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Larval behavior and hydrodynamics may affect the vertical distribution of planktonic larvae and, in turn, spat location in the intertidal zone. This study describes the vertical profile of competent larvae in the water column and the distribution of spat on soft-bottoms, and quantifies the relationship between both distributions for the softshell clam ( Mya arenaria ) and the blue mussel ( Mytilus edulis ). Sampling was carried out in 2007 and 2008 along the coast of New Brunswick (Canada) in two tidally contrasted regions: Bay of Fundy (high tidal amplitude) and Northumberland Strait (low tidal amplitude). The planktonic larvae were collected with a pump at three depths. Spats were collected directly from the top layer of sediments as well as with two types of collectors. Sampling in the Bay of Fundy site took the day/night cycle into account. The distribution of planktonic larvae and spats in the intertidal zone was highly variable for both species. Overall, no general pattern in the larvae distribution was observed. The day/night cycle did not affect the distribution and abundance of planktonic larvae and spats. Only a few statistically significant relationships were observed between the abundance of spats in the intertidal zone and the abundance of planktonic larvae. Soft-bottom habitats are highly unstable and this characteristic may explain, in part, the absence of relationship between spat location and the vertical profile of planktonic larvae.

The erosion and transport of juvenile softshell clams ( Mya arenaria ) was studied in a laboratory flume in relation to free-stream velocity (0, 7, 16, 29 and 35 cm s − 1 ), shell length (0–5, 5–10, 10–15, 15–20 mm) and type of sediment (mud, sandy-mud, sand and gravel). Our results showed that these factors interact together on the erosion of clams from the sediment. Juveniles were eroded in great numbers in sand while mud retained them more easily. Bedload transport was initiated at speeds of 16 cm s − 1 . Most of the clams were eroded in sandy sediments at speeds of 29 and 35 cm s − 1 . The smallest individuals were highly vulnerable to erosion compared to the other size classes studied. A results-based model using the logistic regression statistics was proposed. This allowed the estimation of erosion probabilities for a given hydrosedimentary environment. A field validation of the model was then carried out. Field results confirmed the importance of free-stream velocity, shell length and type of sediment on the erosion rate of clams. The differences observed between predicted and field results suggest that the model underestimated the erosion rate in the field. Results are discussed in the context of hydrosedimentary environments found off the eastern coast of Canada.

In the past decade, many aquatic invasive species have been introduced into Prince Edward Island, Canada, coastal waters, and they have had adverse effects on the aquaculture and fisheries industry. For instance, the mussel aquaculture industry has been overwhelmed by extremely high abundances of the invasive ascidian Styela clava in some areas. To understand and minimize the risk of spread of S. clava to other shellfish aquaculture sites, basic information on the reproductive biology of the ascidian is needed. This study investigated Styela gonad development, larval abundance and recruitment. Gonad development, using histological methods, indicated ovaries were ripe from late June through late October, 2004. Weekly water samples indicated larvae were present from 24 June to 29 October, with a distinct abundance peak in mid-August. Recruitment occurred from 24 June to 21 October. Timing of larval sampling was judged to be a crucial part of evaluating recruitment potential for monitoring purposes and a field experiment was carried out to document spatio-temporal larval concentrations. Data were gathered over 30 h sampling periods on 4 August and 14 September 2004. Water samples were taken simultaneously on an hourly basis at three depths: surface, 2 m and 4 m below the surface. Results indicated peaks in larval abundance were, in most cases, limited to a 3 h time interval in the early afternoon. Larval concentrations increased with water depth.

Erosion and transport of juvenile individuals may alter the distribution pattern of intertidal bivalves. The burrowing success of recently transported juvenile softshell clams ( Mya arenaria ) was studied in a laboratory flume under a wide range of hydrosedimentary environments. Juvenile individuals (5–20 mm) were observed under a simulated 30 min slack tide before initiating the flow for a period of 60 min. Five different free-stream velocities (0, 3, 5, 10 and 24 cm s − 1 ) and four sediment types (mud, sandy-mud, sand and gravel) were used. The mean proportion of juvenile clams that initiated (MPI) or completed (MPC) a burial decreased with increasing shell length. Erosion from the sediment was more important in large juveniles suggesting that large juveniles may have more difficulty successfully relocating once transported. The MPI increased with increasing flow speed in experimental runs held at speed − 1 . This was observed in all sediment types. Most individuals were unable to burrow at 24 cm s − 1 because they got eroded. The MPC also increased with increasing flow speed in mud, sandy-mud and sand. The MPC's response to flow was more complex in gravel because of a shell length × flow speed interaction effect. Our observations suggest that water movement may induce the burrowing behaviour of recently eroded juvenile clams. Results are discussed in an ecological and aquacultural context.

Planktonic cyprid larvae of the intertidal barnacle, Semibalanus balanoides (L.) and the infralittoral/sublittoral Balanus crenatus Brug., are readily captured in small, chambered, passive traps deployed on rocky shores. Several structural developments of a previous trap design improved urea (killing solution) retention and capture of cyprids of both species. The design adopted for assessment of the larval supply/settlement relationship of the focal species, S . balanoides , included additional internal baffles and the replacement of the cylindrical trap opening with a coned aperture. Three sizes of cone aperture area were compared, with the intermediate size (1 cm 2 ) being optimal for measuring larval supply over the full range of wave action on local shores. Most daily catches included larvae that were recognizable as having been dead before they were trapped, and had recently passed through the guts of grazing limpets ( Patella vulgata L.). One site showed that ∼32% of trapped S . balanoides were so-called ‘faecal’ cyprids. An inability to distinguish these in trap samples would lead to a significant over-estimation of larval supply. Preliminary data indicated that S . balanoides larval supply to the intertidal is enhanced by onshore winds (or perhaps increased wave turbulence), whereas B . crenatus supply was positively correlated with offshore winds (or decreased turbulence). A clear ‘supply/settlement’ relationship for S . balanoides at six sites along ∼40 km of coastline was derived from 1 cm 2 coned trap catches and daily counts of settlement on ceramic tiles. There were no instances of disproportionately high settlement in relation to larval supply, but at five sites there were days when settlement apparently failed. The identification and explanation of settlement success and failure is fundamental to understanding the importance of larval supply in structuring marine benthic populations and communities.

Sediments and macroinvertebrate diversity underneath suspended mussel lines were examined in a shallow water system in Prince Edward Island, Canada. The objectives of the study were to describe the benthic environment in a typical mussel farm from eastern Canada and to underline various relationships between benthic parameters and husbandry practices. Benthic parameters included granulometry of the sediments, organic matter and sulfide contents as well as redox potential and common macroinvertebrate diversity indices. Husbandry operation parameters investigated were the number of years of operation and mussel culture density for a given lease. The results did not show any particular spatial patterns. The sediments' mud content varied between 96 and 100%. Redox potential varied between −150 and 250 mV while sulfide concentration ranged between 100 and 9500 μM. Organic matter content varied between 1 and 16%. A total of 31 species were identified. Diversity indices were small throughout the study site. The number of years of operation for a given site varied between 0 (control sites) and 16 years while mussel culture densities ranged between 0 (control sites) and 0.70 kg/m 2 . Overall, no strong relationship was underlined between benthic parameters and studied husbandry practices. BIOENV analyses showed that culture density explained a small proportion of the benthic assemblages variability underneath mussel lines when using the macroinvertebrate abundance data set ( r = 0.137). Similar analyses showed that water depth better explained the variability observed under mussel lines when using the macroinvertebrate presence/absence data set ( r = 0.263). The absence of a strong relationship between husbandry practices and the studied benthic parameters might be related to the oceanographic characteristics and land-based activities associated with the water system rather than direct and cumulative effects of mussel culture.

Previous field and flume studies have shown that scallop spat collection in the field can be enhanced by modifying the structural design of collectors. In this study we examine, in a flume, how structural components of collectors and water velocity might influence larval collection. Spherical plastic particles (200 μm) were used to mimic larvae. Structural components considered were monofilament diameter, heterogeneity in the arrangement of monofilament, and mesh size of external bags. Particle speed, deflection ratio, and the number of contacts with a monofilament strand were the response variables measured by means of video endoscopy and image analysis. With increasing monofilament diameter particle speed decreased while the deflection ratio and number of contacts with monofilament increased. The number of contacts per unit area, however, increased with decreasing monofilament diameter. Particle speed, deflection ratio, and number of contacts with monofilament (as well as contacts expressed per unit area) were greater in heterogenous collectors. Particle speed decreased with decreasing mesh size of external bags. Deflection ratios were more variable. In general, highest deflection values were observed closer to the external bag with increasing mesh size. The number of contacts with monofilament peaked at intermediate mesh size. Accordingly, the number of vortices observed immediately downstream of external bags was greater using intermediate mesh size than with other mesh sizes. Overall, our results showed that the number of particles trapped by spat collectors is a complex function resulting from the interaction between particle speed and the capture efficiency of monofilament strands used inside collectors. The ultimate objective of the study was to provide the scallop industry criteria to improve collector design to maximize scallop spat collection.

The settlement behaviour of Balanus crenatus (Brugiere) was examined in field experiments in relation to different patterns of distribution of adult conspecifics. The study was carried out in August 1994 in Anse du Petit Mitis, Quebec, Canada. Flat panels supporting random, aggregated, and uniform distributions of adult conspecifics or ceramic mimics were moored vertically on 3 lines. Panels were placed at random 2.5 m below the water surface. Settlement only occurred on panels supporting barnacles. Over 30% of the observed settlement occurred on adult conspecifics. ANOVAs showed no significant effects of distribution on number of settlers at the scale of the panel. Settlement tended to become homogenized over the panel with uniform distributions, while it became aggregated on panels with random and aggregated adult distributions. Mean nearestneighbour distances of spat did not vary among spatial patterns tested. When settling on adults, cyprids settled preferentially on the rostrum, facing current flow. A nested ANOVA carried out on the number of spat per adult on a given panel showed no effect of adult distribution. Differences in spat distribution among replicate panels, barnacle individuals, and positions were observed, suggesting that settlement of B. crenatus was affected by variations of the hydrodynamic environment at the scale of the adult barnacle. Flume experiments using inert particles and the same field panels were carried out to determine the position of initial contact on the panel. Comparison of field and flume results suggests that it is the small-scale behaviour taking place after initial contact on the panel and prior to permanent attachment that determines the patterns of spat distribution.

The behavioural response (i.e. ventilation rate, duration of ventilation bursts and length of pauses between ventilation bursts) of Nereis virens (Sars) from mercury polluted sediment (close to the Cheminova chemical plant) in the western part of the Limfjord, Denmark, was compared with the response of non-exposed populations from the eastern part of the Limfjord. Individuals from the non-exposed site reacted strongly to 30 ppb Hg by increasing their ventilation rate. At higher Hg concentration ventilation rates decreased and at 3000 ppb it almost ceased. Worms from the same site pre-acclimated to 50 ppb Hg did not react at the 30 ppb level. Ventilation rates of these worms increased when exposed to 300 ppb and decreased at 3000 ppb. Individuals from the Cheminova site pre-acclimated in Hg-free water did not react at the 30 ppb level and showed only low responses at 300 and 3000 ppb. Durations of ventilation bursts and rest periods decreased during Hg exposure. No significant ventilation response of worms from the Cheminova site was evident at any Hg exposure when pre-acclimated to 50 ppb Hg in the laboratory. The present results show that the ventilation response of N. virens to Hg is an excellent behavioural biomarker of acute Hg stress.