Associations between land use and Perkinsus marinus infection of eastern oysters in a high salinity, partially urbanized estuary

Abstract

Infection levels of eastern oysters by the unicellular pathogen Perkinsus marinus have been associated with anthropogenic influences in laboratory studies. However, these relationships have been difficult to investigate in the field because anthropogenic inputs are often associated with natural influences such as freshwater inflow, which can also affect infection levels. We addressed P. marinus-land use associations using field-collected data from Murrells Inlet, South Carolina, USA, a developed, coastal estuary with relatively minor freshwater inputs. Ten oysters from each of 30 reefs were sampled quarterly in each of 2 years. Distances to nearest urbanized land class and to nearest stormwater outfall were measured via both tidal creeks and an elaboration of Euclidean distance. As the forms of any associations between oyster infection and distance to urbanization were unknown a priori, we used data from the first and second years of the study as exploratory and confirmatory datasets, respectively. With one exception, quarterly land use associations identified using the exploratory dataset were not confirmed using the confirmatory dataset. The exception was an association between the prevalence of moderate to high infection levels in winter and decreasing distance to nearest urban land use. Given that the study design appeared adequate to detect effects inferred from the exploratory dataset, these results suggest that effects of land use gradients were largely insubstantial or were ephemeral with duration less than 3 months.

The Potential for Oysters,Crassostrea virginica, to Develop Resistance to Dermo Disease in the Field: Evaluation using a Gene-Based Population Dynamics Model

“…Multiple generations per year may further insulate the population from a reduction in abundance that should accompany an increment in mortality; but here, too, the rate of development of disease resistance is little changed if not slowed. The mortality rate drives selection and, thus, the rate of increase in disease resistance and the mortality rate are independent of abundance and other abetting processes maintaining abundance (discounting the possible contribution of density to transmission (Andrews 1988, White et al 1998, Ford 1992, Gray et al 2009).…”

“…The potential for the development of disease resistance would appear to exist, however. Oyster strains are observed to vary in their response to Dermo disease (Ray & Chandler 1955, Andrews & Hewatt 1957, Bushek & Allen 1996, Gaffney & Bushek 1996, Brown et al 2005a, Brown et al 2005b), suggesting a potential for disease resistance, although associations with environmental variables that might degrade the immune response (Craig et al 1989, Chu & Hale 1994, Lenihan et al 1999, Bushek et al 2007, Gray et al 2009, also well documented, limit the inference based on currently available data. Of more significance, perhaps, alleles associated with resistance or tolerance are known, so that an inherent capability would seem present.…”

Spatial and Temporal Dynamics of Mass Mortalities in Oysters Is Influenced by Energetic Reserves and Food Quality

“…Disease mortality is expected to show strong spatial and temporal dependence due to the epidemic process of local transmission. Although terrestrial studies on the spatial aspects of diseases have a long history, driven by a necessity to understand diseases of humans, crops, farm animals and wildlife [25], spatial studies of aquatic diseases are much less frequent and generally focused on distribution of macro-parasites [26]–[33].…”

Development and applications of Ray’s fluid thioglycollate media for detection and manipulation of Perkinsus spp. pathogens of marine molluscs

“…Reporting prevalences of higher-intensity infections provides an alternative statistic for projecting mortalities (Gray et al, 2009), in which it is critical to understand what infection intensity threshold increases the probability of mortality. In Fig.…”