Stylochus mediterraneus (Turbellaria: Polycladida), predator on the mussel Mytilus galloprovincialis

The polyclad Stylochus mediterraneus Galleni has been found associated with the mussel Mytilus galloprovincialis Lmk., on which it feeds. Polyclads allowed to feed freely on groups of mussels of different sizes preyed mainly on small mussels <25 mm in length. The predation rate (number of mussels eaten per no. of polyclads per no. of days) ranged between 0.07 and 0.33. The average amount of food ingested by 1 polyclad feeding on mussels 16 to 25 mm or 26 to 35 mm in length was 7.1 and 11.2 (dry weight) mg per day, respectively. Before penetrating the mussels, the worm first straddles the valves at the posterior edge of the shell and then, after having digested the posterior adductor muscle, removes and swallows the soft parts of the prey.     

Uptake and depuration of organic contaminants by blue mussels (Mytilus edulis) exposed to environmentally contaminated sediment

Experiments were designed to expose blue mussels (Mytilus edulis) to contaminated sediment collected from Narragansett Bay, Rhode Island, USA in 1982. Measurements were taken to allow comparisons of the uptake and depuration of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). In addition, concentration factors in the mussels were calculated separately against the dissolved and particulate phase concentrations and the results from the exposure and control systems were compared. Both PAHs and PCBs were rapidly accumulated by the mussels exposed to the contaminated sediment. After the mussels were transferred to control seawater, individual PAHs were depurated with half-lives ranging from 12 to 30 d. Individual PCBs showed depuration half-lives which ranged from 16 to 46 d. Concentration factors in the mussels calculated against the particulate phase concentrations were very different in the exposure and control systems. Concentration factors calculated using only the dissolved phase concentrations (bioconcentration factors) showed excellent agreement in the two systems, possibly an indication that the dissolved phase was the direct source of the contaminants accumulated by the mussels. The bioconcentration factors for PCBs were higher than those of PAHs when compounds with similar n-octanol/water partition coefficients were compared.     

Variabilité à court terme du phytoplancton de l'estuaire du Saint-Laurent

Within the framework of a general study on time variability in the St. Lawrence Estuary, phytoplankton was sampled at 10-min intervals for 13 h. A symmetric, cosine, tapered filter was applied to the time series of cell counts, the cyclical trend being interpreted in relation to physical variables. Autocorrelation coefficients were computed for residual phytoplankton data, in order to investigate fine-scale effects in the series. The main pattern (trend) of variation in the phytoplankton data had a frequency of about 1 cycle/190 min and was related to physical variations, following therefore the tidal movement of water masses in the estuary. On the other hand, the correlogram suggests that phytoplankton is aggregated in patches of an average diameter of about 0.75 km.

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Contribution au programme du Groupe interuniversitaire de recherches océanographiques du Québec (GIROQ).     

Effects of substrate type on growth and mortality of blue mussels (<Emphasis Type="Italic">Mytilus</Emphasis><Emphasis Type="Italic">edulis</Emphasis>) exposed to the predator <Emphasis Type="Italic">Carcinus</Emphasis><Emphasis Type="Italic">maenas</Emphasis>

Structure and complexity of the substrate are important habitat characteristics for benthic epifauna. The specific growth and mortality rates and inducible defence characters on medium-sized blue mussels (Mytilus edulis L.) exposed to shore crabs (Carcinus maenas L.) were examined on three different substrate types in combined field and laboratory experiments. The experiments showed that complexity of the substrate increased blue mussel survival significantly, through a decrease in predation pressure. However, increased intraspecific competition for food on the complex substrate resulted in significantly lower growth rates of the mussels. Inducible defence characters were also influenced by substrate type. Blue mussels were more affected by predators on the structurally simple substrate, where they developed thicker shells and a larger posterior adductor muscle.     

Physiological responses of Mytilus edulis and Cardium edule to aerial exposure

Physiological responses of two bivalves (Mytilus edulis L. and Cardium edule L.) to intertidal conditions were studied. Specimens were collected from S. W. England in autumn/winter, 1980, and acclimatized to either intertidal or subtidal regimes before measurement of rates of heat dissipation and oxygen uptake during 5 h of air exposure, and rates of , particle clearance, ammonia excretion, and food-absorption efficiency during 7 h of reimmersion. Subtidal individuals were either intermittently or continuously fed in order to distinguish the effects of periodic food supply from the effects of air exposure. Specimens of M. edulis had low aerial rates of (14 to 20% of aquatic rate), and was greater than the energy equivalent of , indicating that they were largely anaerobic. In contrast, C. edule air-gaped and had higher aerial rates of and (50 to 75% of aquatic rate). There were behavioural and metabolic differences in the responses of intertidally and subtidally acclimatized mussels and cockles to air exposure. Intertidal individuals of both species were more quiescent, had lower aerial rates of and , and showed a conditioned response at the expected time of reimmersion. The reduction in aerial rate of was an energy-saving mechanism and the payment of the oxygen-debt within 2 h of reimmersion represented a significant cost. The heat increment associated with feeding and digestion was estimated as 15 to 17% of the oxygen uptake by M. edulis during all stages of recovery. M. edulis adapted to the intertidal regime by reducing its time-averaged aerial and aquatic rates of ammonia excretion. In contrast, C. edule maintained a high aerial and aquatic rate of ammonia excretion. The clearance rates of M. edulis recovered rapidly (0.5 to 1.5 h) following reimmersion, whereas those of C. edule recovered more slowly, particularly for the subtidal individuals following acute exposure (>4 h). There was no evidence of increased clearance rate or absorption efficiency by intertidal individuals to compensate for the loss of feeding time. Intertidally acclimatized individuals of M. edulis and C. edule had more energy available for growth (scope for growth) integrated over a 12 h period and higher growth efficiencies than subtidal individuals subjected to acute air exposure and intermittent feeding regimes. This was the result of reduced aerial and aquatic rates of energy expenditure, a relatively small cost in terms of the payment of oxygen-debt and a rapid recovery of clearance rate following reimmersion.     

背角无齿蚌不同组织的基因组DNA甲基化分析

用甲基化敏感扩增多态性(MSAP)对背角无齿蚌(Anodonta woodiana)腮、唇瓣、闭壳肌、外套膜和斧足五个组织基因组DNACCGG区域的甲基化水平进行了分析.结果表明,背角无齿蚌腮基因组DNA甲基化比例为47.9%,唇瓣甲基化比例为35.5%,闭壳肌甲基化比例为50%,外套膜甲基化比例为46.3%,斧足甲基化比例为56%;基因组中CCGG区域存在甲基化现象.不同组合甲基化比例不同说明该区域甲基化可能参与到基因的调控中.通过比较不同地点的采集的背角无齿蚌,发现污染严重地区(太湖三山岛水域)采集到的样品和非污染地区(南泉养殖水域)采集的蚌样甲基化区域略有变化.其中的相关性有待进一步的研究.     

Influence of simulated tidal cycles on aromatic hydrocarbon uptake and elimination by the shore crab Hemigrapsus nudus

Specimens of the intertidal crab Hemigrapsus nudus (Dana, 1851) were collected near Sitka, Alaska, in 1983, and were used in laboratory experiments to determine the influence of periodic exposure to air on the toxicity, uptake, and elimination of two aromatic hydrocarbons, toluene and naphthalene. Three tidal cycles were simulated; i.e., crabs spent 0, 33, or 66% of the time in air and the remainder of the time in toxicant or seawater solutions. Naphthalene was 10 to 20 times more toxic than toluene: naphthalene caused locomotory impairment or killed the crabs more rapidly and at concentrations lower than those of toluene. In tissues, naphthalene was accumulated faster and to higher concentrations than was toluene. Exposure to air 66% of the time reduced mortality as well as the rate at which toluene and naphthalene were accumulated and lost. Crabs exposed to air had significantly higher respiration rates than those submerged in seawater; thus, reduced rates of accumulation and loss of hydrocarbons were not caused by general metabolic quiescence. Exposure to air reduced the time the crabs were in contact with water-borne hydrocarbons and, therefore, reduced toxicity of the hydrocarbons. Once crabs had accumulated the toxicants, however, elimination was hindered by exposure to air, even for the somewhat volatile compound toluene.     

The distribution of primary production relative to a cyclonic gyre in Baie des Chaleurs

Primary production within the Baie des Chaleurs, Canada, is dominated by a cyclonic gyre system. The pattern of production fits the theoretical expectation of increased productivity associated with colder, nutrient-rich water being brought closer to the surface within the gyre. Upper reaches of the bay, west of the gyre, follow a normal esturine form of circulation with lower rates of production. East of the gyre, in the Gulf of St. Lawrence, primary production is less.Travaux sur les Pêcheries du Québec, no. 30, Direction des Pêcheries, Ministère de l'Industrie et du Commerce du Québec.     

Significance of small-scale spatio-temporal heterogeneity in phytoplankton abundance for energy flow in Mytilus edulis

The effect of small-scale heterogeneity of phytoplankton abundance on mussel (Mytilus edulis L.) energy flow was studied by comparing filtration rate, consumption and assimilation efficiency in two groups of mussels fed under constant (control) and fluctuating (24 min) seston regimes of the same average. The experiment was carried out twice. Mussels appeared to regulate their filtration rate in response to varying seston concentration in one experiment, but not in the other. This behavioral difference may have been caused by differences in mean food level. Mean consumption was not different in the two feeding regimes, but assimilation efficiency was probably lower under fluctuating seston concentration. This suggests that small-scale heterogeneity in phytoplankton abundance would not affect the total transfer of energy between plankton and benthos. However, since a higher proportion of consumed energy was probably lost as faeces and/or pseudofaeces under the fluctuating seston regime, it may be expected that growth rate of mussels is depressed by small-scale heterogeneity in phytoplankton availability.Contribution to the programme GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec)     

Shell shape variation in populations of Mytilus chilensis (Hupe 1854) from southern Chile: a geometric morphometric approach

The pattern of shell shape variation in populations of the mussel, Mytilus chilensis (Hupe 1854) from Southern Chile was analyzed as a function of sample origin (cultivated vs. wild) and latitude, using standard tools of geometric morphometrics for landmark data. Additionally, posterior adductor muscle index (PAMI), Freeman condition index and shell thickness were measured in each sample. Highly significant differences in shell shape components were found among mussel populations. These differences are related to the origin of samples (expansion of the posterior adductor muscle scar, elongation of the lateral ligament and of the ventral umbo position in non-cultivated samples) and to latitude (more elongated shells and more extended posterior adductor muscle scar in most southern samples when compared with the northernmost ones). PAMI and shell thickness were statistically higher in wild population, and Freeman condition index was higher in cultivated shells. It is suggested that in wild populations of M. chilensis, the mussels may face higher predator pressures and other environmental stress factors. Consequently, individuals may be using higher energy fraction to reinforce shells and to promote adductor muscle growth at the expense of somatic growth. In contrast, individuals found in calm aquaculture environments are relatively protected from predators and use most of their assimilated energy in somatic growth. In turn, this growth depends on changes that covariate with shell morphology.     

Allometry and growth of the green-lipped mussel Perna canaliculus in New Zealand

Length is the most precise (and the most practical) linear measurement for predicting total weight (r>0.98 at P=0.001) in the green-lipped mussel Perna canaliculus Gmelin. The allometry varies with the environmental conditions under which the mussels grow, resulting in morphologically distinct forms of raft- and shore-grown mussels. Mussels grown intertidally are wider, less high and heavier than mussels of similar length grown in suspension. Increase in length and total weight of P. canaliculus grown in suspended cultivation was recorded at 8 experimental sites around New Zealand, during 1973–1975. Comparisons are drawn with growth on an intertidal mussel bed, where length increase was less than half that in the same period in suspension. The growth rate of mussels transferred from intertidal to suspended conditions depends on the size at transfer. Close similarity in growth rate occurred at the majority of sites in spite of a direct correlation between water temperature and length increment and substantial, differences in temperature between sites. Reasons for the uniformity are suggested. Average values for growth at sites over the northern half of New Zealand were 73 mm length (32.5 g weight) after 12 months, 113 mm (110 g) after 2 years. Growth continued throughout the year, highest growth rates corresponding to highest water temperatures. Variation due to depth was not significant. Larger mussels grew more slowly. P. canaliculus can be grown in suspended cultivation in New Zealand at a rate comparable to that in other commercial mussel-farming areas.     

Optimizing the design of giant scallop (Placopecten magellanicus) spat collectors: field experiments

Field experiments were carried out in 1991 and 1992 in the Gulf of St. Lawrence (Québec, Canada) to examine the influence of various structural components of spat collectors on recruitment of the giant scallop (Placopecten magellanicus) and associated species. Components considered were monofilament diameter, heterogeneity (presence of knots), mesh size of external bags combined with monofilament density, and spatial arrangement of monofilament inside collectors. P. magellanicus spat were more abundant in collectors made with bags of intermediate mesh size (0.4x0.5 cm) containing low densities (2030 cm²) of monofilament than in other types of collectors. significant variations in spat numbers were, however, observed with other taxa such as Mytilidae, Hiatella arctica, Cerastoderma pinnulatum, Mya arenaria, Anomia simplex, Tellina sp., Veneridae, Dacrydium vitreum, Mactridae, Buccinidae, Littorina sp., Ostracoda and Foraminifera. Abundance of scallop spat did not vary significantly with spatial arrangement, diameter and heterogeneity of monofilament.Contribution to the program of GIROQ (Groupe Interuniversitaire de Recherches Océanographiques du Québec) and REPERE (Recherche sur le Pétoncle à des fins d'Élevage et de Repeuplement).     

Variation in life-history patterns between intertidal and subtidal populations of the meiobenthic copepod Microarthridion littorale

Life history patterns of the meiobenthic harpacticoid copepod Microarthridion littorale (Poppe) differed between intertidal and subtidal sites in a South Carolina, USA estuarine salt-marsh system. Throughout the summer and fall, densities of M. littorale were significantly greater intertidally than subtidally; however, for the remainder of the year the population sizes were not statistically different. Maximum densities occurred intertidally in July and subtidally in October. The number of eggs · gravid female^-1 was significantly greater subtidally than intertidally at all times. The mean length of all adults increased from summer to spring and was similar between areas. Birth rates and death rates paralleled one another in each area and with the exception of August, birth rates were higher subtidally than intertidally. Juvenile mortality appeared highest subtidally, the mortality apparently occurring in the early naupliar stages. The variation in life history patterns across the tidal gradient was likely the result of differences in food quality and quantity, increased exposure to potential epibenthic predators subtidally, and to differential competitive pressure in the 2 areas.     

Combining heat-transfer and energy budget models to predict thermal stress in Mediterranean intertidal mussels

Recent studies have emphasised that organisms can experience physiological stress well within their geographic range limits. Developing methods for mechanistically predicting the presence, absence and physiological performance of organisms is therefore important because of the ongoing effects of climate change. In this study, we merged a biophysical–ecological (BE) model that estimates the aquatic (high tide) and aerial (low tide) body temperatures of Mytilus galloprovincialis with a Dynamic Energy Budget (DEB) model to predict growth, reproduction and mortality of this Mediterranean mussel in both intertidal and subtidal environments. Using weather and chlorophyll-a data from three Mediterranean sites along the Italian coasts, we show that predictions of sublethal and lethal (acute) stress can potentially explain the observed distribution (both presence and absence) of mussels in the intertidal and subtidal zones, and the maximum size of animals in the subtidal zones. Importantly, our results suggest that different mechanisms limit the intertidal distribution of mussels, and that these mechanisms do not follow a simple latitudinal gradient. At the northernmost site (Palermo), M. galloprovincialis appears to be excluded from the intertidal zone due to persistent exposure to lethal aerial temperatures, whereas at the southernmost sites (Porto Empedocle and Lampedusa) sublethal stress is the most important driver of mussel intertidal distribution. Our predictions provide a set of hypotheses for future work on the role of climate change in limiting intertidal distribution of mussels in the Mediterranean.     

Stades initiaux de colonisation de substrats durs dans la Baie-des-Chaleurs,Québec

In the first settlement stages on immersed glass slides, the degree of colonization by an organism is determined by the duration as well as the season of immersion. Therefore, in the first period of settlement no ecological succession is obvious, but different ecological groups are favoured according to the prevailing environmental conditions. The development of these groups is regulated by well-defined physico-chemical conditions. First settlement stages would therefore play only a minor role in the subsequent development of a colony and attainment of its and final steady state.

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Contribution au programme du groupe interuniversitaire de recherches océanographiques du Québec (GIROQ).     

Reproduction ofCalanus glacialis under ice in spring in southeastern Hudson Bay,Canada

In situ egg production rates ofCalanus glacialis Jaschnov females caught under the ice cover of southeastern Hudson Bay, Canada, between early April and mid-June 1986 were measured by direct observations and by an egg-ratio method in order to investigate the role of ice microalgae and under-ice phytoplankton production in copepod reproduction. Egg production commenced, although at low rates, in early May, about 3 wk after the onset of measurable concentrations of ice microalgae at the ice-water interface. Egg production increased to about 12 eggs female^–1 d^–1 in early June, after the ice cover began to melt. The time taken by immature adult females to reach maturity in the field was estimated to be ca. 3 wk (between late April and mid-May) by visual evaluation of gonad maturity in preserved females. In the laboratory, females caught on 10 April and maintained in saturating concentrations of the diatomThalassiosira weissflogii took only a few days to produce eggs at high rates, indicatingC. glacialis was food-limited during the ice algal bloom at the interface. We suggest that ice algal grazing changes the timing, relative to high food concentrations in the water column, of reproduction inC. glacialis by promoting oogenesis and oocyte maturation.Contribution to the programme of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec)Please send all reprint requests to Dr. Runge at his current address: Institut Maurice-Lamontagne, Ministère des Pêches et Océans, C. P. 1000, Mont-Joli, Québec G5H 3Z4, Canada     

Feeding and cleaning mechanisms in the suspension feeding bivalve Mytilus edulis

Feeding and pseudofeces formation were studied in intact Mytilus edulis clearing suspensions of graphite particles, and the processes were compared with activities observed in mussels with a severed adductor muscle. Most particulate material in the stomach was present in the suspended state. Ingestion of particles in suspension could take place concurrently with the production of pseudofeces. Severing of the adductor muscle resulted in profuse secretion of mucus that gradually subsided to a constant low level. Addition of graphite particles at concentrations that did not cause mucus secretion in the intact mussels strongly stimulated secretion in the operated mussels, resulting in the accumulation of highly viscid, mucusparticle aggregates. These aggregates were mechanically stable, in contrast to the fragile pseudofeces. It is indicated that normal feeding depends upon hydromechanical mechanisms that produce highly concentrated suspensions of particles for ingestion, and that mucociliary mechanisms serve to clean the gills and other organs of the mantle cavity for excess particulate material. It is further indicated that intact mussels secrete mucus only in the amounts needed to consolidate excess particulate material, and that lesions affect the normal balance between particles in suspension and mucus secretion by enhancing the sensitivity of the mechanisms that control mucus secretion.     

Assessment of intertidal growth and capacity adaptations in suspension-feeding bivalves

Curves relating instantaneous growth rate to aerial exposure were determined for six species of bivalves in laboratory and shore experiments. A dimensionless index equatable with the relative intertidal growth performance of a species was calculated by integration of the growth curve after converting both growth rate and aerial exposure to decimal fractions. Intertidal growth performance of the bivalves tested corresponded well with their natural levels of occurrence on the shore, and improved in the following order: Modiolus modiolus < Argopecten irradians < Ostrea edulis < Mytilus edulis < Crassostrea virginica. Geukensia demissa, for which an index value could not be determined, grew faster intertidally than subtidally. The relative contributions made to intertidal growth performance by energy-conserving and energy-supplementing capacity adaptations were assessed by resolving the growth curves into energy-input and energy-loss components. The rate of energy loss due to intertidal exposure was lower in the high-shore species, and also less affected by harsher subaerial conditions, than in the low-shore species. Moreover, M. edulis and C. virginica showed abilities to supplement energy input such that growth per unit immersion time was better at certain intertidal levels than subtidally. Energy conservation and supplementation in these forms made roughly equal contributions to their improved intertidal growth relative to species occurring lower on the shore.     

Influence of substratum heterogeneity and settled barnacle density on the settlement of cypris larvae

On the Atlantic coast of Canada, Semibalanus balanoides (L.) is widely distributed in the mid-intertidal zone, whereas in the Gulf of St. Lawrence, this species is mostly limited to crevices. We tested the hypothesis of regional differences in microhabitat selection by barnacle larvae at settlement in 1984 and 1985 at St. Andrews, New Brunswick, Canada. Since larvae settle in microhabitats already colonized by adults, the relative influence of settled barnacle density and of different scales of substratum heterogeneity on settlement were evaluated experimentally at Capucins, Québec, (Gulf of St. Lawrence) and at St. Andrews, New Brunswick (Atlantic coast). On a large scale (>10 cm deep crevices) of heterogeneity, results show that, in the Gulf, cypris larvae settled nearly exclusively (93%) in natural crevices rather than on adjacent horizontal surfaces. On the Atlantic coast, settlement was more important outside than inside of crevices, when the substrata were either natural or artificial. This result is unique and contrasts sharply with all known reports on barnacle settlement in relation to surface contour. The influence of barnacle density on settlement was greater than that of large scale heterogeneity. On a small scale (<1.5 cm deep cracks), the presence of conspecifics had a stronger effect on settlement than heterogeneity in both regions. Field observations showed a relationship between larval settlement density and percentage of adult cover. Settlement increased up to 22 or 30% (Gulf and Atlantic coast) of adult cover and decreased afterwards. The results confirm the hypothesis of larval selection for cryptic habitats in the Gulf and the opposite behaviour (preferences for horizontal surfaces) on the Atlantic coast. This microhabitat selection is apparent at large scales of heterogeneity, whereas at small scales, the presence of conspecifics is the predominant factor.Contribution to the programme of GIROQ (Groupe interuniversitaire de recherches océanographiques du Québec)