Comparison between the Nereis diversicolor and Nereis virens marine worms in the transformation of ingested hydrocarbons

A feeding experiment was conducted on the marine worm Nereis diversicolor to compare the fate of a hydrocarbon mixture during the gut passage in this species with the hydrocarbon breakdown process demonstrated for Nereis virens. Hydrocarbon dissolution/solubilization processes in the gut of N. diversicolor were found to have similar qualitative and quantitative importance in the hydrocarbon transformation as those observed in N. virens

Alteration and release of aliphatic compounds by the polychaete Nereis virens (Sars) experimentally fed with hydrocarbons

In the laboratory, marine worms were fed with a mixture of algae and several aliphatic hydrocarbons for 15 days. After ingestion by the worms, 34.9% of hydrocarbons are found in the faeces and only 3.1% accumulated in the gut. The comparison between the initial mixture and the faeces shows that the worm’s digestive process lead to changes in the distribution of the n-alkane mixture. These changes are different from those only due to physical processes in the experimental conditions. In our experiment, no variation in the distribution of hydrocarbons in faeces with time and no microbial hydrocarbon biodegradation were evidenced. Our results suggest that marine worm feeding can substantially affect the fate of hydrocarbons in the sedimentary marine ecosystem by predominantly stimulating dissolution processes

Effects of temperature on in vitro sediment reworking processes by a gallery biodiffusor, the polychaete Neanthes virens

Temperature-induced variations in bioturbation could affect sediment mixing processes in the marine benthic environment. In this study, sediment reworking by Neanthes virens (Sars), a widely distributed polychaete in muddy sand communities of northern temperate latitudes, was studied under different temperature conditions representing winter (1°C), spring and fall (6°C), summer(13°C), and tide pool (18°C) temperatures in the lower St. Lawrence Estuary, Québec, Canada. Sediment reworking was quantified using inert fluorescent particles (luminophores) deposited at the sediment surface. Based on the 1-D luminophore distributions obtained after 5 and 30 d, the use of the specific ‘gallery-biodiffusor’ model allowed us to quantify both biodiffusion (Db) and biotransport (Vb) due to the organisms. Our results showed temperature effects on sediment transport. The lowest biotransport and biodiffusion coefficients were measured at 1 and 6°C and did not change with time. The highest biodiffusion occurred at 13°C for both sampling periods. At 18°C, biodiffusion was intermediate while biotransport was maximal. Differences between the 13°C biodiffusive transport and the other temperatures increased with time. Low transport values at 1 and 6°C suggest that a quiescent stage exists for this species at these temperatures, with sediment mixing occurring mostly during burrow construction. On the other hand, sediment mixing resulted from both the burrow construction and maintenance phases at higher temperatures (13 and 18°C)

Sediment reworking by marine benthic species from the Gullmar Fjord (Western Sweden): Importance of faunal biovolume

In order to compare and quantify sediment reworking activities by different species/functional groups of macrofauna, a laboratory experiment was carried out with species from the Gullmarsfjord (Western Sweden). Monospecific communities of Amphiura filiformis, Echinocardium cordatum, Scalibregma inflatum and Abra nitida were introduced in experimental mesocosms, with identical densities (795 ind. m−2), for 10 days. Sediment reworking was studied by quantifying downward and upward movements of fluorescent inert tracers (luminophores). Luminophores with different colour were initially deposited both at the sediment surface and within the sediments. Population biomass and biovolume were also determined. Surface tracers reworking coefficients ranged from 0.6 to 2.2 cm2 y−1 and 0.9 to 4.1 y−1, respectively for the biodiffusive-like and non-local transports. Calculated biodiffusive-like coefficient was between 1.0 and 2.3 cm2 y−1 for the deep tracers. For both tracers, the E. cordatum population presented the highest reworking coefficients. Among the morphological and/or ethological parameters that could determine overall patterns of reworking and differences between species, results have shown a direct relationship between the apparent biodiffusive mixing and the biovolume of the individuals (Db=0.35 ⁎ Biovolume). This suggests that the biovolume of macrofauna may allow a rough estimate of the biodiffusive-like reworking intensity of particles deposited on the sediment surface

Use of axial tomography to follow temporal changes of benthic communities in an unstable sedimentary environment (Baie des Ha! Ha!, Saguenay Fjord)

In the upper layer of the sediment column, organic matter recycling is greatly influenced by bioturbation. However, there are many physical changes in the nature of the sediment that may disturb benthic communities and create a biogeochemical imbalance. Following a very heavy rainfall between 26 and 29 July 1996, an intense flash flood in the Saguenay Fjord caused discharges of 6 million cubic metres of sediments into Baie des Ha! Ha!. Unstable sediment deposits located at the top of the delta of the Rivie`re des Ha! Ha! were sporadically exported to the deep basin. After this physical disturbance, meiobenthic and macrobenthic organisms progressively re-colonised the sediment column. To determine the impacts of such sedimentary depositions on benthic fauna, two stations, one at the head and one at the mouth of the Baie des Ha! Ha!, have been monitored since 1996. During this survey, we developed a new method for the quantification of biogenic structures using computer axial tomography (CAT-Scan). Benthic fauna analysis showed that the two stations were characterised by different temporal changes in the benthic dynamics according to their geographic location. Using CAT-Scan analysis of sediment cores, we were able to characterise the stability of the sediment column for the two stations in 1999 and 2000. Scan results suggest that colonisation processes were closely linked with the stability of the sediment column. Erosion and redeposition of surficial sediments caused a succession in the formation of biogenic structures. These variations were characterised for the first time using CAT-Scan, which is a nondestructive, rapid, and precise method. Tomographic analysis showed the importance of the production and destruction rates of biogenic structures and the sedimentation rate for the preservation of burrows and potentially reactive components. This study finally demonstrated that each erosional event could be followed by a rapid formation of biogenic structures, allowing the re-oxidation of old deposits

Rôle de la diversité fonctionnelle de la communauté à Macoma Balthica (Estuaire du Saint-Laurent, Québec, Canada) sur les flux biogéochimiques à l'interface eau-sédiment et sur le mélange particulaire

L objectif de cette thèse de doctorat est de caractériser et de quantifier l effet des groupes fonctionnels de bioturbation dominants de la communauté à M. balthica et de leur diversité, sur les flux biogéochimiques à l interface eau-sédiment (oxygène, carbone organique dissous, ammonium, nitrate, phosphate), le remaniement sédimentaire et les communautés microbiennes. Les groupes fonctionnels de la communauté à M. balthica de l estuaire du Saint Laurent (Québec, Canada) ont été définis selon leur mode de remaniement sédimentaire : Les biodiffuseurs, Macoma balthica et Mya arenaria, et le diffuseur à galerie, Nereis virens. Les mesures ont été réalisées dans des microcosmes expérimentaux répliqués avec les groupes fonctionnels isolés (allopatrie) et assemblés (sympatrie). Ceux-ci ont été soumis aux mêmes conditions expérimentales sur toute la durée de l expérience (40 jours). Les effets ont été comparés à des sédiments sans organisme servant de contrôle. Les organismes ont été introduits avec des biovolumes identiques, déterminés à partir des densités naturelles. L espace d occupation par les macro-invertébrés était donc similaire pour chaque traitement. Les résultats montrent clairement, qu à biovolume identique, les biodiffuseurs et le diffuseur à galerie ont des effets différents sur la stimulation des flux biogéochimiques, le transport des particules vers le fond des terriers et l activité bactérienne. Les effets du diffuseur à galerie, variant avec le temps, sont nettement supérieurs en raison de la dynamique spatio-temporelle des structures biogènes et des activités d irrigation, ainsi que de sa profondeur d enfouissement maximale. Des différences de profondeurs d'enfouissement expliquent par ailleurs les variabilités intra-fonctionnelles observées entre les deux biodiffuseurs sur les flux d ammonium et de nitrate et sur l activité bactérienne. Les deux groupes fonctionnels combinés (diffuseur à galeries + biodiffuseurs) ont des effets importants sur les paramètres mesurés, souvent supérieurs aux effets attendus par simple additivité. Les interactions spatiales positives entre les deux groupes fonctionnels expliquent ces effets. Les intensités des interactions affectant essentiellement les flux de nitrate, de phosphate, d ammonium et d'oxygène montrent une nouvelle fois, qu à biovolume identique, la profondeur d enfouissement de chaque groupe fonctionnel et l organisation spatiale entre groupes fonctionnels apparaissent effectivement comme des facteurs clés dans la stimulation des processus biogéochimiques sédimentaires. Les résultats obtenus, directement comparables du fait de l'utilisation de biovolume identique, valident donc l approche fonctionnelle pour l étude de la bioturbation et ses effets sur les flux biogéochimiques, le remaniement sédimentaire et les communautés bactériennes. De nouvelles voies de recherche sont proposées pour (i) développer l'approche fonctionnelle dans le cadre d'études basées sur les échanges à l'interface eau-sédiment, (ii) affiner la notion de biovolume, et (iii) approfondir les effets des relations entre groupes fonctionnels au sein d une communauté, sur le fonctionnement des sédiments côtiers.The objective of this Ph.D. thesis is to characterise and quantify the effects of the dominant functional groups of the Macoma balthica community, maintained separately and in various combinations, on: i) biogeochemical fluxes at the sediment-water interface (oxygen, dissolved organic carbon, ammonium, nitrate, phosphate), ii) sediment mixing, and iii) bacterial communities. The functional groups of the M. balthica community of the St Lawrence estuary (Quebec, Canada) were defined according their sediment mixing mode: two biodiffusers (M. balthica and Mya arenaria) and one gallery-diffuser (Nereis virens) were studied. Experiments were performed in replicated microcosms with the functional groups being either isolated (allopatry) and combined (sympatry); control microcosms contained sediment but no macrofauna. All treatments were subjected to identical experimental conditions over the duration of the experiment (40 days). Microcosms contained similar biovolumes of organisms, these volumes being determined from natural densities. The space occupied by macro-invertebrates was thus similar in all treatments. The results clearly show that the biodiffusers and the gallery-diffuser, at similar biovolumes, have different effects on the stimulation of biogeochemical fluxes, on particle transport towards deeper layers, and on bacterial activity. The effects of the gallery-diffuser are highest and vary over time, due to the spatio-temporal dynamic of biogenic structures and irrigation activities, and to different maximal burrowing depths. The different burrowing depths of the two biodiffusers also explain the observed intra-functional variation in nitrate and ammonium fluxes, and in bacterial activity. The combination of both functional groups (gallery-diffuser+biodiffusers) has important effects on measured parameters, the latter often being higher than would be predicted based on additive effects. Positive spatial interactions between the two functional groups explain these effects. The interactions between functional groups, which essentially act on nitrate, phosphate, ammonium and oxygen fluxes, suggest that, at similar biovolumes, the burrowing depth of each functional group and the spatial organisation of these groups are key factors in the stimulation of sedimentary biogeochemical processes. The results obtained are directly comparable due to the use of similar biovolumes, and thus validate the functional approach for the study of bioturbation and its effects on biogeochemical fluxes, sediment mixing and bacterial communities. Further research is proposed to (i) develop the functional approach for studies based only on solute exchange at the sediment-water interface, (ii) refine the notion of biovolume, and (iii) examine in more detail the effects of relationships between functional groups within a benthic community on coastal sediment functioning.AIX-MARSEILLE2-BU Sci.Luminy (130552106) / SudocSudocFranceF

Determination of the Area Prospected by a Baited Trap from a Tagging and Recapture Experiment with Snow Crabs (Chionoecetes opilio)

The area of influence of a baited trap of the type used in the southwestern Gulf of St. Lawrence snow crab fishery was studied by releasi ng tagged crabs at increasing distances from the bait and noting recaptures after fishing periods of 24 and 48 hr. For the shorter fishing period, the recapture rate decreased with increasing distance of released crabs from the trap. The radius of the prospected area was estimated to be in the range of 100-140 m, with the radius of the effective fished area being about 50-70 m. Results from the48-hr experiment were inconclusive. The low recapture rates (maximum 5%) and the long distances travelled by the tagged crabs (up to 3,000 m in 48 hr) lead to the belief that biological factors, inasmuch as they interfere with the simple bait stimulus-response mechanism, play an important role in variation of catch success. The results of this study also indicated that the trap's influence extends over a greater area than has been suggested in previous studies

Growth and Sexual Maturation of the American Sand Lance (Ammodytes americanus Dekay) off the North Shore of the Gulf of St. Lawrence

Samples of American sand lance (Ammodytes americanus) were collected in JuneSeptember 1983 off the north shore of the Gulf of St. Lawrence, at depths varying from 1 to 40 m. Length-frequency modes identified by modal analysis corresponded closely with mean lengths of fish based on otolith annuli counts, supporting the hypothesis that the number of annuli corresponds to the age of the fish. The otolith length was linearly correlated with the fish length. An opaque annulus was deposited over a short period, primarily August. The study indicated that 75-100% of the annual growth was achieved during the June-September period. Maximum life span was estimated to be 12 years. The parameters of the von Bertalanffy growth equation were: K = 0.24 year", Lao = 188.2 mm, to = -1.14 year. The growth of the American sand lance in the study area was slower than for the same species and for A. dubius in more southern areas. The length-weight relationship indicated that the growth in weight was isometric and identical for both sexes. Length-weight relationship, gonadosomatic index and the observation of maturity stages suggested that reproduction takes place shortly after September. All the fishes were matured at 20 months of age. Males mature at a smaller size «85 mm) than the females (90 mm)