Life cycle and early development of the thecosomatous pteropod Limacina retroversa in the Gulf of Maine, including the effect of elevated CO2 levels

Thecosomatous pteropods are pelagic molluscs with aragonitic shells. They are considered to be especially vulnerable among plankton to ocean acidification, but to recognize changes due to anthropogenic forcing a baseline understanding of their life history is needed. In the present study, adult Limacina retroversa were collected on five cruises from multiple sites in the Gulf of Maine (between 42A degrees 22.1'aEuro"42A degrees 0.0'N and 69A degrees 42.6'aEuro"70A degrees 15.4'W; water depths of ca. 45-260 m) from October 2013 to November 2014. They were maintained in the laboratory under continuous light at 8 A degrees C. There was evidence of year-round reproduction and an individual life span in the laboratory of 6 months. Eggs laid in captivity were observed throughout development. Hatching occurred after 3 d, the veliger stage was reached after 6-7 d, and metamorphosis to the juvenile stage was after similar to 1 month. Reproductive individuals were first observed after 3 months. Calcein staining of embryos revealed calcium storage beginning in the late gastrula stage. Staining was observed in the shell gland, shell field, mantle and shell margin in later stages. Exposure of two batches of larvae at the gastrula stage to elevated CO2 levels (800 and 1200 ppm) resulted in significantly increased mortality in comparison with individuals raised under ambient (similar to 400 ppm) conditions and a developmental delay in the 1200 ppm treatment compared with the ambient and 800 ppm treatments.