Long-term effects of predicted future seawater CO2 conditions on the survival and growth of the marine shrimp Palaemon pacificus

The increasing atmospheric concentration of carbon dioxide (CO2) has been driving all marine organisms to live in increasingly acidic environments. In the present study, we evaluated the long-term effects of increased seawater CO2 on survival, growth, feeding and moulting of the marine shrimp Palaemon pacificus. The shrimps were reared in seawater equilibrated with air containing 1,000 ppmv (parts per million by volume, seawater pH 7.89 ± 0.05) or 1,900 ppmv (pH 7.64 ± 0.09) CO2, the atmospheric CO2 concentrations predicted for the year 2100 and 2300, for 30 and 15 weeks, respectively. Survival was significantly suppressed in both experimental groups compared to respective controls; final survival rates were 55% (experimental) vs. 90% (control) in the 1,000 ppmv experiment, and 65% (experimental) vs. 95% (control) in the 1,900 ppmv experiment. Growth was unaffected in the 1,000 ppmv experiment but significantly depressed compared to the control after 7 weeks in the 1,900 ppmv experiment. Feeding was unaffected by either treatment. Moulting frequency was significantly affected in both 1,000 ppmv (experimental > control) and 1,900 ppmv (experimental < control) experiments. Egg production was suppressed in the 1,000 ppmv shrimps compared with the control (no observation was made in the 1,900 ppmv experiment). In addition, the second antennae determined at the end of the experiment were significantly shorter in the 1,000 ppmv shrimps than in the control. The present results demonstrate for the first time that the predicted future seawater CO2 conditions would potentially reduce shrimp, and possibly other crustacean, populations through negatively affecting mortality, growth, and reproduction. This could threaten entire marine ecosystem through disrupting marine food web.