Impact of Perkinsus marinus on Oyster Health: Survey Findings after a Regional Data Gap

Oyster reefs worldwide are experiencing a concerning decline, driven not only by overharvesting but also by parasites and diseases that threaten oyster and estuarine health. Here, the effects of the protozoan parasite Perkinsus marinus, which is known to cause dermo disease, were assessed after a 7-y gap in data gathering in a known infection center in the Gulf of Mexico: Galveston Bay (Texas). Eastern oysters (Crassostrea virginica) were collected from four sites across the bay from September to November of 2022 (a weak La Niña year) and 2023 (a strong El Niño year). Surveys revealed much higher infection levels (prevalence, infection intensity, and weighted prevalence) across almost all sites in 2023 compared with 2022. These high infection levels were likely driven by warm and saline conditions resulting from local droughts and potentially linked to large-scale climatic events. Parasite levels in 2023 resembled historical peaks reported in the late 1990s and early 2010s. High infections of P. marinus were also associated with poorest condition of the soft tissue and lower oyster quality, with temperature and oyster size as additional confounding factors. Given the potential for climate change to exacerbate conditions conducive to the reproduction of P. marinus, frequent monitoring is critical to understanding mortality trends associated with parasite outbreaks. This study provides information on recent parasite levels impacting oyster health and their links to local and large-scale climatic events to support scientists and resource managers in the restoration and conservation of estuarine ecosystems.