THE INTERACTIVE EFFECTS OF ACIDIFICATION AND WARMING ON THE GROWTH OF JUVENILE BLUE CRAB, Callinectes sapidus, FROM THE PATUXENT RIVER, CHESAPEAKE BAY.

Future climate scenarios predict increases in both oceanic temperature and dissolved carbon dioxide (pCO₂) over the next century.  Calcifying invertebrates, which depend on specific conditions of temperature and carbonate chemistry for many biological processes, may be especially impacted by these climate changes.  Here we report the results of a study on the combined effects of increased water temperature and CO₂ on the growth of juvenile blue crab, Callinectes sapidus.  Our system was constructed using filtered Patuxent River water and pCO₂ treatments were nested within temperature treatments in order to appropriately control both environmental variables and achieve adequate replication of treatment levels.  pCO₂ was calculated in experimental tanks from observed pH and total alkalinity data.  pH was controlled in the system using a "pH-stat" system, such that a solenoid valve allowed the input of CO₂ gas when the pH of the tank was above the desired level.  Crabs were kept individually in one of four temperature/pCO₂ treatments (26°C/800ppm, 26°C/8,000ppm, 32°C/800ppm, 32°C/8,000ppm) for two complete molts (approximately 30 days).  The growth per molt (GPM; mm and percent) and growth rate, quantified as intermolt period (IMP; days and degree days), were quantified for each crab and analyzed by temperature/pCO₂ treatment.  

GPM was not impacted by the combined effects of increased temperature and pCO₂ (P>0.05); crabs were approximately 25% larger after each molt regardless of treatment.  While crab growth rate (measured as length of intermolt period) was significantly faster in warmer water (P<0.05), acidified conditions had no significant impact on the growth rate of crabs (P>0.05).  These data indicate that juvenile blue crab growth rates may be faster in future climate scenarios due to warming temperatures, with little impact of acidification on crab growth rates.  The energetic impact of this change in growth rate on both crabs and the Chesapeake Bay ecosystem are a target of future data analyses focused on the impact of future climate scenarios on crab metabolic rate, food consumption, and carapace chemistry.