Effects of Climate Variability on Interannual Variation in Parasites, Pathologies, and Physiological Attributes of Bivalves from the U.S. East, Gulf, and West Coasts

Abstract

We analyzed weighted prevalence of various parasites and pathologies for 1995 to 2006 along with a set of physiological variables to determine the degree of concordancy in their interannual variations over 500-km stretches of coastline using data from the National Oceanic and Atmospheric Administration's (NOAA's) National Status and Trends “Mussel Watch” Program. The variables examined in mytilid mussels fell into three groups based on the temporal patterns observed: ceroid bodies, taxon richness, digestive tubule atrophy, and major pathologies varied concordantly along the Northeast and West Coasts. For reproductive stage, sex ratio, and gill ciliates, concordant temporal trends were limited to the northeast coast. Gregarines, found only in West coast mussels, behaved similarly to those variables falling into the first group. A final group, trematode metacercariae and sporocysts, tissue pathologies, and the prokaryotes, was characterized by limited concordancy. For oysters, a similar triplet of groups was identified. Digestive tubule atrophy, tissue pathology, ceroid bodies, and body/mantle gregarines showed concordant temporal trends on both the East and Gulf Coasts. For Dermo disease, gill gregarines, reproductive stage and nematodes, temporal concordancy in interannual variation was limited to the Gulf coast. Little concordancy was observed for the prokaryotes, gill and digestive tract ciliates, haplosporidians, cestodes, sex ratio, and taxon richness. Overall, principal pathologies and diseases, bivalve physiological indicators, and the common gregarine parasites tended to show concordant behavior, suggesting that large-scale climatic processes [e.g., the El Niño/Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO)] are important determinants of their interannual variation. Overall, multicellular parasites, prokaryotes, and ciliates rarely showed concordant behavior, indicating that parasite body burden was controlled by local (within-bay) forcing factors. Mussels and oysters exhibited amazing similarity in their responses to local and climatic forcing. For both taxa, concordant behavior was observed for the most commonly observed pathologies, ceroid bodies, digestive tubule atrophy, reproductive stage, and the most abundant single-celled parasites such as the gregarines. These variables encompass the majority of the biological non-parasite variables measured and the majority of the common parasites. For both taxa, concordant behavior was rarely observed for the multi-cellular parasites. Both bivalve groups contained variables that expressed concordant behavior not only over long stretches of coastline, but on multiple coasts and variables that expressed concordant behavior for more limited coastline stretches. The degree and pattern of concordancy are fingerprints for the relative influence of local versus climatic forcing as the determinants of population dynamics in these bivalves populations and the populations of their parasites.

Keywords:

• climate change
• ENSO
• oyster
• mussel
• parasitism
• pathology
• disease
• Mussel Watch

ACKNOWLEDGMENTS

We thank the Status and Trends field and laboratory teams at Texas A&M University and TDI-Brooks International who collected the animals for histopathological analysis. The Status and Trends Program is supported through contracts with the U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Ocean Service.