THE ORGANISMAL AND POPULATION EFFECTS OF CLIMATE CHANGE ON JUVENILE BLUE CRAB (CALLINECTES SAPIDUS) IN THE PATUXENT RIVER, CHESAPEAKE BAY

Abstract

Future climate scenarios predict an increase in temperature and dissolved carbon dioxide (pCO2) of the marine environment in the next century. Calcifying marine invertebrates are thought to be especially vulnerable to increases in pCO2 and although the effect of increasing temperature in many of these taxa is understood, less is known about the interactive effects of these stressors on the physiology of calcifying invertebrates. In the present study, juvenile blue crab (Callinectes sapidus) were exposed predicted future levels of temperature and pCO2 in a 2x2 factorial design for two complete molts (approximately 30 days). Increased temperature caused a significant increase in crab growth rate and food consumption, but at a cost to carapace thickness and chemistry. The carapaces of individuals exposed to increased temperature were significantly thinner and had significantly lower percent high-magnesium calcite (HMC), the mineral from which the carapace derives its strength. Although there was a significant increase in percent HMC in response to increased pCO2, this was paired with an increase in the concentration of magnesium, complicating the overall effect of increased pCO2 on the carapace. The temperature range tested in this study was not large enough to elicit a significant difference in mean oxygen consumption rate. Crabs were resilient to exposure to extremely high levels of pCO2; there was no significant effect of increased pCO2 on crab growth rate, food consumption, or oxygen consumption rate. Individual physiological response data were utilized in concert with historical and predicted water temperatures to determine effects of future predicted increases in water temperature on blue crab overwintering behavior in the Chesapeake Bay. Model data indicated a significant shortening of the overwintering period from approximately 3.5 months currently to between 1.5 and 3 months, depending on the climate model utilized for the predictions. Increases to growing season length, combined with predicted increases in crab growth rate and food consumption, indicate that in the future blue crab will mature faster and may possibly grow year-round, similar to individuals that live in the southern extent of the species’ range.