Lethal and sublethal responses of native mussels (Unionidae: Lampsilis siliquoidea and Lampsilis higginsii) to elevated carbon dioxide

Abstract

Levels of carbon dioxide (CO2) that have been proposed for aquatic invasive species control (24 000 – 96 000 μatm partial pressure of CO2 (PCO2); 1 atm = 101.325 kPa) were tested on two juvenile mussels, the fatmucket (Lampsilis siliquoidea) and the US federally endangered Higgins’ eye (Lampsilis higginsii). A suite of responses (survival, growth, behavior, and gene expression) were measured after 28 days of exposure to CO2 and 14 days postexposure. The 28-day LC20 (concentration lethal to 20% of organisms) was lower for L. higginsii (31 800 μatm PCO2, 95% confidence interval (CI) 15 000 – 42 800 μatm) than for L. siliquoidea (58 200 μatm PCO2, 95% CI 45 200 – 68 100 μatm). Treatment-related reductions occurred in all measures of growth and condition. Expression of chitin synthase, key for shell formation, was downregulated at 28 days of exposure. Carbon dioxide caused narcotization and movement to the substrate surface of mussels, behaviors that could increase mortality by predation and displacement. We conclude that survival and growth of juvenile mussels could be reduced by continuous exposure to elevated CO2, but recovery may be possible with shorter-duration exposure.