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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 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.

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.