RELATING BIVALVE GROWTH SHUTDOWNS TO LATITUDE AND TEMPERATURE

The periodically deposited growth bands of bivalves have applications as a recorder of aquatic paleoenvironmental conditions. Many bivalves deposit alternating light and dark growth bands, with organic-rich dark bands typically representing periods of a reduction or cessation of calcification and carbonate-rich light bands representing optimum periods of rapid shell growth. These periodic bands are useful for constructing time series at annual and seasonal resolutions, but such cessation in shell growth could introduce biases into climatic reconstructions. In this study we constructed a database of the season and temperatures of growth shutdown and the latitude of collection for eighty extant species across multiple bivalve clades. We then applied logistic regression to determine whether latitude exerts a significant influence on bivalve growth. Results indicate that there is a significant tendency toward winter growth shutdown among species in high latitudes as well as in individuals collected at the northern end of their range, and summer growth shutdowns appearing at low latitudes. These broad latitudinal associations suggest that temperature is the dominant control on calcification across bivalve clades, as opposed to other proposed explanations of growth cessation such as seasonal spawning and food availability. Work is currently in progress to compare vulnerability between clades as well as to normalize results by species range. If the tendency to shut down in response to seasonal extremes is significant in these contexts, such information could have applications for future work in the field of sclerochronology and improve understanding of metabolic constraints regulating bivalve growth.