Invasive parasites can spill over to new hosts in invaded ecosystems with often unpredictable trophic relationships in the newly arising parasite-host interactions. In European seas, the intestinal copepod Mytilicola orientalis was co-introduced with Pacific oysters (Magallana gigas) and spilled over to native blue mussels (Mytilus edulis), with negative impacts on the condition of infected mussels. However, whether the parasite feeds on host tissue and/or stomach contents is yet unknown. To answer this question, we performed a stable isotope analysis in which we included mussel host tissue and the primary food sources of the mussels, microphytobenthos (MPB) and particulate organic matter (POM). The copepods were slightly enriched in δ15N (mean Δ15N ± s.d.; 1·22 ± 0·58‰) and δ13C (Δ13C 0·25 ± 0·32‰) with respect to their host. Stable isotope mixing models using a range of trophic fractionation factors indicated that host tissue was the main food resource with consistent additional contributions of MPB and POM. These results suggest that the trophic relationship of the invasive copepod with its mussel host is parasitic as well as commensalistic. Stable isotope studies such as this one may be a useful tool to unravel trophic relationships in new parasite-host associations in the course of invasions.

The Sydney rock oyster (Saccostrea glomerata) (SRO) is an oyster species that only occurs in estuaries along Australia’s east coast. The SRO industry evolved from commercial gathering of oyster in the 1790s to a high production volume aquaculture industry in the 1970s. However, since the late 1970s the SRO industry has experienced a significant and continuous decline in production quantities and the industry’s future commercial viably appears to be uncertain. The aim of this study was to review the history and the status of the SRO industry and to discuss the potential future prospects of this industry. This study summarised findings of the existing literature about the industry and defined development stages of the industry. Particular focus was put on the more recent development within the industry (1980s-present) which has not been covered adequately in the existing literature. The finding from this study revealed that major issues of the industry are linked to the management of prevailing diseases, the handling of water quality impairments from increasing coastal development, increasing competition from Australia’s Pacific oyster (Crassostrea gigas) industry and the current socio-economic profile of the industry. The study also found that policy makers are currently confronted by the dilemma of saving a “dying art”. Findings from this industry review may be vital for current and future fisheries managers and stakeholders as a basis for reviewing industry management and development strategies. This review may also be of interest for other aquaculture industries and fisheries who are dealing with similar challenges as the SRO industry.

The toxic dinoflagellate Alexandrium catenella recurrently blooms on thecoasts of France and produces Paralytic Shellfish Toxins (PSTs) that accumulate inbivalves. These toxins can affect various physiological functions including reproduction.The present study aims to validate measurements of sperm viability, DNA content andmitochondrial membrane potential in Pacific oyster Crassostrea gigasusing flow cytometry coupled with fluorescent markers, and to use thesemeasurements to assess the cellular parameters of sperm from Pacific oysters exposed toA. catenella. These parameters may influence fertilization,embryogenesis and larval development in free-spawning shellfish. Sperm viability and DNAcontent estimation were assessed using SYBR-14, which only penetrates cells with intactmembranes. Cell mortality was measured with propidium iodide (PI), which penetrates cellswith membrane damage. Mitochondrial membrane potential, used as an estimate ofmitochondrial function, was measured using JC-1 dye, which selectively enters intomitochondria and reversibly changes colour from green to orange as the membrane potentialincreases. To assess the effect of toxic algae on oyster sperm, broodstock (ripe oysters)were fed toxic (A. catenella) or non toxic (Heterocapsatriquetra) dinoflagellates at 250 cell ml-1 for 9 days. After thisexposure period, mature oysters were stripped and cellular responses of sperm analysed.Average DNA staining, as measured by SYBR-14, appeared lower and more variable in gametesfrom A. catenella-exposed oysters than in those from control oysters fedH. triquetra. Additionally, mitochondrial membrane potential of spermfrom A. catenella-exposed oysters was significantly higher (1.5 fold)than that of sperm produced by oysters fed H. triquetra. Both theincrease of mitochondrial membrane potential and the modification of DNA structure can beexpected to impact spermatozoa ability to fertilize oocytes and could thus impact relatedreproductive processes.

A reliable anaesthesia and sampling protocol for Pacific oysters will enable experiments to be conducted without sacrificing animals and will facilitate successive sampling of individuals for gametogenesis studies. As no such techniques were available for Crassostrea gigas, the present study aimed to define suitable anaesthetic conditions for use with this species. Three groups of ten oysters (mean weight ± SD, 32.1 ± 9.0 g) were anaesthetised in 5 L containers. Among different chemicals: benzocaine, eugenol and three different types of magnesium chloride (a laboratory one – Flucka® – and two designed for agriculture – DEUSA International® and Dead Sea Works®) and concentrations tested, one laboratory (concentration: 72 g L−1) and one agricultural (Dead Sea Works® 50 g L−1) type of magnesium chloride were the most effective, respectively inducing anaesthesia in 73 ± 3% and 80 ± 3$% after three hours. Lower oyster weight and a two day period of starving prior to treatment significantly increased the number of anaesthetised animals. Using this protocol, losses of 0 to 10% of oysters were observed one week after anaesthesia. Increasing anaesthesia duration from 3 to 16 h resulted in a significant increase in the number of anaesthetised oysters (from 50 ± 10 to 97 ± 7%) but no increase in mortality (7 ± 11%). On the other hand, reducing water temperature from 19.5 °C to 15.3 °C, resulted in a significant decrease in anaesthesia efficacy. A reliable anaesthesia protocol was developed: 100% of Pacific oysters are anaesthetised using 50 g L−1MgCl2 Dead Sea Work®for a 16 h duration. This long duration facilitates tissue sampling and does not increase the working time needed. This protocol was validated by monthly anaesthesia and gonad sampling during a three month period with the loss of only a single oyster. It can thus be used for routine applications.