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Oyster recruitment to spat collectors can result in the clumping of two or more individuals, whereby they naturally cement to each other's shells. On‐bottom oyster farmers typically separate these oysters and re‐deploy them on the seafloor, potentially exposing them to predators. This raises the question of whether refraining from separating these oysters might provide an advantage against predation. We addressed this question using eastern oysters (Crassostrea virginica) and the non‐indigenous European green crab (Carcinus maenas) from part of their invaded range in Atlantic Canada. We assessed the influence of oyster arrangement (single vs. paired) and oyster size (small‐ vs. mid‐size) on mortality caused by two sizes of this invasive predator. Mortality rates were assessed with 24 h trials in which 30 oysters of a given size and arrangement were exposed to green crab predation. We found a significant influence of oyster arrangement (paired

Eutrophication, the biological response to nutrient enrichment, is a well-studied process that poses a threat to coastal ecosystems around the world. Despite an understanding of the mechanisms that contribute to nutrient impacts, there is no universal method for their quantification or monitoring. Herein, a monitoring indicator is presented and evaluated for estuaries that empty into the southern Gulf of St. Lawrence. Two monitoring indicators were assessed, the first evaluating responses of the regionally dominant seagrass, eelgrass (Zostera marina), and the second examining changes in dissolved oxygen (DO). Eelgrass coverage as a percentage of available habitat was previously quantified for each estuary and related to a suite of environmental variables. The only variable for which a significant relationship was found was nitrogen loading which explained 53.0% of the variability in eelgrass coverage using a nonlinear response function. The relationship shows that -63% of available habitat occupied is the maximum for estuaries within the region. Interpolations using that relationship show eelgrass declines correspond to estuarine external nitrate-N. Evidence is also presented that DO is suited to be a primary indicator of nutrient impacts in systems with high levels of both benthic and pelagic primary production. DO loggers were deployed in the upper estuary, defined by a salinity range of 15-25 PSU and an average water depth of 1-2.5 m of 27 distinct estuaries from 2013-2020 across the southern Gulf of St. Lawrence. Time series data were parsed into biologically relevant metrics that captured symptoms of eutrophication: hypoxia, dissolved oxygen supersaturation, and coefficient of variability. These metrics were analyzed using multivariate statistics and distinct groups formed around habitat type, with algae-dominated habitat reflecting these eutrophication symptoms. The combination of hypoxia and dissolved oxygen supersaturation metrics led to a new metric termed "Eutrophic Time" (the percentage of time an estuary spends <4 mg/L and >10 mg/L dissolved oxygen) which effectively captured estuaries with a tendency towards hypoxia and those towards supersaturation. This new measure was then analyzed through multiple regression with nitrate-N loading and water residence time as predictor variables which were ultimately well correlated (R2 = 0.81). This relationship can be exploited to provide estuary-specific nitrate-N loading targets for nutrient impacted systems at management's discretion. [ABSTRACT FROM AUTHOR]

The American eel (Anguilla rostrata) occupies a vast range in the West Atlantic Ocean and inflowing waters. Despite its presumed panmictic status, management of this species is geographically fragmented. There have been widespread calls for internationally coordinated efforts towards a range-wide stock assessment, but such an objective faces obstacles of a high degree of heterogeneity in major life history characteristics and the near-absence of such data in the northern, western, and southern parts of the species' range. This paper reviews novel and underutilized methods and data sources that may aid progress to an eventual range-wide assessment. Methods for obtaining information on distribution and abundance include mining of extant data and field surveys by glass bottom boat, electrofishing boat, net enclosures, environmental DNA (eDNA) and ocean larval tows. Analytic resources and tools include environmental databases, fetch as a covariate of abundance, accounting for the net effects of small ponds, GIS-oriented habitat modeling, glass eel-oriented population modeling, estimation of age structure from length structure, use of life history parameter clines to fill gaps in assessment input values, and life cycle modeling. eDNA is a cost-effective technique that has the potential to clarify American eel distribution, and possibly relative abundance, over the very large areas where data for this species are sparse. Most other techniques reviewed in this paper have substantial costs, which may constrain their use in the southern part of the American eel range where resources of aquatic science are often limited. [ABSTRACT FROM AUTHOR]

Atlantic Canada’s American oyster (Crassostrea virginica) beds, while economically and ecologically important, have been in decline over the past few decades. Predation by crabs, in particular by the European green crab (Carcinus maenas), has been proposed as one of the potential causes of such decline. Hence, this study examined oyster mortality levels in multiple beds across Prince Edward Island (PEI) and then experimentally assessed the contribution of green crab predation to oyster mortality. Results from surveys conducted in 10 estuaries across PEI in 2014 indicate that the probability of mortality for small oysters was significantly higher when green crabs were present then in areas without green crabs. This probability of mortality was significantly less when there was the presence of alternative prey like natural mussel beds (Mytilus edulis). The odds of oyster mortality were also higher when beds had rock crabs (Cancer irroratus) compared to beds with no rock crabs. Given the potential importance of green crab predation, its influence was assessed in 2015 using two field experiments with tethered oysters. Our results indicate that odds of small oyster mortality occurring were much higher in green crab inclusion cages than in the open environment and the exclusion cages. These results reaffirm that oysters up to ~40 mm SL are vulnerable to predation, and at least some of the mortality affecting these oysters can be causally attributed to green crab predation. Green crab predation rates upon small oysters are relevant given the economic benefits and ecosystem services provided by these bivalves. They highlight the need for the industry to consider mitigation measures and potentially adapt their oyster growing strategies. [ABSTRACT FROM AUTHOR]