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Aquaculture Canada and WAS North America 2022, 15-18 August, Mussel farming is an important economic resource for Canada, producing 26101 tonnes of mussels in 2019 worth more than 43 million Canadian dollars. A major cause of loss of production for mussel farmers originates from the fall-off of mussels during their growth. This phenomenon is particularly important during the reproduction season, as mussels invest most of their energy in the reproduction and have less energy for byssogenesis. This leads to byssal weakening, which can ultimately end with the fall-off of the mussels. Recently, there has been an increasing interest in the development of mussel hatcheries and more specifcally on the production of triploid mussels. Indeed, it is known that triploidy often reduces the fertility of bivalves and can even produce sterile bivalves that have more energy to invest in their growth and other vital tissues (e.g. byssus). In this study, we compared the production and mechanical properties of byssal threads of diploid and triploid mussels in relation to their energy budget and reproductive investment. To determine the effect of triploidy on byssal threads, diploid and triploid mussels were placed in a recirculating fume to induce production of byssal threads, then their scope for growth were estimated. The threads were counted and collected for tensile testing. Results show that triploid mussels produced up to 40% more threads than diploidfmussels, with triploid threads eliciting better mechanical properties. From May to September, during the reproductive season, diploid and triploid mussels were harvested in Georgetown Harbour, Prince Edward Island. Gonadosomatic index (GSI), gonad volume, gonad maturation, and sex ratio were determined for both groups. Results showed that while triploid mussels do invest a part of their energy in reproduction, they had lower GSI and gonad volume than the diploids. Also, for all tested groups, triploid gonads were less mature than those of diploids, and their sex ratio was signifcantly altered with absence of females in triploids. Furthermore, triploid gonads showed signs of gamete resorption, suggesting that triploid mussels could use their gametes for energetic storage. This study shows that triploid mussels have lower energetic investment in reproduction and suggests that this energy could be usedffor a higher byssal production with better performance. Thus the creation and production of triploid mussels are of great interest for mussel farmers as they are less likely to fall-off during production, and have higher energy available after spawning, which could result in increased survival and production

Poster.-- Poster.-- VIII International Symposium on Marine Science, Las Palmas de Gran Canaria, 6-8 July 2022, High-energy hydrodynamic events associated to currents and waves may disturb bivalve mollusks´ ecophysiology, especially those buried in the the sea bed due to sediment mobilization. Evidences of massive mortality for the clam Polititapes rhomboides (banded carpet shell clam) in Galicia (NW Spain) have been associated to warm water temperatures and high wave magnitudes above climatic averages and the presence of rickettsias (intracellular prokaryotic colonies) in gills (Villalba et al. 1999; Darriba et al. 2019; Villacieros-Robineau et al. 2021), Project PID2019-106008RB-C21 financed by MCIN/AEI/10.13039/501100011033

Poster.-- 4th Congress of the International Society of Fish & Shellfish Immunology, December 12-15, 2022, Bode, Norway, High-energy hydrodynamic events associated with currents and waves may disturb bivalve mollusks' ecophysiology, especially those buried in the sea bed where the bottom boundary layer dynamics may mobilize and resuspend the surface sediments. Evidence of massive mortality for the clam Polititapes rhomboides (banded carpet shell clam) in 2010 in Galicia (NW Spain) has been associated to warm water temperatures and high wave magnitudes above climatic averages and the presence of rickettsias (intracellular prokaryotic colonies) in gills. To monitor in the laboratory the environmental conditions observed in 2010, clams were subjected to intense sediment mobilization (four cycles of sediment remobilization, each followed by a calm period) and seawater warming (from 15°C to 18°C). Immune system, behavioral, and ecophysiological clams' responses were then evaluated. Nitric oxide (NO) production increased synergistically with seawater warming and sediment remobilization. Taking into account the four cycles of sediment remobilization, clams responded by increasing NO production as early as the first cycle in what we could call an acute effect. However, the most striking effect was the increased NO response after a second stimulation (the following sediment remobilization cycles), suggesting that clams achieve a kind of alertness the first time they are exposed to a stimulus through a mechanism possibly related to "trained immunity". Seawater warming and sediment mobilization presented also synergistic effects causing the lowest valve opening amplitude. Besides, sediment remobilization caused abrupt decrease in clearance rates of clams suggesting that reduced valve opening during this stage may have altered filtration processes of phytoplankton uptake. Metabolic rate as oxygen consumption showed a synergistic increase with both abiotic stressors. Considering the NO response and the ecophysiology data we could suggest that clams respond to stress increasing metabolism to obtain energy (ATP) and oxygen consumption by aerobic respiration. ATP production involves the generation of reactive oxygen species (ROS) including NO as by-products. The anti-oxidant system can balance the ROS production but this could be drastically altered (disruption of cytoskeleton and apoptotic cell death) if ROS production is greater and faster than the antioxidant system can regulate, which seems not to be the case for this particular experiment, Project PID2019-106008RB-C21 financed by MCIN/AEl/10.13039/501100011033

17 pages, 7 figures, 3 tables.-- This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY), Valvometry is a non-invasive technique used to continuously monitor gaping behaviour of bivalves at high frequency. In previous laboratory studies, valvometry has revealed a behavioural sensitivity of bivalves to the presence of toxic microalgae in seawater. However, the application of valvometry as an early-warning system for detecting natural occurrences of toxic microalgae and their resulting toxicity in bivalves remains largely unexplored. In this study, valvometry was used to characterise changes in blue mussels (Mytilus edulis) gaping behaviour during gradual exposure to the toxic dinoflagellate, Alexandrium catenella, which produces paralytic shellfish toxins (PST). Laboratory experiments were first performed to identify specific gaping behaviour changes and these responses were subsequently validated in natural seawater conditions in a second experiment. Under both laboratory and natural seawater conditions, mussels exposed to A. catenella tended to remain open (yawning) longer than non-exposed mussels. This change in gaping behaviour was observed at PST concentration as low as 30 μg STXeq 100 g–1 of mussel tissue. We suggest that increased opening is likely related to temporary muscular paralysis induced by toxic algae, as this mechanism has been previously reported in other bivalve species. Furthermore, we observed that biological rhythms of valve behaviour related to tidal and daily rhythms were modified when mussels were intoxicated by PSP (Paralytic Shellfish Poisoning). In conclusion, the effects of toxic algae on mussel gaping behaviour reveals that valvometry could be used as an early-warning tool for the presence of toxic Alexandrium sp. in the environment prior to mussels reaching the regulatory threshold (80 μg STXeq 100 g–1) for harvest interdiction, This project was undertaken with the financial support of the Government of Canada, specifically by a research grant from Environment and Climate Change Canada provided to RT’s (FDE-CA-2017i002) and by the Ressources Aquatiques Québec research network (Fonds de Recherche du Québec – Nature et Technologies, no. 2014-RS-171172)

Póster.-- Close Encounters IIM (2nd Kind) Virtual Conference, 26th February 2021

2021 Physiomar & Australia New Zealand Marine Biotechnology Society (ANZMBS) Conference, 7-9 September, During the last decades, intensive work has been put into the production of triploid bivalves, as triploidy can lead to reduced investment in fertility and faster growth. In mussel farming, the seasonal weakening of their byssal attachment can cause fall-off from mussel socks. In this study, we investigated the production and mechanical properties of byssal threads of diploid and triploid mussels related to their physiological performance by measuring the scope for growth. Finally, the seasonal gametes’ production of juvenile and adult stage were estimated through histological observations. Production of byssal threads was induced with the use of a hydrodynamic flume to standardize the abiotic factors, including current and turbulence conditions. The triploid mussels produced 40% more threads than diploids characterized by different mechanical properties, particularly a higher Young’s modulus. Scope for growth was calculated through measurement of clearance rates, respiration rates and excretion rates and triploid mussels showed higher scope for growth, as well as higher clearance rates. Preliminary results of the histological measurement tend to show a reduced investment or a delay in triploid gametogenesis. Indeed, primary observations, performed mid-May 2021 just before the beginning of spawning events demonstrated more advanced development stage in diploid gametes. Overall, this study showed that triploid mussels can be of great interest in mussel farming as they seem to have better attachment, better growth potential, and reduced or delay gametogenesis investment

9th International Workshop on Marine Technology (MARTECH), virtual, 16-18 June 2021, High-Frequency Non-Invasive (HFNI) instruments are currently used in bivalve mollusks in order to use them as bioindicators of the local conditions of the environment. Under the STRAUSS project an Arduino controlled equipment has been developed to log the valve movements activity of clams (Polititapes rhomboides) using Hall-efect sensors. The equipment is able to record at 10Hz the signals of 16 Hall-sensors, to store the records in internal microSD cards and to send the stream of data to a personal computer for storing and plotting them in real-time

Poster.-- 19th International Conference on Harmful Algae, october 10-15, The okadaic acid (OA)-producing dinoflagellate Dinophysis acuminate is a well-known microalga that causes diarrhetic shellfish poisoning (DSP) in many coastal regions of the world. In this laboratory study, we applied high-frequency valvometry to follow the valve movements of mussels Mytilus galloprovincialis feeding on toxic D. acuminate (n = 34 mussels, shell length = 60.1 ± 2.0 mm, xÌ ± SD) or a morphologically similar, but toxin-free dinoflagellate, Prorocentrum micans (n = 31 mussels, shell length = 60.0 ± 1.6 mm). Dinoflagellate inoculations were conducted in four sequential ¿pulses¿ intended to increase cell concentrations in a stepwise manner up to ~14,000-20,000 cells L-1 over a 6 h period. Rising concentrations of the toxic D. acuminate induced no immediate response from the mussels, whereas P. micans prompted an increase in shell opening over a short period of time (~ 9 h). More striking behavioral features emerged ~12-24 h following D. acuminate exposure, and these features persisted over a 3-day period when mussels had accumulated 43-64 µg OA equivalent per kg of meat (EU regulatory limit is 160 µg kg-1 shellfish meat). It was found that OA - contaminated mussels were more frequently and widely opened than control mussels, suggesting that OA altered the contraction of the adductor muscle. These observations are consistent with growing evidence that bivalves are sensitive to low concentrations of harmful microalgae. Deploying in situ valvometry sensors in recurrent HAB areas constitutes a promising tool to use bivalves as early warning sentinels.

In Canada, reports of marine harmful algal blooms (HABs) have increased over the past few decades. HABs are caused by the growth of certain phytoplankton that produce phycotoxins or otherwise cause harm. Phycotoxins are problematic to human health, and their cumulative effects are stressors to marine ecosystems by causing the mortality of marine fish, birds and mammals, including species designated at risk. Paralytic Shellfish Poisoning (caused by saxitoxin group toxins produced by Alexandrium spp.) has been problematic for years on both the east and west Canadian coasts. Amnesic Shellfish Poisoning (caused by domoic acid produced by Pseudo-nitzschia spp.) was identified for the first time worldwide following consumption of blue mussels from eastern Canada in 1987. Domoic acid has since also been found on the west coast. Diarrhetic Shellfish Poisoning (caused by okadaic acid group toxins produced by Dinophysis spp. and Prorocentrum spp.) was first recognized as a hazard in eastern Canadian waters in 1990, and these phycotoxins have since been found on both the east and west Canadian coasts. Other phycotoxins that may cause harm to human health in Canada include pectenotoxins, yessotoxins, azaspiracids, and cyclic imine group toxins (spirolide toxins, pinnatoxins, and gymnodimines). Multiple harmful algal species have been associated with fish-killing blooms on both east and west Canadian coasts. The range of exotic toxic/harmful algae is expanding in Canadian waters due in part to introductions from ships’ ballast water and climate change. The detection of domoic acid and the discovery of several toxigenic diatoms and dinoflagellates in the Canadian Arctic is of increasing concern because of the limited knowledge of HABs in this region. Canada’s experience in dealing with toxic events resulted in research and monitoring programs designed to understand HABs and to assist the fishing and aquaculture industries. In spite of decreases in research and phytoplankton monitoring efforts, consumers of molluscan shellfish are still protected by phycotoxin monitoring, which is conducted by the Canadian Food Inspection Agency. Novel phycotoxins and toxic algae will continue to be discovered. Continued vigilance and the maintenance of an effective capacity to manage developing problems via strategic research programs is essential. This document reviews Canadian marine HABs and phycotoxins up to late 2018, and provides a foundation for any future research in this area.