Growth and development of larval bay scallops (Argopecten irradians) in response to early exposure to high CO2

Abstract

Coastal and estuarine environments experience large variability and rapid shifts in pCO2 levels. Elevated pCO2, or ocean acidification, often negatively affects early life stages of calcifying marine invertebrates, including bivalves, but it is unclear which developmental stage is most sensitive. I hypothesized that initial calcification is a critical stage during which high pCO2 exposure has severe effects on larval growth and development of bay scallop (Argopecten irradians). Using five experiments varying the timing of exposure of embryonic and larval bay scallops to high CO2, this thesis identifies two distinct stages of development during which exposure to high CO2/low pH causes different effects on bay scallop larvae. I show that any exposure to high CO2 consistently reduces survival of bay scallop larvae. I also show that high CO2 exposure during initial calcification (12-24 h post-fertilization) results in significantly smaller shells, relative to ambient conditions, and this size decrease persists through the first week of development. High CO2 exposure at 2-12 h post-­ fertilization (pre-calcification), does not impact shell size, suggesting that the CO2 impact on size is a consequence of water chemistry during calcification. However, high CO2 exposure prior to shell formation (2-12 h post-fertilization) causes a high incidence of larval shell deformity, regardless of CO2 conditions during initial calcification. This impact does not occur in response to high CO2 exposure after the 2-12 h period. The observations of two critical stages in early development has implications for both field and hatchery populations. If field populations were able to time their spawning to occur during the night, larvae would undergo initial calcification during the daytime, when CO2 conditions are more favorable, resulting in larger veliger larvae. Hatcheries could invest minimal resources to monitor and modify water chemistry only during the first day of development to ensure larva are exposed to favorable conditions during that critical period.