A field experiment was used to assess the relationship between the physiological condition of barnacle larvae and habitat selectivity at settlement. Three experiments were carried out on methacrylate (Plexiglas) disks precolonized with biofilms of different ages (0, 7, 14 and 21 d) that were arranged within 3 blocks and placed at 3 intertidal positions correspond- ing to the upper limit, mid zone and lower limit of the adult Balanus amphitrite (Darwin) habitat. To limit the effect of post-settlement mortality, each experiment was conducted over 2 full tidal cycles only. During these periods, larvae in the water column were sampled and abundance estimated at each high tide at the depths corresponding to the 3 intertidal positions. Lar- val physiological condition was assessed using lipid classes analyzed by liquid chromatography. Ratios of total triacylglycerols to sterol content (TAG/ST) were used to quantify the energy status of larvae. Our results indicate that the cyprids' TAG levels reflect the level of settlement success independent of cyprid abundance in the water column. Intertidal position and biofilm char- acteristics were significant factors determining the settlement success with respect to cyprid energy con- tent. The number and the energy content of settling cyprids were maximal on clean surfaces and decreased gradually with the degree of biofilm precolonization. Our study shows (1) the importance of lipid levels, particularly TAG, in habitat discrimination at small temporal scales in B. amphitrite cyprids and (2) that larval energy content is a critical variable for under- standing benthic-pelagic coupling.

A field experiment was used to assess the relationship between the physiological condition of barnacle larvae and habitat selectivity at settlement. Three experiments were carried out on methacrylate (Plexiglas) disks precolonized with biofilms of different ages (0, 7, 14 and 21 d) that were arranged within 3 blocks and placed at 3 intertidal positions corresponding to the upper limit, mid zone and lower limit of the adult Balanus amphitrite (Darwin) habitat. To limit the effect of post-settlement mortality, each experiment was conducted over 2 full tidal cycles only. During these periods, larvae in the water column were sampled and abundance estimated at each high tide at the depths corresponding to the 3 interticlal positions. Larval physiological condition was assessed using lipid classes analyzed by liquid chromatography. Ratios of total triacylglycerols to sterol content (TAG/ST) were used to quantify the energy status of larvae. Our results indicate that the cyprids' TAG levels reflect the level of settlement success independent of cyprid abundance in the water column. Intertidal position and biofilm characteristics were significant factors determining the settlement success with respect to cyprid energy content. The number and the energy content of settling cyprids were maximal on clean surfaces and decreased gradually with the degree of biofilm precolonization. Our study shows (1) the importance of lipid levels, particularly TAG, in habitat discrimination at small temporal scales in B. amphitrite cyprids and (2) that larval energy content is a critical variable for understanding benthic--pelagic coupling.

For the last years scale issues have contributed to the understanding of the complex organization of communities. In practice however the choice of observational scales remains one of the major issues of discussion among ecologists. Case studies showing the implications of tuning up the observational scales are still needed to illustrate the crucial role played by sampling designs on the perception of population and community variability. On the ground of simulations on real data sets, this paper presents empirical evidence showing how the abundance patterns of benthic intertidal species change according to the scale (grain size and extent) of observation. A field experimental study was carried out in which abundance of rocky shore intertidal benthic species and physical factors associated to the substratum were recorded in contiguous quadrats (5×10 cm) along three 100‐m transect lines. Subsampling routines were developed to generate different scale scenarios by monotonically increasing the grain size and extent of the data. Results showed that: 1) changes in the observational grain size and extent convey different information about the spatial patterning of the recorded factors, and 2) the strength of the relationship between species abundance and physical factors tends to decrease as extent increase. Under the continuous simulations of scale scenarios along transects, variance estimation was the criterion adopted to make explicit the degree of precision in patterns description obtained by each scale scenario. The experimental variogram demonstrated to be a useful statistic for estimating the variance associated with discrete levels along the continuous varying function of scale.

Elucidating the processes responsible for maintaining polymorphism at ecologically relevant genes is intimately related to understanding the interplay between selection imposed by habitat heterogeneity and a species' capacity for dispersal in the face of environmental constraints. In this paper, we used a model-based approach to solve equilibria of balanced polymorphism, given values of fitness and larval dispersal among different habitats in the acorn barnacle Semibalanus balanoides from the Gulf of St Lawrence. Our results showed that allele frequencies observed at both MPI* and GPI* loci represented stable equilibria, given empirical estimates of fitness values, and that considerably more larvae dispersed from one region (north) to the other (south) than vice versa. Dispersal conditions were predicted to be similar for the maintenance of polymorphism at both loci. Moreover, the values of asymmetrical dispersal required by the model to reach stable equilibria were compatible with empirical estimates of larval dispersal and oceanic circulation documented in this system. Overall, this study illustrated the usefulness of a modified and computable version of Bulmer's model (1972) in order to test hypotheses of balanced polymorphism resulting from interactions between spatial selection and asymmetrical dispersal.

Organisms living in highly heterogeneous environments are useful for examining the effects of associations between phenotypes and ecologically relevant genes in the field. Here, we tested the null hypothesis of no association between the variation in 2 fitness-related traits (growth and fecundity) and polymorphism at 2 enzymatic loci, MPI* and GPI*, known to be subject to strong spatial selection. We also tested if such an association was related to the intensity of genotype selection observed for both allozymes at sampling locations in 2 barnacle cohorts. For both cohorts, individuals with the GPI(center dot)286/286 genotype were larger in size than individuals with the GPI(center dot)100/100 genotype, particularly in sites and microhabitats south of the Miramichi Estuary, Gulf of St. Lawrence, Canada. This coincided with a reduced GPI(center dot)100/100 frequency in this region. In contrast, the growth-MPI center dot genotype association showed no clear pattern. Overall, our results indicate that the phenotype-genotype association differed strikingly between the 2 genes, and that both the growth-GPI(center dot) genotype association and genotype selection occur in localities south of the Miramichi Estuary only, and at different times during development, first a few days after settlement (genotype selection) and later through growth-genotype association.

It is generally assumed that larvae of benthic species are thoroughly mixed in the plankton and distributed randomly at settlement. Yet, it has also been hypothesized that a combination of larval gregarious behaviour coupled with particular oceanographic conditions may prevent larvae from mixing completely, and result in nonrandom spatial distributions following settlement. Using microsatellite markers, the main objective of this study was to investigate the occurrence of statistical connections between relatedness and settlement in the intertidal acorn barnacle from the Gulf of St Lawrence, Canada. A second objective was to test the hypothesis that patches of kin-related individuals came from a common parental site. Our results indicated that a significant number of barnacles within a given sample were more closely related than expected by chance despite the enormous potential for admixture during the planktonic phase. Thus, eight out of 37 samples analysed had relatedness values significantly higher than expected from random settlement. Moreover, analyses of sibship network construction and network complexity tests provided evidence for the occurrence of networks within several samples that were characterized by strong connections among individuals. Thus, nonrandom planktonic dispersal associated with relatively stable oceanic currents, as well as additional ecological factors to be rigorously investigated (e.g. behavioural mechanisms), may be more important in determining patterns of genetic structure in marine benthic invertebrates than generally assumed. Therefore, documenting genetic patterns associated with kin aggregation should be a fruitful and an important avenue for future studies in marine invertebrates.

Using data published in 15 major marine ecology journals (from 1970 to 1999), we examined global patterns of marine benthic macroinvertebrate production and its distribution among feeding guilds and taxonomic groups and physical variables such as substratum type, water depth and temperature. Our database contains 547 production datasets, from 147 studies including 207 taxa, assessed by classical methods (cohort and size-based methods), from 170 sites (77 degrees 50' S to 69 degrees 35' N; 0 to 930 in depth). In general, higher values of production to biomass (P/B) ratios were observed in the Northern Hemisphere than in the Southern Hemisphere. High values of P/B ratios were observed in mid-latitudinal zones while low values of P/B ratios were observed in high (80 to 60 degrees S) and low latitudinal zones (40 degrees S to 20 degrees N). Highest production was observed on hard substrata, for filter feeders and for mollusc (e.g. bivalves) species. Highest P/B ratios were observed on algae (or high organic substrata), omnivores and predators, and arthropods (e.g. amphipods). Regression models explained a significant percentage of the amount of variance of benthic production (92%) and P/B ratios (50 to 86%). Production and P/B ratios were negatively related to water depth and positively related to water temperature, but these abiotic variables did not greatly improve the predictability of production by biotic variables (e.g. life span, mean body mass). Biotic variables were more important than environmental variables in explaining observed variations in production and P/B ratios. For the latter, life span explained most (45 to 83%) of the variation of the models.

A mussel bed was sampled monthly at four intertidal levels (mid: 2.15; mid-low: 1.65; low: 1.2 and sublittoral fringe: 0.7 m from chart datum) from July 1979 to July 1980 at Pointe-Mitis in the St. Lawrence estuary. A strong spring reduction of abundance (both in density and biomass) suggested that the mussel bed was being degraded. Community perturbation was attributed to ice scour. Partial reestablishment of the mussel bed (all age classes) was observed during late spring and early summer and occurred mainly at the mid-low intertidal level. Changes in the size structure of the mussel bed with level suggest that the annual windstorm regime may be an important factor in the dynamics of the bed. Mean body mass decreased at the three lower shore levels but increased at the highest shore level. Overall, net secondary production (assessed by the increment-summation method) was negative due to the decrease in mean body mass. Annual production rates (kJ m−2 y−1) from the mid intertidal level to the sublittoral fringe were 1130, − 4072, − 4013 and − 3258, respectively, while P/B ratios (y−1) were 0.17, − 0.69, − 0.50 and − 0.45. The calculated production and the productivity (potential production) are compared and used to provide insight into the condition of the mussel bed.

Mytilus edulis and M. trossulus are the two molluscan species co-occurring along the Gaspe coast, eastern Canada. Few studies examine the effects of environmental factors (temperature, salinity, tidal height and wave action) on the local or regional distribution of these two species in areas where they co-occur. This study is designed precisely to examine the niche of each of the two species, particularly in relation to environmental factors in the northeastern part of the Gulf of St. Lawrence, Canada. Mussels were sampled on rocky shores according to a factorial design including six locations, 3 degrees of wave exposure (exposed, semi exposed and sheltered) and 2 intertidal levels (mid and low). Species were distinguished with polymerase chain reaction amplification using a diagnostic DNA marker (Glu-5). Relative frequencies of each species showed no clear patterns of distribution with wave exposure or tidal height. A pattern of distribution at the regional scale does occur, but this pattern could not be related to salinity or temperature gradients observed.

We have tested both the usefulness of high-resolution digital photography for data acquisition and digital image analysis, by non-supervised classification and high pass filter, for recognition and abundance estimation of benthic intertidal organisms. These digital tools were compared with visual scan and photo quadrat conventional methods. The comparison was done using 40 quadrats (10×5 cm) randomly selected along a 5-m transect on the rocky shore of the Pemaquid Point, Maine, USA. ANOVA for repeated measures was used to test differences among methods. Monte Carlo simulation analysis was used to explore differences among methods over a large set of data (n=100, 500, 1000 quadrats). Differences among methods were observed when 40 quadrats were used. Tukey multiple comparison test showed that abundance estimation from visual scan, photo quadrat and digital image analysis by high pass filter do not differ significantly among them but differ from non-supervised classification results. Due to its accurate estimation, high pass filter (Prewitt) method was chosen as the most reliable digital method to estimate species abundance. Monte Carlo simulation of visual scan, photo quadrat and high pass filter results showed significant differences when the number of quadrats was larger. These results showed that the combined use of digital photography and digital image analysis techniques for the acquisition and analysis of recorded data is a powerful method for the study of intertidal benthic organisms. Results produced using these techniques were similar than those produced by conventional methods but were obtained in a much-reduced time.

Elucidating the ecological processes by which adaptive genetic polymorphism is maintained in heterogeneous environments requires knowledge on the spatial scale at which alternate habitats affect genotype-specific fitness. The general objective of this study was to document patterns of temporal and spatial variation of genetic polymorphism in the acorn barnacle (Semibalanus balanoides) at MPI* and GPI* allozyme loci. A total of 7261 barnacles were sampled in the intertidal at various locations north and south of the Miramichi estuary, New Brunswick, Canada. The results of this study supported the hypothesis that both MPI* and GPI* are under the effect of strong directional selection south of the Miramichi, whereas neutrality cannot be ruled out at sampling sites located north of the estuary. Comparisons between this study and previous ones also question the generality of current hypotheses regarding ecological processes that are responsible for maintaining polymorphism at MPI* and GPI* in the acorn barnacle.

This study reports the effect of additions of dietary microspheres of triacylglycerol (TAG, extracted from the diatom Chaetoceros muelleri) on larval development and settlement of Mytilus sp. The first experiment showed that mussel larvae successfully ingested TAG microspheres as soon as they acquired the ability to feed from exogenous sources. In a second experiment, larvae were fed for 28 days on diets consisting of 0, 1, 20, or 50% TAG microspheres (based on the cell concentration of a full algal ration) added as partial replacements for a ration of Isochrysis sp. (T-ISO). Lipid content and growth of larvae fed on a diet composed of 20% TAG were higher than those of the control groups, whereas survival was negatively affected. No growth or survival effect was detected with larvae fed on a diet composed of 1% TAG, whereas high mortality after 14 days was observed for larvae fed on a diet composed of 50% TAG microspheres. In a third experiment, 22-day-old larvae were fed on rations of Isochrysis sp. supplemented with 0, 1, 10, 20, 50, and 100% TAG for 2 days and allowed to settle for a 7-day period. TAG content of the larvae increased with TAG added to the diet until a saturation threshold was reached between a 20 and 50% supplementation level. Similarly, free fatty acid (FFA) content increased with TAG level in the diet and was linearly correlated with TAG content of larvae. Increased levels of FFA in larvae were attributed to digestion of TAG supplements. Settlement success and survival of larvae were not affected by diet; however, regression analysis revealed that TAG level in pre-metamorphic larvae explained 28% of survival variability among cultures.

The present study was conducted to evaluate the relative roles that water column stratification intensity and possible inter-population behaviour differences play in determining depth of larval settlement of giant scallops, Placopecten magellanicus, in relation to thermoclines. Differences in timing of settlement of larvae from various populations were also examined. Two separate experiments were conducted in a 10.5-m-deep, 3.7-m-diameter, thermally stratified tank with larvae spawned from scallops collected from several adult beds located in areas with differing oceanographic regimes (Georges Bank, Mahone Bay, Passamaquoddy Bay). Previous mesocosm experiments had shown that veligers from these various populations differ in their vertical migration patterns. In the first experiment (December 1992–February 1993), larvae from all three populations were held in separate 9.5-m-deep tubes and exposed to a 1.5 °C temperature differential established over a depth interval of 1 m. The number of settled juveniles (spat) of each population collected at the end of the experiment increased with depth and showed no peak at or above the thermocline. This depth distribution of spat was most likely driven by preferential larval settlement. In the second experiment (February–May 1994), larvae spawned from Georges Bank and Passamaquoddy Bay stocks were held in 9.0-m-deep tubes and exposed to a 5 °C temperature differential established over a depth interval of 1 m. The number of settled spat of both populations was greater above this thermal boundary and increased with decreasing depth. This depth distribution was most likely driven by preferential settlement above the thermocline followed by upward post-settlement migration. The results from the two experiments indicate that larvae from various populations show similar trends in settlement patterns in response to similar thermal stratifications. Stratification intensity, however, does affect depth of larval settlement. In the second experiment, both populations of larvae settled throughout the time interval of collector deployment (larvae 32–82 days old). These results extend the range of planktonic developmental times generally reported in the literature and may be more indicative of natural planktonic development in the field. While Georges Bank larvae settled in consistent numbers through time, Passamaquoddy Bay larvae showed peaks in settlement at certain time periods, indicating that pulses of larval settlement may occur even from an individual spawning event.

This paper presents results of the effect of water flow in experimental 'downwelling' systems on settlement success, settler distribution and behavior of Mytilus spp. larvae. The hypothesis of active habitat selection in relation to hydrodynamics was tested by direct observation of larvae during settlement using an endoscope camera and the comparison of distribution of settled larvae with that of inert particles mimicking passive behavior. The downwelling system consisted of cylinders in which water inflow was controlled. Six water flows, from 0 to 50 1 h(-1), were used in quadruplicate. An acoustic Doppler velocimeter (ADV) was used to measure velocity fluctuations in 3 dimensions along 4 transects per experimental unit. Settlement success was positively correlated with centrifugal and advective flow velocity and turbulence measured immediately above the mesh bottom. Mussel larvae actively selected microhabitats characterized by low shear stress and high advection when water flow in the cylinders ranged from 0 to 40 1 h-1. At higher water flow, mussel larvae were distributed similarly to passive particles and are apparently unable to overcome the flow regime, thus limiting their ability to exhibit settlement preference. In this study, total conformity between settlement and inert particle patterns was never reached, suggesting that settlement was, to a certain extent, under behavioral control.

Early benthic stages of the snow crab Chionoecetes opilio are presumed to be very stenothermic; they may be sensitive to environmental changes and thus affect subsequent adult population abundance. Little quantitative information exists on the habitat preferences of juvenile snow crabs to verify this. We determined the distribution pattern of juveniles in the NW Gulf of St. Lawrence, Canada, in May 2001. Temperature and substratum preferences were evaluated through controlled laboratory experiments in aquaria that had a temperature gradient and offered a choice of 3 sediment types (mud, sand and gravel). In general, early benthic stages displayed sharp size-/age-dependent distributions and habitat preferences. In the field, juveniles from Instars I to IV were scarce in the core of the cold intermediate layer (CIL) but present immediately above and below this layer, where temperatures were >0degreesC. Older juveniles (Instars VI to VIII) were concentrated at depths <27 m above the CIL. An analysis of historical data from 1989 to 2000 supported this depth-distribution pattern. Temperature preference in the laboratory shifted from a cold (0.0 to 1.5degreesC) to a warmer temperature range (1.0 to 4.5degreesC) between Instars III and V. Juveniles preferred mud in general. Early juvenile instars could represent the weakest link in the snow crab's life cycle because of their narrow habitat requirements.

The aim of this study was to test the validity of a lipid based indicator of larval quality of sea scallop Placopecten magellanicus. Objectives were 2-fold: (1) to determine the link between lipid class content and reproductive state of adults in the field and in the laboratory and (2) to follow lipid class content, growth, and survival during embryonic and early larval development. Adult scallops were periodically sampled during gametogenesis for lipid class and histological analysis of the gonads in the field at two locations and in the laboratory after feeding three different diets. Females were induced to spawn and lipid class content, larval growth, and survival of five batches of eggs were followed for 8 days after fertilization. Site, diet, and time had significant effects on lipid class composition of male and female gonads and gametogenesis of females. Triacyglycerol accumulation during vitellogenesis was characteristic of female gonads and explained respectively 56.4% and 71.3% of the variability in maturity and egg size. When spawning was induced, no major effect of location or diet on lipid composition of gonad and subsequent eggs was detected. Nevertheless, the mean number of eggs produced by females increased with atresia level in gonad, suggesting that egg quantity was incompatible with egg quality. Lipid class composition during embryogenesis and young larval development showed a high demand for triacyglycerol.

The distribution of epibenthic invertebrate biomass in relation to environmental factors was examined in the St. Lawrence system. Biomass estimates for epibenthos sampled yearly for 9 years on 102 suspended collectors (navigation buoys), were related to environmental data from the literature (surface water temperature, water salinity, water transparency, current velocity, chlorophyll a and primary production) using a weighted multiple linear regression analysis. Regression models were generated for total biomass and the biomass of the single dominant sessile species: Mytilus edulis, Semibalanus balanoides, Balanus crenatus, Obelia longissima and Hiatella arctica. Water temperature and water transparency, as well as some biogeographic groups of buoys represented by dummy variables, collectively explained 90.6% of the variance in total biomass. Water temperature, water transparency, biogeographic groups and, to a lesser degree, primary production, were the variables having a significant influence on the biomass of individual species. The lognormal weighted multiple regression model explained up to 84.5% of the variance in M. edulis biomass data and 67.9, 70.0, 71.6 and 38.9%, respectively, of the variance in S. balanoides, O. longissima, B. crenatus and H. arctica biomass data. The need to consider simultaneous biological and environmental sampling at the relevant temporal and spatial scales to model large marine coastal ecosystems is discussed.

We compared patterns of genetic structure at potentially selected (two allozyme loci) and neutral molecular markers (six microsatellite loci) in the acorn barnacle, Semibalanus balanoides from the Gulf of St. Lawrence. Our results confirmed the presence of a geographical shift in alleles MPI and GPI near the Miramichi River. In contrast, no significant patterns of population differentiation among samples located north and south of the river mouth were detected for four of six microsatellite loci. However, analysis of molecular variance (amova) at individual loci revealed that a significant proportion of the total variance in allele frequencies was partitioned among samples located north and south of the river for both the allozyme and the other two microsatellite loci. The two most common alleles at these microsatellites showed frequencies that were highly correlated (r = 0.65-0.74, P < 0.05) with those of the MPI*2 allele, perhaps because of either physical linkage or epistasis. The two allozyme loci were significantly correlated in barnacles located north of the Miramichi River (r = 0.86, P < 0.05). Overall, our results supported the hypothesis that the broad scale pattern of allozyme allelic shifts is maintained by selection. They also indicated that microsatellites may not always behave in a neutral way and must be used cautiously, especially when evidence for genetic structuring relies on only a few assayed loci.