Effects of ocean acidification driven by elevated CO2 on larval shell growth and abnormal rates of the venerid clam, Mactra veneriformis

Abstract

The venerid clam (<em>Mactra veneriformis Reeve</em> 1854) is one of the main cultured bivalve species in intertidal and shallow subtidal ecosystems along the west coast of Korea. To understand the effects of ocean acidifi cation on the early life stages of Korean clams, we investigated shell growth and abnormality rates and types in the D-shaped, umbonate veliger, and pediveliger stages of the venerid clam <em>M . veneriformis</em> during exposure to elevated seawater <em>p</em>CO₂ . In particular, we examined abnormal types of larval shell morphology categorized as shell deformations, shell distortions, and shell fissures. Specimens were incubated in seawater equilibrated with bubbled CO₂- enriched air at (400±25)×10^-6 (ambient control), (800±25)×10^-6 (high <em>p</em>CO₂), or (1 200±28)×10^-6 (extremely high <em>p</em>CO₂ ), the atmospheric CO₂ concentrations predicted for the years 2014, 2084, and 2154 (70-year intervals; two human generations), respectively, in the Representative Concentration Pathway (RCP) 8.5 scenario. The mean shell lengths of larvae were signifi cantly decreased in the high and extremely high <em>p</em>CO₂ groups compared with the ambient control groups. Furthermore, under high and extremely high <em>p</em>CO₂ conditions, the cultures exhibited signifi cantly increased abundances of abnormal larvae and increased severity of abnormalities compared with the ambient control. In the umbonate veliger stage of the experimental larvae, the most common abnormalities were shell deformations, distortions, and fissures; on the other hand, convex hinges and mantle protuberances were absent. These results suggest that elevated CO₂ exerts an additional burden on the health of <em>M . veneriformis</em> larvae by impairing early development.