Using Pectinaria koreni as a biological model of larval dispersal, we coupled the analysis of differently evolving genetic markers (mitochondrial cytochrome oxidase I and four microsatellite loci) to ...hydrodynamic modeling of larval transport in the English Channel. To determine the influence of historical and contemporary processes on the genetic structure of our study populations, genetic relationships between English Channel, Irish Sea, and southern North Sea populations were assessed in relation to the long-term pattern of marine currents and to postglacial colonization pathways. Although significant, low level of overall nuclear genetic differentiation was best explained by the recent origin of populations within the study area and the retention of ancestral polymorphism. Both genetic data sets suggest that two ancestral gene pools contributed to the origin of our study populations, and secondary contacts occurred in the English Channel and southern North Sea as a result of two migration routes around the British Isles. Although Irish Sea and Belgium populations appeared more recently connected, populations of the eastern English Channel were more isolated. English Channel patterns of connectivity indicated high dispersal and gene flow along the French coast, from Normandy to the southern North Sea. Despite significant genetic differentiation between both coasts, migration model selection favored cross-channel gene flow and long-distance migration following the coastlines. Our results highlight the influence of postglacial colonization on genetic patterns in the English Channel, and indicate that contemporary mesoscale connectivity inferred by hydrodynamic modeling cannot, alone, explain the present genetic structure of populations in this area.
The benthic macrofauna of the Bay of Muggia and its evolution in time was analysed in order to assess the impact of man-made pollution in this port area. The north and NE zones are totally ...industrialised while the southern zone is mainly used for tourism and aquaculture. The most important anthropic impacts were stagnation and direct urban and industrial discharges, which operated until the beginning of the 1990s. Forty-four stations were sampled in 1981, 12 of which were monitored over time (1975, 1981 and 1994). From 172 taxa 11
783 organisms were identified. Polychaetes were the richest group, followed by molluscs, crustaceans and echinoderms. The dominant species was
Corbula gibba (39.5%) followed by
Pectinaria koreni (9%). Uni- and multivariate analyses showed a declining pattern for the fauna along a gradient of environmental stress. The very high concentrations of heavy metals in the Bay's sediments, especially Pb, contrasted with the diversity and biological index values found, indicating that many species could survive these conditions. The enforcement of the Italian ecological laws regarding water pollution control benefited the local macrofauna and evidenced the resilience of the system.
C. gibba constituted a good biological indicator of zones of high instability (especially sedimentary) and of intermediate levels of pollution.
U ovom radu prikazan je jedan edukativni softver za računanje korena realnih i kompleksnih polinoma stepena manjeg od pet. Dat je opšte poznat postupak za računanje korena polinoma stepena dva. Zatim ...je napravljena generalizacija za polinome stepena tri i četiri (Kardanove i Ferarijeve formule, respektivno). Napravljene su tri interaktivne Jupyter sveske koje omogućavaju korisniku da menja vrednosti koeficijenata polinoma i da prati sve korake u simboličkom računanju korena polinoma.
Several species of marine polychaetes reside in individual protective tubes. These tubes may be agglomerated in patches of varied sizes with very high densities, or form massive reef-like mounds ...which can be stretch over several kilometers. These polychaetes can thus be considered as the most important building organisms after corals in coastal environments. We especially focused on several species belonging to the families of Sabellariidae, Terrebeliidae and Pectinariidae. Tubes grains are glued together with biomineralized cement secreted from a building organ connected to specialized glands. Different methods of micro-analysis were used to analyze the biomineral components of these cements for four varyingly gregarious tube-building polychaetes:
Lanice conchilega,
Pectinaria koreni,
Sabellaria alveolata and
Phragmatopoma caudata. The aim of this study is to describe and compare the inter- and the intraspecific variability in the main biomineral components of cement at local, regional and continental scales. Scanning Electron Microscopy confirms an identical structure of the cement within species of Sabellariidae in Europe and America. Electron Probe Micro-Analysis (EPMA) confirms the presence of calcium, phosphorus, and magnesium plus traces of manganese in all cements, with varying concentrations of these elements at different locations for the same species or for different species at the same location. Finally, our dataset is compared with previous studies from literature.
Plusieurs espèces de polychètes marins vivent isolées dans des tubes protecteurs. Ces bioconstructions peuvent être non jointives, mais réparties sur de grands espaces, et pouvant atteindre de très fortes densités individuelles ; d’autres construisent des formations récifales massives étendues parfois sur plusieurs kilomètres carrés. Ces polychètes peuvent ainsi être considérés comme les plus importants organismes bioconstructeurs de la zone littorale après les coraux hermatypiques. Les tubes des Sabellariidae, des Terrebeliidae et des Pectinariidae, par exemple, sont élaborés à partir de grains de sables et de fragments de coquilles d’une taille et d’une forme bien particulières, adaptées à l’organe préhensile du ver constructeur. L’organisation des clastes dans les parois des tubes est variable : celle des Sabellariidae ressemble à l’agencement des tuiles d’un toit alors que les fragments de coquilles utilisés par les Terrebeliidae sont assemblés de manière aléatoire. Les grains sont collés à l’aide d’un ciment biominéralisé secrété par un organe spécialisé connecté aux glandes cémentaires. Différentes méthodes de micro-analyse ont été utilisées pour analyser la composante biominérale de ces ciments pour quatre espèces de polychètes tubicoles :
Lanice conchilega,
Pectinaria koreni,
Sabellaria alveolata et
Phragmatopoma caudata. L’objectif de cette étude est de décrire et de mesurer la variabilité inter- et intraspécifique des principaux éléments du ciment aux échelles locale, régionale et continentale. La Microscopie Électronique à Balayage montre que la structure du ciment entre les espèces de Sabellariidae en Europe et en Amérique est identique. L’analyse par micro-sonde électronique (EPMA) confirme la présence de calcium, de phosphore et de magnésium, avec des traces de manganèse dans tous les ciments. La teneur de ces éléments varie selon l’environnement pour la même espèce et selon les espèces dans un même environnement. Une comparaison des données acquises avec celles de la littérature est présentée.
Physical disturbance by disposal of dredged materials in estuarine and coastal waters may result in burial of benthic fauna. Survival rates depend on a variety of factors including the type and ...amount of disposed materials and the lifestyle of the organisms. Laboratory burial experiments using six common macrobenthic invertebrates from a brackish habitat of the western Baltic Sea were performed to test the organisms' escape reaction to dredged material disposal. Experimental lab-results were then extrapolated to a field situation with corresponding bottom topography and covering layer thicknesses at experimental field disposal study sites. Resulted survival rates were then verified by comparison with results of an earlier field study at the same disposal sites.
Our experimental design in the lab included the disposal of two types of dredged material (i.e. ‘till’ and ‘sand/till mixture’) and two covering layer depths (i.e. 10–20 cm and 14–40 cm). All three bivalves
Arctica islandica (Linnaeus),
Macoma balthica (Linnaeus),
Mya arenaria (Linnaeus) and the polychaete
Nephtys hombergii (Savigny) successfully burrowed to the surface of a 32–41 cm deposited sediment layer of till or sand/till mixture and restored contact with the overlying water. These high escape potentials could partly be explained by the heterogeneous texture of the till and sand/till mixture with ‘voids’. The polychaete
Bylgides (
Harmothoe)
sarsi (Malmgren) successfully burrowed through a 16 cm covering layer whereas the polychaete
Lagis koreni (Malmgren) showed almost no escaping reaction. No general differences in escape behaviour after burial were detected between our test species from the brackish habitat and those reported in the literature for the same species in marine environments. However, a size-dependence in mobility of motile polychaetes and
M. arenaria was apparent within our study. In comparison to a thick coverage, thin covering layers (i.e. 15–16 cm and 20 cm) increased the chance of the organisms (
N. hombergii and
M. arenaria) to reach the sediment surface after burial. This was not observed for the other test species. While crawling upward to the new sediment surfaces burrowing velocities of up to 8 cm d
−
1
were observed for the bivalves and up to 20 cm d
−
1
for
N. hombergii. Between 17 and 79% of the test organisms showed burrowing activity after experimental burial. The survival rate (defined as the ability to regained contact with the sediment surface) ranged from 0 to 33%, depending on species and on burial depth. The organisms reached the sediment surface by burrowing (polychaetes and bivalves) and/or by extending their siphons to the new sediment surface (bivalves). The extrapolation of laboratory survival rates to the two disposal sites was obtained based on the
in situ thicknesses of the dredged spoil layers measured by multi-beam echo sounder. This resulted in total average survival rate estimates for the test species of 45 and 43% for the two disposal sites. The results obtained during the laboratory tests and the following extrapolation to the field were verified by the range of results from a previous field study, using grab sampling shortly before and after a disposal event in June 2001. The effect of dredged material disposal on the tested Baltic Sea benthic macrofauna was assessed by extrapolating the verified laboratory results to the field.
The dispersal of Pectinaria koreni larvae released from the eastern Bay of Seine (English Channel) was studied using a two-dimensional hydrodynamic model which integrates tides, wind-driven currents ...and eddy diffusion, in order to examine the influence of environmental forcing and mortality on larval population dynamics. A broad agreement between predicted larval dispersal for two spawning events observed in 1987 and field data suggests that numerical modelling may be useful to analyse processes involved in the transport and the dynamics of larval populations. Larval mortality may be as important as hydrodynamic processes on larval losses for the adult population. Tides and eddy diffusion had some effects on larval dispersal, but wind forcing and the timing of spawning in relation to the meteorological environment are predicted to be the main source of variability in larval dispersal rates. Although wind-induced larval transport may produce interannual variations in larval retention and recruitment, predicted retention rates were always sufficient to ensure the maintenance of the adult population, regardless of hydrodynamic conditions. The long-range transport of larvae from the eastern Bay of Seine to distant populations was conditioned by constant strong winds, lasting 15 consecutive days, and should be considered an extremely rare event.
In a recent paper, Clarke & Warwick (1998; Oecologia 113: 278-289) developed a method of quantifying the complementarity of species assemblages, and demonstrated that in some marine benthic ...communities the redundancy in community composition was remarkably high. The concept of structural and functional redundancy was tested using macrobenthic species abundance data from 2 eutrophic lagoons, the Valli di Comacchio and the Sacca di Goro, in the northern Adriatic Sea. Samples were collected at approximately seasonal intervals: the Comacchio data set spanned from November 1996 to January 2000, while the Goro data set was from January 1993 to December 1998. The level of structural redundancy in such habitats was quite low, while functional redundancy seemed higher. These findings are probably of great importance in considering conservation action and management of such habitats.
The relationship between biological community structure and particle size composition is investigated in coastal deposits off the southeast of England. Sediments in the survey area fall into ...well-defined groups when analysed by multivariate techniques, indicating similarities and differences which could not be identified by mere inspection of the data. Biological resources also fall into relatively distinct groups, or communities, when analysed for species composition and population density, although similarity within the groups is lower than that obtained for the sediments. There is, however, little evidence of a close correspondence between the distribution of different sediment types and benthic communities in the survey area: comparison of the similarity matrices yields weighted Spearman rank correlation of less than 0.37. This suggests that factors other than sediment composition play a significant part in controlling biological community structure on the seabed. Still, there is evidence that some species such as the tube-dwelling worm Sabellaria spinulosa are associated mainly with sands and gravels whilst fine mobile silts and sands are characterized by “opportunistic” species such as the tube-worm Lagis koreni. The results suggest that although modification of sediment composition from mixed sands and gravels to silts would be expected to result in colonization by “opportunistic” species capable of survival in mobile deposits, restoration of sediment composition after cessation of dredging for marine aggregates is not, within broad limits, a prerequisite for establishment of biological communities which are comparable with those that occurred in the deposits prior to dredging.
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.
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
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