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Blue mussels ( Mytilus edulis ) that are cultivated in the marine area around Prince Edward Island, Eastern Canada, are susceptible to the heavy biofouling of their shells by an invasive solitary tunicate, Styela clava , which rapidly proliferates. To mitigate this issue, mussel farmers periodically lift the longlines on which the mussels are suspended out of the water to spray a highly alkaline (~ 12.7 pH units) calcium hydroxide solution onto fouled individuals. Here, we tested the hypothesis that calcium hydroxide exerts behavioural stress on mussels and other bivalves. Field surveys revealed that the alkalinity of the seawater in the vicinity of longlines increased (9.3–11.7 pH units) immediately after treated mussel sleeves were returned into the water column. Thereafter, pH values declined rapidly, and met federal water quality guidelines (7.0–8.7 pH units) within 3.1 ± 0.5 min (range 0.3–10.5 min, n = 31 sleeves). Cultivated mussels challenged to both emersion and calcium hydroxide closed their valves for 14.0 ± 3.3 min ( n = 18) compared to 6.5 ± 1.6 min ( n = 17) by control mussels (emersion only). We subsequently assessed how three benthic bivalve species ( M. edulis , Crassostrea virginica (eastern oyster) and Argopecten irradians (bay scallop)) respond to weak (pH ≤ 9.2) but sustained (3-h daily for 3 days) alkalinity conditions. All three species consistently responded by completely or partially closing their valves. However, all behavioural responses were short-lived (0.2–4.7 h), and were generally confined to the treatment period. In conclusion, spraying calcium hydroxide onto cultivated mussels has limited impact on seawater alkalinity and the behaviour of nearby bivalves.

In Eastern Canada, an increasing number of pests, predators and pathogens in downriver areas (close to the ocean) have led the aquaculture industry to consider growing oysters in upriver areas (close to the river source). In this study, oyster growth performance was compared between downriver and upriver environments by means of stock transfer experiments within the Richibucto estuary. In May 2009, seed oysters (~26 mm shell height) originating from two downriver sites (salinity ~20–30 ‰) were transferred upriver (salinity ~5–20 ‰). Follow-up measurements in October 2009 revealed that the seed transferred upriver grew and survived as well as seed that remained downriver, while the mortality rates of adult oysters (shell height ~66 mm) were lower at the upriver site. Meat content was unaffected in adult oysters transferred upriver. However, there were indications that the upriver environment promoted shell growth (mm) in adult oysters. Oysters transferred upriver had a gain in shell height (LSM ± SE) over the oysters that remained downriver (2.7 ± 0.5 vs. 1.8 ± 0.5 mm) and in shell width [Median (95 % CI); 2.8 mm (1.9, 3.6) vs. 1.0 mm (0.3, 1.2)]. Therefore, the holding of adult oysters upriver during the spring–summer period confers productivity advantages on top of protection from diseases and predation. By contrast, productivity losses were recorded when relocating adult oysters originating from the upriver environment. More specifically, final organic meat content were approximately 35 % less in adult oysters transferred downriver compared to those that remained upriver (0.48 ± 0.04 vs. 0.74 ± 0.04 g). Results suggest that transfers along the river impact physiological processes such as gametogenesis and shell formation in adult oysters.

The Mercenaria mercenaria notata line was introduced into the Canadian Atlantic provinces in the late 1990s because of its fast growth rate when compared with that of the current native line. The purpose of this study was to compare the development of two groups of M. mercenaria notata, according to the initial size of the individuals, in order to check whether the current hatchery practice of keeping only the largest larvae may ultimately eliminate the best performing animals. The larvae were raised and sorted by size according to standard hatchery practices. On the tenth day post-fertilization, the two larval size groups were formed. The “initially smaller” (IS) and the “initially larger” (IL) animals were grown separately. Mortality, shell length and energy reserves were measured for both groups at three stages: veliger, post-settling and juvenile. The observed mortality in the two groups was low varying from 8.1 to 19.6%. The IS animals had a higher shell growth rate (18.2 μm/day) when compared to the IL group (12.7 μm/day) with the result that at the end of the experiment, the IS animals were larger than the IL. In both groups, the lipid and protein concentrations diminished rapidly during the veliger stage but faster in the IL group. The glycogen level remained at the limit of detection for all the three stages. The use of energy reserves followed a different pattern according to the group size. This study indicates that culling would have led us to discard the animals which in fact have the best growth potential in that their rate of shell growth is the highest.

The objective of this study is to identify possible causes of the high winter mortality noted in juvenile Mercenaria mercenaria notata in eastern Canada. The percentage mortality, shell growth, concentration of energy reserves, and production of cryoprotectant molecules were compared between notata and native quahogs kept at intertidal and subtidal levels. Overwintering mortality of the notata strain reached 47.2% and was 3–9 times higher than that of the native strain. Shell increment was higher in the native than in the notata strain and also at the intertidal than at the subtidal level. The quahogs from the subtidal zone had a higher concentration of protein than those from the intertidal zone in August and April but a lower concentration in February. The notata strain had a lower concentration of lipids and glucose (34.9 and 0.21 mg g−1 dry weight) than the native strain (42.2 and 0.28 mg g−1 dry weight). Thermal hysteresis was detected in none of the quahog groups. High winter mortality in the notata strain seems to be caused, in part, by a lower capacity to stock lipid compared with the native strain. The higher concentration of glucose in the native strain may favour survival in cold water by helping to reduce the freezing point of the animals’ fluids.

This paper describes the historical development of blue mussel ( Mytilus edulis ) farming in Tracadie Bay (Prince Edward Island, Canada) and relates the spacing of suspended sleeves ( S S ) on longlines to seston uptake. From 1990 to 2001, mussel biomass in Tracadie Bay increased by a factor of four (from 1137 to 4743 t). By 2001, seston uptake rates were approximately three-fold water renewal rates, and harvest yields (kg sleeve − 1 ) were significantly lower than in the early 1990s. A one-year field experiment was carried out to determine whether a change in S S could restore harvest yields. We found that S S (10, 20, 40, 60, 80 cm) had no significant effect on the condition index of mussels. However, high S S positively affected shell growth and abundance for small seeds that were densely packed within sleeves. A complete husbandry shift toward high S S and high seeding densities (within sleeves) may enhance farm productivity (production per unit of effort) and curtail seston uptake at the bay scale.

Anecdotal reports from mussel growers suggest that increased stocking density decreases the settlement and growth of the fouling organisms Styela clava (clubbed tunicate) and Ciona intestinalis (vase tunicate). To evaluate this hypothesis, 15 mussel socks of low (90 mussels per 30 cm), medium (250 mussels per 30 cm) and high (500 mussels per 30 cm) densities were placed on three longlines in the Brudenell estuary in the fall 2005 and in the spring 2006. Sampling was conducted in June, August and October of 2006 to determine the effect of different stocking densities and socking time on mussel productivity and C. intestinalis recruitment and growth. Mussel Condition Index and shell length were not significantly different between the three stocking densities by the end of the field trial in October. In August, the mean length of C. intestinalis was significantly lower on the medium and high density socks and C. intestinalis weight was less on medium and high density socks from the fall socking period (no difference within spring socked densities), however, by the October sampling there was no biologically significant difference in the weight of C. intestinalis between stocking density treatments. Time of socking did not appear to have any significant effect on the results, although the abundance of C. intestinalis was marginally higher in August on the socks deployed in December, 2005. Mussel loss was between 50 and 60% for all treatments, with no clear pattern being evident.

This study examined the effects of two selection treatments (elevated water temperature and air exposure) on the genetic and physiological characteristics of the juvenile marine mussel, Mytilus edulis (

Over the past decade, four exotic tunicates (Styela clava, Ciona intestinalis, Botrylloides violaceus and Botryllus schlosseri) have been reported in the Brudenell estuary in Prince Edward Island (PEI), Canada. Styela clava was the first exotic tunicate to arrive in 1997, rapidly establishing, spreading, invading, and eventually becoming a nuisance in several estuaries of PEI. In the Brudenell estuary, S. clava remained the only exotic nuisance tunicate until 2003. In the fall of 2004, the vase tunicate C. intestinalis, was reported in low abundance, followed by the two colonial species, B. schlosseri and B. violaceus, reported in the spring of 2005. The abundance of C. intestinalis rapidly increased post-introduction, eventually replacing S. clava as the foremost nuisance species on mussel farms in the estuary. To date, C. intestinalis continues to colonize this estuary at epidemic proportions, resulting in the continuing drop of S. clava abundance. The current abundance of C. intestinalis is estimated at 5 cm−2, which is similar to S. clava abundance at its height in 2003. The 2006 abundance of S. clava is estimated to have fallen to near 0 cm−2. The dominance of C. intestinalis as a fouling organism on mussel farms is considered a serious threat to this aquaculture industry, mainly due to its unmanageable weight. The process of the detection, establishment, invasiveness, and eventual rise to nuisance level of exotic tunicates in the Brudenell River is presented.

A major problem for the mussel aquaculture industry on Prince Edward Island, Canada surfaced in the late 1990s with the introduction of a fouling organism commonly known as the clubbed tunicate, Styela clava. This organism has the ability to infest mussel cultivation equipment to the point where productivity is severely compromised. This study examined the effects two anti-fouling treatments, air exposure and acetic acid, had on experimental mussel populations. Socked mussel seed obtained from a mussel farm on Prince Edward Island was exposed to three treatment regimes and subsequently placed on a long-line in New London Bay, P.E.I. The treatments were a 40-h air exposure, 30-s 5% acetic acid immersion and a 2-min 5% acetic acid immersion. Treatment effects on mussels were measured after seven months in the field, along with untreated controls. Mussel quality was assessed using mussel sock weights, length, condition index and changes in genetic characteristics measured at allozyme loci. A significant decrease in mean sock weights was found for all three treatments compared to control sock weights (p

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.

SUMMARYA temperature decrease usually induces an ordering effect in membrane phospholipids, which can lead to membrane dysfunction. Poikilotherms inhabiting eurythermal environments typically counteract this temperature effect by remodeling membrane lipids as stipulated in the homeoviscous adaptation theory (HVA). Hard clams, Mercenaria mercenaria, can suffer high overwintering mortalities in the Gulf of St Lawrence, Canada. The selectively bred M. mercenaria var. notata can have higher overwintering mortalities than the wild species, thus suggesting that the two varieties have different degrees of adaptation to low temperatures. The objective of this study was to investigate the changes in lipid composition of soft tissues in wild and selected hard clams in relation to their metabolic and genetic characteristics. Clams were placed at the northern limit of their distribution from August 2003 to May 2004; they were exposed to a gradual temperature decrease and then maintained at

The first objective of this study was to document the design of subsurface longlines used for the farming of blue mussels ( Mytilus edulis ) in Prince Edward Island (PEI), Canada; the second objective was to identify possible associations between longline design and mussel growth. In 2003, SCUBA divers visited 54 farms distributed in 16 culture embayments; they measured the spacing between longlines and the spacing between individual socks (sleeves) attached to longlines; they also sampled one-year-old mussels for the determination of the shell length, condition index, and sock weight. Here we report a remarkable degree of variation in longline configuration, with the following range of values: 1.2 to 3.0 m for sock length, 1.5 to 29.5 m for longline spacing, 26.4 to 62.4 cm for sock spacing, and 6.2 to 179.9 socks/100 m 2 for stocking density at the farm scale. A negative correlation was found between stocking density at the farm scale and total farming area at the bay scale, suggesting that growers adjusted husbandry in relation to the surrounding level of farming activity. In one major culture bay, Tracadie Bay, measurements were repeated over a three-year period (2002–2004). This monitoring led to the discovery of a coordinated effort by growers in raising the average sock spacing by 30% (+ 11 cm). Multiple regression analyses identified sock spacing as the only explanatory variable correlated with mussel weight in Tracadie Bay. The model suggests that an 11-cm increase in sock spacing can lead to an 18% weight gain for pre-market mussels (∼ 34 mm), the size group investigated in the study. However, this correlation between sock spacing and sock weight was tenuous over the three-year study period, showing up only in 2002. A similar correlation was found between sock spacing and condition index, although only in 2004. We conclude by suggesting that close spacing of mussel socks can negatively affect mussel yield, although only under certain conditions.

The impact of Eastern oyster culture (Crassostrea virginica) on the benthic environment at a shellfish farm in New Brunswick, Canada, was assessed using recommended methods for routine environmental monitoring, specifically measurements of sediment redox and sulfide levels. Maximum culture density was equivalent to 4000 oyster bags per hectare, or a final oyster biomass of 8 kg m− 2. Two culture sites, one with floating bags and one with oyster tables, as well as two reference sites were monitored over 17 months (June 2002–October 2003). Seasonal variations in sediment redox and sulfide levels were observed, but no significant differences were detected between the culture and the reference sites. Biodeposition associated with the oyster biomass contributed to increased sedimentation rates of organic matter at the oyster table site, but there was no indication of organic enrichment in the sediment. Macrofauna biomass, abundance and number of species were higher at the oyster table site than at the other sites in September 2002, but values were similar for all sites in September 2003. In this region of eastern Canada, the bays are typically shallow and the upper layers of the sediment are frequently subjected to re-suspension by wave activity and physical erosion by winter ice. Given these highly dynamic conditions and the relatively low stocking densities per hectare, we would argue that the potential impact of oyster culture on the environment should be assessed on the basis of parameters other than sediment redox and sulfide levels.

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...

Mussel aquaculture on Prince Edward Island (PEI), Canada, is an important but relatively new industry. Although seed manipulation using hatcheries for mussel culture occurs on the west coast of North America, seed supply on the east coast of Canada, including Prince Edward Island (PEI), is based solely on wild collection. Two techniques for culling seed (

Innovative Fishery Products Inc. (IFP) has managed a 1682-ha northern quahog (Mercenaria mercenaria) lease in St. Mary's Bay, Nova Scotia, Canada, since 1997. This study describes the commercial harvest and age structure of the northern quahog population from St. Mary's Bay and provides estimates of total mortality and exploitation rates for the lease area. Overall, mean densities ranged from 48.3–88.4 individuals/m2 for surveys conducted in June 2001 and 2002, and in May 2003. Catch and effort in the fishery increased from 1999 to 2001. The mean age to market was 7 y. Recruitment of spat (SL 60 mm or >8 y old) was low. Catch curve analyses resulted in a high estimate of total mortality (Z) for quahogs of ages 7–10. Commercial exploitation only represented 5% to 10% of the estimated standing stock of commercial size quah...

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 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.

European smelt Osmerus eperlanus (n = 501) from the German Wadden Sea (North Sea) near the city of Cuxhaven were examined for their infestation with parasitic anisakid nema- todes, especially with sealworms of the genus Pseudoterranova. The distribution of third-stage lar- vae (L3) in the musculature and viscera of the fish was analyzed. In total, we isolated 543 L3 from the hosts' body cavity and musculature. A subsample of 105 larvae were identified as the (sibling) species P. decipiens s.s. using direct sequencing of the highly variable ribosomal ITS1-5.8S-ITS2 genetic marker. The mean abundance was 1.1, the mean intensity was 2.3 P. decipiens s.s. and the prevalence was 47.3%. Total length and total weight, but not Fulton's condition factor (K), were significantly different in infected compared to uninfected smelt. No correlation was found between the total length of infected fish and the intensity of anisakid nematodes. The vast major- ity of P. decipiens s.s. was found in the musculature of the smelt. More than half (55.7%) of all nematodes were located in the 3 parts of the epaxial musculature, whereas 18.4 and 26.0% were found in the hypaxial musculature and the compartments of the tail muscles, respectively.