An apicomplexan parasite drives the collapse of the bay scallop population in New York

Abstract

The bay scallop, Argopecten irradians, represents a commercially, culturally and ecologically important species found along the United States’ Atlantic and Gulf coasts. Since 2019, scallop populations in New York have been suffering large-scale summer mortalities resulting in 90–99% reduction in biomass of adult scallops. Preliminary investigations of these mortality events showed 100% prevalence of an apicomplexan parasite infecting kidney tissues. This study was designed to provide histological, ultrastructural and molecular characteristics of a non-described parasite, member of the newly established Marosporida clade (Apicomplexa) and provisionally named BSM (Bay Scallop Marosporida). Molecular diagnostics tools (quantitative PCR, in situ hybridization) were developed and used to monitor disease development. Results showed that BSM disrupts multiple scallop tissues including kidney, adductor muscle, gill, and gonad. Microscopy observations allowed the identification of both intracellular and extracellular stages of the parasite. Field surveys demonstrated a strong seasonal signature in disease prevalence and intensity, as severe cases and mortality increase as summer progresses. These results strongly suggest that BSM infection plays a major role in the collapse of bay scallop populations in New York. In this framework, BSM may synergistically interact with stressful environmental conditions to impair the host and lead to mortality.

Study of the Impact of the Parasitic Microalgae Coccomyxa parasitica on the Health of Bivalve Modiolus kurilensis

“…Hypertrophy, as well as severe infection, can lead to the death of artificially grown mussels and scallops [74]. In 2023, a new apicomplexan parasite infection (provisionally named BSM) was discovered in Argopecten irradians Lamarck, 1819 (Pectinida: Pectinidae); it caused deformation or loss of integrity of the renal tubules and detachment or destruction of nephrocytes, but did not cause noticeable hemocyte infiltration [75]. In mollusks infected with Coccomyxa, we have observed the destruction of nephrocytes in the nephridia.…”