, and Cometograptus. The Sokolovograptus group, the first retiolitids bearing ancora sleeve lists with seams facing out, did not survive the lundgreni crisis. The only survivors were Upper Wenlock retiolitids of the Gothograptus lineage. The new genus Cometograptus includes Cometograptus koreni n.gen. and n.sp., Cometograptus tomczyki n.gen. and n.sp., as well as the previously described Cometograptus nevadensis, Cometograptus marsupium and Cometograptus apoxys.
For marine benthic invertebrates exhibiting complex life cycles, changes in populations' distribution and abundance are governed by a large variety of physical, chemical and biological processes. ...From field observations in the Bay of Seine and laboratory experiments conducted since 1987 on the polychaete Pectinaria koreni, the present study highlights the relative importance of hydrodynamical and biological factors which affect individuals within both the planktonic and benthic phases at different scales of space and time in a macrotidal area. Pectinaria koreni is one of the main macrofaunal component of the Abra alba muddy fine sand community of the eastern Bay of Seine. Despite a highly advective and diffusive environment, a relative larval retention near adult population was reported due to some local hydrodynamics features (e.g. tidal residual circulation, Seine river plume front) and the interaction between the vertical current structure and the larval vertical migration. Although larval retention could be disrupted by wind induced currents, multiple spawning events over the reproductive period increase the likelihood that at least one larval cohort ensures a high recruitment during the life-span. Following a massive settlement whatever the sediment grain size, the newly settled larvae exhibited a high immediate decrease of their densities as a result of postlarval mortality and migration. Postlarval drifting was induced by a combination of physical factors (i.e. tidal currents and swell) and postlarval behaviour in response to sediment texture and adult/settlers interactions. According to the hydrodynamics of the bay, this process may generate a postlarval transport from offshore bottoms to coastal suitable habitats and counteract the demographic effects of larval dispersal. A conceptual model of factors governing the recruitment and population maintenance of Pectinaria koreni is proposed and discussed in comparison with results obtained on another polychaete, Owenia fusiformis, in the same area.
Data from samples of the macrobenthic
Abra alba–
Pectinaria koreni community of the eastern Bay of Seine (English Channel) collected in winter 1986 are analysed to illustrate the advantages of a ...novel method of multivariate analysis of spatial patterns described by Thioulouse et al. (Environ. Ecol. Stat., 2 (1995) 1–14), consisting of local and global approaches. Multivariate ordination procedures are applied that take spatial components into account explicitly through the construction of a neighbourhood graph between closely placed sampling sites, which is then used to weight the data. The result is a decomposition of spatial structure on local and global scales. This method is for the first time applied to macrobenthic data of this region. It shows the underlying importance of spatial scaling in analysis and proves to offer more information than classical ordination methods such as correspondence analysis, which may confuse the two different spatial scales. Global analysis is proposed as a powerful tool to define species assemblages and local analysis as an additional instrument to define partitions resulting from biological interactions. Additionally, this method appears capable of incorporating rare species (which influence classical analyses, often resulting in their elimination from datasets) by minimising their effects on the global scale and conversely maximising them on the local scale. This analysis demonstrates the importance of explicitly incorporating spatial information into the detection and interpretation of patterns in a macrobenthic community.
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