Rockefeller had the highest probability of shell disease infections,
particularly in the summer and winter. Salinity was not a significant
explanatory variable for this site ⁄ season interaction,
which was expected because previous research has not suggested
that shell disease varies with salinity (Shields and Overstreet,
2007). The site variation could be explained by water quality
and/or sediment substrate differences (Malloy, 1978; Vogan and
Rowley, 2002). Because Rockefeller is a wildlife refuge, we do not
expect it to have poorer water quality with increased fecal coliforms
or chitinoclastic bacteria than the other sites. However, if
the substrate at Rockefeller is different in composition and size,
the sediment may more readily hold bacteria or fungi that can
cause shell disease. It has been documented that areas with higher
sediment organic content have higher bacterial loads in the sediments
(Vogan and Rowley, 2002). In the future, sediment samples
should be collected to determine whether sediment composition
and particle size could explain variation in the prevalence and
intensity of shell disease across sites.