No abstract

Bonamiosis due to the intrahaemocytic protistan parasite Bonamia ostreae is a European endemic disease affecting the flat oyster Ostrea edulis. The parasite has been described in various ecosystems from estuaries to open sea, but no clear correlation has yet been demonstrated between disease development and environmental parameters. In this study, the effect of temperature and salinity on the survival of purified parasites maintained in vitro in seawater was investigated by flow cytometry. Purified parasites were incubated in various seawater media (artificial seawater, natural seawater, seabed borewater) at various temperatures (4, 15 and 25°C) and subjected to a range of salinities from 5 to 45 g l -1. Parasites were collected after 12, 24 and 48 h of incubation for flow cytometry analyses including estimation of parasite mortality and parasite viability through detection of non-specific esterase activities. Artificial seawater appeared unsuitable for parasite survival, and results for all media showed a significantly lower survival at 25°C compared to 4°C and 15°C. Moreover, high salinities (≥35 g l -1) favoured parasite survival and detection of esterase activities. Flow cytometry appears to be a suitable technique to investigate survival and activities of unicellular parasites like B. ostreae under varied conditions. Although these results contribute to a better understanding of existing interactions between the parasite B. ostreae and its environment, validation through epidemiological surveys in the field is also needed.

Horseshoe crabs Limulus polyphemus range along the East Coast of the United States and over 150,000 of them have been marked with U.S. Fish and Wildlife Service disk tags. It has been assumed that the tags do not harm the animals and are similar to common epibionts often found on the shells of horseshoe crabs. We investigated whether newly tagged adult female horseshoe crabs would exhibit higher short‐term mortality rates than untagged adult females. All crabs were collected from a beach in Connecticut and then were transported to a laboratory for the experiment. Tagging involved drilling a small hole through the carapace in the lower back corner of the prosoma and then inserting the tag into the hole. Overall mortality of tagged and untagged females held in flow‐through raceways for 44 d was minimal (0% mortality among 53 tagged crabs; 4% mortality among 52 untagged crabs). None of the horseshoe crabs lost or shed their disk tags over the course of the experiment. In field mark–recapture studies of horseshoe crabs, typically between 11% and 20% of the initial numbers of tagged crabs are recaptured. Crabs that are recaptured but reported dead are unlikely to have died from the initial tagging process. Our results indicate that newly tagged adult horseshoe crabs have the potential to survive as well as untagged crabs through the Connecticut spawning season (∼30–45 d). Recapture data also suggest that these crabs can survive for as long as 8–10 years with the tags in place.