Influence of climate change on interannual variation in population attributes of Gulf of Mexico oysters

Gulf of Mexico oysters were sampled each winter for 8 y (1986 to 1993) as part of the National Status and Trends Mussel Watch Program. Each oyster was analyzed for the prevalence and infection intensity of the oyster pathogen Perkinsus marinus, condition index, length, sex, and reproductive stage. Interannual variation occurred in each of these biological variables. In some cases, interannual variation was produced by changes in local environmental conditions. In other cases, larger-scale climatic phenomena were implicated. Reproductive stage, length, P. marinus infection intensity, and condition index showed concordant yearly shifts (simultaneous shifts of equivalent direction) in populations from bays as far apart as 500 to greater than or equal to 1000 km. No concordant changes were observed for sex ratio and P. marinus prevalence. Prevalence and sex ratio are less affected by key climatic variables such as temperature and rainfall (salinity) than are the others and, so, are somewhat insulated from climate change. Interannual variations in oyster populations in some regions of the Gulf were chiefly produced by interannual variations in climate, whereas, in other areas, populations were more heavily influenced by variations in the local environment. Sex ratio and P. marinas prevalence showed concordant temporal trends in southern Texas and, for prevalence, southern Florida, but not in the northern Gulf. Length varied concordantly only in the northwestern Gulf region. P. marinus infection intensity, condition index, and reproductive stage were concordant in the northern Gulf from north Texas to northern Florida. Length, condition index, reproductive stage and P. marinus infection intensity were characterized by strong concordancy in interannual variations in the period 1986 to 1990, when a strong El Nino/La Nina shift occurred, and weak concordancy in the period 1990 to 1993, during a period characterized by weak climatic shifts, suggesting that regional concordancy in interannual variations of biological variables in Gulf of Mexico oyster populations may originate from the influence of strong El Nino/La Nina climatic shifts