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Mudworm ( Polydora websteri) parasitism is known to result in unsightly mud blisters in eastern oysters ( Crassostrea virginica), resulting in reduced product quality and increased vulnerability to illness and environmental stress. While typically a concern only for bottom-grown oysters, an abnormal severe outbreak of P. websteri in surface-cultured oysters in New Brunswick, Canada, was reported in 2013, along with an anecdotally reported concurrent increase in siltation. Although heavier loads of silt are reported to increase P. websteri infestations in oysters, studies report mixed effects of siltation to this regard. Here, we report the results of a field experiment testing the effect of siltation on P. websteri recruitment in surface-grown oysters at an aquaculture site in Richibucto, New Brunswick. Live oysters of similar size were deployed at the aquaculture site and were left to collect P. websteri recruits under one of two siltation treatments (high vs. low) for 50 days. Results suggested that P. websteri recruitment correlated with metrics of oyster size (shell weight, length, width, depth and surface area). When P. websteri counts were standardized for oyster shell morphometry, P. websteri recruitment was significantly higher in oysters exposed to the high siltation treatment, accumulating approximately 1.5× as many P. websteri as oysters exposed to the low siltation treatment. Our results suggest that higher amounts of siltation on surface-cultured oysters can result in increased rates of P. websteri parasitism. Enhanced cleaning regimes may help to alleviate the impacts of P. websteri in surface-grown oysters, although other mitigation strategies exist. [ABSTRACT FROM AUTHOR]

This study was designed to assess the physiological impact of transferring oysters between upriver and downriver aquaculture sites, a common practice in North America that is primarily aimed at reducing disease infections and predation on cultured stocks. In May 2009, oysters ( Crassostrea virginica) were reciprocally transferred between an upriver and a downriver site in the Richibucto estuary in eastern Canada. Mortality, tissue and cellular stress responses were subsequently evaluated in August and October 2009. Overall, oyster mortality remained low (~5%) throughout the 5-month study period with no significant difference between sites or oyster sources. However, by October oysters reared at the upriver site, regardless of their origin, had significantly higher levels of lysosomal membrane destabilization (63.6%, SE = 1.9) and digestive tubule atrophy (33.3-42.4%, SE = 3.6) than oysters reared at the downriver site (47.5%, SE = 1.8; 15.6-19.1%, SE = 3.8 respectively). They also exhibited a greater salinity differential between their mantle/haemolymph fluids and the ambient seawater, possibly indicating more restricted exchange with the environment. In general, the transfer of upriver oysters to a downriver site had a positive impact, i.e. lower levels of lysosomal destabilization and tubule atrophy, whereas transfer of downriver oysters upriver had the opposite effect. These results suggest that upriver environmental conditions negatively impact cellular and tissue integrity in oysters without leading to mortality during the summer-autumn period. [ABSTRACT FROM AUTHOR]

This study compares the effect of two anti-fouling treatments, hot water immersion (15 s at 60°C) and air drying (72 h) on the physiological status of the Eastern oyster Crassostrea virginica. The negative impact of hot water immersion was greater than that of air drying, but varied depending on the initial size of the oysters (40 vs. 60 mm shell height) and the time of the year (June vs. August). Groups treated with hot water exhibited a higher proportion of haemocytes with destabilized lysosomal membranes ( HDLM; 47.5 ± 3.1%) than those exposed to air drying (37.5 ± 2.9%). This suggests that the oyster immunocompetency may be lowered by hot water immersion. Overall, the large oysters had lower HDLM values (32.9 ± 3.5%) than the small individuals in June (45.7 ± 2.8%) but similar values in August (46.6 ± 3.5%). Small oysters subjected to hot water immersion in June exhibited a 50% reduction in shell growth and a 50% mortality rate after one month. Our results indicate that air drying is more suitable than hot water immersion as an anti-fouling treatment for <45 mm oysters. [ABSTRACT FROM AUTHOR]

Approximately 73 000 Atlantic rock crab ( Cancer irroratus) were captured in coastal waters and transferred to an estuarine mussel aquaculture site in Prince Edward Island, Canada, in an effort to control overgrowth by the invasive tunicate Ciona intestinalis. To assess whether transplanted crabs remained in the vicinity of mussel farms, acoustic tags were attached to 25 resident and 25 transplanted individuals (all males) and their movements were monitored for 1 year, from September 2006 to August 2007. Resident crabs tended to occupy (within 1.6 km) the middle estuary where the majority of mussel farms are located. They left this area during winter, possibly to reach upstream overwintering grounds, and most returned to the middle estuary in spring. In contrast, translocated crabs exhibited a marked downstream movement (<5.5 km distant) in autumn and winter and few returned into the middle estuary in spring. Results suggest that transplanting large numbers of additional rock crabs is not an effective means to reduce the effects of invasive tunicates on mussel farms. [ABSTRACT FROM AUTHOR]