TESTING CLIMATE'S EFFECT ON OYSTER LIFE HISTORY USING GEOHISTORICAL RECORDS

The metabolic theory of ecology (MTE) proposes that variations in metabolic rate—which scales with an organism’s body mass and temperature—are responsible for many patterns in ecology, including covariations in lifespan, body size, and temperature. If temperature and mass estimates are available, predicting shifts in biological rates and times (e.g. lifespan) with temperature change is possible, making MTE a potentially powerful tool for examining LH responses to climate change in the fossil record. The MTE predicts that even modest increases in temperature (~1^oC) can reduce ectotherm lifespans by between 3% and 19%.

To test this prediction, we collected body size and lifespan data for 1067 oysters (Crassostrea virginica) from Pleistocene fossil deposits and modern reef death assemblages in South Carolina. Lifespans were estimated using models based on sclerochemical analyses of 34 fossil and 26 Recent specimens. The lithology, associated fauna, and information from the shells themselves (e.g., height-length ratios and attachment scar lengths) suggest that the fossil and Recent environments are similar. However, amino acid racemization dating suggests that the Pleistocene oysters lived during marine isotope stage 9 (MIS 9), when sea surface temperatures were warmer and sea level was higher than today, making this an opportunity to compare LH of oysters living in different climates. The slope of a preliminary plot of log average lifespan of Pleistocene and Recent oysters versus inverse temperature (assuming an average temperature difference of 2^oC) was 1.998—far above the MTE prediction of 0.65. However, the difference in average lifespans is supported by cumulative frequency distributions of the size and age data, showing that South Carolinian oysters were smaller in size (KS test, est. = 0.39, p = <0.0001) and had shorter lifespans (KS test, est. = 0.57, p = <0.0001) during MIS 9 than they do today. Thus, although preliminary results indicate that metabolic effects were not the only determinants of oyster LH changes through time, the results are consistent with general expectations from MTE and LH theory, suggesting that studying LH changes in the fossil record may yield useful information for managing natural oyster populations in the coming decades as the climate warms.