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While high levels of siltation are known to be deleterious to eastern oysters (Crassostrea virginica), the collective effect of suspended and bedded sediment is understudied from the perspective of oyster farming and bed restoration. In this study, we used laboratory experiments to explore spat settlement rates on a wild bed proxy substrate (i.e., empty shells on the bottom of experimental tanks) in conditions simulating a siltation event and the presence of suspended spat collectors. Using high-frequency valvometry, we also described the behavioural effects of acute sediment burial on wild adult oysters in situ. The vast majority of larvae settled on bottom substrate as opposed to suspended collectors. Sediment negatively affected overall oyster spat settlement on bottom shell, as spat densities were ≈3 × lower when sediment was present. This negative effect was largely attributed to severely depressed spat densities on the upper side (top) of bottom shells. Settlement on the underside of bottom shell was less affected. Wild adult oyster behaviour was negatively affected by acute burial, which ultimately resulted in death. We suggest that the reduction in settlement in the presence of siltation is likely due to the combined effects of suspended sediment on cue detection and bedded sediment on substrate availability. Given that oysters are ecosystem engineers, the negative effects of siltation on both larval and adult oysters can ultimately result in cascading effects to the surrounding biological community.

Frequent heat waves caused by climate change can give rise to physiological stress in many animals, particularly in sessile ectotherms such as bivalves. Most studies characterizing thermal stress in bivalves focus on evaluating the responses to a single stress event. This does not accurately reflect the reality faced by bivalves, which are often subject to intermittent heat waves. Here, we investigated the effect of intermittent heat stress on mitochondrial functions of the eastern oyster, Crassostrea virginica, which play a key role in setting the thermal tolerance of ectotherms. Specifically, we measured changes in mitochondrial oxygen consumption and H2O2 emission rates before, during and after intermittent 7.5°C heat shocks in oysters acclimated to 15 and 22.5°C. Our results showed that oxygen consumption was impaired following the first heat shock at both acclimation temperatures. After the second heat shock, results for oysters acclimated to 15°C indicated a return to normal. However, oysters acclimated to 22.5°C struggled more with the compounding effects of intermittent heat shocks as denoted by an increased contribution of FAD-linked substrates to mitochondrial respiration as well as high levels of H2O2 emission rates. However, both acclimated populations showed signs of potential recovery 10 days after the second heat shock, reflecting a surprising resilience to heat waves by C. virginica. Thus, this study highlights the important role of acclimation in the oyster's capacity to weather intermittent heat shock.

In 2010, more than 20 associations representing harvesters from five provinces bordering the range of American lobster (Homarus americanus) in Canada, from the Gulf of Maine to southern Labrador, joined government research scientists at Fisheries and Oceans Canada (and one provincial department) and researchers from Canadian universities (two English- and four French-speaking) to establish the Lobster Node. This partnership was formed to address knowledge gaps on lobster productivity, stock structure, and connectivity through collaborative research under the auspices of the Canadian Fisheries Research Network (CFRN), which was funded by the Natural Sciences and Engineering Research Council of Canada. In so doing, the research partners overcame barriers of geography, language, culture, education, and, in some cases, longstanding disputes around management and conservation measures. This paper reviews why and how the Lobster Node was formed, what it achieved scientifically, what benefits (and challenges) it provided to the partners, and why it succeeded. It concludes by advocating for the creation of a permanent collaborative platform to conduct research in support of lobster fisheries in Canada.

International audience; In the context of increasing demand for environmental recovery, aquatic systems may face the challenge of evolving under oligotrophication. This is the case in Mediterranean lagoons, in particular the shellfish-farmed Thau lagoon in France, where we studied recruitment of the Pacific oyster Crassostrea gigas. Oyster spat and environmental parameters were monitored at several sampling sites for 3 yr (2012 to 2014) using an original method with a temporal overlap deployment of collectors to study pre- and post-settlement processes and to identify the best conditions for recruitment. Contrary to the ‘no Pacific oyster reproduction’ paradigm in Mediterranean lagoons, our study showed that recruitment of this introduced species is possible in the Thau lagoon at levels comparable to those in other traditional French breeding basins. We identified a favorable environmental window for recruitment characterized by high water temperature (>26.5°C) and high nanophytoplankton and Chaetoceros spp. abundances (>4.3 × 106 and 345 × 103 cells l-1, respectively). In these favorable conditions, we hypothesize that the ecosystem functions as an autotrophic system, in contrast to the heterotrophic system that characterizes unfavorable conditions. Under heterotrophic conditions, high abundances of mixotrophic and heterotrophic organisms (ciliates and dinoflagellates) limited the metamorphosis of C. gigas larvae, leading to poor recruitment. This study provides new knowledge on the reproduction of the Pacific oyster in a Mediterranean lagoon under warming and oligotrophication. The shellfish industry will profit from the discovery of spatfields to develop new nursery practices that are eco-friendly and limit risks of transfers with other spatfall areas.

Eastern oysters (Crassostrea virginica) are ecosystem engineers that are important to the ecological and economic sustainability of Atlantic Canada’s estuarine resources. Recently, there has been an increased industry demand for oyster spat (i.e., newly-settled larvae), which is often collected using artificial spat collectors suspended in the water column. Little is known, however, about the interactions between artificial spat collectors and naturally occurring substrates, and whether or not such collectors can affect oyster recruitment to wild beds which are simultaneously fished. In the laboratory, we mimicked the typical set-up of artificial spat collectors used in Atlantic Canada to measure differences in spat recruitment between locally-used artificial collectors and natural shell substrate under real-life spat-collection scenarios. Larvae were allowed to settle on various substrates where they occur in a natural system and were subsequently counted. In both single substrate and choice experiments, results indicated that oyster larvae recruited in higher numbers to natural shell substrate located on the benthic surface compared to suspended shell; and there were no significant differences among suspended substrates. This experiment provides evidence supporting existing theories around recruitment behaviour by oyster larvae, mainly that settling oysters tend to sink before they settle, suggesting that spat collectors in the wild may have little effect on wild recruitment. With increasing densities of artificial collectors in estuarine systems to meet system demands, however, further research is needed to investigate the potential draw of oyster larvae away from benthic oyster beds under more realistic natural conditions before broad conclusions regarding spat collector effects on wild oyster populations can be achieved. Crown Copyright © 2019 Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/BY-NC-ND/4.0/).

Japanese oysters spatfields were recently discovered in the French Mediterranean Thau lagoon farmed for shellfish. This discovery led to interesting issues concerning research for a highly seashell exploited ecosystem. The analyses of various environmental parameters characterized favorable sites and periods for spat collection. Spat collection in Thau lagoon presented high temporal and spatial heterogeneities related to hydrodynamic, predation, competition and trophic resource variability. Here, the results highlight various explicative factors of the Japanese oysters recruitment within Thau lagoon and underline the high ecological variability in the studied system under oligotrophication.

The benthic settlement success of American lobster (Homarus americanus) postlarvae is a key factor in population dynamics, with the temperature being a key factor. Given the spatial distribution of the species, its pelagic larvae probably encounter various thermal zones during development. Little information is available on the ability of lobster larvae to acclimate to temperature or if this ability varies among geographic areas. The main objectives of this study were to characterize (i) the settlement behavior of the postlarvae in relation to (a) temperature during larval development and (b) the geographic origin of the maternal parent and (ii) the behavioral response of postlarvae with different thermal histories in the presence/absence of a thermocline. Results did not support the hypothesis of thermal adaptation among local populations, as settlement behavior of postlarvae did not differ among females from different geographic regions. In contrast, larval survival and settlement behavior and postlarval energetic conditions varied with development temperature. Behavioral plasticity in the benthic settlement was observed in relation to temperature structure of the experimental water column. This study suggests that there may be links between development temperature and the natural variability in survival and settlement of American lobsters. Findings emphasize the need for an integrated approach in lobster recruitment studies with the inclusion of behavior in dispersion models.

The behavior of stage IV American lobster (Homarus americanus) larvae in relation to various water temperatures was observed in laboratory. Time budgets were documented in 2009 in trials using a single larva per experimental enclosure in relation to three temperature exposures (10°C. 15°C. and 20°C). Larvae acclimated at a given temperature (15°C and 20°C) were used. The same treatments were used in 2010, where one larva was observed within a group of five individuals per experimental enclosure. Larvae took less time to hide when they were acclimated to 15°C and then exposed to 20°C. Video observations showed that larvae were stressed (repeated tail flicks) when treatments simulated important heat shocks (e.g., larvae acclimated at 20°C and exposed to 10°C). Results for single larva were similar to those from groups of larvae. The tail-flicks display was also observed in 2010 with larvae acclimated at 15°C and then exposed to 10°C. Observations from both years showed that the time budget was simi...

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 green crab (Carduus maenas L.) is an exotic species in many parts of the world. It successfully invaded, at the end of the 1990s, the coast of Prince Edward Island, Canada, where rock crabs (Cancer irroratus Say) are commonly found. The relationship between these 2 species is still not well documented. The short-term time budget of both species was studied in autumn 2006 and spring 2007 under different experimental conditions to assess the effect of the green crab on the behavior of the rock crab. Crabs were observed in 3 competition treatments (1 crab, 2 conspecifics, or 2 heterospecifics) using 3 temperatures (5, 12, or 20°C) and 2 prey densities (4 or 30 mussels). The time spent foraging and in agonistic interactions by both species generally increased in high-temperature challenges, whereas the time spent inactive decreased, regardless of the season. Both crab species responded differently when facing a conspecific. Time spent foraging increased in certain cases whereas it decreased in ot...

We investigated the predation behaviour of rock crab Cancer irroratus and green crab Carcinus maenas in laboratory experiments in autumn 2006 and spring 2007 during various conspe- cific and heterospecific challenges. The number of prey eaten by a focal crab during a given chal- lenge was recorded for both crab species using competition treatments (solitary crab, 2 conspecifics or 2 heterospecifics) crossed with 2 different prey densities (4 or 30 mussels) and 3 different temper- atures (5, 12 or 20°C). To validate laboratory results, complementary field experiments were carried out in aquaculture leases in Prince Edward Island, Canada, in 2007, during which crab stomach con- tents from identical competition treatments were studied and mussel socks were surveyed monthly for crab abundance. In the laboratory, predation rates of both crab species generally increased with temperature and mussel density, and were not affected by the presence of a heterospecific regardless of the season. During autumn 2006, the Temperature × Mussel density interaction influenced the pre- dation rate of rock crab while only temperature affected the predation rate of green crab. During spring 2007, the predation rate of green crab varied again according to temperature whereas the pre- dation rate of rock crab was affected by the Temperature × Mussel density × Competition interaction. In the field, blue mussels Mytilus edulis were the most abundant food item observed in stomach con- tents. The competition treatments did not affect the stomach contents. Both crab species displayed different abundance patterns and seemed to avoid each other on mussel socks. Overall, our results suggest that the 2 crab species can potentially coexist.

A population of European oysters (Ostrea edulis) was recently discovered off the eastern coast of Canada. The occurrence of this newly established population led various aquaculture stakeholders to consider this species commercially. To better assess recruitment capacity, the physiological quality of the adults, eggs, and larvae was described using glycogen and various lipid contents, including a TAG/ST ratio. Adults, early nonfeeding stages (eggs, pretrochophores, trochophores, veligers) and newly-released larvae were periodically sampled in the wild and/or the hatchery during the spawning period. The initial glycogen content was higher in wild oysters than hatchery-conditioned ones. The following larval stages showed higher lipid content in wild individuals as well. Spat collection in the wild was abundant. The free-living larvae, however, did not survive more than 10 days in the hatchery. TAG/ST ratios decreased during the veliger stage development and were lower when larvae were released from the paleal cavity of the female. The high spat collection observed in the wild suggests that observed TAG/ST ratios in early nonfeeding larvae are representative of a good larval quality. The physiological quality of the larvae in the wild seems to be good enough to allow larvae to settle in this particular environment.

Various biological characteristics of the exotic green crab (Carcinus maenas) were studied in 2000 and 2001 to describe its population structure and reproductive strategy off the coast of Prince Edward Island (PEI), Canada. This particular population is found at the northern limit of the green crab distribution off the east American coast. Results showed that the number of female crabs was higher during springtime compared with the rest of the year. Male crabs were found in higher numbers from August to December. Ovigerous females were observed from early July to mid-September, their numbers peaking in early July. This was confirmed by a gonadosomatic analysis, which showed that the relative gonadal wet weight dropped from late July to mid-September 2001. Fecundity was estimated at 140,000–200,000 embryos per mass. Mating occurred after larval release, which occurred from late August to December with a peak in September. Mature males were molting from June to December, but mainly in July. This wa...

A European oyster population (Ostrea edulis) was recently discovered off the Eastern coast of Canada. The occurrence of this population led various aquaculture stakeholders to consider this species commercially. The aim of this study is to determine the best time to collect the European oyster larvae to maximize their collection. Gonad observations and plankton tows were carried out in 2005 and 2006 to estimate the time of settlement. Nine days after the first free-swimming larvae were observed, Chinese hat collectors were suspended in the water column every three days at two sites. The collectors were removed from the water after a mean streaming duration of 35 days. Spat were thereafter numbered on each collector. The spawning period lasted from mid-July to the end of August in 2005 and from mid-July to the beginning of August in 2006. Temperature was approximately 18°C during that time. The major peaks of free-swimming larvae were observed at the beginning of August (43,276 larvae m−3) in 2005...

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.

We examined the fouling organisms on the exoskeleton of 762 adult male snow crabs (Chionoecetes opilio) from 10 sampling stations situated in the southern Gulf of St. Lawrence (SGSL) and the Scotian Shelf (SS) off the eastern coast of Canada. A total of twenty-one sessile invertebrate families were observed on the exoskeleton of crabs. Epibiotic families occurring on 10% or less of crabs were considered minor foulers, while families occurring in 50% or more were considered major foulers. Nine minor and 3 major families were observed in the SGSL. The most important taxa were the bryozoans Alcyonidium spp. (87.5%) and Hippothoa spp. (77.5%), as well as the polychaetes Spirorbis spp. (68.8%). Eight minor and 3 major families were observed in the SS. The principal taxa belonged to the cirripeds Balanus spp. (89.1%), the bryozoans Alcyonidium spp. (78.2%) and the polychaetes Spirorbis spp. (77.2%). The relative abundance of each of the taxa observed on crabs suggests that differences in the structure ...

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.

The prey and size-class preferences of four marine epibenthic predators was examined in a laboratory study by determining the mortality rates of four commercial bivalve species in 4-d trials where predators were present or absent. Bivalve species used were quahogs (Mercenaria mercenaria), eastern oysters (Crassostrea virginica), blue mussels (Mytilus edulis) and soft-shell clams (Mya arenaria). Prey size-classes investigated were 0–15, 15–25 and 25–40 mm. A first set of experiments compared the mortality rates of prey in the presence of the invasive green crab (Carcinus maenas) and the native rock crab (Cancer irroratus). The second set of experiments compared the predation behavior of the green crab, the common starfish (Asterias vulgaris) and the moon snail (Euspira heros). Single- and multiple-choice experiments were carried out in relation to the prey species being challenged by the predator. Results from the first set of experiments showed that green crabs preyed on all prey species from all...

The presence of predators at soft-shell clam (Mya arenaria) culture sites is of great concern in Atlantic Canada. Laboratory studies were undertaken (i) to monitor the surface-exploration activity of the nemertean Cerebratulus lacteus to obtain a general indication of its activities throughout a 24-h period, and (ii) to describe its behaviour while feeding on M. arenaria to obtain a better understanding of the predation mechanisms involved. The first experiment showed that surface exploration varied significantly according to the presence or absence of prey. When clams were present, C. lacteus left its burrow at all times. In their absence, no predators were observed exploring the sediment surface between 21:00 and 03:00. Predator density also had an impact on surface-exploration activity. The second experiment showed that initial encounters between C. lacteus and its prey did not necessarily trigger proboscis eversion. Attacks with the proboscis, before consumption of the prey started, were concentrated in the siphon and foot areas. Cerebratulus lacteus introduced itself into the mantle cavity of M. arenaria through the same siphon and foot areas to feed. Our observations also revealed that C. lacteus may feed in a group on a single prey individual. The observations from this study provide preliminary and fundamental information for use in investigating adequate predator-control measures that may be useful for aquaculture.

The vertical distribution of veligers, pediveligers and post-larvae of the mussel Mytilus edulis L. was examined in Kandalakshsky Gulf (White Sea), Russia. Plankton samples showed that about 65% of all planktonic larvae were collected from a depth of 1.5 to 3 m. Maximum numbers of veligers were found at 3 m, immediately above the thermocline. The vertical distribution of veligers was stable throughout the study. The vertical distribution of pediveligers, however, varied over time. Pediveligers were mostly observed at 3 m before settlement peaked while they migrated closer to the water surface (1.5 m) during the settlement period. Pediveliger concentrations were correlated posi- tively with small phytoplanktonic cell (

The nemertean, Cerebratulus lacteus Verrill (Nemertinea: Heteronemertini), has been identified as an important threat to soft-shell clam (Mya arenariaL.) populations in Atlantic Canada. The biology of this species, however, is still largely unknown. Field and laboratory studies were undertaken in 1998 and 1999 in Prince Edward Island, Canada, to test certain control measures to reduce predation on soft-shell clam populations and to better describe the relationship between C. lacteus and M. arenaria. Field abundance of C. lacteus, M. arenaria and Nereis virens Sars were evaluated in relation to particular habitat modifications that were used as control measures. Sediment manipulations tested were: (1) addition of shells and (2) use of a hydraulic rake. No difference was observed on the abundance of C. lacteus, M. arenaria and N. virens after treatments were applied. In the laboratory, C. lacteus was shown to be an efficient predator of M. arenaria. Clam mortalities reached 100% in the presence of C. lacteus while 0% mortality was observed in its absence. A complementary set of experiments was carried out to see if the sympatric polychaetes N. virens and Glycera dibranchiata Ehlers had any impact on the relationship between C. lacteus and M. arenaria. N. virens showed no impact on C. lacteus predation on clams. The presence of G. dibranchiata significantly reduced the nemertean predation rate. Analysis of clam size selection revealed no significant preference by C. lacteus. Other experimental studies revealed that high predator densities did not impede predation on clams and that C. lacteus preferred soft-shell clams among other commercial bivalve species presented (Mercenaria mercenariaL., Crassostrea virginica Gmelin and Mytilus edulisL.). This study should provide a better understanding of the relationship between C. lacteus and M. arenaria and lead to the development of improved nemertean control measures.

Behavior of laboratory-reared larvae of the bar- nacle Balanus amphitrite was examined in Beaufort. North Carolina (USA), relation to their physiological condition. Cyprid substratum exploration was monitored by means of video endoscopy using various experimental surface types (clean, biofilm, 1 and 2 wk fouled) and 2 water flow regirnes (still water and ca 5 cm s-') at room temperature (21°C). We used the triacylglyceroYDNA (TAG/DNA) ratio of small batches of larvae as a measure of physiologicai condition in 0 to 12 d old cyprids. The physiologicai condition of cyprids decreased significantly with age (p < 0.001), ratios severely dropping between 5 and 8 d. Although exploration behavior did not show much variation with age, the overail number of active exploring cyprids appeared to be age dependent. Additionally, the relationship between surface exploration behavior and age also appeared to vary with substratum type as weil as flow rate. For example, fewer young cyprids (0 to 5 d old) explored unfavorable substrata (clean and biofilm treatments) than older ones in still water. Exploration re- sponses, however, appeared to differ in relation to flow regirnes (still vs moving water trials). Time spent by cyprids on surfaces before returning to the water column (non- exploratory behavior) appeared to vary in relation to age and substratum type in stiu water trials. Duration of exploration and distance explored by cyprids in flow generally peaked with cyprids from the 3 d cohort. Overall, our results showed that habitat selection in barnacle cyprids results from a com- plex relationship involving substratum type, hydrodynamics and larval age (i.e. physiological condition and competency).

In the marine environment, competent larvae of sessile invertebrates are influenced by water flow and a variety of biological, chemical and physical cues. Most research has focused on how these biotic and abiotic factors influence where individual larvae ultimately settle. Much less is known about post-contact exploration prior to metamorphosis. This is, in part, due to limitations associated with directly observing small larvae (100 to 500 μm) in flowing seawater. A study was conducted in Beaufort, North Carolina, USA to understand how larvae of the barnacle Balanus amphitrite and the bryozoan Bugula neritina respond to a variety of flow rates (0, 1.3, 6.1 and 8.3 cm s -1 ) and surface types (clean, biofilmed, 1 and 2 wk fouled). Larval behavior was studied by means of endoscopy in a running-seawater chamber. Larval movements were observed at 30 frames s -1 for individuals that remained in contact with surfaces from

The roles of larval supply, selection of habitat, availability of space, larval physiological condition, and early post-settlement mortality in determining vertical distribution patterns of the barnacle Semibalanus balanoides (L.) were simultaneously examined in Passamaquoddy Bay, New Brunswick, Canada. Pump samples and settlement surveys showed that about 60% of planktonic cyprids were collected from 1.5 to 4.0 m depth, while over 90% of newly settled cyprids colonized low intertidal levels. Selection of habitat by cyprids and patterns of settlement were studied using precolonized planks that had been previously placed to obtain various periphyton gradients. These planks precolonized at the low, mid-, and high intertidal levels and placed in different orientations, induced variations in the distribution of newly settled cyprids. For example, vertical planks turned upside down had fewer settlers at low intertidal levels compared to surfaces maintained in the same orientation at the same level. When placed horizontally at the same level, sections precolonized at the low intertidal level collected more larvae than sections initially placed at the high and mid-intertidal levels. We used the triacylglycerol/cholesterol ratio (TAG/CHOL) as a measure of physiological condition in planktonic and newly settled cyprids, and newly metamorphosed spat. The TAG/CHOL ratio in planktonic cyprids decreased over the sampling period, but there was no variability with position in the water column. For newly settled cyprids and newly metamorphosed spat, the TAG/CHOL ratio increased with decreasing intertidal level. Quadrats freed of conspecific adults were colonized by more cyprids than were uncleared controls. Early post-settlement mortality was greater in uncleared than in cleared quadrats, but this effect varied with intertidal level. Early post-settlement mortality increased with increasing intertidal level in cleared quadrats, while it did not significantly vary in uncleared controls. The present study shows that the vertical distribution of S, balanoides on the shore results from a complex relationship involving larval supply, selection of habitat, availability of space, and early post-settlement mortality. We also present the first evidence of correlations between larval physiological condition and early vertical distribution in S. balanoides.

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.

Conceptual models in manne benthic ecology have been reinforced with the use of larval recruitment as a key factor to predict fluctuations in the abundance and distnbution of sessile adult populations In turn, larval recruitment is determined uslng vanous indicators of planktonic larval abundance (larval supply) Based on plankton and settlement data collected over an entire settlement penod of the barnacle Sem~balanus balanoldes, we explore the vanability in the strength of the relationships between the abundance of newly settled individuals sampled dally at 3 shore levels and the daily larval abundance at 3 different depths over a 10 d study period The best correlation was obtained between the number of larvae collected near the bottom and the number of spat sampled in the low intertidal More than 75% of the vanability in the abundance of newly settled spat In the lower intertidal was explained by vanations in the larval abundance near the bottom Larval abundance integrated over the entire water column explained -50% of the vanability In low shore settlement, but failed to be significant All other comparisons showed a lack of correlations Our approach demonstrates that indicators of larval supply must be carefully and solidly documented to reflect the relationships between abundance of competent larvae settlement intensity and subsequently recruitment

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.

We studied the effects of food intake, intraspecific density, and interactions between individuals on the growth of laboratory-raised juveniles of Nereis diversicolor fed different quantities of Tetramin. A daily intake of 3.33 mg of Tetramin per individual resulted in an optimal mean mass gain. At densities above 3000 individuals/m2, not only was the growth rate reduced, but biomass and survival rates were also diminished. Frequent handling and the thermodifferential shock that ensured created a stress that had the same negative effects. Variations in responses to aggregation or isolation were high, as revealed by groups of juveniles captured in winter or in spring reacting differently: growth was not affected by the breeding conditions in the winter-caught worms but was faster in spring-caught individuals kept in isolation.