Since 2019, bay scallop populations in New York have been suffering large-scale summer mortalities resulting in over 90% reduction in biomass. These events were associated with heavy infections by an undescribed parasite dubbed Bay Scallop Coccidia (BSC). BSC infects and disrupts multiple scallop tissues including kidney, adductor muscle, gill, and gonad. This presentation summarizes some of our latest findings on BSC and on disease dynamics in the field.
Light and transmission electron microscopy analysis of infected scallop tissues allowed the identification of both intracellular and extracellular stages of the parasite, including sporozoite stages that display structural characteristics of the Apicomplexa (e.g., micronemes). Field surveys performed in 2020 and 2021 demonstrated a strong seasonal signature in disease prevalence and intensity, with severe cases increasing as summer progresses before slightly decreasing (Figure 1), likely as a result of the mortality of most heavily infected scallops. Laboratory investigations underline higher mortalities in most severely infected scallops exposed to ecologically-relevant high temperature, while dissolved oxygen appears to have less effect on disease dynamics. Overall, our results suggest that BSC infection plays a major role in the collapse of bay scallop populations in New York. In this framework, BSC may synergistically interact with stressful environmental conditions to impair the host and lead to mortality. Our current investigations target the characterization of host-parasite interactions, including molecular cross-talks and possibility to breed resistant scallops.